metal, and the negative over the other. Volta knew nothing of the chemical actions of the pile. The decomposition of water was first noticed by Nicholson and Carlisle. The study of its phenomena soon introduced the idea that chemical action, and not the mere contact of different metals, was the true source of voltaic power. Faraday plunged with ardour into this controversy. He saw chemical effects going hand in hand with electrical effects, the one being strictly proportional to the other. He produced currents without metallic contact; he discovered liquids which, though competent to transmit the feeblest current, were absolutely powerless when chemically inactive. This investigation was communicated to the Royal Society, 17 April 1834. But, despite the cogency of the facts and the conclusiveness of the logic, the supporters of the contact theory remained long immovable. With our present views of the interaction and convertibility of natural forces such a position is hardly conceivable. The astounding consequences of Volta's assumptions and of the views of his followers were laid bare by Dr. Roget as early as 1820. His words deserve to be kept in perpetual remembrance. 'If,' he says, 'there could exist a power having the property ascribed to it by the hypothesis, namely that of giving continual impulse to a fluid in one constant direction, without being exhausted by its own action, it would differ essentially from all the known powers in nature. All the powers and sources of motion with the operation of which we are acquainted, when producing these peculiar effects, are expended in the same proportion as those effects are produced; and hence arises the impossibility of obtaining by their agency a perpetual effect, or, in other words, a perpetual motion.'

Faraday's experiments and reasonings on electrolysis compelled him to look into the very heart of his decomposing liquids and to bring their ultimate molecules within his range of vision. He had no doubt that the current was propagated from particle to particle of the electrolyte, and he became more end more impressed with the conviction that ordinary electric induction was also transmitted and sustained by the action of contiguous particles. The idea of action at a distance obviously perplexed and bewildered him, and it may be added that in our own day this idea is retreating more and more; both electric and magnetic actions, like those of light, being held to be transmitted through an all-embracing medium. In relation to this subject, Faraday repeatedly quotes the memorable words of Newton: 'That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance through a vacuum, and without the mediation of anything else, by and through which this action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man who has in philosophical matters a competent faculty of thinking will ever fall into it. Gravity must be caused by an agent acting constantly according to certain laws, but whether this agent be material or immaterial, I have left to the consideration of my readers.' Two great tests were accepted by Faraday as sufficient to prove the existence of a medium: the transmission of power in curved lines, and the consumption of time in transmission. As regards the electric force he thought he had proved that it could act round a corner. His experiments on this subject were not accepted as conclusive, nor were his views clearly expressed. They formed, however, a groundwork for his successors, who are now successfully working in the direction which he pointed out. But if electric induction be transmitted as he supposed, by contiguous particles, is it not probable that the particles of different bodies will exhibit different powers of transmission? He set to work to test this idea, and ended by the discovery of that quality of 'di-electrics' which in submarine cables now plays so important a part, and which retains the name that Faraday gave it. By suitable devices he placed a small metal sphere in the middle of a larger hollow one, leaving a space of somewhat more than half on inch between them. The inside sphere was insulated, the outside one uninsulated. To the former he communicated a measured charge of electricity, which acted by induction upon the concave surface of the larger sphere. Two instruments of this kind, and of the same size and form, were constructed, the inside sphere of each communicating with the external air by an insulated brass stem ending in a knob. The apparatus was obviously a Leyden jar, having the two spheres as coatings, between which any insulator could be introduced. One of the jars being charged, and its knob caused to touch the knob of the other jar, it was found, when air was the insulator, that the charge was equally divided. Permitting shellac, sulphur, or spermaceti in one of the jars to take the place of the air, it was found that the jar occupied by the 'solid di-electric' took more than half the original charge. The electricity was obviously absorbed by the di-electric. It, moreover, took time to penetrate the latter, from which it gradually returned. This is an effect familiar to experimenters with the Leyden jar. Faraday