890 Prof. E. P. Adams on Electrostriction. 



constant resulting from the strains in the dielectric. For a 

 homogeneous uncharged isotropic dielectric the three com- 

 ponents of the force acting on unit volume are* 



^^=-w^ h 4hbl)™> ■ (2) 



where R is the resultant electric intensity measured in 

 electrostatic units, and h Y and S 2 are two material constants 

 which may be defined as follows : — Let, in the notation of 



the theory of elasticity f, e xx e xy be the strain components, 



and let the #-axis be taken in the direction of the electric 

 intensity at a given point of the medium. Then 



"be xx l 'fteyy ~ ~&e 



BK BK BK__ , 



while the derivatives of K with respect to the other strain 

 components all vanish for an isotropic medium. 



The complete system of stresses in an uncharged homo- 

 geneous isotropic dielectric is given by % 



P xx = f (X 2 -Y 2 -Z 2 )-^ (X^ + Y^ + Z 2 ^ 



yy 0?zz /q\ 



5-(Y 2 -Z 2 -X 2 )- i-, 



07T C7T 



Pyy= E: (Y 2 -Z 2 -X 2 ) - ^(Y 2 ^ + Z 2 S, + X 2 S 2 ) 



M 4 ) 



i\ z = 5. (z 2 - x 2 - y 2 ) - ^ (z% + x 2 s 2 + Y 2 a 2 ) 



G7T 07T 



P.= |.XY +8 i(8 2 - Sl )XY 



X, Y, Z being the three components of the electric 

 intensity R. 



* Pockels, Encvklopiidie tter mathematisclieyi Wissemchaften, Band v 2 , 

 Heft 2, p. 350. The units employed in this article are different from 

 those here employed, thus accounting for the factor 4n in this and the 

 following equations. 



f Cf. Love, ' The Mathematical Theory of Elasticity,' 2nd ed. 



\ Cf. Pockels, I. c. 



