This principle of loose contact has since been employed for another instrument which is perhaps even more wonderful than the telephone. It is the “microphone,” which was first constructed by Edwin Hughes in 1878. A current was sent through a Bell telephone and through two pieces of carbon joined by a rod of carbon which was laid loosely across them. The slightest sound produced on the board which held the carbons was converted into a loud sound in the telephone. When a fly walked across the board, the patter of its feet could be heard in the telephone. CHAPTER XIII 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. [Illustration: Fig. 63.--An Arc Lamp.]