Polytechnic Association Proceebings. 993 



tilted, with a view to develop the induced current in a separate or 

 secondary coil, Faraday should have used the longer coil for the 

 battery circuit, and the shorter for the secondary circuit. Simply 

 reversing the order of his coils would have given him quite a differ- 

 ence in his results. From the secondary, by volta-electric induc- 

 tion, he says: " I could obtain no evidence by the tongue, by spark, 

 or by heating of fine wire or charcoal; nor could I obtain any 

 chemical effects." The current was indicated only by the galvano- 

 meter and its magnetic effects. 



On the 30th March, 1832, Mr. Forbes, of Edinburgh, obtained 

 a spark from the use of the steel magnet. (May number. Annals 

 of PMlosoj)hy ; also SilUman^s Journal^ vol. 22, page 408.) 



In the latter part of June, 1832, Prof. Henrj^ commenced experi- 

 ments on magneto-electric induction, of similar purport with those 

 of Faraday, and was more successful in the production of sparks. 

 These were communicated in the July number of S Hitman's Journal 

 for 1832. In the same number, Prof. Henry announced the interest- 

 ing facts, that when a very short wire (a foot in length), joined the 

 poles of a small battery, in such a condition as to give no spark 

 with this wire, a wire thirty or forty feet in length would give a 

 bright'spark on breaking the circuit, and that the "effect appeared 

 to be somewhat increased by coiling the wire into a helix." 

 The battery m this case, was spoken of as "a small battery," 

 the number of pairs of plates, a very important point, not being 

 mentioned. It is stated that " if moderately excited by diluted 

 acid, it would not give a spark with a wire one foot in length on 

 breaking the circuit," but if the action of the battery be very 

 intense, a " a spark will be given by a short wire." The inference 

 is rather in favor of one pair of plates, or perhaps several pairs 

 joined as one, inasmuch as one foot of wire was used to join the 

 poles. 



Prof. Henry referred this phenomenon to the class of volta or 

 magneto-electric induction. No shock was obtained in either the 

 experiments of Henry or Forbes. 



In the early part of 1833, Prof. Dal "Negro asserted that the 

 " separating spark of a voltaic pile originated at least in part, 

 from magneto-electricity, and hence would be more intense if the 

 conducting wire were coiled around a bar of iron." {Annali delle 

 Scienze^ March and April, 1833; also Bihliolh. Univ., July and 

 August.) This was the first public announcement in relation to the 

 augmentation of the spark of separatiou as produced by a coil 



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