CHAPTER XIII. Electric Light

ELECTRIC LIGHT

MAN is not the only living being which sees by artificial light. Cats’ eyes shine in the dark. So do glow-worms, and in South America there are some insects which shed so bright a light that they are used by the natives as lamps. These lights produced by animals are much superior to the artificial lights which we can produce. They are very economical. The animal expends very little of its strength in producing the light, and the light is much cooler in proportion to its brightness than any other light we know. Ever since man has learned how to kindle a fire he has been able to light up the darkest night. He no longer depends upon the sun and moon. But the fire which savages make with logs of wood not only gives light, but also heat. It gives far more heat than light. It is so hot that one cannot touch it, and yet we can look into its blaze without feeling hurt by the glare. It could be much brighter than it is without blinding us.

Lamps were invented probably by the ancient Egyptians. They consisted of a shallow vessel full of oil, with a wick dipping into it. Candles were used later, when it was found that certain kinds of fat could be made to melt just where the wick touched them. But even the best candles give a poor light, unless hundreds of them are lighted at the same time, and then they give a great deal of smoke. The best light of all would be a light which was very bright, but gave no heat, smoke, or smell. It would have to be also very cheap, and so arranged that it could be lighted at once at any time and in any place.

The last century has seen wonderful improvements made in lamps, and further improvements are made every day. The most convenient light invented up to the present time is the electric light. It gives no smoke, it is clear and bright, it can be turned on with a slight touch, and it is cheap. It is better than oil lamps, since there is no trimming of wicks and no oil to fill up. It is better than gas, since it requires no match for lighting it, and there is no danger of explosion.

The invention of the electric light belongs entirely to the nineteenth century. Sir Humphry Davy was the first to produce it. He had a great battery of two thousand cells at the Royal Institution, and he found that when he joined the two ends of the battery by wires and separated the wires again, a vivid light played between the two ends of the wires. This light or flame was so hot that it melted all metals, including platinum, which is extremely difficult to melt. He tried to find some substance which would not melt, but would yet conduct electricity. He tried charcoal, but found it conducted the current very badly. He plunged it in mercury, and so obtained a fairly good conductor, which did not melt in the electric flame, but burned away rather quickly. However, he showed this light at the Royal Institution so long ago as the year 1808, and it excited great wonder and curiosity.

For many years this remained the only experiment, and it was only towards the middle of the century that a substance was found which burned away very slowly. That substance was discovered at the bottom of the crucibles used for making coal gas. When all the coal gas had been driven out of the coal by heat, and only the coke remained, it was found that a very hard and compact black mass remained at the bottom of the crucible. That substance was called “gas carbon.” It conducted electricity well, and made a very good substance for experiments on the electric flame. It was cut into small rods, and the flame was made to play between the ends of two such rods.

The flame was always seen to be in the form of an arch or arc, curving upwards between the two rods. This was due to the heat of the flame which produced an upward current of air between the pencils. The flame was therefore called the “electric arc,” and a lamp containing it was called an “arc lamp.” Such arc lamps are used to the present day for lighting streets and squares. One such lamp is as bright as several thousand candles burning together. The light which comes from the white hot ends of the carbons is the brightest that it is possible to produce artificially.

But the arc lamp is really too bright for ordinary use. It is quite blinding, and it would not do to bring it into an ordinary room. For many years electricians were busy trying to make another kind of electric lamp which would not give such a glaring light as the electric arc. The two men who did most to solve this problem were Thomas Edison in the United States of America and Joseph Swan in England.

Edison was born in the year 1847. He never went to school. All the education he ever got was given to him by his mother.

At the age of twelve he was put to work on a railway. Having a great deal to do with newspapers, he managed to pick up the art of printing, and by and by he printed a newspaper of his own in a luggage van. One day he rescued a station-master’s child which was nearly run over by a train. The station-master, out of gratitude, taught him how to work the telegraph, which had been introduced just then. Young Edison very soon acquired great skill at the telegraph, and was soon employed as a telegraphist.

When only twenty-one Edison invented a new telegraph which could print its own message. That invention was found extremely useful, and several telegraph companies asked him to invent other things for them which were wanted badly. Edison set up a factory of his own for making printing telegraphs, but within a few years he sold his factory, which had become too small, and set up a large new establishment at Menlo Park, in the city of New Jersey. That establishment has since grown to a great size, and Edison is still working in it at many wonderful inventions.

Edison’s great idea was to use electricity to make life easy and pleasant. In order to do this he proceeded in a rather different manner from the earlier discoverers. In Europe the object of men of science has usually been first to discover a new truth, and then to find in what way the discovery could be made useful to humanity. Some scientific men consider that the first object is much more important than the second.

It is told of a certain professor who had made a great discovery in chemistry, that his greatest satisfaction was the thought that it was never to be of the slightest use to anybody. The story, of course, is not true, or at least it is greatly exaggerated, for no great discovery in science can be entirely useless. It enlarges our knowledge of the nature and constitution of the world, increases our power over matter, and with every increase of power we are better able to improve our surroundings and make nature do our will.

Edison, however, proceeded in a different way. He first of all asked himself what great problem wanted a solution. Having found the problem, and stated it clearly, he collected all the facts and observations that had any connection with the problem. Then he looked for the best way in which to attempt the solution, and if necessary he made a vast number of new experiments and investigations. In this way he not only made great inventions, but great scientific discoveries as well.

When he set himself to find a convenient electric lamp, he knew that when a strong current is sent through a thin wire, that wire becomes red hot, or even white hot, and therefore gives a light. Such a light is not a glaring one, and therefore is better in one respect than an electric arc. Edison tried a great many different wires, and although many of them gave a good light, they did not last long. A platinum wire could be made white hot for some time, but in the end it always broke in some place.

As the electric arc had been constructed successfully with carbon, Edison naturally tried carbon next. Charcoal was found to be too porous, and gas carbon could not be drawn into wires. It then struck Edison that if a silk thread were subjected to great heat, it was turned black. It would, so to speak, be made into carbon like charcoal, and would not require thinning down, as it would be quite thin. He tried the threads of silk, cotton, and flax, and heated them strongly in a closed vessel. They produced very fine threads of carbon, but these threads broke when they were in the least disturbed. Of all the substances which Edison tried, a bamboo fibre was found to be the best, but even that wore away after being used in a lamp for six hundred hours.

Edison next invented what he called an “electric candle.” It was a short rod made of platinum powder mixed with lime. But he shortly afterwards came to the conclusion that nothing but a fine thread resembling a wire, but made of carbon, would really answer the purpose. It is strange that this conclusion was reached just about the same time by Mr. Joseph Swan in England. The two inventors were working along the same lines, and in the end they arrived at the same point. Edison obtained good results by mixing lamp black and tar, and drawing it into a fine thread. Joseph Swan, on the other hand, soaked a thread of carbon in sulphuric acid, which made it into a kind of parchment. He then blackened it by exposing it to great heat. Both inventors were very successful, and produced lamps which were in every respect satisfactory.

Both men had patented their inventions, and for some time there was great rivalry between them, but in the end they decided that it was better to be friends than enemies. They formed an alliance, and their lamps were all made in the same way, and distinguished by the word “Ediswan,” which is a combination of “Edison” and “Swan.” Cotton wool was soaked in a solution of chloride of zinc. This gave a pasty substance called cellulose. A lump of this was forced by pressure through a very small hole, and so drawn out into a fine thread. The thread was then blackened by heating it in a crucible made of plumbago, and so the fibre was finished. The fibre was called a filament.

The next thing was to enclose the filament in a glass globe in which not a trace of air would get near it. For if even the smallest quantity of air got near the filament while it was glowing, it would at once burn up. It was easy enough to pump all the air out of a glass globe, and leave only some other gas in the globe that would do no harm, but the difficulty was to mount a filament in the globe and to conduct a current through it from the outside.

This was done by melting thin platinum wires into the glass. Platinum wires were the only wires which would not break the glass. For when platinum is heated it expands in the same way and to the same amount as glass, and therefore it does not break away from it. The filament was joined to the platinum wires by a special cement. After all this had been done, the air was pumped out, and the globe was melted off the pump at the lower end where the little point of glass is seen. The glass globe is called a bulb. It is provided with a brass collar from which two points stick out sideways. These points fit into recesses in another brass collar into which the wires bearing the electric current are led. This kind of joint is known as a bayonet joint.

The current for the lamps is furnished from a special factory in which a steam-engine is made to turn an electric machine called a dynamo. Such a dynamo is constructed on the principle of the induction currents discovered by Faraday. Faraday’s whole life was spent in discovering new truths. He did not think first of all of the use his discoveries might be to mankind. He knew well that there were plenty of engineers and inventors ready to take advantage of his discoveries. It is very well that the discoverer and inventor should work hand in hand. The discoverer shows the way in which great achievements can be attained. The inventor makes these great practical achievements, and the good that results from them comes back to the discoverer in the gratitude of those who have been benefited by his discoveries and the happiness which followed from them.