Page:Popular Science Monthly Volume 1.djvu/677

Rh Let me here allude to those stupendous processes, the manufactures of sulphuric acid and of soda. To sketch the influence of chemistry upon life would carry us too far. Glass and soap are better to-day, and, despite their hundred-fold increased consumption, no dearer than in former times. Chlorine, as a bleaching agent, in place of the sun, has restored to agriculture thousands of acres of meadow-land.

But the powerful impulse carried also the kindred sciences. The Italian physician Galvani accidentally noticed the convulsions of a frog recently killed, whenever he touched him with two metals in contact with each other. This observation became the starting-point of the electric telegraph. The experiments of Volta resulted in the pile named after him. Two heterogeneous metals, such as zinc and copper, are immersed in a glass of water, to which a few drops of sulphuric acid have been added; both metals we connect by means of a long wire, and then we find the wire possessed of a new force which can transmit a motion through the distance of a hundred miles and over. For a long time the voltaic pile had been the subject of unsuccessful experiments for the purpose of finding its relation to the magnet, to which, on account of its poles, it bears a certain resemblance. One day, Oersted, at a lecture in Copenhagen in 1819, noticed that a magnetic needle on his table was disturbed by a communicating wire that happened to pass over it. He removed the wire, and the needle resumed its polar direction; he then replaced the wire, and the needle again turned aside. Electro-magnetism was discovered. At once he recognized the immense bearing of the phenomenon, repeated the experiment in presence of the magistrate, a notary public, and other witnesses, and made a Latin affidavit; this places his name, for all time to come, among the benefactors of the human race. The advantage of his invention is enjoyed by all of us who daily read telegrams from distant parts of the world as if this rapid transmission of news were a matter of course. The wonder has become a fact of daily occurrence; it rises with us and accompanies us through the day. Do you ever consider that, without this discovery of Oersted, the telegraph would not exist?

We place thirty or forty glasses of water in adjacency, each containing a plate of zinc and one of copper, together with a small quantity of sulphuric acid; we join the vessels by means of metallic wires soldered to the opposite plates, and connect the two extreme plates of the series with the ground, the extreme zinc plate by a short wire, the last copper by, say, a hundred-mile wire. A slight pressure of the finger upon a knob supported by a spring, and a dash or dot is produced a hundred miles away; thought is transmitted to that distance by the electric current; it makes its own record, the recipient needs simply to read off the marks. And through still greater distances it may be flashed by what is termed a relay, so that there is no greater difficulty in forwarding a dispatch from New York to San Francisco than from New York to Boston.