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 17/9 the Academy of Sciences at Paris, being desirous of ren- 
dering the laws of friction, and the effects 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 “ Theorie des Machines simples, en ayant egard au Frottement de 
leurs Parties, et a la Roideur des Cordages^.” The 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, &c. (not published.) 
4 Memoires des S 9 avans Etrangers, tome 1G3 & 333 . 
