64 G. F. Firzceratp—On the Mechanical Theory of Crookes’s Force. 
We may evidently include the ; saxd +c) in the mean value of Nv} and take B,=1 
so that calling MN=p the dusts of the gas our pressures become 
1 4 i 
Pry= 390" [1 + Ip(@ = 96 + c)} | 
] = 
1 aa 2T1+ 5 (b-5(e +4] 
4 1 4 
Pes=gpv? 7 [1 + Tae —5(4 + b)} | 
> 2 Yo 
J ye—] 5PM =P, 
Similarly from nv°=Nov, - v? we can get 
and hence 
i) Aa 
Q.=Zhpr,> * a Q= 
The normal pressures may also be put into the form 
I 1 1 
essays ° (Glcp aelO@POs2@) a 5(4—5 —c)} 
1 
Py=aeve (1 ale +b+ce)+ =(0- c—a)} 
1 1 1 
Pz2=30t,” (1+ TAG +b+¢)+ 5(C —a—b)} 
So that the state of stress is a uniform pressure, and superposed upon it a system 
of pressures represented by the equations 
1 1 1 2; 
Paz=3P Vv," (OO c) Pye=3P Po e 5 Pry 
1 1 il 2 
Py =30Vo ‘i 5 (b—c—a) Pex 30. 3 RU aries 
1 ] 1 2 
22—= RN. E 5(c—a—b) Pry= 30% 0™ : 5 Px 
Now it isremarkable that if aa?+by?+czt+ 2yz+2gzat+2h xy=(latmytnz) we should 
have expressions for these additional unequal pressures, the same es Prof. Clerk 
Maxwell gives (See his “Electricity and Magnetism,” vol. 1., p. 129, and vol. i1., 
p. 256.) as expressing that state of stress in the ether which produces electrical 
phenomena. In order to make them identical all that is necessary is to put 
Sir 8x Sy 
X=l hte Y—=m ppee Z=n ee 
