MECHANICS, 97 



over the other, or by bending and abrading the emi- 

 nences which oppose the motion. 



MUSCHENBROEK, 512. EuLER, Mem. de Berlin, 

 1748, p. 122. COULOMB, Mem. Presentes, torn. x. 

 p. 164, &c. 



. The difference between the friction of rubbing and 

 rolling bodies, seems to arise from this, that the 

 asperities do not require to be bent down or abra- 

 ded in the latter case ; the eminences being lifted 

 out of the cavities. 



b. When the rising up of the one body over the other 

 is completely prevented, the friction becomes ex- 

 tremely intense, as appears in what may be account- 

 ed an extreme case, the drawing of wire, tubes, 

 &c. where the extension of the metal is the effect 

 of the friction acting all around. 



c. In bodies sliding on one another, the surfaces may 

 be held together by the attraction of cohesion, so 

 that the friction is not always diminished in pro- 

 portion as the polish of the surfaces is increased. 

 Professor LESLIE is of opinion, that the phenomena 

 of friction are not fully explained by these causes, 

 and that they arise chiefly from a tremulous or vi- 

 bratory motion in the parts of bodies. Inquiry into 

 the Propagation of Heat, p. 299 to 302. 



162. The distance to which a given body will 

 be moved by percussion, in opposition to friction, 

 is as the square of the velocity communicated to 

 it. 



VOL. I. G Tins 



