106 OUTLINES OF NATURAL PHILOSOPHY 



Hence the great use of this kind of resistance to stop 

 motion quickly, and to make fast one end of a rope 

 when a great force or strain is to be applied to the 

 other. 



176. Though friction destroys motion, and ge- 

 nerates none, it is of essential use in mechanics. 

 It is the cause of stability in the structure of ma- 

 chines ; and is necessary to the exertion of the 

 force of animals. 



A nail, a screw, or a bolt, could give no firmness to 

 the parts of a machine, or of any other structure, 

 without friction. Animals could not walk, or ex- 

 ert their force any how, without the support which 

 it affords. Nothing would have any stability but 

 in the lowest possible situation, and an arch which 

 could sustain the greatest load when properly di- 

 stributed, might be thrown down by the weight of 

 a single ounce, if not placed with mathematical ex- 

 actness at the very point which it ought to oc- 

 cupy. 



SECT. 



