explaining the work on which he was engaged. There was no affectation of mystery, no attempt at keeping his experiments a secret. Even the laboratory notes were open to inspection. Menlo Park became a kind of Mecca to the scientific pilgrim; the newspapers and magazines despatched reporters to the scene; excursion parties came by rail, and country farmers in their buggies; till at last an enterprising Yankee even opened a refreshment room.
The first of Edison's greater inventions in Menlo Park was the 'loud-speaking telephone.' Professor Graham Bell had introduced his magneto-electric telephone, but its effect was feeble. It is, we believe, a maxim in biology that a similarity between the extremities of a creature is an infallible sign of its inferiority, and that in proportion as it rises in the scale of being, its head is found to differ from its tail. Now, in the Bell apparatus, the transmitter and the receiver were alike, and hence Clerk Maxwell hinted that it would never be good for much until they became differentiated from each other. Consciously or unconsciously Edison accomplished the feat. With the hardihood of genius, he attempted to devise a telephone which would speak out loud enough to be heard in any corner of a large hall.
In the telephone of Bell, the voice of the speaker is the motive power which generates the current in the line. The vibrations of the sound may be said to transform themselves into electrical undulations. Hence the current is very weak, and the reproduction of the voice is relatively faint. Edison adopted the principle of making the vibrations of the voice control the intensity of a current which was independently supplied to the line by a voltaic battery. The plan of Bell, in short, may be compared to a man who employs his strength to pump a quantity of water into a pipe, and
