332 Mr. W. P. Boynton on the 



(fig. 6), which gives the observed effective primary current 

 for a primary spark-length of 4 mm. All the curves for 

 1^ T 2 , and Y~ 2 arc of similar character, and show a decided 

 rise with what may be called increasing excitation. The 

 same was true, but in less degree, of the maximum spark- 

 length in the secondary circuit, the data for which in Table I., 

 however, are not classified with reference to this point. The 

 question immediately arises as to the reason for this behaviour. 

 The most obvious suggestion is that, on account of the excess 

 of current supplied to the condenser, the maximum potential 

 effective at the primary spark-gap is greater than that indi- 

 cated by its length. This suggestion is decidedly negatived, 

 however, by the fact that the spark-length in the secondary 

 circuit consistently falls short of the value possible on theo- 

 retical grounds. It would appear rather that the cause of the 

 variation in our phenomena is the variable resistance of the 

 primary spark, and that the helpful influence of increasing 

 excitation is simply due to the increase of current poured 

 through the spark-gap at instants of formation of the spark, 

 which serves to decrease its resistance. 



If we substitute in equation (28) the values of the constants 

 of our system, we get, for ti=125, 



E 1 + -387R 2 =(5G-8 + ^5?)xl0«Ij 



V 2 



= 2-5 x lO" 18 -4L 

 7 2 



= 190 x 10- 18 ^| ; 

 and for 7* = 136, A i 



K 1 + -387R 2 = (61-8 + ^|?- 2 )xl0 6 ^J 



V„ 2 



= 2-72 x 10- 18 44 



I 2 



= 206xl0- 18 44. 



Ii 2 



These values are for the absolute system of units. To 



change them into ohms, volts, and amperes, we must write 



for the coefficients of 10 —3, —9, and —9 respectively. 



The values of R 1 +"387R 2 , computed according to these 



equations (assuming in the first that ~ is small), are given 



-L*2 



in Table III., in the columns headed by R x . R 2 is a purely 

 metallic resistance, while R x contains the spark-gap; so that 

 the resistance of this spark is in all probability the Greater 

 part of the resistance Rj •+- '387 R 2 . 



