regard to electricity, we seldom reflect that gravitation is as great a mystery as electrical attraction. What is this force which acts instantly through space, and which holds our entire solar system together? "We know only its simple law—that it attracts bodies directly as their masses and inversely as the square of their distance; but we do not know what relation it bears to electrical force or magnetic force. Here is a field in which we are to push back our boundary of electrical knowledge. I will not call it electrical knowledge, but rather our knowledge of the great doctrine of the conservation of energy. What is the relation between electricity, magnetism, and oravitation, and what we call the chemical force of attraction? It seems to me that this is the question which we must strive to answer; but, when this question is answered, shall we not be as far as ever from the answer to the question, "What is electricity?"
The question of the connection between electricity and gravitation dwelt much in Faraday's thoughts. It is interesting to recall the experiments which he instituted to discover if there is any connection between these great manifestations of force. In his first experiment he suspended vertically an electro-magnet, which was connected with a delicate galvanometer, and let various non-magnetic bodies, such as brass bodies, pieces of stone and crystals, fall through the center of this electro-magnet, thinking that there might possibly be a reaction from the influence of gravitating force on the falling body which would be manifested as an electrical current. He did not, however, obtain the slightest electrical disturbance which might not have been caused by simple electrical induction. He then arranged a somewhat complicated piece of apparatus by means of which a body could be moved alternately with the direction of gravitation and against it, and the terminals of a galvanometer were so connected that the intermittent effects, if they existed, could be integrated or summed up. He failed, however, to find the slightest relation between gravitation and electricity, and he closes his account of his experiments with these words: "Here end my trials for the present. The results are negative. They do not shake my strong feeling of the existence of a relation between gravity and electricity, though they give no proof that such a relation exists."
Since Faraday's time no connection or relation has been found except in the similarity of the law of inverse squares. I have often reflected upon these experiments of Faraday, and have asked myself, Was the direction in which he experimented the true direction to look for a possible relation; and can not the refined instruments and methods of the electrical science of the present aid us in more promising lines of research? Should we not expect that, when two balls of copper, for instance, are suddenly removed from each other, a difference of electrical potential should manifest itself, and that the electrical force thus developed should be opposed to our endeavor to
