18 Prof. Maxwell on the Theory of Molecular Vortices 



whose density is p, and having its normal inclined 6 to the axes 

 of z ; then the tangential force upon it will be 



pR8Ssin0=2T8S, (99) 



T being, as before,, the tangential force on each side of the sur- 

 face. Patting p = 7p- as in equation (34)*, we find 



-R=-2irma(e + 2f) (100) 



The displacement of electricity due to the distortion of the 

 sphere is 



SSSJp/ sin 6 taken over the whole surface ; . (101) 



and if h is the electric displacement per unit of volume, we shall 



have 



*ircPh = $tfe, (102) 



or 



*-S5«*J ( 103 ) 



p t = 4 ^ m l±3/^ (104) 



so that 



or we may write 



K=-4,TrWh, (105) 



provided we assume 



W=-7rm e -±y. (106) 



e 



Finding e and /from (87) and (90), we get „ 



E 2 =™-4r- - (107) 



The ratio of in to fi varies in different substances; but in a 

 medium whose elasticity depends entirely upon forces acting 

 between pairs of particles, this ratio is that of 6 to 5, and in this 

 case 



E 2 =7T»i (108) 



"When the resistance to compression is infinitely greater than the 

 resistance to distortion, as in a liquid rendered slightly elastic 

 by gum or jelly, 



E 2 =37rm (109) 



The value of E 2 must lie between these limits. It is probable 

 that the substance of our cells is of the former kind, and that 

 we must use the first value of E 2 , which is that belonging to 



Phil. Mag. April 1861, 



