High- Frequency Induction- Coil, 337 



where k is the conductivity. For n= 500,000 and £ = -0006, 

 this gives the rather startling result 



ir = 36,000rR, 



which for wire of 1 millim. diameter would be 



R/= 1,800 R. 



This deduction assumes, however, that the wire is at an 

 infinite distance from other currents, while in our case the 

 distance between wires is comparable to their diameters. The 

 results of our experimental work would also entirely contradict 

 any assumption of such excessive increase in metallic resistance. 

 ^ A brief comment upon the degree of accuracy attained and 

 attainable in such work may be of interest. The behaviour 

 of the dynamometers left nothing to be desired. They acted 

 with much greater uniformity than the phenomena to be 

 Observed, so that any irregularity observed in their readings 

 must be attributed to actual variations in the currents, As 

 much can hardly be said of the electrometer. To give con- 

 venient readable deflexions with the mean potentials observed, 

 it required to be adjusted with such sensitiveness that the 

 directive force was not large enough to prevent frictional 

 disturbance of the position of equilibrium. Further, the 

 inertia of the moving system was such as to prevent prompt 

 reading of deflexions, and in case of intermittent action the 

 readings obtained were a time-average, which was necessarily 

 small. The observations were of great value, however, 

 because they were of a wholly different type of phenomenon, 

 and furnished so good a check upon both the theoretical 

 reasonings and the accuracy of the other work. In general 

 the accuracy of the results obtained seems to have been con- 

 ditioned almost entirely upon the uniformity of the phenomena 

 of a blown-out spark in air. 



In the foregoing work an attempt has been made to verify 

 experimentally the agreement of the actual behaviour of an 

 oscillating system with two degrees of freedom with the ap- 

 proximate theory, As specific conclusions resulting from this 

 comparison we see that : — 



1. The main period of oscillation of the primary circuit is 

 very nearly that deduced from the dimensions of the system. 

 The same may be said also of the maximum potential attained 

 in the secondary circuit. 



2. The effective currents and potentials, which are functions 

 of the damping factors, and these in turn factors of the resist- 

 ances, would indicate that the resistances of the sparks are of 

 the order of from 10 to 100 ohms, depending upon the amount 



