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 3700lbs. 
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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