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 xmgiients 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-f-, 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 cele'brated 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 Jrd of the pressure ; the same as Amontons. Of the effect of velo- 

 cities he was however imcertain ; 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 Honames et des Chevaux, et de la Resistance cause dans les Machines. 

 + Memoires de I'Academie des Sciences. t Ibid, 



§ Brisson, Traite de Physique. 

 MDCCCXXIX. U 



