PIERCE. 



OSCILLATIONS OF A HERTZ OSCILLATOR. 



331 



tion for the wave-length of a thin rod in terms of its length and 

 diameter, is 



A = 2/(1 + 5.6 e 2 ), 

 where 



1 



4log eT 



in which / is the length of the whole oscillator, and d its diameter. 

 The formula was derived by applying Maxwell's equations to a long, 

 perfectly conductive ellipsoid of revolution, and taking the limit ap- 

 proached by A when the square of the minor axis of the ellipsoid 

 vanishes in comparison with the square of the major axis. Under 

 these conditions the major axis becomes the length of the rod-oscil- 

 lator and the minor axis its diameter. 



, To show the size of the 5.6 e 2 term of Abraham's formula, the follow- 

 ing table (Table III.) has been computed for various values of l/d, cov- 

 ering the range of the experiments by Webb and Woodman and those 

 by Conrat and by me. 



TABLE III. 



Computation op the 5.6e 2 Term of Abraham's Formula. 



It is seen that in the range of my experiments, the 5.6 e 2 term raises 

 the theoretical value of the wave-length to 2.006 /, and in Conrat's 

 range to 2.01 /. This term is, therefore, entirely inadequate to account 

 for the 5 per cent excess of the experimental values over the theoretical 

 values of Abraham. 



