162 Prof. E. Taylor Jones on the Potential 



curves showing the oscillations of the circuits could be 

 obtained. The frequencies of the circuits are so high that 

 probably no oscillograph with material moving parts would 

 be suitable for the purpose. The difficulty cannot be over- 

 come by merely connecting condensers of large capacity with 

 the circuits in order to increase the periods, for since the 

 effective resistances are very considerable the logarithmic 

 decrements of the oscillations then become too great. 



When, however, a suitable coreless coil was connected in 

 series with the primary or the secondary coil, as well as a 

 condenser, the damping factor was so far reduced that 

 curves suitable for the measurement of frequency and 

 effective resistance could be obtained. This method was 

 accordingly adopted in the following determinations of 

 the inductances and effective resistances of the circuits. 

 Although the results were thus obtained for frequencies 

 considerably below those which the circuits possess when 

 unprovided with such additional inertia and capacity, they 

 nevertheless correspond much more closely with actual 

 working conditions than would results obtained by the use 

 of slowly alternating currents or by other " slow " methods. 



In the following experiments the various coefficients of 

 the circuits, as well as those of the coils used as auxiliaries, 

 were all determined for frequencies of about 600 oscillations 

 per second. The quantities regarded as known and used as 

 standards in the measurements were the frequency of a 

 certain tuning-fork, the capacities of certain standard mica 

 condensers, and the self-inductance of a certain air-core 

 coil. 



The self-inductance of the primary coil of the magneto 

 was determined by connecting in the primary circuit, 

 between the point J and the condenser (fig. 1), an air- 

 core coil the self-inductance, L 3 , of which was 0*0609 henry. 

 Across the interrupter was connected a mica condenser of 

 0*6 microfarad. The oscillograph was connected to the 

 H.T. terminal and to the frame of the machine. In these 

 circumstances the circuits are loosely coupled and the 

 oscillation-constant of the secondary is very small in com- 

 parison with that of the primary. Consequently, the 

 frequency, n, of the oscillation — excited by interrupting 

 a measured current in the primary circuit — gives the value 

 of (L 1 -r-L 3 )C 1 subject to a small correction for the effect of 

 the secondary. The expression is 



a +t \o - 1 U («-i+**)L»Q, 7 



