Spark-Length of an Induction- Coil. 

 Fig-. 6. — Zinc Poles. 



147 

















\ 













i w 

















^-£L 





"-*-■ -o 













-i 







































•4 -6 -8 , 1-0 



Capacity in microfarads. 



1-4 



by curves which connect the spark-length with the capacity 

 for different rates of break and for several different materials. 



As far as the influence of the primary electromotive force 

 is concerned, it seems to matter little whether a high or 

 a low electromotive force is used. At all events, I found 

 that, so long as the capacity of the condenser was anything 

 appreciable, it made no difference to the length o£ the spark 

 whether I used 10 or 100 volts to produce the primary 

 current of 2*5 amperes. Accordingly, over the somewhat 

 narrow range which these experiments cover, the best 

 capacity, as well as the maximum spark-length, is inde- 

 pendent of the primary electromotive force. 



On the other hand, both best capacity and maximum 

 spark-length are very greatly affected by the nature of the 

 primary poles. Speaking broadly, we may say that the more 

 easily disintegrate the character of the poles the greater is 

 the capacity needed to give the longest possible spark. Thus, 

 with a slow break, the values in microfarads of the best 

 capacities are: — for platinum "15, for copper *38, for zinc *45, 

 and for carbon l'l; the corresponding spark-lengths being 

 29, 27, 15, and 12 millimetres respectively. 



Turning, lastly, to examine the effect of varying the rate of 

 break, we observe that the tendency is for the best capacity to 

 decrease and the maximum spark-length to increase as the 



L2 



