Changes in Dielectric Constant produced by Strain. 507 



If 7 is not constant but increases with pressure, poa will 

 increase with pressure also. 



Comparing this with experimental results, we observe that 

 h is proportional to molecular weight in either case. 



Again, since V' = \Xds, where V is the potential dif- 

 ference, if we write p = aW + b (for a simple gas during the 

 rotatory stage), a and b will be constants depending on the 

 induction-coil and the nature of the gas. 



Substituting in (7), we have (assuming X to be constant 

 along the discharge) 



V 1 



p^ds.^ds (a+^Jf^^Jrf/ 



Therefore for any given discharge-tube b is obviously small, 

 sincej9ft) = constant nearly, as we have just seen, fr 2 dsand ^ds 

 being taken to be constant (as we are justified in doing). 



We notice, moreover, that since experiment yields the 

 result that pco is proportional to the E.M.F. of the induction- 

 coil, a must be proportional to this quantity also. 



Finally, if the distance between the electrodes is changed, 

 we have, taking J r 2 ds cc \ ds = I, very nearly, where I is the 

 distance between the electrodes, p(ol 2 = const., very nearly. 



This is also verified by experiment. 



XL VII. Changes in the Dielectric Constant produced by Strain. 

 ^y E. P. Adams, Professor of Physics, and 0. W. Heaps, 

 Experimental Science Fellow, Princeton University* '. 



IN the Philosophical Magazine for December 1911, one 

 of the writers of the present paper showed that the 

 elongation per unit length of a charged thin cylindrical 

 condenser, open at the ends, is given by the expression 



«-(!)' (S ^ « 



if d, the thickness of the dielectric, is small compared with its 

 internal radius, a. V is the difference of potential to which 

 the condenser is charged, <r Poisson's ratio and K the 

 specific inductive capacity of the dielectric. S L and B 2 are 

 two constants of the dielectric, supposed isotropic, the former 

 the change in K for unit strain along the lines of force, and 



* Communicated by the Authors. 



