Prof. E. P. Adams on Electrostriction. 889 



ways of experimental test, more especially in connexion with 

 spectroscopic work of the kind already done by Ramsay, 

 Soddy, Rutherford, and others. They do not appear to be at 

 variance with any established experimental result where 

 comparison is possible, and they may serve to suggest useful 

 directions of experimental inquiry, or the outlines of an 

 interpretation of radioactive changes. It may be noted that, 

 according to these views, the number of electrons in an 

 atom is roughly proporiional to the atomic weight. The 

 ratio is generally about 2'b, rather smaller than Crowther's 

 estimate. 



LXXXV. On Electrostriction. By E. P. Adams, Ph.D., 

 Professor of Physics, Princeton University* . 



PT^HE object of the present paper is the development of 

 JL formulas for some important cases of electrostriction, 

 particularly those involving cylindrical condensers. M. P. 

 Sacerdotef found the elongation per unit length of a charged 

 cylindrical condenser to be 



where E is Young's modulus, K the dielectric constant, and 

 d the small thickness of the dielectric, and k 1 a constant 

 involving the dependence of K upon the state of stress in 

 the dielectric. This expression was obtained by the energy 

 method ; when applied to a finite portion of an infinitely 

 long cylinder there is some doubt as to the validity of this 

 method. In the present paper this and other problems are 

 solved by means of the general equations of equilibrium of 

 elastic solids. An entirely different result is obtained for 

 the elongation of a charged cylindrical condenser, and this 

 has an important bearing upon the interpretation of the 

 experiments of Prof. L. T. More J, who concluded that the 

 whole elongation he obtained could be accounted for by 

 the heat developed as a result of the high difference of 

 potential it was necessary to employ; this conclusion is 

 supported by the result of the present investigation. 



It is well understood now that the system of stresses in 

 dielectric media formulated by Maxwell is only approximate, 

 no account being taken by him of the change in the dielectric 



# Communicated by the Author. 



t ' Becherches Theoriques snr les deformations electriques des dielec- 

 triques bolides isotropes.' Paris, Theses No. 1012, 1899. 



I Phil. Mag. [o] 1. p. 198 (1900) ; [6] vi. p. 1 (1903; ; x. p. 676 (190.5). 



