:i:it Al. MOMKT VANISHES. 



the other describe an a , then, by the seventh 



the string disappears from the equation of vir- 

 tual Vi-lor. 



>< placements considered it 

 no*, we can produce any displacement 

 particle.* Ifrgo, *o long a* :ig is 



i. 11 of a string conn* 



cS. 



supposed the string to pass in a straight line from 

 one ] the same result would 1> 





 rings, supposing it always kcj 



. for an extensible string. 



257. We can now understand more distinctly the meaning 

 of the words, without a / the connexion of the part* of 



the system with each other, which are introduced into the 



.u theorem i.t shewn in A 

 r a particle ; if then we consider a rigid body to be 



Aether by molecular forct- 



theorem will every displacement of the particles of 



molecular forces and 



.several virtual moments. But from the demon- 

 , Hiars that we need not consid< 

 i we give to the 

 .-uch displacements only as are consistent with the unbroken 



body. So with respect to such forces as are 



preceding Ai we take them 



lacements we 



please; but if we do not take them into consideration, we 

 must ;ive jueh <li-j'lacr!iu -nt* only a* we can j-r-'Vi- \\ill !. : 

 introduce > of these forces. Hence, the 



wonls which we arc i-xj.lainiii:; aiii.-unt t-. ;i ilin--:'...!i t . 1 



f the system, except BIJ* 



we know have th- 1 moments icro ; articular 



: we arc considering. 



25s tollowing example will shew how the prir 



..-i-t in the solution of problems, 

 qual rods are fastened together by hinges at each end, 



