The London, Edinburgh and Dublin philosophical magazine and journal of science . ed ; and with those experiments also wephotographed the spark. In order to compare the values for the period of oscillationas obtained experimentally for those sparks with the corre-sponding theoretical values, it would be necessary to knowthe self-induction of the spirals, whose dimensions are recordedon page 22. As theoretical formulas to calculate accurately these self-inductions are wanting, we had to compare them with that ofcircuits capable of being theoretically calculated. For these comparisons we availed
The London, Edinburgh and Dublin philosophical magazine and journal of science . ed ; and with those experiments also wephotographed the spark. In order to compare the values for the period of oscillationas obtained experimentally for those sparks with the corre-sponding theoretical values, it would be necessary to knowthe self-induction of the spirals, whose dimensions are recordedon page 22. As theoretical formulas to calculate accurately these self-inductions are wanting, we had to compare them with that ofcircuits capable of being theoretically calculated. For these comparisons we availed ourselves of the Nernst*differential exciter slightly modified, as to obtain the equi-librium we maintained constant the two comparison varied one of the two self-inductions. The variable self-induction was made up of a copper wire spiral, of which anynumber of spires could be employed in our experiments(mean radius of spiral 0*713 cm., thickness of wire 0*8 mm.,number of spires to the unit of length 6*3025). The arrangement adopted is shown diagrammatically by. fig. 7, where Lj denotes the spiral, L2 is the comparison circuit,Cj. and Co are the two comparison condensers, and R is thedetector. * Wied. Ann. lx. p. 600 (1897). Oscillatory Discharges. 33 After connecting the points C and D with the electrodesof a spark-gap and with the poles of a Ruhmkorff coil, therecould be sent through the differential exciter currents with afrequency of the same order of magnitude as those of thesparks we have photographed. Then it was tested whether the contact points A and Bbetween each self-induction and the corresponding condenserwere at the same potential. For this purpose we found mostconvenient the detector suggested by Nernst, made up of avacuum-tube without electrodes, on whose terminals twostrips of tinfoil connected with A and B respectively hadbeen wound. As is known, the luminosity of the tube will be minimumwhen the condition -Liv--1==-L^2^2 is satisfied. The accur
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