32 Prof. A. Battelli and Mr. L. Magri on 



Hence for the three tubes used by us, being 90 cms., 80 cms., 

 and 71 cms. in length respectively, we have the values 



L x =762 cms. 



L 2 =658 ,, 



I*=567 „ 



and for the strip, 20 cms. in length, 

 L 4 =103 cms. 



29. With those experiments which served us to determine 

 the resistance of the spark and whose results we availed 

 ourselves of in order to compare the energy disposable in the 

 discharge with the energy exhibited by the various portions 

 of the circuit, we made use of circuits wound in spirals, as has 

 already been stated ; and with those experiments also we 

 photographed the spark. 



In order to compare the values for the period of oscillation 

 as obtained experimentally for those sparks with the corre- 

 sponding theoretical values, it would be necessary to know 

 the self-induction of the spirals, whose dimensions are recorded 

 on page 22. 



As theoretical formulas to calculate accurately these self- 

 inductions are wanting, we had to compare them with that of 

 circuits 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 capacities 

 .and varied one of the two self-inductions. The variable self- 

 induction was made up of a copper wire spiral, of which any 

 number 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, L 2 is the comparison circuit, 

 Cj. and Co are the two comparison condensers, and R is the 

 detector. 



* Wied. Ann. lx. p. 600 (1897). 



