by integration, x=c—m log r\ or x—m log — , m which n is a 

 new constant. It appears then that the curve of the effective 

 molecular repulsion, which resists contact pressure, is the loga- 

 rithmic curve. 



This force of molecular contact repulsion cannot be identical 

 with the effective repulsion in operation in the interior of 

 bodies, when they suffer compression ; for the same force of 

 pressure produces a vastly greater diminution of molecular dis- 

 tance at the surface of contact than in the interior of bodies. 

 Thus, in our experiments, a pressure equivalent to 30 lbs. to • 

 the square inch, diminished the contact distance by ^jV? of ^° 

 inch. This pressure operating on an iron rod one inch in 

 length would compress it gooVnn of an inch. The distance 

 between its individual molecules would be reduced goAott 

 part. This is immeasurably smaller than the observed diminu- 

 tion of contact distance ; and therefore than the diminution of 

 molecular distance at the point of contact, if the decrease of 

 contact distance consisted simply in the closer approximation 

 of the contiguous molecules of the two surfaces. It is not im- 

 probable, however, that it consists in part in a compression of 

 a thin layer of molecules at the surface, having a comparatively 

 small coefficient of elasticity. If such a layer have a thickness 

 as great as j-i^ of an inch, the compression it would receive from 



of 30 lbs. to the square inch, would still be 32000 

 times greater than a layer of the same thickness in the interior 

 of a mass of iron would experience from the same pressure. 



We must conclude, therefore, that the force of molecular 

 contact repulsion has, for the same diminution of the distance 

 between the molecules, an exceedingly feeble intensity in com- 

 parison with that of the internal molecular repulsion. It must 

 operate then at greater molecular distances ; and accordingly 

 the range of its action must lie outside of that of the attraction 

 of cohesion. In confirmation of this conclusion it may be 

 stated that in none of the experiments was any evidence 

 obtained of an attraction between the surfaces, operating out- 

 side of the contact distance. 



It would seem, then, that the experiments discussed have 

 served to establish the existence of an effective force of molecu- 

 lar repulsion, in operation at the surface of contact of bodies, 

 whose sphere of action is external to the rauge of the attraction 

 of cohesion for the same molecule, and which has a mucb 

 feebler coefficient of intensitv than the effective molecular repul- 

 sion exerted within the sphere of this attraction. Thev have 

 also mude known the law of variation of this force with the 

 change of molecular distance, and shown that its coefficient ot 

 intensity is the same, or nearly the same, for the different suD- 



