146 MR. rennie's experiments on the friction and 



but principally with reference to the rigidity of cords. He however quotes the 

 experiments of Camus as best calculated to illustrate the subject ; nevertheless 

 they were made on too small a scale to derive any satisfactory conclusions. 

 ScHOBER and Meister coincided with Muschenbroek in the opinion, that 

 the spaces were as the squares of the times in the case of a body uniformly 

 accelerated. The opinions of many other eminent philosophers, such as 

 Leibnitz, Varignon, Leupold, Bulfinger, Daniel Bernoulli, Ferguson, 

 RoNDELET, Gregory, Leslie, Young, Olivier*, &c. might be quoted. But it is 

 to Coulomb principally that we are indebted for the knowledge we possess 

 of this kind of resistance. 



In the year 1779 the Academy of Sciences at Paris, being desirous of ren- 

 dering the laws of friction, and the eflFects resulting from the rigidity of cords 

 applicable to machines, — Coulomb undertook in the arsenal at Rochfort a very 

 extensive series of experiments, which he afterwards published in 1781 under 

 the title of " Th6ori6 des Machines simples, en ayant 6gard au Frottement de 

 leurs Parties, et k la Roideur des Cordages-^-." ITie memoir is divided into two 

 parts. The first treats of the friction of surfaces gliding over each other, and 

 the second enters into an examination of the rigidity of cords, and the friction 

 of the rotary movements of axles. Coulomb commences his work by examin- 

 ing the friction of plane surfaces gliding over each other, distinguishing it into 

 two kinds ; the first resulting from time, and the second from velocity. The 

 first may depend on four different causes, viz. 

 1st. The nature of the bodies in contact. 

 2nd. The extent of surface. 

 3rd. The pressure on the surface. 



4th. The time the surfaces have been in contact. And he even adds a 

 5th. The state of the atmosphere ; which he however thinks may have little 

 influence. 



The case of bodies gliding over each other with a certain velocity he con- 

 sidered to be referable to the first three causes, besides the velocity of the 

 planes in contact. 



With regard to the physical cause of friction, he coincides with the opinions 

 of Amontons and others, that it arises from the entangling of the asperities, 



• Sur les diverses Especes de Frottements, &e. (not published.) 

 ■\ Memoires des Sjavans Etrangers, tome 163 & 333. 



