MECHANICS. 95 



constant. Journal dt Phys. torn. xxvu. p. 204, 

 &c. COULOMB'S experiments received the prize of 

 the Academy of Sciences in 1781, and are publish- 

 ed in the tenth volume of the Memoires presentes. 

 An abstract of them is given in the Journal de 

 Phys. above quoted, and also in PEONY'S Arch Hyd* 

 Sect. v. 1089, &c. 



Motions retarded by friction are therefore subject to 

 the laws explained, Articles 90 and 91 ; only that 

 the retarding can never be converted into an acce- 

 lerating force, so that the formulas of those articles 

 cannot be applied in their full extent. 



159. The force of friction is the greater, the" 

 greater the roughness or asperity of the surfaces 

 moving on one another ; it is also the greater, the 

 greater the power by which these surfaces are 

 pressed together ; but it is very little affbcted by 

 their extent. 



a. That the quantity of friction does not depend on 

 the extent of the surfaces that rub on one another, 

 was affirmed by AMONTONS, and proved by a varie- 

 ty of experiments. Mem. Acad. de Sciences, 1699, 

 p. 208. The fact, however, has been since ques- 

 tioned, particularly by LAMBERT, Mem. de Berlin, 

 1772; but the experiments of COULOMB, though 

 they have pointed out certain exceptions, as those 

 of some other writers have done, have shewn, that 

 it holds in general, and that in practical mechanics* 

 the ratio of the friction to the pressure, may be re- 

 garded 



