570 



Prof. E. Taylor Jones on 



0*61 cm. thick. The results are given in Table II., the 

 capacities being in descending order of magnitude. 



Table II. 



Condenser. 



Frequency w 

 open. 



ith primary 



closed. 



P. 



A 



99-1 

 218-0 

 276-0 

 355-6 

 408 

 4550 

 599-4 



247-3 

 519-0 

 630 



792 



897 



989 



1246 



•839 

 •824 

 •808 

 •798 

 •793 

 •788 

 •768 



B 







D 



E 



F 







Specimens of the photographs used in these measurements 

 are shown in Plate VIII. figs. 4 & 5. In fig. 4 the first three 

 waves correspond to the exciting spark, the remainder to the 

 free oscillation. The lower wave is the trace of a 768 tuning- 

 fork photographed simultaneously. The numbers in the 

 fourth column show a gradual falling off of the coefficient of 

 coupling as the capacity connected to the secondary coil 

 diminishes, i. e. as the current changes from the uniform to 

 the cosine distribution. The question, however, arises whether 

 this diminution of k 2 is due to the change in the distribution 

 of the current, or whether it is not due to some other cause, 

 e. g. to a falling off in the intensity of magnetization of the 

 core as the frequency of the oscillation increases. For a 

 given potential at the terminals of the secondary condenser 

 the magnetizing current diminishes as the capacity of the 

 condenser diminishes, being in fact inversely proportional 

 to the frequency of the oscillations. Hence it might be 

 expected that the permeability of the core, for oscillations of 

 given amplitude, would fall off as the capacity of the con- 

 denser diminishes. The question whether this appreciably 

 affects the value of P was tested by repeating the experiment 

 with the largest capacity (condenser A) with a much smaller 

 potential. The method was the same, but a much smaller dis- 

 charge was employed for starting the oscillation, and the most 

 sensitive form of electrometer * was used for obtaining the 

 curve. The potential and current in this experiment were 

 not more than one-fifth of those employed in the former deter- 

 mination, and the value of k 2 obtained was *820. Hence the 

 * Cf. Phil. Mag. xiv. p. 240 (1907). 



