Page:Popular Science Monthly Volume 84.djvu/117

Rh electricity was embraced in the knowledge obtained by the Frenchman Coulomb regarding the law of force with which electricity at rest upon conducting bodies attracts and repels other electricity. Nothing was known of the phenomena of electricity in motion, flowing, as we say, in a current. It was not until 1827 that the law stating the dependence of the strength of the current on the driving-power of the battery causing it was discovered by the German Ohm. But a fundamental discovery was made in 1820 by the Dane Oersted when he found that the current in a wire would act upon a magnet anywhere in its vicinity, or would produce what we now call a magnetic field. Upon this discovery depends the possibility of all our telegraphs, for which the current was soon utilized. But a more powerful intellect than that of Oersted, namely that of the Frenchman Ampère, inspired by Oersted's discovery that a current acted like a magnet, reasoned that in that case two currents would exert magnetic forces upon each other, and in a wonderful series of researches determined the mathematical laws of these mutual actions of currents in the most complete manner. When we see the primitive apparatus with which Ampère made these brilliant discoveries, we are led to have the most profound admiration for his brilliant experimental and mathematical genius, and we may secretly wonder whether we have not laid too much emphasis to-day on fine laboratories and equipments. The next commanding genius that appears on the scene, whose work is more important than any of those yet mentioned, is Michael Faraday, professor at the Royal Institution, a laboratory for research and popular lectures, founded by our own countryman who later became Count Rumford, but made forever famous by the discoveries there made during a long term of years by Faraday. Those who have visited the laboratories at the Royal Institution will be surprised at the total lack at that time of all the conveniences that we today expect, but Faraday was no doubt perfectly satisfied with it. Today electric lighting and supply of current in a laboratory is a commonplace—then there was not even gas, and all currents had to be made by batteries laboriously filled with chemicals for each time of use. There was no insulated wire, and Faraday had to wind his own with thread or ribbon. Among the greatest triumphs of Faraday was his discovery of the converse of the production of magnetism by electrical current; I mean the production of current by magnetism. After long attempts, he found that if a magnet was moved into, out of, or in the neighborhood of a coil of wire forming a complete circuit, then a current of electricity was induced, as he put it, in the coil during the motion of the magnet. This is the germ of our dynamo-electric machines which to-day supply all the current for our light, power and electric traction. Could Faraday have seen the huge dynamos of ten thousand horsepower each that convey the power of Niagara Falls to regions a