84 THE POPULAR SCIENCE MONTHLY. 



overcome the attractive force between the masses of copper ? More- 

 over, when we force the copper balls together, should we not expect 

 that an electrical charge should be developed of such a nature as to op- 

 pose our motion ? And thus in these mutual relations, which are appar- 

 ently 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 con- 

 ditions than I have been able to devise ? If we could prove that when- 

 ever 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 at- 

 tractive 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 experi- 

 ment 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 equiva- 

 lent of the difference of electrical potential in the summation of the 

 entire work which is done ? I can make ray meaning clearer by re- 

 ferring to an experiment of Hirn 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 equiv- 

 alent 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 



