1 66 Mr, VmcE on the Motion of 



the weight of a body the fridioii does not always increafe exadl 

 in the fame ratio ; and that the fame body, if by changing its 

 pofition you change the magnitude of the furface on which it 

 moves, will have its quantity of fri6lion alfo changed. Hel- 

 SHAM and Ferguson, from the fame kind of experiments, 

 hav€ endeavoured to prove, that the friction does not vary by 

 changing the quantity of furface on which the body moves ; 

 and the latter of thefe afferts, that the fridlon increafes very 

 nearly as the velocity ; and that by inCrealing the weight, 

 the fritflion is increafed In they^;;?^' ratio. Thefe different con- 

 clufions induced me to repeat their experiments, in order to fee 

 how far they were concluiive in refpe^l: to the principles de- 

 duced from them : when it appeared, that there was another 

 caufe operating belides fri6lion, which they had not attended 

 to, and which rendered all their deductions totally inconclufive. 

 Of thofe who have written on the theory, no one has efta- 

 blifhed it altogether on true principles: Euler (whofe theory 

 is extremely elegant, and which, as he has fo fully confxdered 

 the fubje£l, would have precluded the neceHity of offering any 

 thing further,, had its principles been founded o\\ experiments) 

 fuppofes the fridion to vary in proportion to the velocity of the 

 body, and its preffure upon the plane, neither of which are 

 true : and others, who have imagined that friction is a uni-^ 

 formly retarding force (and which conjecture will be confirmed 

 by our experiments), have ftill retained the other fuppofition, 

 and therefore rendered their folutions not at all applicable to 

 the cafes for which they were intended. I therefore endea- 

 voured by a fet of experiments to determine, 



ift, Whether fridiion be a uniformly retarding force, 



2dly, 'The quantity of fridiion, ^"^ ^' "^^ 



