overcome the attractive force between the masses of copper? Moreover, when we force the copper balls together, should we not expect that an electrical charge should be developed of such a nature as to oppose our motion? And thus in these mutual relations, which are apparently consistent with the doctrine of the conservation of energy, should we not expect to find the relation which we are in search of? Our experiment, therefore, would have to be conducted in this way: We should carefully insulate our two copper masses, estimate the effects that would be due in any way to cutting the magnetic lines of force of the earth, and then with a delicate electrometer, the masses having been placed in a vacuum to get rid of the effect of friction of the air, we should proceed to test their electrical relations. This experiment also gives negative results, but may we not try it under better conditions than I have been able to devise? If we could prove that whenever we disturb the relative position of bodies, or break up the state of aggregation of particles, we create a difference of electrical potential, and, moreover, if we could discover that the work that this electrical potential can perform, together with the heat that is developed by the process, is the complete work that is done on the system against attractive force, whether expressed in gravitation attractive force, or as so-called chemical attractive force, we should greatly extend our vision of the relation of natural phenomena. In thus pursuing the line of argument of my address, I venture to state an hypothetical law which it seems to me is at least plausible in the present state of electrical science, and may serve as a scaffolding to be taken down when experiment shall have properly proportioned the edifice.
This hypothetical law I should state as follows: "Whenever the force of attraction between masses or molecules is modified in any way, a difference of electrical potential results."
In what I may therefore call the physical chemistry of the future, may we not expect that in the reactions we must express the equivalent of the difference of electrical potential in the summation of the entire work which is done? I can make my meaning clearer by referring to an experiment of Him by which he obtained a fair value for the mechanical equivalent of heat. In principle it is this: A heavy weight falls upon a lead vessel which contains a given amount of water at a definite temperature. The lead vessel suffers compression by the blow, and the water is raised in temperature. It is found, on properly estimating the amount of heat taken up by the lead and the loss radiated during the experiment, that the heat produced by the blow is the equivalent of its mechanical work. Suppose now that the vessel containing the water should be made of two metals of about the same specific heat or capacity for absorbing heat, and suppose that wires should connect the two different metallic portions with a similar vessel containing water. We should have here two thermo-electric junctions at the same temperature. When the weight falls upon one junction and
