﻿the Electric Spark is an Electromotor, 49 



Series 6. 



To obtain a measure for the magnitude of the electromotive 

 force, the conducting-wires of a battery were interposed between 

 e and m. When a spark passed between/ and g, the voltaic cir- 

 cuit was closed by the conducting spark, but was open in the 

 other case ; and the current which formed in the spark had to 

 pass through the voltaic battery. Both currents had therefore 

 to traverse the same circuit, and both only existed during the 

 time in which the spark passed between /and g. The ratio be- 

 tween the deflections which each current produced in the galva- 

 nometer must be equal to the ratio between their electromotive 

 forces. By means of a commutator the current of the battery 

 might be reversed ; so that it either went in the same direction as 

 the spark-current, or in the one opposite to it. If the deflection 

 of the galvanometer from the spark-current is x, and that from the 

 battery-current y, we have in one case x + y and in the other oc — y. 

 From this, x and y may be easily calculated, as well as the ratio 

 between them, by which the electromotive force of the battery- 

 current is known. In order that this method may be regarded 

 as perfectly correct, the conducting-power of the spark must not 

 vary with the direction of the battery-current. This is undoubt- 

 edly the case ; for the battery-current in its passage through the 

 spark is so enfeebled, that it can have no perceptible influence 

 on the conducting-power. In all the following experiments the 

 battery consisted of ten Bunsen's elements. The specific gravity 

 of the nitric acid was 1*32. In order that the deflections of the 

 battery-current might be greater than in the preceding experi- 

 ments, the resistances m and h were altered. 



Experiment 18. The knobs/and #were of iron, at a distance 

 of 3 millims. Formation of sparks between them. The posi- 

 tion of rest of the needle when no current traversed the galva- 

 nometer = 244-0. 



Position of rest when the currents went in opposite direc- 

 tions : — 



x — y. 



179-5 

 174-5 



Position of rest when the currents went in the same direction : - 



x+y. 

 148-0 

 150-5 

 151-5 



Mean . . 150-0 

 Phil. Mag. S. 4. Vol. 37. No. 246. Jan. 1869. E 



