generated in a High-tension Magneto. 



163 



the second term in the brackets amounting in the present 

 case to 0'005. Thus L 3 and C^ being known, 1^ can be 

 calculated. The result was L x = 0*0135 henry at 0*4 ampere. 

 This value of L^ is considerably smaller than that found by 

 the galvanometer method, which was, moreover, determined 

 at a much smaller current. 



For the determination of the self-inductance of the 

 secondary coil, the H.T. terminal of this coil was connected 

 through a large air-core coil (70*15 henries) with one plate 

 of an oil condenser (0'00088 microfarad), the other plate of 

 this condenser being connected with the frame of the 

 machine. The oscillograph was connected with the plates of 

 the condenser. The primary circuit contained neither series 

 inductance nor a condenser. In these circumstances the 

 period of the oscillation is equal to 2tt\/ (sh 2 + Li4)C 2 , where 

 2 is the capacity of the oil condenser with certain small 

 additions for the capacities of the coils and the oscillo- 

 graph, and L 4 represents the self-inductance of the air- 

 <jore coil. The total value of C 2 in this experiment was 

 0*00091 microfarad. The value of L± being known, and 

 s being taken as 1*05, L 2 was calculated from the observed 

 frequency. The result was L 2 — 19*3 henries, which value 

 is again much smaller than that determined by the galvano- 

 meter method. 



In this experiment the oscillation was started by inter- 

 rupting a primary current, but it may instead be started by 

 sparking with a small induction-coil to the terminals of the 

 •oil condenser. The value of L 2 found from the oscillation 

 excited in this way was found to be 1 per cent, less than the 

 value given above, and this difference is probably to be 

 accounted for by a slight difference in the degree of 

 magnetization of the core, the amplitude of the oscillation 

 being smaller in the sparking method than in the other. 



It should be observed that the value of L 2 given above 

 holds for oscillating currents which are nearly uniformly 

 distributed along the secondary wire ; when the secondary 

 terminals are not connected with a condenser, the value 

 of L 2 is still smaller. 



The sparking method of excitation, still with the oil 

 condenser and the large air-core coil, was also used for 

 the determination of the coupling. By equation (16) the 

 ratio of the squares of the frequencies of the system with 

 the primary coil open and with it closed is (l — k 2 )/s', 

 where s' now refers to the whole secondary inductance, 

 including that of the air-core coil. The value of P so 

 found was 0*199. Hence without the air-core coil the 



M2 





