352 W. A. Norton—Force of Effective Molecular Action. 
in contact, were determined. The following are the general 
results obtained.* 
(1.) The diminutions of contact distance are very nearly 
the same, for the same increments of pressure, whatever is the 
nature or condition of the surfaces in contact. 
(2.) They are very nearly independent of the extent of the 
surface of contact. 
(8.) The diminution of distance for a given increment of 
pressure (say 1 oz.), is nearly inversely proportional to the pres- 
sure. 
of the maximum repulsion the curves answering to different 
values of &, and therefore to different materials, approach 
very near to each other, and beyond 1007 are very nearly coinci- 
dent, and have nearly the same inclination to the axis of x. This 
results from the fact that the attractive term in the formula for 
the effective foree becomes at such distances very small, in 
comparison with the repulsive term which has the same value 
for different materials when the temperature is the same. To 
the same small diminution of distance should then correspond 
very nearly the same increment of the repulsive ordinate, for 
the molecular curve of each substance. 
The second law follows as a consequence from the third. 
As for the third law, it is to be observed that at the contact 
distances that obtained in the experiments, which must have 
been much greater than that, Od, answering to the maximum 
repulsive ordinate dn, the first term in equation (1), (p- 346) 
nearly vanishes, and so the effective repulsion (2) expressed by 
R=, is nearly inversely proportional to the square of «. 
Theoretically then, the diminution of distance (dz) for small 
increments of the repulsion (dR) should be inversely propor- 
tional to R*, or nearly so, instead of inversely proportional to 
R, as experiment showed. Here, as in previous cases, the dis- 
such compression should increase the value of &, bring the repul- 
sive portion en, etc., (fig. 1) of the curve of effective molecular 
action nearer the axis Ocd, and so cause dx to decrease according 
to a less rapid law than would obtain if & and the corresponding 
curve remained constantly the same (which is represented by 
z In confirmation of this explanation it may be added that a 
change in the mechanical condition of the contact molecules, 
* See this Journal, June, 1876. 
