56 On the Motion of Bodies affected l>y Friction. 



considerable the cohesion was in proportion to the friction^, 

 when the body was in motion ; it being, in the latter case, 

 almost one-third, and in the former it was found to be very 

 nearly equal to the whole friction. All the conclusions, 

 therefore, deduced from the experiments which have been 

 instituted to determine the friction from the force necessary 

 to put a body in motion (and I have never seen any described 

 but upon such a principle), have manifestly been totally 

 false ; as such experiments only show the resistance which 

 arises from the cohesion and friction conjointly. 



8. I shall conclude this part of the subject with a remark 

 upon Art. 5. It appears from all the experiments which I 

 have made, that the proportion of the increase of the fric- 

 tion to the increase of the weight was ditlerent in all the 

 different bodies which were made use of: no general rule 

 therefore can be established to determine thi:^ for all bodies j 

 and the experiments which I have hitherto made have not 

 been suflieient to determine it for the savie body. At some 

 future opportunity, when I have more leisure, I intend to 

 repeat the experiments in order to establish, in some par- 

 ticular cases, the law by which the quantity of friction in- 

 creases by increasing the weight. Leaving this subject, 

 therefore, for the present, I shall proceed to establish a the- 

 ory upon the principles which we have already deduced from 

 Our experiments. 



PROPOSITION I. 



Let e, f, g, (fig. 1. Plate II.) represent either a cijlinder, 

 or that circular section of a lody uh which it rolls down the 

 inclined plane CA, in consequence of its friction, to find the 

 time of descent and the nnmber of revolutions. 



As it has been proved in Art. 5. that the friction of a 

 body does not increase iu proportion to its weight or pres- 

 sure, we cannot, therefore, by knov/iug the friction on any 

 other plane, determine the friction on CA; the friction 

 therefore on CA can only be determined by experiments 

 made upon that plane, that is, by letting the body descend 

 froni rest, and observing the space described in the first 

 second of time: call that space a, and then, as by Art. 3. 

 friction is an uniformly retarding force, the body must be 

 uniformly accelerated, and consequently the whole time of 



/Ac 

 descent in seconds will be = / — . Now to determine 



yAc 

 a 



the number of revolutions, let s be the center of oscillation 



to 



