﻿the Electric Spark is an Electromotor. 53 



merits it cannot be more than the 0*0001 of second. The num- 

 ber of sparks which passed in each second did certainly not ex- 

 ceed 10. With this assumption we arrive at the conclusion that 

 the passage of sparks from one pole to the other does not occupy 

 more than 0001 of the time during which the machine is being 

 worked. Moreover it must be considered that each spark, as 

 Feddersen has shown, is no continuous whole, but consists of 

 a number of partial sparks. In order to compare the mechanical 

 activity of the luminous arc and that of the current of sparks as 

 regards the disintegration of the polar surfaces, we must on these 

 assumptions first multiply that of the latter by 1000 ; and it is 

 possible that in fact a still larger number must be taken. And, 

 secondly, the metallic polar surfaces on the luminous arc have 

 so a high temperature that they are often near their fusing-point, 

 while with the spark they are only slightly warmer than the sur- 

 rounding medium. Hence in the latter case the disintegration 

 requires much more work than in the former. Taking into con- 

 sideration this circumstance, the difference between the mecha- 

 nical work in the luminous arc and that in the spark is quite 

 different from what might at first have been supposed. 



5. In the previous experiments for determining the electro- 

 motive force the distance between the knobs b and d was un- 

 changed. To determine the influence which a change in this 

 distance might produce, the following experiments were made : — 



Experiment 25. The battery consisted this time also of ten 

 Bunsen's elements. The distance between the knobs b and d 

 was about 8 millims. Formation of sparks between / and g. 

 Position of equilibrium of the magnetic needle = 231-7. 



x-y. 



x-\-y. 



x-y. 



1500 



111-5 



1580 



150-5 



106-0 

 101-0 

 1130 



1530 



Mean . . 



1079 





Mean for x—y — 152*8. 







From this we obtain 







# + z/ = 123-8, x-ij = 78'9, # = 101-3, y = 22-5, and - = 4-50. 



The electromotive force, therefore, is equal to that of 45 

 elements. 



Experiment 26. Distance between the knobs b and d about 

 16 millims. In other respects no change. Position of equili- 

 brium of the needle =231*0. 



