154 



Lord Kelvin 



on 



are placed between consecutive atoms near each end of the 

 row so as to keep all their consecutive distances exactly equal 

 to a. For brevity we shall call them ties, though in ordinary 

 language any one of them would be called a strut if its force 

 is push instead of pull on the atoms to which it is applied. 

 Calling A 1? A 2 , A 3 , . . . the atoms at one end of the row. 

 suppose the tie between A x and A 2 to be removed, and A L 



Fie. 7. 



allowed to take its position of equilibrium. A single equation 

 gives the altered distance AiA 2 , which we shall denote by 

 a + !#!. Let an altered tie be placed between A x and A 2 to 

 keep them at this altered distance during the operations which 

 follow. Next remove the tie between A 2 and A 8 , and find by 

 a single equation the altered distance a + x x 2 . After that 



