On /he Motion of Bodies affected by Friction. 1 13 



Mfi Cavallo has candidly acknowledged the difficulty of 

 reconciling various properties of charged electrics with any 

 received theoiT. Where, for instance, docs the charge re- 

 side ? Not in the coating, as may satisfactorily be shown : 

 if in the glass, and the fluid can penetrate any the smallest 

 portion, a glass might be made so thin that the fluid would 

 freely pervade its substance; but a glass ball gJ^Tjth of an 

 inch thick will receive a powerful charge. The hypothesis 

 etill remains incumbered with numerous difiicuUies ; and it 

 must be left to future investigation to determine whether 

 it shall be wholly rejected, or whether subsequent discove- 

 ries may enable us to apply the foregoing principles with 

 Jiiore certainty and success* 



XIV. On the Motion of Bodies affected ly Friction. By the 

 Rev. Samuel Vince, ^. M. of Camlridge. Communi- 

 cated by Anthony Shepherd, D. D. F. R. S. Plumiaii 

 Professor of Astronomy and Experimental Philosophy at 

 Camlridge. Read November 25, 1784* 

 [Concluded from p. 58.] 



PROPOSITION II» 



J^ET the body be projected on an horizontal plane LM 

 (fig. 3.) with a given velocity, to determine the space through 

 ?i'hich the body will move before it stops, or before its motion 

 becomes wnij'orm. 



Case I. — 1. Suppose the body to have no rotator}' mo- 

 tion when it begins to move ; and let a = the velocity of 

 projection per second measured in feet, and let the retarding 

 force of the friction of the body measured by the velocity 

 of the body w hich it can destroy in one second of time, be 

 determined by experiment and called F, and let x be the 

 space through which the body would move by the time its 

 motion was all destroyed when projected with the velocity 

 s, and retarded by a force F; then, from the principles of 



uniformly retarded motion, x = ^., and if / = time of de- 

 scribing that space, we have t =~j ant^' hence the space 



described in the first second of time = . Now it is 



2 



manifest that when the rotatory motion of the body about its 



axis is e(]ual to its progressive motion, the point a will be 



carried backwards bv the former motion as much as it is 



Vol,. X\'Il.No. 60. a carried 



