PROFESSOR KELLAND ON THE THEORY OF WAVES. 

 or ^a = (s + §sy (a. + 8a) 



=^a + s'8a+2sa8s nearly 

 .-. 8s=-^8c. ■ 



Z So, 



= -^8a. 



ds _ s da 

 dl~~2i dl' 



hence 

 24. Now, the moving force on this mass is 



fjdydzp-ffdydz (p + ^8z) 

 \ dx J 



and 



P=gq.s-y—^qu\ 

 dp_^^ds du 



• r^-^^dj-^^'r,- 



Hence moving force . - 





^»«2 — 9m-^--u^ms^ 



ds 

 dx 



ds 



s + —-a 



3 „ ds 

 ■—2Sms^. — a+gmi 



,ds 1 / o ds , du \ 



= -lmgus'^ + lma(u^s^ + s'u^) 

 ^ ax Z \ dx dx) 



and mass moved =^s'^a,q 



„ds , du 



therefore, accelerating force =-g — + ^'^ '^^ 



dx s 



525 



VOL. XIV. PART II. 



4u 



