Oscillatory Discharges. 633 



36. As regards self-induction, we wish to state that 

 different experimenters, having measured the coefficient of the 

 same coil with direct currents and with alternating currents, 

 have found values differing little from one case to another ; 

 but the reversals used were always of few hundredths per 

 second. 



Tallqvist (/. c.) more especially dealt with the influence 

 the method of measuring the self-induction of the circuit may 

 possess, comparing the experimental values of the period of 

 oscillation with those deduced from Thomson's formula. 

 From this comparison, he argues that the true values of L 

 for oscillatory discharges are somewhat smaller than those 

 obtained experimentally by the method of direct currents as 

 well as by the telephone method with alternate currents. 

 As a rule, however, the value of L adopted for the spirals in 

 the researches so far carried out in oscillatory discharges 

 has always been either the one calculated by the formula? 

 true for direct currents, or the one found experimentally 

 with those currents. 



On the other hand, our self-inductions have either been 

 calculated directly and with the proper corrections relative 

 to the frequency of the discharges, or have been determined 

 experimentally with high-frequency currents by comparison 

 with already calculated self-inductions. In the case also of 

 the self-induction, the effect of the damping is wholly negli- 

 gible in our experiments, so that Rayleigh/s formulae may be 

 used instead of those of Barton. 



As regards the case of circuits of any form, the method 

 suggested by Stefan* for taking account of the unequal 

 distribution of the current in the section of a wire may not 

 be applied to the small-radius spirals, as for this it would be 

 required that the thickness of the wire be negligible as 

 compared with the radius of curvature of the circuit, and 

 that the current be distributed symmetrically around the axis 

 of the wire. This of course is not true for the ordinary 

 spirals, on account of the dissymmetry of distribution of the 

 currents, dissymmetry due to the action of one winding 

 on another. This perturbing action tends to localize the 

 currents only on some portions of the surface of the con- 

 ductor ; and that this is really the case is clearly shown by 

 the fact, established by our experiments (see § 24). that in 

 the case of alternating currents a wire bent to a spiral will 

 oppose a much higher resistance than that corresponding 

 to the same wire stretched out in a straight line. As theo- 

 retical formulae able to give us the effective self-induction oi' 

 * Wien. Ber, xcv. II a, p. 917 (1887). 



