1835] WRITINGS OF JOSEPH HENRY. 93 



a time the further prosecution of the subject. I have how- 

 ever been able during the past year to resume in part my 

 investigations, and among others, have made a number of 

 observations and experiments which develop some new cir- 

 cumstances in reference to this curious phenomenon. 



These, though not as complete as I could wish, are now pre- 

 sented to the Society, with the belief that they will be in- 

 teresting at this time on account of the recent publication of 

 Mr. Faraday on the same subject. 



The experiments are not given in the precise order in 

 which they were first made, but in that which I deem best 

 suited to render them easily understood; they have however 

 been repeated for publication in almost the same order in 

 which they are here given. 



1. A galvanic battery, consisting of a single plate of zinc 

 and copper, and exposing one and a half square feet of zinc 

 surface, including both sides of the plate, was excited with 

 diluted sulphuric acid, and then permitted to stand until 

 the intensity of the action became nearly constant. The 

 poles connected by a piece of copper bell-wire of the ordi- 

 narj' size and five inches long, gave no spark when the con- 

 tact was broken. 



2. A long portion of wire, from the same piece with that 

 used in the last experiment, was divided into equal lengths of 

 fifteen feet, by making a loop at each division, which could be 

 inserted into the cups of mercury on the poles of the battery. 

 These loops being amalgamated and dipped in succession into 

 one of the cups while the first end of the wire constantly re- 

 mained in the other, the effect was noted. The first length, or 

 fifteen feet, gave a very feeble spark, which was scarcely per- 

 ceptible. The second, or thirty feet, produced a spark a little 

 more intense, and the effect constantly increased with each ad- 

 ditional length until one hundred and twenty feet were used ; 

 beyond this there was no perceptible increase; and a wire of 

 two hundred and forty feet gave a spark of rather less inten- 

 sit3\ From other observations I infer that the length neces- 

 sary to produce a maximum result, varies with the intensity 

 of the action of the battery, and also with its size. 



