ABRASION OF THE SURFACES OF SOLIDS. 
145 
year 1699, down to the more elaborate researches of Coulomb and Vince in 
1779 and 1784. Amontons was the first that attempted to develope and reduce 
theory to calculation. He affirmed that friction was not augmented by an in- 
crease of surface, but only by an increase of pressure* ; and in a subsequent 
paper, illustrated by some experiments on wood and metals pressed by springs 
of known intensity, he drew similar conclusions, with the addition that friction 
was ^rd of the pressure, and that the amount was the same both with wood and 
metals when unguents were interposed. He likewise concluded, that friction 
increased or diminished with the velocity, and varied in the ratio of the weight 
and pressure of the rubbing parts, and the times and velocities of their motions. 
These hypotheses were adopted more or less by most of the philosophers after 
Amontons, but particularly by De la Hire who satisfied himself by several 
experiments of the truth of Amontons’ conclusions ; but they were questioned by 
Lambert, although without the test of experiment. Parent suggested an in- 
vestigation of the subject in his proposition of the Spheres, and by determining 
the angle of equilibrium, at which a body resting on an inclined plane com- 
menced sliding. And the celebrated Euler, in a very elaborate paper con- 
ceived it to depend upon the greater or less approximation of the asperities 
of the surfaces brought into contact by pressure, the resistance to which he 
allows to be §rd of the pressure ; the same as Amontons. Of the effect of velo- 
cities he was however uncertain ; but observed that when a body begins to 
descend an inclined plane, the friction of the body will be to its weight or 
pressure upon the plane, as the sine of the plane’s elevation to its cosine, 
&c. But when the body is in motion, the friction is diminished one half. 
Muschenbroek and others maintained that friction increased with the surface ; 
and Bossut distinguished it into two kinds ; the first being generated by the 
gliding, and the second by the rolling of the surface of a body over another : 
and remarked, that it was affected by time, but that it neither followed the 
ratio of the pressure nor the mass. Brisson§ attempted to construct a table 
of coefficients, to denote the value of the friction of different substances ; but 
they are inapplicable to practical purposes, for want of proper experiments. 
Desaguliers considered the nature of friction with a good deal of attention, 
* Sur la Force des Hommes et des Chevaux, et de la Resistance cause dans les Machines. 
+ Memoires de FAcademie des Sciences. + Ibid. 
T 
§ Brisson, Traite de Physique. 
MDCCCXXIX. U 
