On the Law of Molecular Force. 113 



mine exactly what the limit is. For when the plates are 

 separated by a considerable interval, even when they are 

 spherical segments, the sparks have a tendency to leave at 

 points removed from the centre, which of course makes 

 their length indeterminate ; and if they are given a smaller 

 radius of curvature, the correction becomes too large to be 

 used with safety. 



It is intended to continue the investigation with plates of 

 different metals. Some later experiments, in which nickel- 

 plated brass plates were used, seem to indicate a smaller value 

 of the electrostatic force, the difference being more marked at 

 small than at great distances. It was noticed that with brass 

 plates the sparks limned out a considerable area around the 

 central point, whereas when the plates were nickel- plated the 

 effects were greatly diminished. This would give rise to 

 greater surface-inequalities in one case than in the other ; and 

 although the plates were frequently polished, might perhaps 

 offer an explanation of the fact just referred to. 



However, the observations are too few in number to furnish 

 reliable information ; and at present (May) the warm weather 

 prevents a continuance of the work by interfering with 

 insulation. 



Johns Hopkins University, 

 Baltimore, June 2, 1887. 



XIII. On the Law of Molecular Force. 

 By William Sutherland, M.A., B.Sc* 



THE object of the present paper is to show that the law of 

 molecular force, which I previously announced (Phil. 

 Mag. Aug. 1886) as holding for matter in the gaseous state, 

 holds also for matter in the liquid state, and therefore, we may 

 be sure, for matter in any state; and that accordingly it is the 

 one fundamental law of the action of molecule on molecule at 

 molecular distances. This general law of molecular force 

 is : — Any two molecules of matter attract one another with a 

 force proportional directly to the product of their masses, and 

 inversely to the fourth power of the distance between them. 



In my previous paper I confined myself to showing that 

 with such a law of force the potential energy of the molecules 

 of a body would be proportional inversely to the volume occu- 

 pied by them, and that this conclusion agreed w r ith the results 

 of Thomson and Joule's experiments on the expansion of gases 

 through porous plugs. Now, of course, since Laplace gave 

 his great theory of capillary action to the world, it has been 

 an obvious result of the general conditions which he postu- 

 * Communicated by the Author. 



Phil. Mag. S. 5. Yol. 24. No. 146. July 1887. I 



