Laplace's theorem, &c. 407 



These forces are derived entirely from the 

 material points which are not placed in the planes 

 parallel to the co-ordinate planes, and passing 

 through P. 



X \ 



2'-^ = the force of all the material points \ 

 parallel to x 



I P 1 A ^^^> 



I'—^zz do. do. y 



S"-^= do. do. z 



These are the forces derived from the material 

 points placed in the lines parallel to the co-ordi- 

 nate axes .?', j/, and z respectively. 



^. p(.« 3^'^ - — the force parallel to c2? 1 



(3) 

 U^^tzpl^ do. do. , 



X y 



The force parallel to z v^ill be nothing from 2* 



X Z f \ 



^'- — 3-^ = force parallel to x 



(4) 

 i 5 — — do. 



X z 



Z 



