IOCITIM. :;:;: 



se three equations are the equations which wo should 



.inr.l l.y ill-- j.iin. i JleS of A 



'/& P /a\* R 



- ' 



We have thus illufttrated the method of application of thu 

 I we observe, in general, that bject 



ea not require certain unknown forces, we 

 must most arbitrary geometrical u. 



possible without giving th* \nn\* of applies 



us. 



i5T. plying th principle of virtual velocities to de- 



duce ns of equilibrium of any system, it is 



give the body such a displacement as to make 



has been exemplified in the preceding Article, and we 

 will ii.. w . numerate some cases in which th<- virtual moment 

 of a force vanishes* 



(1) t, if any particles of 

 the system have r n thrir places, the virtual 



.C at such points ; >. If 



have one point tl rtual 



:iy >t* this point is zero for any hypoth 



of th- l>'nl\ , which docs not break the condition of this point 

 . 



(2) '.^ remain with one point 

 in cot ii a smo plane, so that the plane exerts 



body at the i> in a din 



perpendicular >dy be displaced so as 



to nave the same '1 in contact with the fixed plane, 



i the new positi 



of contact <>n th the action of 



plane meets that dirvctinn at tho -l-l ] 



the virtual v ntact 



is zero. 



f the Ixvlv have more than one point in con- 



plane, ami be so displaced that the #ime point* 



of the lnily n-in. ontact with the fix. . the 



T.S. 



