On Material Molecules and the Etherial Medium. 269 
where ^cr^, b(p^, &c., are given by (3.), (5.), and similar ex- 
pressions. 
Let m be the mass of one of the particles of ether. Then, 
if r-\/r be the law of action of the etherial particles upon 
each other 
or putting x^ — x =^ /? ^ 
<p,r = m 2{'^r^ 
For shortness put <pi\ = ^ -4^' 
dx^ 
= msj p'^ \^ + -I'^i I . . • . (7) 
Similarly 
Now 
And 
( dx-^ ^ dy^ ^ dz^ ^ / 
T du T du T du 
1 r , 2 2 ^ . 7 2 
^ 2) ^1 dx^ ^1 dy^ ^1 
+ + 2Ll^ -i- 2LI I + &c. (10) 
^ ^ acca?/ ^ ^ dxdz ^ ^ dydz j ^ ' 
In finding the value of s| u^ | let us suppose the 
sphere of action of the molecular forces to be so small that 
M\ becomes insensible when multiplied by factors higher 
than the tliird in \ \ l^ . Then since \ \ are of the 
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