And the mystery of the telephone grows no less the more one studies it. You speak against a tiny disc of sheet-iron, and the disc trembles. It has millions and millions of varieties of trembles, as many as there are sounds in the universe. A piece of copper wire, connected with an electric battery, stretches from the disc against which you have spoken to another disc miles and miles away. The tremble of your disc sends an electric thrill along the wire to that other disc and makes it tremble exactly as yours did. And that trembling sounds the very note you spoke, the very note in millions of possible notes, and as accurately as if the sound wave had only traveled three feet through clear air. That is what happens when you telephone, but when you realize it the mystery gains rather than decreases. Scores of men claimed to have invented telephones before Bell did, but none ever proved their claims. Men who were studying improvements on the telegraph had glimpses of the ultimate possibility of transmitting speech by wire, and Elisha Gray filed a caveat on that point later on the very day that Bell filed his application for a patent. But Gray’s was a caveat, or a declaration that the applicant believes he can invent a certain device, and Bell’s was the statement that he had already perfected his invention. Bell’s claim stood against the world, and men now recognize that the telephone was born on that afternoon in June, 1875, when the young teacher of deaf-mutes first caught the faint twang of a snapping reed sent across a few yards of wire. XIV EDISON AND THE ELECTRIC LIGHT 1847- To some men the material world is always presenting itself in the form of a series of fascinating puzzles, to be solved as one might work out a game of chess. The astronomer is given certain figures, and from those he intends to derive certain laws; the scientist knows the properties of certain materials and from those he is to reach some new combination that will produce a new result. He is not an inventor as much as he is a detective; he picks up the clews to certain happenings and constructs a working theory to fit them. In mechanics this theory that he constructs usually takes the form of a machine. And this machine is not so much a new discovery as it is the practical working-out of certain carefully-selected laws of nature.