386 Dr. Norman Campbell : Experiments on 



Deduction of the Constct7its from the (V"2m, Cj) Curves, 



19. Measurements of the relation between the peak 

 potential and the primary capacity were also made with 

 other air-core coils in series with the primary. The results 

 of these measurements are shown in fig. 13, where the self- 

 inductance of the external air-core coil is denoted by L/. 



Fiff. 13. 



C, (mf.) 



Cifag 



It will be seen that, even when L/ is as small as '00025 and 

 only 5 per cent, of L 1? the self-inductance of the primary of 

 the armature itself, the presence of the external coil makes 

 marked minima appear in the (Y 2m , Ci) curve, though they 

 are absent when it is not there. Since the appearance of 

 these minima indicates that, in one respect at least, the 

 predictions of the theory are fulfilled more accurately than 

 before, it is worth while to inquire how far the agreement 

 of theory and observation extends in the new circumstances. 

 Perhaps the best way to investigate the matter is to 

 attempt to calculate from the experimental curves the con- 

 stants of the circuits ; the general consistency of the values 

 obtained will show how far the theory used in their deduction 

 is applicable. The attempt will also have some intrinsic 



