I72 HINTS RELATIVE TO 



Again, fuppofe the body, inftead of being drawn 

 along, to be fuftainedat reft only upon the plane; this, 

 it is evident, will require a lefs force than the other, be- 

 caufe the friction prevents the body in part from descend- 

 ing.* Let Rm be the force required, and let the fame 

 conftruction be made as before; then becaufe Rn is the 

 force that would be neceffary if there was no fri6lion, 

 mn is the effect of the friction itfelf; but mn is equiva- 

 lent to the forces mt and tn ; and as Pn would be the 

 preffure exclufive of friction, Pt is the preffure inclu- 

 live; and as the force loft is as the friclion, and mt is 

 as the force loft, therefore mt is as Pt, for the friclion is 

 as the preffure ; confequently the locus of all the points 

 m is a right line pafling through P, and making the 

 fame angle as DPQ in the former cafe, and only differ* 

 ing by being drawn on the contrary fide of PD, 



SCHOLIUM. 



In what follows, the force requifite to fuftain any 

 body is confidered under three different diftinctions. 

 Firft, when it is juft barely fufficient to overcome the 

 weight and refiftance arifing from friclion, and the body 

 is confidered as j uft beginning to move in the direction of 

 the force applied, and the force in this cafe is called the 

 moving force: fecondly, when this force is diminifhed till 

 the body would begin to move or defcend in a contrary 

 direction if the force was diminifhed farther; this laft I call 

 the fufp ending force : and it is plain that whatever force 

 is applied to the body lefs than the moving, and greater 

 than the fufpending force, the body will remain at reft: 

 laftly, it is manifeft that there is an intermediate ftate, 

 in which fuch a degree of force may be applied, that 

 the friction will have no effect either way ; and this 

 force is the fame as would keep the body in equilibrio 

 if there was no friction, becaufe the effect or tendency 



of 



* Fig. 2. 



