Theory of Crookes's Force. 25 



The normal pressures may also be put into the form 



p--!^.{i+i(«+6+«)+g(«-*-<o}i 



so that the state of stress is a uniform pressure, and super- 

 posed upon it a system of pressures represented by the equa- 

 tions 





Pxx — 



= gK 



5 (« 



-&- 



■«), 





Pyy~ 



3K 



| fr 



— c — 



a), 





fzz- 



1 , 



3 pv * 



ifr 



-a — 



4 





Py*= 



1 , 



3 -K 



V- 



'pzy) 







Pzx = 



1 , 



= 3 Pi 



2 



•5^ = 



=P**, 







P*y = 



1 , 

 = 3 Pi 



■J- 



=Py*- 





Now it is 



remarkable that, if 









aa? 2 + fo/ 2 + cz + 2yz + 2gzx + 2&zy = (Z# + my + w,?) 2 , 



we should have expressions for these additional unequal pres- 

 sures the same as Professor Clerk Maxwell gives (see his 

 1 Electricity and Magnetism/ vol. i. p. 129, and vol. ii. p. 256) 

 as expressing that state of stress in the aether which produces 

 electrical phenomena. In order to make them identical, all 

 that is necessary is to put 



so that the resultant unequal pressures in the gas may be 



