aea. 



Prof. E. P. Adams on Electrostrktion. 899 



(10), (5), 



Equating this to (17) we find 



It is interesting to note that this is the expression found by 

 the energy method for the elongation of an infinitely thin 

 cylindrical condenser open at the ends (cf. eq. 15). The 

 whole increase in internal volume of Wullner and Wien's 

 tubes is now given by 



8v = 27ra{l + 2a)it a + 7ra 2 le, 



or 



Sr = Q') 2 1~ jj K + 8 2 - ff (8, + S 2 ) ] (3Z -M^ 



+ ^(l + <r)[K + ^ 8 i](; + 2a)}. (22) 



Putting in this 6\ = 6\ 2 = we get an expression which differs 

 from the one obtained by Wullner and Wien only in the 

 small term involving the ratio d/a. The reason for the dif- 

 ference lies in the fact that the condition at the junction 

 assumed by them is such as to distort the shape of the 

 tube. 



Inasmuch as 6\ and S 2 enter into (22) in a different com- 

 bination from that in (17) it might seem that the electro- 

 striction experiments of Wullner and Wien, combined with 

 their experiments on the change in capacity by stretching, 

 would enable S l and B 2 to be determined separately. But 

 the term in (22) involving o\ and B 2 in a different combina- 

 tion from that in (17) is multiplied by the small factor d/a, 

 and the experiments are not certain enough to justify any 

 conclusions drawn from such a calculation. It is of interest 

 to neglect the term in d/a in (22) and calculate the values 

 of S 2 — cr(8 1 + S 2 ) from the electrostriction experiments on 

 closed glass tubes. The following table (p. 900) has been 

 prepared in this way, giving this expression for the same 

 kinds of glass tubes as were used in the capacity de- 

 terminations. 



The agreement is seen to be fairlv good for the three last 



