INDUCTIVE ACTION OF AN ELECTRIC CURRENT. 61 



gave scarcely a perceptible spark ; but being opened out and the parts separated, it 

 gave a very good one. The two helices i and ii being joined at their similar ends, 

 and then used at their other extremities to connect the plates of the electromotor, 

 thus constituted one long helix, of which one half was opposed in direction to the 

 other half: under these circumstances it gave scarcely a sensible spark, even when 

 the soft iron core was within, although containing nearly two hundred feet of wire. 

 When it was made into one consistent helix of the same length of wire it gave a very 

 bright spark. 



1097. Similar proofs can be drawn from the mutual inductive action of two sepa- 

 rate currents (1110.); and it is important for the general principles that the consist- 

 ent action of two such currents should be established. Thus, two currents going in 

 the same direction should, if simultaneously stopped, aid each other by their relative 

 influence ; or if proceeding in contrary directions, should oppose each other under 

 similar circumstances. I endeavoured at first to obtain two currents from two dif- 

 ferent electromotors, and passing them through the helices i and ii, tried to effect 

 the disjunctions mechanically at the same moment. But in this I could not suc- 

 ceed ; one was always separated before the other, and in that case produced little or 

 no spark, its inductive power being employed in throwing a current round the re- 

 maining complete circuit (1090.) : the current which was stopped last always gave a 

 bright spark. If it were ever to become needful to ascertain whether two junctions 

 were accurately broken at the same moment, these sparks would afford a test for the 

 purpose, having an infinite degree of perfection. 



1098. I was able to prove the points by other expedients. Two short thick wires 

 were selected to serve as terminations, by which contact could be made or broken 

 with the electromotor. The compound helix, consisting of i and ii (1053.), was ad- 

 justed so that the extremities of the two helices could be placed in communication 

 with the two terminal wires, in such a manner that the current moving through the 

 thick wires should be divided into two equal portions in the two helices, these por- 

 tions travelling, according to the mode of connexion, either in the same direction 

 or in contrary directions at pleasure. In this manner two streams could be obtained, 

 both of which could be stopped simultaneously, because the disjunction could be 

 broken at G or F by removing a single wire. When the helices were in contrary 

 directions, there was scarcely a sensible spark at the place of disjunction; but when 

 they were in accordance there was a very bright one. 



1099. The helix i was now used constantly, being sometimes associated, as above, 

 with helix ii in an according direction, and sometimes with helix iii, which was placed 

 at a little distance. The association i and ii, which presented two currents able to 

 affect each other by induction, because of their vicinity, gave a brighter spark than 

 the association i and iii, where the two streams could not exert their mutual in- 

 fluence ; but the difference was not so great as I expected. 



. 1100. Thus all the phenomena tend to prove that the effects are due to an indue-. 



h2 



