Page:Popular Science Monthly Volume 7.djvu/378

364 two pieces of gold are placed one in a cell of nitric and the other in one of hydrochloric acid, separated by an earthen-ware partition, no chemical action takes place; but, if the two pieces be connected by a wire, the acids immediately attack them. In 1840 he was elected a Fellow of the Royal Society, and in 1841 he published a paper "On the Combinations, by the Voltaic Battery, of Azote and Hydrogen with Metals." This same year he excited a great deal of interest by exhibiting, before the Electrical Society, daguerreotype pictures engraved by electricity. The picture was joined with the positive pole of a battery, and placed in hydrochloric acid; the chlorine set free attacked the silver surface unprotected by mercury, and from this etched surface an electrotype was made to be printed from. Though now in active practice at the bar, he continued his electrical investigations. He brought out his voltaic gas-battery, and wrote a paper on its applications to endiometry; published a "Memoir on the Action of Phosphorus, Sulphur, and the Hydrocarbons in the Gas-Pile;" and a communication on the "Electric Action by the Approximation of Dissimilar Metals without Contact," in which he showed that when a disk of zinc and one of copper are approximated without touching, and then separated, the gold leaves of an electroscope diverge, proving the existence of a radiating force capable of exciting electrical disturbance. In January, 1842, Mr. Grove delivered a lecture at the London Institution "On the Progress of Physical Science," in which the doctrine of the correlation of physical forces was briefly but clearly enunciated. He delivered a course of lectures at the same place, in which he explained and illustrated the propositions briefly laid down the year before. The position he sought to establish was that heat, light, electricity, magnetism, chemical affinity, and motion, are all correlatives; that is, that either of them, as a force, may produce the others. As an illustration, in one of these lectures he used a train of revolving wheels; the smallest, or that which revolved most rapidly, was of metal, and contained a piece of phosphorus in it. While this revolved with great rapidity, the phosphorus remained cool, but by a contrivance the wheel was suddenly stopped, and the phosphorus took fire; the object of the experiment being to show that arrested motion becomes heat. In 1847 he issued his work "On the Correlation of Physical Forces;" and in 1852 he published a memoir in the "Philosophical Transactions," on the "Electro-Chemical Polarity of the Gases." In 1856 he experimented upon the application of electricity as a mechanical power, and showed that, when by electrical attraction or repulsion, a weight is suspended, it is at the expense of electric tension, and that the spark cannot traverse the same distance that it could traverse, with the same apparatus and charge, without the elevation of the weight. Other researches of his have been on "The Electricity of Flame" and the formation of a flame-pile capable of producing chemical decomposition.