The story of electricity

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A CBT PUBLICATION

' THE STORY OF

ELECTRICITY

THE STORY OF

ELECTRICITY By

A. K. Chakraborty and S. C. Bhattacharya

illustrated by

Mrina! Mitra

Children's Book Trust, N e w Delhi

'The Story of Electricity' won the first prize in the non-fiction

category in the Competition for

Writers of Children's Books held in 1983 by the Children's Book Trust. It is jointly authored by Dr. A.K. Chakraborty, who is a Reader of Applied Physics in Calcutta University, and S.C. Bhattacharya, a former Wireless Operator in the Indian Air Force.

Printed 1985 Reprinted 1987, 1989

© by CBT 1985 ISBN 8 1 - 7 0 1 1 - 2 8 9 - 3

Published by Children's Book Trust, Nehru House, 4Bahadur Shah Zafar Marg, New Delhi, and printed at the Trust's press, the Indraprastha Press, New Delhi.

Wonders of electricity

"T JL/ong ago there lived in Turkey a magician who was gifted with miraculous powers. He could melt metal without fire, produce light without oil. He had a wonderful box. He could speak into it and his disciples sitting at the other end of the world could hear him...." That is how a fairy tale written in the 19th century begins. Generations of children must have been thrilled by this account of wondrous feats. But no child today will consider this a fairy tale or that magician a man of miracles. All his magical powers are now within the grasp of any man. What performs those miracles today is known as 'electricity'. It is like the genie of Aladin's magic lamp. Just as the Arabian giant, in obedience to his master's 3

command, accomplished the impossible in no time, so also electricity has turned the incredible into common place. You press a switch, and a light brightens your room. You speak into an instrument and the words reach the far corners of the earth or even into infinite space. Electricity can transmit not only words but also pictures. It drives trains and trams. It makes computers 'think'. It can melt metal and freeze water. It can heal and it can kill. With the aid of electricity man has achieved much more in one century than he had been able to in all the centuries before. True, it cannot be a fairy tale, but how man learned to use the power of electricity is a fascinating story. And, though one can begin it with "long long ago," it is a story without an end. For even as this is being written, new discoveries are being made, and it has to be left to someone in the future to write new chapters.

4

Thales and his discovery

It all began in ancient Greece. The first hero of our story is Thales, a mathematician. He was a native of Miletus, which was then a Greek colony, and he was born about 600 years before Christ. Many tales are told about this extraordinary man. It is said that a friend once told him, "It is easy for an idle thinker to grow up to be a philosopher; but to be a successful man of business one needs much cleverness and industry." Thales retorted, "A philosopher can achieve success even in business if he wishes to. But a businessman cannot be a philosopher however hard he may try." To this his friend said, "Well, then show me that you also can succeed in business." Thales took up the challenge. It so happened that for several years bad weather had affected the olive crop, resulting in a great scarcity of olive oil all over the country. Thales felt that the weather would be better in the coming year, and production of olive ought to be satisfactory. Acting on this conjecture, he hired all the oil mills he could. When, as he expected, there was a bumper olive crop, he bought olive cheaply, worked the mills he had hired and sold the oil at a high price. He made a fortune and proved that he was no idle philosopher. Thales took a deep interest in whatever excited his curiosity, and he loved to experiment with every matter that caught his attention. One day, in winter, when he was at work, he saw on his table a piece of amber, a kind of yellowish resin, covered with dust. He picked up the amber, rubbed it on his coat to clean it and put it back on the table. A great wonder awaited him. He 5

Thales conducting his experiment.

could not believe his eyes. A few small chips of wood on his littered table had moved and were clinging to the amber rod. To make sure that what he saw was not an illusion, he picked up the amber again and rubbed it on his coat. Again he held it near the chips and again they moved to the amber rod and stuck fast. Slowly he lifted the amber with the chips sticking to it. Deep in thought, he looked closely at the amber. He wondered if the amber could also attract material other than wood. He made experiments and found that the amber could, but it acquired the property of attracting other material only after it was rubbed. The discovery excited Thales. He remembered the legend of Magnus, the shepherd of Crete who, while following his flock on Mount Ida, suddenly found that he could walk no farther. He was unable to lift his feet. What was the matter? Magnus noticed that the iron studded soles of his boots were stuck to the rocky surface of the hill. The rock was of the kind called loadstone. This stone has a wonderful property. It attracts iron. All of you must have seen a magnet and have noticed that it attracts things made of iron. The loadstone is a natural magnet and it is found in many parts of the world. It has all the characteristic properties of an artificial magnet. Thales knew much about the loadstone. The Greeks called it 'magnetite' after Magnus, the shepherd. The word 'magnet' in English is also derived from his name. Thales knew that magnetite in its natural state attracts iron. But amber acquired the power of attraction only when it was rubbed with something else. Could there be any relation between the natural property of magnetite and the induced property of amber? He found no answer to the question. 7

Perhaps, Thales assumed, the power of attraction acquired by amber was also a kind of magnetism. Although he could not explain his assumption, he recorded carefully all the results of his researches and experiments. When Thales discovered the attractive properties of amber he could not imagine that his discovery would turn out to be one of the most valuable and significant discoveries in the history of scientific learning, that it would lay the foundation for the study of electricity. Dr. Gilbert, the Royal Physician

Centuries passed by and though many philosophers after Thales pondered over this subject of magnetism, no significant discovery relating to magnetism was made till the time of Sir William Gilbert (1544-1603), personal physician of Queen Elizabeth I. In 1600 A.D. he published 'De Magnete' (about Magnets), in which he recorded the results of his experiments of 17 years and his theories about magnetism. Dr. Gilbert had heard of Magnus and Thales when he was young and was so impressed by their discoveries that he decided to do his own research on the subject. He found that not only amber but also such things as sulphur, glass and wax became magnetic by friction and attracted other materials. He also noticed that there were many things which, when rubbed, would not acquire any magnetic property. It was he who first observed the characteristic difference between the natural magnetic property of loadstone and the induced magnetism of amber. Dr. Gilbert gave the magnetic property of amber the name of 'electricity'. In Greek amber is called 'elektron'. 8

Dr. Gilbert experimented with various objects and classified them according to their properties. He prepared a list of materials that would become electrified by friction and of those that would not. He drew up another list of materials whose electric properties were more powerful than those of others. 10 classify objects according to theii induced power of attraction, he devised an instrument called the 'electroscope'. It was a very simple apparatus, with a dry piece of straw hung in front. Dr. Gilbert would rub different objects with fur or linen, hold them one after another before this straw and carefully note down the extent each attracted the straw. He could not ascertain why and how an object acquired the power of attraction by friction. But the results of his researches paved the way to many scientific discoveries. When Dr. Gilbert wrote his book, he did not imagine that he would raise a controversy that would last over generations to come. Nor that he would one day be hailed as the father of the science of electricity. Gradually Dr. Gilbert's book came to be known to most European scientists. To many of them the theories propounded by the ancient Greek philosophers and scientists were the last word and they were unwilling to accept new ideas. Yet some were fascinated by the author's scientific vision. A few even began their researches along Dr. Gilbert's line, but no significant advancement was made in this field during the next 60 years. Otto von Guericke, the Burgomaster

T h e man who, after Dr. Gilbert, made notable discoveries about electricity was Otto von Guericke 9

(1602-86). He was the Mayor of Magdeburg, a city in Germany. He was a very able administrator, but in spite of his mayoral responsibilities, he found time for scientific research. The people of Magdeburg looked upon their Mayor with suspicion. They believed that von Guericke was devoted to witchcraft and was in league with the devil. On seeing him in the street, many city dwellers would hasten to keep themselves at a safe distance from their burgomaster. Some of them considered him insane.

The day von Guericke announced that he had devised an instrument to create a vacuum, they had no doubt that their Mayor's mental derangement was complete. Could any sound mind conceive such an absurd idea? Was it possible to suck away air from a vessel? Aristotle, the great savant, had said, "Nature abhors a vacuum." Was Guericke, then, refuting Aristotle? Who but a mad man could have such audacity? Guericke was indifferent to what the people said about him, but he became the topic of discussion here, there and everywhere in the country. Rumours spread and at last reached the ears of His Imperial Highness Ferdinand III. The post of mayor was important and the person in the mayoral chair should command the respect of all citizens. The Emperor decided to visit Magdeburg to check whether Guericke was as mad as rumour made him out to be. In a letter to the Mayor announcing his visit, he wrote, "I hear you have invented the art of creating a vacuum. And I hope you will prove the justness of your claim." On receiving such a message from the Emperor, von Guericke was naturally worried. But within two weeks he made all the necessary arrangements to receive the Emperor. And the day Ferdinand arrived, the city of Magdeburg was steeped in colour, with the streets gaily decorated and houses and walls freshly painted. The city dwellers, clad in their best clothes, lined the streets to receive their royal guest. A reception was held at the City Hall. All the elite of the city were invited and there was food and drink in abundance. The feast over, von Guericke stood up and, without any introduction, said, "Presently I shall demonstrate to you the operation of my new air pump. I shall suck out all the air from a hollow spherical vessel and create a vacuum." The City Hall resounded with laughter. The 11

Emperor looked at Guericke in some doubt. One of his companions asked, "Won't there be any device to peep into the sphere to see the vacuum?" Once more there was loud laughter. Even the Emperor could not help laughing. Von Guericke remained calm. He said, "Not far from here is a large open ground. There I will hold my demonstration. Let us all go there." The Emperor rode to the appointed place with the Mayor. The others followed them in procession. On reaching the lawn the city dwellers assembled by the Emperor's side. The Mayor then began his demonstration. He held up two copper hemispheres, each fitted with a metal ring, and showed that, by setting the two halves face to face, they would form a sphere. He repeatedly put the two hemispheres together to form a sphere and pulled them apart to show how easily it could be done. Then he brought his air pump, a metallic cylinder with a spout on one side and a big handle on the other. He again piessed the two halves of the copper sphere together, connected the spout of the air pump to a valve attached to one half, and declared, "Now I shall suck out all the air from this round vessel." The spectators watched silently as von Guericke began moving the pump handle up and down. Within a short time the movement of the handle slowed down. One could see that the Mayor had to use considerable force to operate it. When the handle refused to move, von Guericke stopped. He was bathed in sweat. Wiping his forehead, he looked at the Emperor and said, "Your Majesty, I have sucked out all the air. A vacuum has been created within this sphere." Then, turning to the spectators, he said with a pleasant smile, "One of our guests here wanted to know if he could peep into it. He would see very little there, 12

for we cannot see everything with our naked eyes. Man can see more with the light of intellect and reason than with his physical organ of sight." He went on to explain. "When the sphere was filled with air, the internal pressure within the vessel and the external pressure of the atmosphere remained equal and they annulled each other. That is why it was easy enough to pull the two halves of the sphere apart. Now, there being no air within the vessel, the tremendous pressure exerted by the atmosphere will hold the two halves together so tightly that it will not be quite easy to separate them." Then he picked up the vessel by a ring and began to shake it. All the spectators expected to see the two halves go apart. They stuck firmly to each other. Then von Guericke turned to the Emperor and said, "Your Majesty, I would like to see if you can pull the two hemispheres apart." Ferdinand rose from his seat and von Guericke handed the vessel to him. The Emperor held it firmly in his hands and tugged mightily at the two rings but to no effect. Ferdinand was a strong man. And when he could not pull the vessel apart, the spectators were astonished. More wonders awaited them. Von Guericke made a sign. At once, four powerful horses were brought before him. Two horses were harnessed to each of the two rings of the spherical vessel and, under the lash of whips, they tugged at the vessel from either side. But it did not split apart. Von Guericke made another sign and four more horses were brought. This time eight horses, four on either side, were engaged in this tug-ofwar, but the two halves of the sphere held together. At last 16 horses, eight on each side, were harnessed to the rings. This time the vessel split with a bang. Emperor Ferdinand was highly impressed. He was 13

convinced of von Guericke's genius. The Emperor congratulated the Mayor and told him that he should carry on with his researches. He also said, "If you ever make another such discovery, do not forget to let me know. I expect to see you achieve many more successes in the domain of science." This was a memorable moment in von Guericke's life. And it has a particular significance in this story of electricity. Henceforth von Guericke could do his researches and experiments freely and he turned to electricity. He read Dr. Gilbert's book through and through. Having examined carefully the doctor's theories, he began his own experiments. He observed that to energise amber or glass by rubbing them with fur or linen was a clumsy and tiresome process and it yielded very little electricity. After various experiments he devised an apparatus that could generate a considerable amount of electrical energy. Von Guericke made a ball of sulphur, perforated it in the middle, and then passed a metal rod through the hole. Then he fixed a handle to the rod, so that, by turning the handle, one could turn the sulphur ball round and round. Von Guericke demonstrated that if one held the sulphur ball with gloved hands and turned the handle, the revolving ball would generate plenty of electricity. The electrical energy thus produced remained concentrated within its source which, in this case, was the sulphur ball. Von Guericke named it 'static electricity'; and he called the instrument he ' invented 'electrostatic generator'. He also showed that the sulphur ball, in its energised state, could attract paper, chips of wood, thin metal sheets, feathers. He also discovered that electrical energy could be transferred from one object to another. It was he who first noticed that a sheet of metal brought in contact 16

with an electrified sulphur ball acquired the property of attracting other objects. After having experimented with many different objects, von Guericke came to the conclusion that a thing could be electrified by being brought in contact with another electrified object. In other words, electrical energy could be transferred by contact. Stephen Grey (1670-1736) and his experiments

T h e 'electrostatic machine' invented by Otto von Guericke facilitated the researches and experiments of later scientists. Half a century after his death another significant invention was made in the sphere of electrical science. The name of the inventor was Stephen Grey. Grey belonged to a lower middle class family of England. He was greatly interested in science, but the little amount of money he received as his pension was not enough even for a bare living. So, it was hard for him to buy the books and instruments he needed for his experiments. Luckily, he had a friend, Granvil Wehler, who was rich and was also interested in science. Wehler had no doubt about his friend's genius and was certain that Grey would one day achieve undying fame. So he was ready to give money to Grey for his experiments. One day when Wehler was returning from an opera, by chance he met Grey in the street. Seeing his friend grave and sad, he asked, "What is the matter, Stephen? Why do you look so glum? Is it toothache?" "Granvil," Grey said, "to get rid of toothache, one could get rid of one's teeth. But when a man's pain rises from the deepest recesses of his heart and burns his soul, what can he do?" 17

Wehler could not understand what his friend was driving at. But it occurred to him that what Grey wanted was a sympathetic listener to whom he could open his heart. Wehler put his hand on his friend's shoulder and said, "Come to my house and I shall hear all about your problem." Wehler lived in a beautiful mansion at Otterden Place in London and he took his friend there. As they sat face to face, Wehler said, "Stephen, why are you so broken-hearted? I have never seen you so downcast before. What is the matter?" Grey answered, "You know, my dear Granvil, I was never eager to grow rich, never aspired to fame or social status. I just wanted to comprehend the nature of this world and, through experiments, to discover some facts that would, perhaps, change the whole history of mankind. But a poor man like me can never have his hopes fulfilled." "Stephen, tell me all about your plans. I may be able to help you." "I wish to carry out some researches on electricity. It is a wonderful power. Till now it has not been possible to know its real nature. Yet, Granvil, I often think this electricity will perform miracles some day. It often occurs to me that once we can know the true nature of electricity, the true nature of the universe will reveal itself to us." "I too am curious to know more about electricity," Wehler said. "I have plenty of money, but no brains. If I had your gift of intellect, I would, perhaps, set up my own laboratory and begin my own researches. I like your plans. I like them because, in your hopes and dreams, I hear the echoes of my own. So I give you an offer. If you do not mind I shall make a suitable laboratory for you in my own house. But, of course, on the condition that you take me as your research 18

assistant. Do you agree?" Overwhelmed with joy, Grey took his friend's hands in hi5 and said, "Do you really mean it, Granvil?" Granvil smiled and said, "Yes, Stephen. But do not think I am spending money without any personal interest in the matter. I have faith in your ingenuity. I know you have a great future ahead of you. Given the right opportunity, you will certainly make some valuable contributions to science. When you grow famous as a scientist, I, as your assistant, shall go down into history along with you." A few months later the two friends were busy in their laboratory. But what a laboratory! It had all the appearance of a veritable cobweb. There was an overhanging network of threads tied up all around the walls with metal hooks. The two friends sat in two corners of the room. Grey had a glass rod in his hand. One end of a long thread was fastened to the glass rod and other was attached to an ivory ball. Wehler was sitting beside his friend with a board on which some feathers were placed. Grey rubbed his glass rod with a piece of linen and said, "Granvil, hold the feathers close to the ball." Wehler did as he was told. But the feathers showed no sign of movement. Wehler was silent. Grey grew impatient and asked, "Any result?" "No," replied Wehler. Grey rubbed the glass rod harder and harder, but to no effect. At last he said in despair, "Granvil, there can be no reason why it should not work. What then " Wehler laughed and replied, "My friend, how can you expect success to come to you so easily? Have patience, think coolly and you will certainly be able to spot the trouble. No more today, I pray you. Let us go and sit beside the Thames." 19

The year was 1729 A.D. It was a cold wintry night. The time was about 8 p.m. Thick fog enveloped the area. Grey tucked the collar of his overcoat round his ears and set out for Otterden Place. He had a parcel under his arm. Unconscious of the bustle of the streets, he walked thinking of the experiments he planned for the night. For some months he had been trying to conduct electricity through long threads, but all his efforts had failed. Now he had realized the cause of his failure. Tonight he would not fail. Shouts and curses, the tramp of horses and rattle of speeding wheels nearby rudely made him aware of the world around him. Sensing danger he jumped to a side of the road. Mercifully for him and science, he escaped being run over by a coach. Grey realized that, if he thus remained buried in thoughts while walking, he would sooner reach his grave than his destination. He became more careful and, holding his precious packet tightly, quickened his pace and soon reached Wehler's mansion. Wehler himself opened the door and said, "Come, sit beside the fire and warm yourself." But Grey was so excited with the thought of his experiments that he heard not a word of what his friend said. He had no time to idle away. He must put his theory to the test. "Granvil," he said, "I have found the solution to my problem. There was a serious flaw in our experimental process. This time I am confident of success. Come and help me." The two friends hurried into their laboratory. Grey untied his packet and took out a large reel of thread and an ivory ball. Then he drew out a long cord from the reel and, with the help of his friend, fastened it to the wall from side to side. He tied one end of the cord to the glass rod and the other to the ivory ball. He 20

examined thoroughly the points on the walls to which the thread was fastened and said, "It is all right. Now, hold the featheis near the ivory ball." Wehler did that and Grey began to rub the glass rod with a piece of linen. Within a few moments Wehler cried out, "Stephen, you have done it! The feathers have leaped up and are stuck to the ivory ball!" With these words, Wehler announced to the world a great and significant achievement. Now, for the first time, man could transfer electrical energy from one place to another. Overwhelmed with joy, Wehler embraced his friend and said, "Your success is astounding! Now tell me how you did it. What was the flaw in our previous experiments?" The two friends sat before the fireplace. Grey said, "Only this evening I could realize, by chance, the mistake we made in our experiments. The metal hooks that we used for fastening the cords to the walls are themselves good conductors of electricity. So the electricity generated in the glass rod was being bypassed to earth through them before it could reach the ivory ball. Having realized this, I fastened the thread to the hooks with silk cords so as to avoid any direct contact between the hooks and the thread. Silk being a nonconducting material, it stopped the electric current from bypassing through the metal hooks. So, this time, the electricity produced in the glass rod could easily reach the ivory ball through the long thread." With Wehler's assistance and encouragement Grey continued his researches and found out that some materials were good conductors of electricity, while many others were poor conductors. The materials that prevent the flow of electric current are known as insulators. These insulating materials are now used for isolating or converting live 21

conductors. On the basis of the discovery made by Grey, electrical wires, coated with rubber or plastic materials, are being manufactured on a large scale. Charles Dufay (1698-1739)

T h e next significant discovery was made by Charles Dufay, a Frenchman. He observed that there were two kinds of electricity. And he found that the electricity produced in a glass rod when rubbed with silk and that generated in a resin rod when rubbed with fur are not homogeneal, not of the same kind. Charles Dufay had observed that, if two glass rods were rubbed with silk and then hung side by side on silk cords, the rods repelled each other. And it was 'likes' that repelled. If a glass rod rubbed with silk and a resin rod rubbed with fur, were hung side by side, the two attracted each other. So Charles Dufay came to the conclusion that the electricity of the glass rod and that of the resin were different. Let us electrify different objects by rubbing them with different materials. Now, if we bring these electrically charged objects close to the glass or the resin rods, each of these objects will either attract or repel one of the two rods, the glass or the resin. So we see that the electricity of any electrical object corresponds or, to use a more technical term, is homologous either to the electricity of the glass rod or to the electricity of the resin. We do not come across an electrified object whose electric property is heterologous, that is corresponds to the electric properties of both the glass and the resin rods. We may, therefore, conclude that there are only two kinds of electricity. The electricity produced in a glass 22

rod rubbed with silk was called 'vitreous electricity' or glass electricity. And the electricity of a resin rod rubbed with fur was known as 'resinous electricity'. Later, Benjamin Franklin named the first 'positive electricity' and the other 'negative electricity'. An accidental discovery

It was by accident that another important discovery was made. PietervanMusschenbrock(1692-1761),aprofessor of Leyden University, was experimenting on the possibility of storing electricity in water in a glass flask. He had an iron rod with two silk cords. One end of a metallic wire, attached to the iron rod, was passed through the stopper of the flask. The professor thought that, if the iron rod were to be electrically charged, the current flowing through the wire would electrify the water. And glass, being a nonconductor, the electricity in the water would find no way out. As the professor held the flask in one hand and tried to pull the wire out of the iron rod, he received a terrible electric shock. In trying to ascertain the cause of this phenomenon, he invented, accidentally, an electric condenser for storing electricity. The apparatus is known as Leyden Jar. It consists of a cylindrical glass vessel lined inside and outside with metal foil. A brass rod is passed through the cork at the mouth of the jar. To the lower end of this rod is attached a brass chain which keeps electrical contact between the rod and the metal coatings inside the jar. The Leyden Jar became popular in no time. Professional magicians fired their cannons by igniting gunpowder by the electricity stored in the Leyden Jar, causing fear and wonder among their audience. Some 23

used it to give themselves or others electric shocks. It is said that a French priest, Christophe Claire, found it useful to demonstrate to some sceptical factory workers his power to inspire divine feeling in others. On a Sunday evening, just after prayer, sixteen of them assembled, as they were asked to, in the courtyard in front of the church. Claire appeared carrying a box wrapped in red cloth and two crosses dangling from it. The priest asked the men to stand, hand in hand, in a circle. He then approached them and asked two of the men to hold the two crosses. The moment the two men touched them all sixteen sprang up and were scattered about the courtyard. Whether the feeling this inspired was divine is not known, but there was nothing divine in the power that made the sixteen bedridden for days. Claire had concealed within his box a small portable generator and a Leyden Jar and just before approaching the workers had turned the handle of the generator. The two crosses were connected to the two electrodes of the jar and, when the two men touched the crosses, a powerful electric current began to flow through the human chain, making them bounce. Benjamin Franklin (1706-90) and electricity

Benjamin Franklin has made important contributions to the science of electricity. He was a versatile man, literary artist, politician, social worker and scientist, all in one. In 1746 one Dr. Spence had shown him a few experiments in static electricity and Franklin grew interested in the subject. He repeated these experiments and, observing the similarity between the sparks 24

of electricity he produced and lightning, he wrote a thesis entitled, 'The similarity between lightning and electricity'. In this he expressed the view that by means of a suitable conductor the electricity of lightning could perhaps be brought down to earth. When his papers were read at the Royal Society meeting, the members present laughed. To give a fitting reply to this ridicule, Franklin resolved to prove the truth of his theory by an experiment. He made a big kite and on a cloudy day, he flew it high in the sky. He tied a key to the cord of the kite and held the key with silk lace over it to prevent electricity flowing through the cord from passing through his body. Now, as he brought one end of another conducting wire quite close to the key, a bright spark occurred. Thereafter, by connecting the key to a Leyden Jar, he was able to store in it a good amount of electricity. The experiment was dangerous and Franklin was lucky to escape electrocution. On the basis of this discovery, lightning arresters or conductors were devised to protect building from thunderbolts. The lightning conductor is a metallic rod, with a number of sharp points, put on the roof of buildings. The lower end of the rod is connected by iron or copper wire to the earth. If there is a flash of lightning, it can cause little or no damage to the building because the electrical discharge is drained away to" the earth through the lightning conductor. Another significant contribution Franklin made is his theory about the nature of electricity in material objects. Before Franklin, an apothecary named William Watson had expressed the view that every object contained two kinds of electricity. Franklin studied the implication of this and explained the reason why an object became electrified by friction. He said that every substance in its natural state contained equal quantities 25

Franklin's famous kite experiment

Franklin's famous kite experiment

of vitreous (of glass) electricity and resinous (of resin) electricity. Matter being composed of two converse electrical charges of equal amount, an object, in its normal state, did not manifest any electric property. It was only at the time of friction that the objects responded electrically to each other and became electrically charged. Because glass electricity and resin electricity neutralised each other's action, Franklin called the former positive and the latter negative electricity. It should be mentioned that these two kinds of electricity are equally elemental. It is not that positive electricity is richer in any special property than negative electricity. Nor is it that negative electricity is deficient in any particular property. It is only for convenience that an international convention has been established to call glass electricity 'positive' and resin electricity 'negative'. How a skinned frog excited Galvani

F r o m Stephen Grey's researches man conceived the idea of using electricity, but current produced by the electrostatic generator was transient, that is, not permanent. It was not possible to provide the necessary electromotive force to perpetuate the flow of current in a circuit. The scientist who first made a significant discovery along this line was Luigi Galvani. Dr. Luigi Galvani (1737-98) was a professor of anatomy in Bologna, Italy. He was a specialist in physiology and therapeutics. No one knows for certain how he suddenly grew interested in electricity. But it is said that one day, he hung the flayed carcass of a frog on an iron railing by a copper hook to dry. As it swung in the breeze, Galvani observed that the legs of the frog 28

shrank as they came in touch with the railing. He watched this phenomenon keenly for sometime and came to the conclusion that electricity was the cause of the muscular contraction of the frog's legs. He had heard of the fish called torpedo which kills or disables its prey by electric shock. He also knew of the ray fish that uses its electric organ for defence and to catch its prey. Fishermen often talked about having received severe shocks while catching these fishes. This 29

led him to the conclusion that there was electricity in the body of an animal. He called it animal electricity. He also expressed the opinion that it was this electricity in the body of the frog that made it shrink at the touch of the iron rail. Though Galvani's theory of 'animal electiicity' was discarded, the importance of his contribution to the science of electricity cannot be denied. His discovery paved the way to many new scientific researches which led ultimately to the invention of the 'electric cell'. Going into the history of science we see that many wrong theories have helped the ad vancement of scientific learning. Just as scientists establish a truth by proving a theory, so also they discover new truths while disproving one. Volta's electric cell

C o u n t Alessandro Yolta (1745-1827) was a professor of physics at the University of Pa via, Italy. After repeating Galvani's experiment in his laboratory he began his own research. He demonstrated that, if Galvani's views on 'animal electricity' were accepted, many other experimental truths of science could not be explained. Volta knew that in Galvani's experiment the skinned frog was slung on the railing with a copper hook. He observed that, if the copper hook was replaced by an iron hook, the legs of the frog would not shrink at the touch of the iron rail. So it was established that to effect the contraction of the frog's legs two different metals were necessary. If the electricity within the body of the frog itself was really the cause of contraction, why should two different metals be necessary to effect this? 30

Volta drew the conclusion that in Galvani's experiment the source of electricity was chemical reaction. He said that two different materials coming in contact with a proper solution caused this reaction. In Galvani's experiment it was an aqueous (of water) solution present within the body of the frog that helped the chemical reaction producing electricity. Volta did not stop here. To prove his theory he produced electricity by using a suitable solution instead of a frog's carcass. By this experiment was invented the first man-made 'electric cell', or 'battery'. Volta found that electric cells could be produced by placing paper or cloth, moistened with sulphuric acid, within zinc and copper sheets. In order to strengthen the electric current thus pro31

duced, Volta made a stack or pile of copper and zinc discs arranged alternately. Within each pair of discs he placed a sheet of blotting paper soaked in sulphuric acid. Electric current began to flow in the circuit when the two ends of the conducting wire were connected to two cell plates (electrodes). The pile of metal plates devised by Volta is known as the 'Voltaic pile.' The electric cell he made by dipping a zinc rod and a copper rod into a vessel containing dilute sulphuric acid is called the 'Voltaic cell'. Volta's discovery ushered in a new era in the history of the science of electricity. Many scientists tried to improve the quality of electric cells and succeeded in inventing various kinds of batteries. But none of these could yield any considerable amount of electricity. Nowadays geneiators are used to produce electricity. Portable batteries, however, serve many useful purposes. They are used in torches, portable radio sets and motor cars. Even today batteries are indispensable to our telegraph and telephone systems. The apparatus by which radio signals are transmitted from artificial satellites is powered by electric cells. Ever since Volta published his theory of electricity, the electric cell has become an indispensable article in science laboratories. Volta was more fortunate than most of his predecessors. He achieved honour and fame during his lifetime. A unit of electricity (potential difference) was named after him. The Royal Institution : Sir Humphry Davy

It was soon found that with a combination of many cells very powerful batteries could be made. And from those batteries very high and stable electric current 32

Davy's apparatus for gas analysis.

could be obtained. In 1800 the Royal Institution of London built such a high power battery. This was largely due to the efforts of Count Benjamin Rumford, the founder of the Institution, who was ever trying to improve its research facilities. Rumford was finding it hard to get the money needed to buy equipment. Then he hit upon a novel plan. He knew that the common people were eager to know about the discoveries and inventions relating to electricity. Couldn't he exploit this popular curiosity to raise funds? Would not people be willing to spend a little money to listen to lectures on electricity and to 33

watch demonstrations of scientific 'magic'? He drew up a programme for a lecture series and announced it in the newspapers. This met with an enthusiastic response. As days passed, more and more people began attending the lectures. But Rumford found that, though the scientists of the Royal Institution were learned, giving lectures to the lay public needed more than learning. He started looking for a suitable man, and, on the advice of a friend, appointed Humphry Davy (1778-1829). As Rumford took his seat among the audience to hear Davy's first lecture one evening in 1801, he realized that he had made a wise choice. Though only 23 years old, Davy was learned in the science of chemistry. Above all, he knew how to capture the attention of his audience, how to excite curiosity about things unknown, how to make his lectures enjoyable. His splendid oratory, accompanied by practical demonstrations, enthralled his audience. Davy's skill and novelty of expression made his lectures popular within a short time. Many who heard him once came again and again to hear him. Money flowed into the Royal Institution. Humphry Davy became a familiar name amongst the elite of London. But Davy would not rest satisfied with his popularity. He was a talented scientist and, being associated with the Royal Institution, he found the opportunity to work in its well-equipped laboratory. What attracted him most was the Voltaic battery and he tried several experiments with it. One day, without any set purpose, he took the two wires that were connected to the poles of the battery and dipped them into a beaker of water. He noticed, at once, bubbles rising at the ends of the conducting wires. What caused these bubbles? He remembered having read an essay written by William 34

Nicholson and Sir Anthony Carlisle. They too had sent electric current through water and observed bubbles rising at the two poles of the conductors. They assumed that, during the passage of the electric current, water discharged oxygen and hydrogen gases and this caused the bubbles. But they could not come to any definite conclusion. Davy began experiments to ascertain the nature of the gases and the cause of the bubbles. He took distilled water in a beaker and put into it two conducting wires. Beneath the two dipped ends of the wires he placed two test-tubes so that the gas produced in the water in the beaker might accumulate in the test tubes. Then he connected the wires to the poles of a battery and let the electric current flow through the water. At once, the gas produced in the water came out in the form of bubbles and began to gather in the test-tubes. Davy noticed that the gases were not accumulating in the same proportion in the two tubes. The volume of gas in one was twice as much as that in the other. After letting the current flow through the water for sometime, he managed to gather some amount of the gases. Davy tested and analysed the gases, and found that they were hydrogen and oxygen. He also observed that the volume of hydrogen was twice as much as that of oxygen, the exact composition of water. Davy realised that electric current had caused this chemical dissociation of water into its two basic elements. If water could be divided into its basic ingredients, why not other matter as well? This was an epoch making idea. As a chemical scientist, Davy knew that there were materials whose ingredients could not be separated by any process yet known. It occurred to him that, perhaps, electricity could accomplish this. Davy began new experiments and succeeded at last in separating such materials as could never before be found in 35

their pure state. Davy's success began a new era of chemical science. And a new method of employing the mysterious power of electricity came into our hands. The process invented by Davy is known as electrolysis and it is now being extensively used in the industrial field. The process had enabled man to use metals for various purposes and to extract metals at less expense. Metals have been used by man from the very early days of human civilization. It was perhaps copper that man first began to use, because copper was the only metal that was available in its original state and could be used without being refined. The ancient people knew that copper could be forged into desired shapes and made into weapons. They had also been using iron with other metals. Yet centuries passed before man could learn the process of extracting metals from minerals. And even when it was learnt, the process of separating metals from mineral ores was found to be laborious and expensive. It was the science of electricity that changed all that. Extraction of metal : Charles Martin Hall

T o d a y we use aluminium for various purposes. It is a light and shining metal and that is why it is more useful than any other. There is a great store of aluminium on the surface of the earth. Scientists realized that the physical property of aluminium had immense practical value. But till about the end of the 19th century, production of aluminium was very expensive. In 1852, the cost of production of a pound of aluminium was nearly 550 U.S. dollars. That made it costlier than gold and silver. 36

A few years later Henri de Ville, a French chemist, invented a better and less expensive method of extracting aluminium. In an exhibition in Paris, he displayed before his spectators a number of aluminium rods. The aluminium was produced at a cost of 50 dollars a pound. Napoleon III, the Emperor of France, visited that exhibition and was fascinated by the aluminium rods. De Ville presented to the Emperor an aluminium toy for his little son. The Emperor placed an order for plates, knives, spoons, made of aluminium, to be used at royal banquets. Distinguished guests had aluminium plates and cutlery, while others had to be content with plates and spoons made of gold or silver! The Emperor wanted to have weapons made of aluminium. But at that time aluminium was not readily available and there was no means of increasing its production. Man had not yet mastered the art of extracting pure aluminium from minerals. That was why aluminium could not be extensively used like other metals. Scientists, however, knew the potential of this metal and many were doing research to find a way to extract aluminium at low cost. The first scientist to succeed in such experiments was Charles Hall (18631914). In 1880, Hall was a student of Oberlin College in the city of Ohio. He took special interest in chemistry and spent much of his time in the chemical laboratory. One day, one of his professors casually remarked, "The man who can invent a method of producing aluminium at low cost will have done a great service to mankind and become a man of wealth." Charles Hall decided that he would be that man. After graduation from Oberlin College, Hall went home and talked to his father about his plans for research. His father, sure of his son's genius, asked him 37

to go ahead. Charles Hall built his working shed in the backyard of their house, installed the equipment he needed and started his experiments. Working day and night he was able to find within nine months a simple and inexpensive method of producing aluminium with the aid of electricity. Hall's process was to melt aluminium oxide and send an electric current through the molten metal, causing a chemical dissociation. The oxygen liberated from the mineral gathered round one of the electrodes, while pure aluminium accumulated at the bottom of the other electrode. With the advent of this electrolytic process of extracting aluminium, the price of aluminium began to fall. As a result of Hall's achievement, aluminium no longer remained the metal of the rich. Things made of aluminium began to be used in every household. Today, not only aluminium but also other metals, such as copper, lead, zinc, are being extracted and refined by electrolysis. Another important application of the electrolytic process is what we call electroplating, that is, coating of iron, copper, tin and other metals with nickel, chromium, zinc, gold or silver. Such a coating on iron prevents its rusting. It was known from Volta's discovery that electricity could be produced by chemical reaction. And Davy's researches had shown that just as chemical reaction causes electric current, so also electric current can cause chemical reaction. Now, Charles Hall had gone a step further. After them other scientists made significant discoveries in close succession. As a result the actual relation between electricity and magnetism became clear. 38

Magnetism and electricity : Hans Oersted

F r o m olden times man had been thinking of the wonderful magnetic property of the loadstone. But the cause of magnetism was not known. Many scientists assumed that magnetism and electricity were interrelated. One day, in 1820, in a classroom at the University of Copenhegen, it was proved accidentally that they were not wrong in their assumption. Professor Hans Christian Oersted (1777-1851) was explaining to his students the functions of the various components of a battery that was on the table before them. He connected a wire to the two poles of the battery to demonstrate how electric current was flowing through the conducting wire. On the table was a small compass. It was not in any way related to their topic of discussion that day. The compass happened to be just beneath the wire connected to the battery. Suddenly Oersted noticed that the needle of the compass, instead of pointing to the north, was pointing to the east. He could not believe his eyes! He disconnected the wire from the battery. Instantly the compass needle swung several times, then stopped, pointing steadily to the north. Oersted was astonished. Had he really seen the needle pointing to the east? Could electric current have had an effect on the compass? The young students in the room looked at him in surprise as he stopped what he was saying about the Voltaic cell in mid-sentence. He appeared distraught. They started whispering and Oersted suddenly realized where he was. It was impossible for him, that day, to take his class. He told his pupils, "Let us stop here today. We shall discuss the rest tomorrow." The moment the students left the classroom, he 39

took up the compass. Was the compass all right? It was. The needle was pointing steadily to the north. He connected the wire again to the two poles of the battery and held the compass close to the wire. No, his eyes had not belied him. Just as electric current began to flow through the wire, the needle flung itself away from the true north. He also observed that if the direction of the electric current was changed, the needle of the compass changed its direction. Highly excited, the Professor ran from one classroom to another calling to his colleagues to come to his laboratory. Seeing him thus excited, his fellow professors knew that he must have made a very important discovery. They came and assembled in his laboratory. Prof. Oersted repeated the experiment before his colleagues. All of them, were amazed. It was proof that there was magnetism in electric current. Oersted published the results of his experiment. The news of his discovery soon spread far and wide and reached Andre Ampere, professor of a polytechnic college in Paris. Ampere and his electromagnet

A n d r e Marie Ampere (1775-1836) was a very sad and lonely man. Never could he forget a dreadful night of his boyhood. He was only 14 then. The family had just finished supper and Andre was absorbed in his studies. All of a sudden he heard an outcry. A group of rebel soldiers broke into their house and dragged Andre's father away. All his entreaties and all his mother's tears were in vain. Andre's father never came back. He was one of the numberless men and women who weie the victims of the guillotine during the 40

French Revolution (1789-92). The tragic death of his father changed Andre overnight. From his childhood, his father had been his only companion and playmate. Andre's father could discern in his son the possibility of a great future. So he tried to give his son what opportunities he could for the full flowering of his genius. He even helped Andre in his studies. Along with other subjects he taught him Greek and Latin. But Andre took no special interest in these classical languages. He was in love with mathematics. Though Andre's father could not help him much in his favourite subject, he bought his son many valuable books on mathematics. Andre began to learn on his own. As all the good and dependable books on mathematics were written in Latin, he learnt that language. After his father's death, it was he who became the main support of their family. He began to earn money by teaching children mathematics in their houses. After his day's toil he would pursue his own studies. He grew learned in mathematics, physics and chemistry. He married at the age of 20. Some time later, he joined a school in Lyons as a teacher of physics and chemistry. But even then he was absorbed in the study of mathematics. Within a few years he published his first book, 'Considerations on the Mathematics of Gambling.' In the book he presented his theory that a habitual gambler would surely be a loser in the long run. The subject he treated in his book was not one to attract academicians, but the manner in which he presented his mathematical arguments highly impressed many of the distinguished mathematicians of his time. In 1804 came another shock to Andre Ampere. His wife died. He was only 29 then. A year after that Ampere left his job at the polytechnic school and went to Paris, where he joined a college as a professor. 41

When he read Oersted's thesis, it excited his interest in magnetism and he began his researches. Within a

short time Ampere discovered that when electric current flowed through a conductor, its magnetic effect could be felt all round the wire itself. In other words, a magnetic field was created around the path of the 42

electric current. He also observed that when electric current was sent through two parallel wires in the same direction, the two wires attracted each other. And, if the direction of one current was changed, the two conducting wires repelled each other. Then, in order to determine the relation between the forces of attraction and repulsion with reference to the value or strength of the current, he worked out a mathematical equation which is even now used by scientists. Ampere also showed that the magnetic field around the conductor was circular. This phenomenon led him to the assumption that, if the conducting wire could be twisted and turned into a loop, the intensity of the magnetic field through the loop would increase. Ampere experimented with his idea and proved it beyond all doubt. Then he wound the conducting wire spirally into a coil and succeeded in creating a very powerful magnetic field at the centre of that coil. Thereafter Ampere invented the process of making an artificial magnet. He noticed that an iron rod placed within the centre of a coil of insulated conducting wire turned into a powerful magnet. This artificial magnet was much more powerful than a natural magnet. A magnet thus artificially made is called electromagnet. Through his experiments Ampere was able to show that for making artificial magnets bars of soft iron were more suitable. Such an iron rod, placed within a coil of wire through which electric current was flowing, instantly became a magnet. But. the moment the circuit was broken and the current stopped flowing, the iron rod lost its magnetism. In other words, soft iron became a temporary magnet under the influence of electric current. Ampere saw that for magnetising a steel rod high electric current was necessary. Once magnetized, a steel 43

rod retained its magnetism even after the electric current flowing through the coil was stopped. Thus electric current turned a steel rod into a permanent magnet. The application of electrical science on a wide scale began with the discovery of the electromagnet. The artificial magnet is now being used not only in various electrical instruments but also for generating electricity. The electromagnet serves many of our household needs. A visitor to our house presses a button at the door and an electrical bell within announces his arrival. The telephone rings and draws our attention to one who is far away. The action of electric bells and telephones depends on the property of the electromagnet But the most wonderful use of the electromagnet is in transmission of messages to distant lands. This system of transmitting messages is known as telegraphy. Samuel Morse and his telegraphic code

T i l l the middle of the 19th century, news was sent from one place to another through letters and newspapers carried by horse-drawn carriages, stage coaches and, where possible, by railway trains. These coaches were slow and messages would take days, weeks or even months to reach their destination. With the advent of electricity, many scientists had thought of the possibility of using it to send messages quickly and several carried out experiments to that end. But they did not succeed in their endeavours. The man who did was not a scientist but a painter. His name was Samuel Finlay Breese Morse (17911872). As a painter he enjoyed a good reputation in America. Many distinguished men and women came 44

to him for their portraits. Even President Monroe had his portrait done by Morse. But few were to remember him as a painter. After graduating from Yale, Morse told his father 45

of his desire to become an artist. His father was a congregational minister and he was rather disappointed. But he yielded to his son's entreaties and sent him to London to take lessons in painting. He was not able to give him much money and Morse had to spend a few years in London in great poverty. Nevertheless, he worked hard and became a good painter. Morse went to Italy in 1829 to acquaint himself with the artistic tradition of that country and the styles of the great Italian painters. After a few years he decided to return to America. On October 1, 1830, he embarked on a vessel named Sully and set out on his journey home. The voyage not only changed Morse's career, but brought about a significant change in the history of human civilization. At the dining table in the ship, some of Morse's fellow passengers began to discuss electricity. They talked about the experimental efforts made to invent a system to transmit messages by means of electricity. Several of them were learned in science and described various instruments that were being tried. Morse listened to their discussion with eager attention. He knew very little about electricity. But as he sat listening to them he thought what a wondrous thing it would be io be able to send messages instantly from one end of the earth to the other. And it occurred to him, 'Why can't I try just once? If I try, maybe I would succeed in inventing telegraphy?' He remembered the first letter he had written to his father and mother on reaching London: "Just as I sit here to write to you, a very strange and impracticable idea haunts my mind—O, that my words would reach you in an instant! I guess you are eagerly and impatiently waiting for my news and are ill at ease to think of my safety and well being. I am quite safe, hale and hearty—O, if I could only convey these words to you 46

this very moment! But, alas! that is not to be! This message of mine will take no less than four weeks to reach you." Morse gathered as much information as he could about electricity from his fellow passengers at the dining table. The more learned among them explained to him matters related to electrical science and discussed in detail the functions of the electric cell and electromagnet. Morse rose from the dinner table and went to his cabin with an idea slowly taking shape in his mind. He knew it was presumptuous of him to hope to succeed where specialists had tried and failed. But the idea possessed him. For days thereafter, he confined himself to his cabin, thinking how he could test his own theory. He drew sketches of all the devices he thought of. Within a few days he could formulate a method of sending signals through a wire with a device using the magnetic effect of electricity. Morse decided to pass an electric current, at required intervals, through a closed circuit in order to energise an electromagnet which, by its actions, would bring a pencil into contact with a moving sheet of paper. The pencil was to imprint dots and dashes produced by electrical impulses of different duration. He devised an alphabetical code by a combination of dots and dashes. Each of the different combinations of these dots and dashes would symbolise a letter or figure of the English alphabet and numerals. All the way to America, Morse sat in his lonely cabin thinking of his telegraphic instrument. By the time his ship berthed, he had invented what came to be known as the Morse Code. On reaching America Morse became successful as a painter, but he refused many alluring offers so that he 47

Morse's first design for a telegraph apparatus.

could devote his whole time to his research. For a long time he worked, with batteries, iron bars and levers. But the road to success was not easy. The first instrument he devised did not work. He went on making changes and alterations in his apparatus till at last he realized his dream. He was able to send signals through electric wire from one end of his laboratory to the other. For a public demonstration of his telegraphy, he needed money, and that was not easy to get. Metallic wire was costly and he needed miles of it. The other materials required were also expensive. He could find no sponsors. Morse continued his experiments without 48

anyone to help him and soon became destitute. Then fortune smiled on him. A number of Senators and influential men, realizing the importance of his discovery, managed to get him a public grant for a demonstration of his apparatus. A 40-mile-long cable was laid between Washington and Baltimore. March 24, 1844, was the day set for the demonstration before a group of experts selected by the government. Morse sat in Washington, at the end of his telegraph line, and Vail, his assistant, at the other end in Baltimore. A tense, silent group watched as Morse took his seat before his telegraph machine. When the machine produced a sound, 'click, click, click', Morse began to send this signal, in his own code: "What hath God wrought?" Having transmitted his message, Morse left his seat. Within seconds Morse's receiving apparatus came to life. The pencil attached to the receiver began to print on the paper, 'dot, dash, dash', representing the letter 'W'. And the entire signal, "What hath God wrought?" was inscribed in code on the paper. Morse had wrought a revolution in communication! Shortly thereafter, cables were laid between several cities in America. Later the telegraph system was introduced in other parts of the world as well. It made its appearance in India in 1851, when the first telegraph cable was laid between Calcutta and Diamond Harbour. Graham Bell invents telephone

T h e telegraph had come to be and scientists were trying to improve on it. Among them was a young man 49

named Alexander Graham Bell (1847-1922). He was studying the possibility of sending through the telegraph line several messages at the same time. Bell did not succeed in improving the system of telegraphy. But he accidentally came by another bright possibility. It occurred to him that, if sound could be transmitted as dots and dashes, the human voice could also be sent to distant places by electric cable. Bell was born in Scotland. Both his father and mother were teachers of philology and phonetics. Along with his scientific studies, he also learnt much about the tonal characteristics of the human voice, the different sounds produced by such vocal organs as tongue and lips. His two brothers died of tuberculosis. When Bell showed the symptoms of the same disease, his parents decided to take him to a healthier place. They left Scotland for Canada and settled in the city of Ontario. Bell soon regained his health and went to Boston to join a school as teacher of philology. It was while he was there that Bell became interested in telegraphy. He set up a laboratory in two rooms at his house and began to spend all his leisure hours with his friend, Watson, doing experiments. One day Watson was working a telegraph transmitter in one room of the laboratory, while in the other room sat Bell with the receiver. One of the metal plates of the transmitter was not working satisfactorily and Watson moved it back and forth a couple of times. Hardly had he done so when Bell came rushing into Watson's room excitedly and asked, "What were you doing, Watson? I heard a clattering noise in my receiver!" Watson was astonished. He told Bell what he had done. "Do that again, Watson," cried Bell, rushing back to the telegraph receiver in the other room. 50

Watson again jerked the metal sheet to and fro. Instantly there was a clatter in Bell's receiver. "Watson!" Bell shouted excitedly, "I bet we can send any sound through a wire by means of electricity." 51

Bell found that, if a thin iron plate placed within a magnetic field was made to vibrate, the vibration would disturb the magnetic field. If such a thin plate or diaphragm vibrated near an electromagnet, the intensity of the field around it would wax and wane alternately. This was the principle Bell made use of in his speech machine. When a man speaks before a transmitter, the diaphragm placed near an electromagnet vibrates to the sound wave. And its vibration causes a fluctuation in the magnetic field, inducing an electric current in the wire wound about the magnet. This current, upon reaching a receiving apparatus, causes its diaphragm to vibrate by similarly fluctuating the nearby magnetic field. The nature of this electric current will depend on the acoustic characteristics of the speaker's voice. The electric current of a fluctuating intensity and frequency generated by the transmitter is sent to the receiver through another electromagnet. The vibration caused in the diaphragm of the transmitter by the impact of a voice will produce exactly the same vibration in another diaphragm placed within the receiving apparatus. That is how the diaphragm of the receiver generates in the air a sound wave which is exactly the same as the sound wave produced by the speaker's voice. On the basis of this theory, Bell and Watson tried for years to invent an electric speech machine. Their initial efforts failed. Yet they continued their endeavour to improve their instrument. One day, again accidentally, they achieved their objective. That was on March 10, 1897. Bell was experimenting with the transmitter of his speech machine in one room and Watson was in the other room, sitting in front of a receiver. The door between the two rooms was shut. On Bell's table lay a voltaic battery. In a careless moment, 52

Bell's

magnetic telephone.

the battery turned over and toppled from the table. Some acid spilt on the floor and stained Bell's clothes. "Mr. Watson, come here at once," Bell shouted. As the door between the rooms was closed, Watson could not have heard Bell's shout directly. However, he heard it clearly. The sound had come from the receiver! Astonished and excited, Watson rushed into the adjoining room and cried out, "Mr. Bell, your speech machine is working. I heard your voice over the receiver!" Bell had invented the telephone. But again it was almost by accident that the invention came to the world's notice. On the anniversary of American Independence, a great exhibition was arranged at Philadelphia. 53

Among the exhibits on display was Bell's telephone. The day on which the exhibits were to be judged and selected for awards was a Sunday. That day special guests were allowed to attend the exhibition. Among them was Don Pedro, Emperor of Brazil, who was on a tour of America. The judges walked about looking at the things displayed in different stalls. Time passed by and, in the heat of summer, all grew tired. Bell realized that it would not be possible foi the judges to see everything at the exhibition. They would not have time even to look at his telephone. Disappointed, he was about to leave the exhibition when he heard a voice calling, "Mr. Bell!" He turned and saw the Emperor stepping towards him with a smile on his face. Years earlier, Emperor Pedro had visited the school in Boston where Bell was a teacher. There, for a long time the two had discussed matters concerning education of the dumb. The Emperor remembered Bell. Bell showed him his invention and the Emperor brought it to the judges' attention. They were as impressed with the apparatus as the Emperor. One by one, all of them tried it. Thereafter the judges had nothing, to judge, nothing to decide. Bell's telephone was awarded the first prize. Calcutta again has the distinction of being the first city in India to introduce the telephone system. A 50-line exchange was established in Calcutta in 1881, about 30 years after telegraphy made its debut. Michael Faraday and his discoveries

It was the voltaic battery that made Bell's invention possible. But the power a voltaic battery yielded was 54

limited. In the industrial field, man had to explore other more powerful sources of electricity. A high-power generator of electricity was made possible on the basis of a theory propounded by Michael Faraday (17911867). Faraday was born in a poor family. So, even at a tender age, Faraday had to go out in search of a living. He got himself appointed as a page boy in a book stall. Fortunately, his master, Ribean, was kind. After about a year, he took Faraday as a paid apprentice in the trade of book binding. But Faraday was more interested in the contents of a book than its cover. He had a great fascination for science. The boy read all the books on physics and chemistry that came to him for binding. One day, one of their clients was talking to Ribean about the brilliant lectures Sir Humphrey Davy was delivering on electricity. Faraday happened to be standing nearby. "Mr. Ribean," said the client, "I am going to attend Davy's lectures. I have an extra ticket. You may come with me." "Thank you", Ribean replied. "But I know nothing about science and so will not be able to enjoy lecture on matters of science." Then, pointing to Faraday, he said, "Take this boy with you. He loves science. And he has read all the books on electricity that I have in my shop." Faraday's eyes sparkled as he looked at Ribean. "All right, I shall take the boy with me," he said. Faraday was delighted to have this unexpected opportunity to hear the lecture of a renowned scientist. That day, and on three other subsequent evenings, he listened to Davy's lectures. He took notes on each and, in his spare time, recorded the details of the lectures. Having set down the notes with his own comments on each point, he bound them into a volume. 55

After Faraday's apprenticeship was over, he found a j ob as book-binder. But his new master was not as kind and sympathetic as Ribean. Faraday found that he had neither the time nor the opportunity to study as 56

before. Annoyed with the rudeness of his new master, he decided to give up book-binding. But he had to find another job. Suddenly he remembered Humphrey Davy. But what would an eminent scientist like Davy have to do with a poor book-binder like him? After ruminating for some days, he decided to try his luck. He wrote to Davy. With his letter he sent the bound volume of the notes and comments he had made on the four lectures he had attended. Days, weeks and months passed, but there was no response from Davy. Faraday was disappointed. 'Why should a great scientist like Davy bother about a letter written by a poor young man like me?' he asked himself. On December, 1812, on Christmas Eve, a coach came and stood before Faraday's place of work. A man alighted and enquired about Michael Faraday. When Faraday came out, the man handed him a letter. With trembling hands, he opened the envelope and read the letter. It was more a note than a letter. But, what a wealth of joy it brought to his sad and weary heart! It was from Davy and it said: "The proof you have given me of your self-confidence and your tenacity of purpose has made me glad. This testifies to your zealous interest, your fine memory and your great attentiveness. I am going out of London for some days and I shall not be able to come back and settle down here before the end of January. Any time thereafter, I shall be eager to meet you. It shall give me immense pleasure to be of any help to you. I wish it would be within my power." Towards the end of January, soon after his return to London, Davy sent word to Faraday, asking him to come and see him at the Royal Institution. Faraday met him, but Davy gave him no promise. Faraday was again in despair. Was he destined to 57

remain a book-binder all his life? But about a month later, he received another letter from Davy saying that Faraday could, if he wished, join the Royal Institution as an assistant. Faraday joyously accepted the offer. Davy had made many significant contributions to the science of electricity. But his best contribution was, perhaps, the opportunity he gave to Faraday to work at the Royal Institution. Davy himself was aware of this. Once a journalist asked him, "What, in your own opinion, is your greatest discovery?" "It is Michael Faraday," was the prompt reply. Faraday had to perform many jobs apart from his routine duties. He had to keep the laboratory instruments clean and be at the beck and call of his superiors. But he was happy to have the opportunity to work in an environment of his choice. Now he could devote much time to his studies and experiments. The subject of electromagnetism excited his special interest after he learnt about the work and achievements of Oersted and Ampere. He repeated, in his own way, the experiments of the two great scientists and made other experiments to test his own ideas. Davy was greatly impressed by Faraday's devotion and irgenuity. He began to guide Faraday in research. As days passed by, Faraday's reputation grew. From the post of laboratory assistant, he was raised to membership of the institution. After Davy's death in 1829, Faraday continued his researches and experiments independently. A particular idea began to haunt his mind. If electricity could produce magnetism, why cannot magnetism produce electricity? In 1831, in the course of an experiment, Faraday realized that he was not wrong in his assumption. He observed that an electric current was induced in a coil of wire placed within a fluctuating magnetic field. The discovery was of 58

immeasurable significance. Based on this principle electric generators capable of producing immense electric power came to be made. Sir Robert Peel was Prime Minister of Britain at that time. Faraday had occasion to explain to Peel the principle underlying his electrical theory. He gave a demonstration as well. He connected a galvanometer to a coil of wire and showed that, if a bar magnet was swung round the coil, the needle of the galvanometer also swung in response to the movement of the magnet. But that made no impression on Peel- He commented in a disparaging tone, "I have just seen that a needle moves when a magnet is moved about. But what useful purpose will this discovery of yours serve our country?" In reply Faraday only said, "No one can foretell what a newborn baby will grow up to be. Even so, my discovery may, some day, accomplish the impossible. It may be that, by making practical use of my invention, your government will, in the near future, realize a large amount of money by way of taxes from the people of this country." It was not long before Faraday's prophecy came to be fulfilled. The generators or dynamos by which electrical energy is produced nowadays work on Faraday's principle of electromagnetic induction. Apart from this theory, he made several other significant contributions, especially his principles of electrolysis. In the history of electrical science, 1831 is a significant year. That was the year in which Faraday found the process of electromagnetic induction. The same year, Joseph Henry, a teacher of Albany Academy, New York, made the same finding on his own. For many years he had worked to improve the electromagnet. The electromagnet he built for the Yale College laboratory was so powerful that it could lift 1600 kilograms and that too by means of electric 59

current obtained solely from a voltaic battery! There is difference of opinion about who first built an electric generator or a dynamo. According to some the credit goes to Faraday. Others say it should go to Henry. In modern times a huge amount of electric power is being used to operate various machines, to drive electric trains and trams, to light houses and streets. Modern power houses are equipped with enormous generators driven by turbines which are rotated by the pressure of steam or water. Steam turbines are now being used to drive thermoelectric generators, while, in the hydro-electric centres, the armatures of the generators are rotated by water turbines. In steam turbines, coal is burnt to heat water in a boiler and turn it into steam. The steam is directed by jets against blades of the turbine. The pressure exerted by the steam, kinetic pressure as it is called, sets the turbine in motion. In the thermo-electric system, only a portion of the total mechanical energy applied to the turbine of the generator is converted into electrical energy. In a hydro-electric generator, it is the pressure of water that rotates the turbine. Thomas Alva Edison (1847-1931)

Generation of electricity was no longer a problem. But it was yet to be brought to the house to be the common man's genie. The man who did that was Thomas Alva Edison. Edison was born in Milan, Ohio (America), on February 11. Though he became one of the greatest 60

inventors the world has ever seen, he received little or no formal education. He attended primary school for only three months or so. His mother took him out of the school when she heard that one day his teacher, after beating and scolding him, had said, "You are a veritable dunce. You will do nothing in life." Edison's mother, a teacher herself, started educating him. The result was astonishing. Edison grew more and more attentive to his studies. With unusual eagerness and interest he began to learn many subjects. When he was only 12, he began to look for a job. A new railway line had just been laid between Port Huron and Detroit and Edison applied to the railway authorities for permission to sell newspapers and food to passengers. As Edison was very young, his application was rejected. But he was persistent and, at last, was given permission to be a vendor. Not only could he earn a good deal, but also find much time for his studies. As the train usually stopped at Detroit for five or six hours, he became a member of a public library there. He began reading books on various subjects. What interested him most was chemistry. He made up his mind to be a chemist. This meant that he had to do experiments. With the permission of the train conductor, he set up a laboratory in a luggage van. All went well till one day a bottle filled with chemicals tumbled down and the van caught fire. At this the conductor flew into a rage and threw away all the chemicals and instruments in the laboratory. It was no longer possible for Edison to have a laboratory in the train. So he set up one at home, and resumed his experiments. Edison also got interested in telegraphy. Once he asked a telegraph operator, "Can you tell me how, in 62

this telegraph system, a message is conveyed through a wire?" The operator said, "Suppose the telegraph line is a dog with a very, very long body and the distance between its head and its tail is a few hundred miles. Now, when somebody pulls at the dog's tail, its head begins to bark. That is how a message goes from one end to the other end of the cable." Edison asked, "Well, but how does the signal come from the tail up to the head?" The operator grew annoyed and said, "Nay, I can tell you no more about it." But there were books and magazines to give Edison more reliable information about telegraphy and he read all he could. He also laid a telegraph line between his house and a friend's. After a long trial the two friends succeeded in exchanging messages through the wire. When he was barely 16, he did a heroic deed that brought him the chance to become better acquainted with telegraphy. His train had stopped at a wayside station and he was standing on the platform when he noticed a boy of two or three playing on the railway track. He was in imminent danger of being run over by wagons that were being shunted on the line. Edison flung himself on to the track, picked up the child and managed to jump clear with hardly a second to spare. The boy's father happened to be the telegraph operator at the station and on learning of Edison's interest in telegraphy, offered to teach him. Edison readily accepted the offer and within three months became an expert telegrapher. He gave up the job of vendor and got himself employed as a part-time telegraphist. Later he was posted as operator at Stratford, Canada. Edison was happy with his new job. Having been put on the night shift, he had all day to continue studies and experiments. 63

To make sure that the night operators stayed awake, the authorities had ruled that each should send a code message to the head office every half an hour. For Edison, the code signal was the number six in Morse. Edison found this annoying and soon made a device to transmit automatically his code number to the head office at the required intervals. It worked well. Before long, the matter became an open secret. And the telegraph authorities were not amused, even if the operators were. Edison had to leave the job. As there was a great demand for good telegraphists, it was easy for him to find employment elsewhere. But the work was not interesting and during the next five years he changed jobs. At the age of 22 he went to New York. One day, while looking for a job, he went to the office of the Gold Reporting Telegraph Company. Work there had been disrupted because the telegraph equipment had broken down. As the business of the company was to send out and receive the ever-fluctuating bullion prices, the owner was desperate. No one seemed to know how to set the instrument right. Edison saw that it was a special type of instrument, not like any he had used. But he was never lacking in confidence and he offered to repair it. The owner, Laws, looked at the young man with misgiving. Since he had no choice, he asked Edison to do what he could. It took Edison only a few minutes to learn how the machine worked and he set it right. Laws employed him on the spot on a salary of 300 dollars a month to keep the telegraph machine in order and to try to improve it. Edison liked the job. The pay was good and it gave him time to do his own research. He made alterations to make the instrument work better and received several patents for his discoveries. Soon he was recog64

Edison's first electric bulb.

nized not only as one of the greatest inventors of telegraphy but also as a great specialist in electrical science. By selling some of his patents he became a wealthy man. With money no longer a problem, Edison left his job and set up a laboratory and workshop at Newark, New Jersey. He invented various instruments and made them in his workshop. In 1874 Edison made up his mind to concentrate on invention rather than manufacture. He left Newark 65

and settled in a village, Menlo Park, where he built a mansion and set up a well-equipped laboratory. Menlo Park was about an hour's journey by train from New York and Edison thought that the peace and quiet of the countryside would be ideal for his scientific pursuits. Scientists were then trying to make an electric lamp. They had noticed that when an electric current was sent through a wire of high resistance, it generated heat. The wire itself became hot. If the temperature rose beyond a certain limit, it glowed. Ten years after moving to Menlo Park Edison started his own experiments. He let an electric current flow through a thin, thread-like wire of platinum. The filament heated up and began to glow. But only for a few seconds. The high thermal action of the electric current broke the filament. Edison wondered whether it would burn itself out so quickly if denied oxygen. He made an oval glass bulb and placed a filament in it. Then he pumped out all the air from the bulb. As he let electric current flow through the conductor, the filament again gave light. It was eight minutes before it broke. Edison knew that he was on the right track. Perhaps a filament made of a material less frail than platinum might be more suitable. Solid carbon would not serve the purpose, but how about carbonized thread? He heated a cotton thread in an enclosed, airless furnace, causing a black carbon layer to form on the thread. This filament gave light for 45 hours. It was very encouraging, but a better and more durable filament was needed. Edison continued to experiment with various materials. One hot day in summer, he saw a man he knew using a hand fan made of bamboo. It occurred to him that bamboo fibre might make a good filament. He took the fan from the man and pulled a strand 66

from it. The filament he made from it proved to be the best he had used. He then began to experiment with various kinds of bamboo. He sent men to bamboo-growing countries like China, Japan, Brazil and India to gather samples of different species of the plant. After testing about 6,000 samples, he found that a Japanese variety was the most suitable. The quest had cost him 100,000 U.S. dollars. Edison decided to begin making lamps on a large scale. He sent men to Japan to cultivate bamboos there to ensure an uninterrupted supply of fibre. Soon, however, he was able to make, artificially, a kind of filament out of cotton which proved to be even better than the one made of bamboo. Edison's invention was announced in a report in December, 1879, by Marshall Fox of the New York Herald after a two-week visit to Menlo Park. The news set the whole country agog. It was the most exciting topic of discussion everywhere, but many were sceptical of the claims made. Edison announced that he was celebrating New Year's eve with a festival of lights at Menlo Park and those who wished might participate in it. He chartered special trains to bring his guests from Philadelphia and New York. About 3,000 people assembled at Menlo Park on the appointed day. As darkness deepened, the multitude waited in great expectation and suspense. Suddenly, at the touch of a switch, dazzling lights turned dark night into luminous day. The houses and trees in the neighbourhood were also ablaze with lights. The crowd burst into applause. Edison had proved beyond doubt that the New York Herald report had not exaggerated the importance of his invention. But how could the electric lamp be made available to every household? Production of 67

electricity was limited. The existing power houses could supply only enough to meet the requirements of the telegraph and telephone lines and a few factories. Edison decided to establish a power generation centre in New York. So he returned to the city. But before starting production of electric power, he had to get over another great hurdle. People thought that electricity was dangerous. It could start a fire or even kill. To overcome their fears, Edison arranged a nightly parade on Fifth Avenue, a famous street in New York. More than a hundred men marched along the avenue, each carrying an electric light on his helmet. The lights were connected to a generator placed in their midst. In an opera at a famous theatre, he had every dancer appearing on the stage carrying a luminous 'magic wand' connected by wire to a generator beneath the stage. The newspapers published reports and comments on the parade and the opera and gradually people got over their fear of electricity. After winning over the Mayor, who first opposed Edison's plans to lay cables connecting the generator to houses, Edison turned to the banks for loans. It took time to convince them that the project was not as risky as they feared. At least they agreed to lend him a million dollars. And the Edison Electric Illuminating Company was born. Edison needed all his inventive genius and ingenuity to solve the numerous problems that faced him in providing the world's first city power system. It was pioneering work and he had to make all the instruments, fuses, meters, switches, wiring and bulbs that were required. During his lifetime, he received more than 1,000 patents. A good number of them were for his invention during this period. 68

Edison soon completed the work and announced that his company would begin to supply electricity from September 4, 1882. On the evening of that particular day, exactly at the appointed time, Edison inaugurated his historic undertaking by pressing a switch. At once, about 14,000 electric bulbs blazed in 9,000 houses. The same evening, at the office of the New York Herald, Fox, sitting at his desk lit by an electric lamp, wrote a report which was published in the paper the next day. "The wizard of Menlo Park has turned into a common reality what his critics and detractors denounced as impossible." Within a short time, power stations were built not only at many places in New York but also in towns and cities all over the country and in Europe. Humanity had stepped into the era of electricity. Sir Joseph John Thomson : electrons

A few months before the world was startled by Edison's invention, scientists had been even more startled by a discovery. It was made by Joseph Thomson (1856-1940), Director of Cavendish Laboratory, Cambridge. Thomson had observed that, when high voltage was applied to both ends of an airless tube, a ray of light emanated from its cathode and caused a fluorescence around the body of the tube itself. And this 'cathode ray' bent away the moment an electric or magnetic field was applied to it. This led him to the conclusion that the ray was electric. But there was nothing in the tube, called the 'Crookes tube'. Could electricity abide in vacuum? 69

On April 30, 1879, as Thomson sat peering at the tube in the laboratory, his doubts vanished. He was certain that the ray was electric and was composed of numberless electric particles. Emerging from the cathode, they flowed to the other end of the tube, causing the fluorescence. Thomson assumed that these same particles flowed through a metallic wire when an electric current passed through it. Now the question was, where did the particles come from? What was their real nature? They could not have originated from emptiness, from vacuity. What, then? Did they emerge from the atoms of the matter itself? In his excitement, he began to pace up and down the laboratory. If his assumption was correct, his discovery would strike at the root of a belief people had clung to for centuries—that atoms were indivisible. If the particles had really emerged from the atoms of matter, did it not prove that an atom was composed of still smaller particles? Thomson realised that he had made a great and significant discovery. Observing the effect of electric and magnetic fields upon the cathode ray, he learnt that the constituent elements of the ray were negatively charged particles. So he came to the conclusion that the atoms of every matter consisted of negative electric particles. He called them 'electrons'. Thomson also expressed the view that the component particles of the atom could easily be separated. On the basis of this assumption, many problems of electrical science could be solved and many questions answered. Why did materials become electric by friction? And why did an electric current keep flowing through a wire when voltage was applied to the two ends of it? Thomson's theory could answer these questions. The discovery of electtons is a revolutionary event 70

in the history of science. It changed previous conceptions regarding the construction of matter. Scientists now began to think anew about atomic structure and turned to a new line of research. By and by many other facts came to light and gave birth to a new branch of physics called atomic physics. Stephen Grey had once said to his friend, Wehler, "Granvil, it often occurs to me that once we can 71

know the true nature of electricity, the mystery of this whole material universe will reveal itself to us." The more we know about matter, the more we understand that Grey was not wrong. The world of atoms is really the world of electricity. Therefore, in order to comprehend the real nature of atoms, we must study electricity. For this great discovery Thomson was awarded the Nobel Prize in 1906. He lived up to 1940, to witness many miracles of electronics, the outcome of his discovery. Radio telegraphy : a new age

out half a century before Thomson discovered electrons, Michael Faraday had observed that the power of electricity could extend through empty space from one place to another. He noticed that an electric current fluctuating in a conductor induced itself into another placed in its neighbourhood. Even when there was no physical contact between the two, the current in the one could pass to the other. Faraday could not explain this. But in the very year that he made known his observations—1831— was born the man who could. He was James Clerk Maxwell (1831-79), a Scotsman. Maxwell was a great mathematician. He illustrated by mathematical argument that a magnetic field would be created around a particular place where there was an electric field of fluctuating intensity. Not only that, by mathematical formula he could show that whenever any change occurred within an electric or magnetic field, its effect would spread in waves. The waves came to be called wireless waves. 72

1

When Maxwell, with his simple apparatus, proved the existence of wireless waves, he could never guess that the results of his experiments would bring about a miraculous improvement in the whole system of communication. Ten years after the death of Maxwell, a German scientist, Heinricb Hertz (1857-94), testified to the truth of his theory. In 1887 Hertz produced electromagnetic waves. He died seven years later, when he was only 37. Jagadish Chandra Bose (1858-1937)

T h e hero of the next part of the story is Jagadish Chandra Bose, an Indian scientist, who achieved remarkable success in his researches. As a young student of physics at the University of Cambridge he took special interest in electromagnetic theory. Maxwell had been Dean of the Faculty of Physics at Cambridge and the details of his researches and experiments were preserved at Cavendish Laboratory. There can be no doubt that Bose was greatly influenced by these. After completing his studies at Cambridge, Bose returned to India in 1884 with a letter of introduction from Prof. Fosset. It was addressed to Lord Ripon, the Viceroy. Bose met Lord Ripon in Simla and was appointed a professor of physics at Presidency College, Calcutta. At that time, Indian professors were paid much lower than their European colleagues. In protest against this, Bose refused to accept his salary for three years. As he had a good reputation as professor, the managing body of the college and the authorities of the Education Department came to terms with him and granted his 73

demand for fair remuneration. But Bose was not a man to rest satisfied with his reputation as a professor. He decided that the study and pursuit of science should be his main aim in life. The Presidency College laboratory was not well equipped and Bose had himself to make all the instruments and appliances he needed. The skill and ingenuity he 74

displayed in making sophisticated instruments out of tin sheets, iron discs and wood chips, with the assistance of only common blacksmiths and carpenters, had no precedent in the history of science. Soon his research and experimental work on electromagnetic waves drew the attention of scientists in Europe. He was able to prove that invisible electric waves and visible light waves were homogeneal and akin to each other. In 1895 he read to the Asiatic Society a treatise on the subject. And in the course of his research on invisible electric waves, he conceived the idea of sending signals through space by means of electromagnetic waves. In those days a small mechanical contrivance, known as 'coherer', was an essential component of every wireless receiver. Bose experimented with the 'coherer' and made such great improvements that he brightened the possibility of sending and receiving signals by wireless. He demonstrated in his laboratory that electric waves could be transmitted to a distant place through space. His experiments also showed that by the waves of electricity man could control a phenomenon occurring at another place. This in essence is the Remote Control System. Here is what he wrote about an experiment he conducted at the Calcutta Town Hall in the presence of many scientists : "This invisible light can easily make its way through the barriers of bricks, stones and buildings. So, by this light, it may be possible to send signals without wire. In the Town Hall, in 1895,1 gave various demonstrations of its effect and performance in the presence of Mr. Mackenzie, the Lieutenant-Governor of Bengal. "This electric wave penetrated through his enormous body, passed through two close apartments and got into another room to create great confusion there. 75

It threw away an iron ball, fired a pistol and blew up a heap of gunpowder." The Electrician, a journal published in England, commented: "The apparatus invented by Jagadish Bose has paled into insignificance all other instruments that have been devised so far for transmitting signals without wire". Admiral Henry Jackson of the Royal Navy found in Bose's apparatus a solution to the problem of sending signals from one ship to another that had long troubled him. The journal, Electric Engineering, of London, commented in 1897: "The logic which has inspired and led Jagadish Bose to invent wireless telegraphy and the instrument he has devised for this purpose deserve admiration. The superiority of his radio apparatus to other similar instruments is beyond question. Yet, it is really surprising that he had made no secret of his technique. No one is debarred from making use of his instrument and reaping profit out of it." To conceal a scientific truth or to capitalise on it to make money was something inconceivable to a man like Bose. When he went to England to publicize the results of his reasearches a business magnate called on him and said, "Please do not publish in your lectures all the facts of your discovery. Allow me to take a patent in your name. You do not know how much money you are losing by your neglect. By making use of your wireless receiver, we shall set up our telegraph company. I shall defray all its expenses. And half the profit will come to you". This is how Bose mentioned the incident in one of his letters from London to his friend, Rabindranath Tagore, in 1901: "Money, money! O, what a terrible, all-devouring greed! If I ever be caught in such a grinding mill, there 76

Marconi in his laboratory.

would be no way out for me. You see, my friend, the work I have in hand is above all commercial transactions. That is the reason why I declined his offer." If he had come to terms with that business tycoon and taken a patent for his discovery, he, and none else, would have been called the inventor of radio telegraphy. But it is not Bose, but Marconi, whom the world identifies with radio telegraphy. Guglielmo Marconi (1874-1937) was born in Italy. His father was a successful businessman and his mother came from a rich Irish family. So money for his scientific pursuits was no problem. And from early boyhood, he took interest in all matters of science. 77

When he was only 18 he read, in a British journal, a few articles by Heinrich Hertz. Like Jagadish Bose, he realized that, by means of Hertzian waves, signals could be sent through empty space. In 1894, when he was 20, he set up a laboratory in his house and began his experiments. Within a few years he was able to learn the technique and make an apparatus to transmit and receive Morse code signals. While Hertz had used a square metal sheet for aerial, Marconi set up a pole, 40 feet high, to serve as the antenna, increasing the range of the wireless waves. He found that he was able to receive clearly a signal sent from a distance of a mile and three quarters. With the idea of introducing a wireless communication system covering the whole country, young Marconi

Marconi's

78

historic transmitter and receiver.

appealed to the Italian government for assistance. But a prophet is not honoured in his own country. Italy failed to appreciate the scientific genius of Marconi. And the Italian government took no interest in Marconi's project. Having failed to win the patronage of the Italian government, Marconi went to England in 1897 and received a patent for his apparatus. A good number of enlightened people in England took interest in his project. A telegraph company named Marconi Wireless Telegraphy Limited was established. A number of scientists were appointed to help Marconi. They worked together to improve his wireless apparatus, extending its range to eight miles. But Marconi did not stop there. He thought that signals could be sent over hundreds of miles, even across the Atlantic Ocean. Many were sceptical, but not the directors of the company, who did not hesitate to spend 200,000 dollars on the experiment. A wireless transmitter was installed at Poldhu, a town in Britain. Marconi sailed to America to place himself with his receiver at St. John, on a high mountain in New Foundland. Marconi wanted as high a radio antenna as was possible. He suddenly remembered that, about 100 years earlier, Benjamin Franklin had shown that electricity from lightning could be conducted through the thread of a high-flying kite. There was no reason why an aerial could not be kept up by tying it to a kite. On December 12, 1901, Marconi tied one end of a 500 feet long wire to a kite and let it fly up. The other end was connected to his radio receiver. He looked at his watch. Within a few minutes, Fleming would start sending his signal from the other side of the Atlantic. The minutes were the longest he had ever spent. At the appointed time, trembling with doubt and 79

hope, he turned on the receiver. Only a soft gurgling sound came from it. Marconi listened intently. Again a few moments of suspense and, suddenly, he heard something meaningful. "Can you hear anything?" Marconi called out to his two assistants. All three sat close to the receiver and listened. Marconi was not mistaken. They all heard, faintly the dot-dot-dot that they expected to hear, the Morse Code for the letter 'S', the signal that Fleming had been instructed to send. Marconi had accomplished the miracle he had promised. Within a short time there came a revolutionary change in the whole system of communications. Radio transmitting stations were set up in towns and cities. Every ship of the British Royal Navy was equipped with a radio transmitter and a receiver. Many other ships were also similarly equipped, but it needed a disaster to drive home the importance of radio telegraphy. On April 14, 1912, at midnight, the luxury liner, the Titanic, struck an iceberg. As SOS signal, calling for rescue, was sent out from the ship. At that time the ship, the Californian, was only 32 miles away, but its radio operator was not on duty. Another ship, the Carthapia, picked up the SOS signal and changed course to rush to the rescue. But the Carthapia was far away and could reach the place of the accident only twenty minutes after the Titanic sank. Of the 2,224 passengers, 1,513 had already drowned. The Carthapia could save the lives of only 711 men, women and children. The Titanic, after it was severely damaged, had kept afloat for nearly two and a half hours. Had there been a radio operator on duty on the Californian, it could have reached the scene of the accident in time to save all those on board the stricken ship. After the disaster, 80

at an international conference held in London, it was decided that there should be a wireless operator on duty all the time on every passenger ship. Revolutionary achievements of electronics

ile Thomas Edison was engaged in improving the quality of his electric lamps, he made a significant discovery. To test a theory he had, he placed a metal plate within an electric bulb. He observed that, while an electric current could be sent towards the filament by connecting a battery between the plate and the heated filament, in no way could an electric current be sent from the heated filament to the plate. Edison was so busy with his other experiments that he had no time to study and explore this phenomenon. But when his findings were published, Sir John Ambrose Fleming (1849-1945), an English scientist, found them of great interest. After completing his study at Royal College, he went to Cambridge, where he worked at Cavendish Laboratory under Clerk Maxwell. Later he joined the Electrical Engineering Department of London University as a professor. It was there that he came to know of the Edison process of anode-plating. Fleming had been thinking of the possibility of a radio telephone system. He felt the need to devise an instrument through which electric current could flow only in one direction. Using the Edison method such an instrument could perhaps be built. In 1889 he made an airless bulb with two electrodes. The apparatus was called the 'diode valve', because, through this the electronic flow would be impelled in only one direction. In the diode valve of Fleming's 81

device, one of the two electrodes was the filament and the other the plate. A carbon filament was used and round this was fixed a conic metal foil which formed the plate. The action of the valve may be explained in this manner: When a current is sent through the filament, it becomes hot and radiant. A beam of electrons shoots up from the filament. When the positive electrode of the battery is connected to the plate and the negative electrode to the filament, the electrons emitted by the filament rush towards the plate. An electric current 82

begins to flow through the space between the plate and the filament. But the moment the filament is connected to the positive pole and the plate to the negative pole of the battery, the plate repels or drives back the electrons. And so no electric current flows through the valve. In 1907, an American scientist, Lee De Forest (1873-1961), placed between the filament and the plate of a diode valve another electrode composed of spirals or lattices of wire. He thus made a valve of three electrodes, a triode valve'. By means of this valve a weak electric signal can be amplified to a great extent. It is this particular process of signal amplification that made the radio receiver and radio telephony possible. The branch of physics which discusses the principle and the application of these instruments is known as 'electronics'. The science of electronics has brought about a complete change in our way of life in the past seventy years. Besides the electronic valves, the discovery of the photoelectric effect and the invention of the transistor greatiy contributed to the advancement of electronics. The process of converting light into electricity was first found by Willoughby Smith. In 1873 Smith observed that when selenium was exposed to light, its electrical conductivity changed. If a piece of selenium was placed within an electric circuit and the intensity of the light falling upon the selenium was varied, a corresponding variation occurred in the current of the circuit itself. But the variations were not instantaneous and so a better method of converting light into electrical energy was needed. In 1888, a German scientist, Hallwachs, noticed that when ultraviolet rays fell on a polished zinc plate charged with negative electricity, the plate became electrically neutral. But, if the ultraviolet rays were thrown upon the same zinc plate after it was charged ;

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with positive electricity, the plate did not lose its electric charge. Philipp Eduard Anton von Lenard (1862-1947), another German scientist, demonstrated that when ultraviolet rays fell on a metal plate charged with negative electricity, the plate discharged electrons. That was why it became electrically neutral. Two other scientists, Elster and Geitel, noticed that some materials like sodium, potassium and caesium also discharge electrons when light fell on them. The emission of electrons by the effect of light is known as the photoelectric effect. It is the practical application of this photoelectric effect that has made the invention of television possible. The photoelectric effect is also being used for automatic street lighting, recording sound on photographic plate and reproducing sound. The invention of the transistor was spurred by the flaws in the functioning of triode valves. An apparatus fitted with valves does not start working immediately on being switched on. Only when the cathodes become heated do the valves emit electrons. And, being made of glass, these valves are frail and brittle. Besides, an electronic apparatus made with a combination of many such valves has to be large. Soon after the Second World War a group of scientists of Bell Telephone Laboratory in America began looking for alternatives to electronic valves. Of them Walter Brattain, William Shockley and John Bardeen may be mentioned. They succeeded in making transistors by using 'semi-conductors'. Materials through which electric current can easily flow are called conductors. Silver, copper and aluminium are good conductors. Glass, backelite and china clay, through which no electric current can flow are non-conductors. 84

Semi-conductors are a class by themselves. In their pure state semi-conductors are non-conductors. But, in suitable combination with other materials, they acquire conductivity. For instance, germanium, in its natural state a non-conductor, becomes a conductor with a proper mixture of arsenic or gallium. By making use of semi-conducting materials it was possible to devise a 'semi-conductor diode'. The scientists of Bell Laboratory, by using semiconducting properties of matter, were able to make transistors which were not only as efficient as triode valves and less frail, they also work the moment an apparatus fitted with them is switched on. Besides, transistors are easier and less expensive to make. The transistor has made it possible to invent many wonderful instruments. One such is the 'pace-maker', which is planted in the chest of a patient to correct the heart-beat. The most remarkable invention of the century is the computer. This instrument may well be called an artificial brain. It can work out complex mathematical problems with unbelievable speed. It can store in its memory numerous data, analyse them and take decisions. To execute these decisions, it can turn on, by itself, electro-mechanical devices. Computers are now being used extensively in automatic systems of industrial operation. With computers, robots have been made to take on the harder tasks in factories. Computers now help doctors. With the aid of computers it has been possible for man to send pilotless craft into infinite space and to bring them back to earth. But for computers, it would not have been possible for man to land on the moon and return to earth. While computers have opened new vistas that promise much for human welfare, they also threaten human existence. They are already extensively used by 85

the armed forces of all countries, particularly of the super powers. And, in days to come, computers will be helping even more to decide military strategy and conduct operations. The genie of electricity can bless man. It can also annihilate him. It depends on man to make it good or evil, for it acts only as he commands.

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Electricity and magnetism are phenomena which arise from the nature and behaviour of the electrically charged particles—the protons and electrons—which together with the uncharged neutrons are the principal constituents of atoms. The exact nature of an electric charge is still unknown, but it can be measured, and its effects can be predicted and put to use, being the basis of all electrical and electronic equipment. The charge carried by a proton is called a positive (or + ve) charge, and that carried by the electron is called a negative (or - ve) charge. A pair of similar charges, two positive ones,for example, will repel each other, but two unlike charges, one positive and one negative, will attract each other. The region around a charged particle in which these forces of attraction and repulsion operate is called an electric field. The Illustrated Encyclopedia of Science Published by Marshall Cavendish Books Limited.London

The Story of Electricity Thanks to electricity what was incredible has b e c o m e commonplace. The earliest discovery about this 'magic force' was m a d e more than 2500 years ago by a Greek called Thales. Since then man has set about taming the powerful genie. This book tells you how.

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