ABRASION OF THE SURFACES OF SOLIDS. 147 



which can only be disengaged by bending or breaking. These experiments 

 led to some important results, viz. 



1st. That the friction of wood on wood without unguents was in proportion 

 to the pressure which attained its maximum in a few minutes after repose. 



2nd. That the effects of velocities were similar ; but the intensities were much 

 less to keep the body in motion, than to detach it from a state of rest, often- 

 times in the ratio of 22 : 95. 



3rd. That in the case of the metals the results were likewise similar; but the 

 intensity was the same whether to disturb or maintain the motion of the body. 



4th. That with heterogeneous surfaces, such as those of woods and metals 

 gliding over each, the intensity did not attain its limit sometimes for days. 



In general, however, with woods and metals without unguents, velocities 

 were found to have very little influence in augmenting friction, except under 

 peculiar circumstances. 



The treatise of Coulomb is illustrated by a great variety of interesting ex- 

 periments, and forms the most valuable work we possess on the subject. 



In the year 1784, Dr. Vince endeavoured by some very ingenious experi- 

 ments to determine the law of retardation together with the quantity, and the 

 effect of surface on friction. The results were, that the friction of hard bodies 

 in motion was an uniformly retarding force, but not so with cloth and woollen, 

 which were found in all cases to produce an increase of retardation with an 

 increase of velocity. 



That the quantity of friction amounted to about |^th of the pressure, and that 

 it increased in a less ratio than the quantity of matter or weight of the body. 



That when the surfaces varied from 1.61 : 1 to 10.06 : 1, the smallest surface 

 gave the least friction : and finally, that friction was greatly influenced by co- 

 hesion. 



Dr. Vince's conclusions regarding the laws of retardation were partly con- 

 firmed by the late ingenious Mr. Southern of Soho, who in a letter to Dr. 

 ViNCE in 1801, communicated the results of several experiments on the surfaces 

 of the spindles of grindstones moving with great velocities ; when it was found 

 that with the rubbing surfaces moving at the rate of 4 feet per second over a 

 length of surface of 1000 feet, the resistance arising from the friction of S/OOlbs. 

 of matter, only amounted to ^^th of the weight. 



In the year 1786 and subsequently, the late Mr. Rennie made several ex- 



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