1855.] on Ruhmkorff*s Induction Apparatus. 141 



duce certain hurtful or wasteful results. Fizeau, by applying a 

 Leyden jar (or its equivalent,) to the parts of the primary circuit 

 near the contact breaker, took up this extra power at the moment of 

 time, and converted it to a useful final purpose, upon principles 

 belonging to static induction, the effects of which were briefly ex- 

 plained. Masson,* Grove,f and Sinsteden have made a like applica- 

 tion to the terminals of the secondary wire ; and Grove has pointed 

 out striking changes in the character of the currents in it thus 

 produced, and useful applications of the results. For instance, 

 the spark in air between the ends of two platinum wires con- 

 nected with the secondary terminals is flame-like, soft, and 

 comparatively quiet compared with that which is produced when 

 the terminals are respectively connected with the inner and outer 

 coatings of a Leyden jar ; for then it becomes very bright, sonor- 

 ous, and apparently large, so that two sparks can hardly differ 

 more than the same spark under these circumstances. The differ- 

 ences are even greater than the appearances show ; for whilst the 

 powerful rattling spark cannot fire wood, or paper, or even gun- 

 powder, except by the use of expedients, the soft quiet spark at 

 once inflames any of them. The effect of the static induction thus 

 introduced is not so much to vary the quantity of electricity which 

 passes, as the time of the passage. That electricity which, moving 

 with comparative slowness through the great length of the secondary 

 coil, produces a spark having sensible duration (and therefore in 

 character like that of a Leyden jar passed through a wet thread,) 

 is, when the jar is used, first employed in raising up a static induc- 

 tion charge, which when discharged produces a concentrated spark 

 of no sensible duration, and therefore much more luminous and 

 audible than the former. Fixing a piece of platinum wire horizon- 

 tally across the ball of a Leyden jar, and then bringing the platinum 

 wire secondary terminals respectively near its ends, two interruptions 

 are. produced in the secondary circuit, the sparks at which are like 

 each other and equal in quantity of electricity, for the jar as yet 

 forms only an insulating support. But if, in addition, either 

 secondary terminal be connected by a wire with the outside of the 

 jar, the spark on that side assumes the bright loud character before 

 described, but ceases to fire gunpowder or wood ; and no one would 

 at first suppose, what is the truth, that there is the same electricity 

 passing in one as in the other. 



Another interesting effect of the static induction is the double 

 spark. If one of the secondary terminals be connected with the 

 outside of a Leyden jar, and the other be continued until near the 

 knob or a wire connected with it, a soft spark appears at that inter- 

 val for every successive current in the primary circuit. This spark, 

 however, is double ; for the electricity thrown into the jar at the 



* Prize Essay, Haarlem Trans. 1854, pp. 46, 47. 

 t Phil. Mag. Jan. 18.55, ix. p. 1. 



