304 On Lightning Conductors to Powder Magazines. [No. 99. 





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29. I select an experiment with the Leyden bottle to exem- 

 plify my statement. 



Let a, be a ball and wire connected 

 with the inner coating, b b with the outer 

 coating of a charged bottle — let c be a 

 metallic ball placed near, but not touching 

 the rod b ; when the discharge is made by 

 bringing a and b into contact, by means of 

 the moveable rod d, as the electricity 

 passes through the rod b a spark takes 



place between it and the ball c, although the ball c is out of 

 the direct circuit. 



30. This spark all electricians have seen ; its existence 

 is universally admitted. The ball c may be connected with 

 the ground, or with a long wire, and the spark will still pass. 

 If the ball be connected with a wire, and the opposite end 

 of the wire with the apparatus called " Volta's cannon," 

 charged with inflammable air, at the instant of connecting 

 the outer and inner coatings or discharging the jar, the cannon 

 is exploded also. Gunpowder, spirits, and other inflammable 

 matters may be fired by this spark, although it is manifestly far 

 out of the course of the main discharge. 



31. There have been several attempts to explain the oc- 

 currence of this spark. The older electricians, and Henry of 

 New York, regard it as the effect of induction in the bodies 

 adjacent to the main conductor ; that it is not a direct emana- 

 tion of electricity from the conductor to the lateral objects. 

 Mr. Daniell says it is only the excess from an insufficient con- 

 ductor which passes to the adjacent object. This idea any 

 one possessed of a Leyden jar and a few pieces of wire may 

 set aside by a simple experiment, when he will find the success 

 of each attempt at obtaining the lateral spark increased by 

 increasing the mass of the prime conductor. Mr. Faraday how- 

 ever supposes this extra spark to be a direct expansion of the 

 electricity — that with a good lightning rod it can be but small, 



