660 PHILOSOPHICAL TRANSACTIONS. [ANNO 1785. 



after its acceleration ceased, 5^- inches before it stopped. The edge was then 

 applied, and the moving force descended through the same space, and it was 

 found, from a mean of the same number of trials, that the space described was 

 7£ inches before the body lost all its motion, after it ceased to be accelerated. 



Eocper. 6". Another body was then taken whose flat surface was to its edge as 

 60 : 19, and by proceeding as before, on the flat surface it described, at a me- 

 dium of 12 trials, 5-l inches, and on the edge 6^ inches, before it stopped, 

 after the acceleration ceased. 



Exper. 7. Another body was taken whose flat surface was to its edge as iQ : 3, 

 and the spaces described on these two surfaces, after the acceleration ended, 

 were, at a mean of 10 trials, 4-f- and 7 tV inches respectively. 



From all these different experiments it appears, that the smallest surface had 

 always the least friction, which agrees with the consequence deduced from the 

 consideration that the friction does not increase in so great a ratio as the weight ; 

 we may therefore conclude, that the friction of a body does not continue the 

 same when it has different surfaces applied to the plane on which it moves, but 

 that the smallest surface will have the least friction. 



7. Having thus established, from the most decisive experiments, all that was 

 proposed relative to friction, it may be proper, before concluding, to give 

 the result of my examination into the nature of the experiments which have 

 been made by others ; which were repeated, in order to see how far they were 

 conclusive in respect to the principles which have been deduced from them. The 

 experiments which have been made by all the authors that I have seen, have 

 been thus instituted. To find what moving force would just put a body at rest in 

 motion : from which they concluded, that the accelerative force was then equal 

 to the friction ; but it is manifest, that any force which will put a body in motion 

 must be greater than the force which opposes its motion, otherwise it could not 

 overcome it ; and hence, if there were no other objection than this, it is evident 

 that the friction could not be very accurately obtained ; but there is another 

 objection which totally destroys the experiment, so far as it tends to show the 

 quantity of friction, which is the strong cohesion of the body to the plane when 

 it lies at rest ; and this is confirmed by the following experiments. 1st, A body 

 of 12i oz. was laid on a horizontal plane, and then loaded with a weight of S lb. 

 and such a moving force was applied as would, when the body was just put in 

 motion, continue that motion without any acceleration, in which case the fric- 

 tion must be just equal to the accelerative force. The body was then stopped, 

 when it appeared, that the same moving force which had kept the body in 

 motion before, would not put it in motion, and it was found necessary to take 

 off 4-i-oz. from the body before the same moving force would put it in motion; 

 it appears therefore that this body, when laid on the plane at rest, acquired a 



