PHILOSOPHICAL SOCIETY OP WASHINGTON. 259 



an iron core, " the spark appeared a little more intense than 

 without the iron." The infei*ence is also drawn "from these ex- 

 periments, that some of the effects heretofore attributed to mag- 

 neto-electric action are chiefly due to the reaction on each other 

 uf the several spirals of the coil which surround the magnet." 



In these researches it was found that when the two plates of 

 a single pair were placed even fourteen inches apart in an open 

 trough of diluted acid, " although the electrical intensity in this 

 case must have been very low, yet there was but little reduction 

 in the apparent intensity of the spark." It was also shown that 

 " the spiral conductor produces however, little or no increase of 

 effect when introduced into a galvanic circuit of considerable 

 intensity." When for example an "intensity" battery of two 

 Cruickshank's troughs, each containing 56 elements was employed 

 with the larger copper spiral, "no greater effect was perceived 

 than with a short thick wire :" in either case, only a feeble spark 

 being given.* An abstract of the results thus announced (and 

 which were obtained by Henry during the summer of 1834,) was 

 communicated by Dr. A. D. Bache, as a Secretary of the Ameri- 

 can Philosophical Society, to the Franklin Journal, in order to 

 give these interesting facts an earlier currency.f The date of 

 original discovery was however so well established, that this 

 friendly effort was scarcely necessary. | 



Combined Circuits. — In 1835, or early in 1836, wires had been 

 extended across the front campus of the College grounds at 

 Princeton from the upper story of the library building to the 

 Philosophical Hall on the opposite side, through which signals 

 were occasionally sent, distinguished by the number of taps of 

 the electro-magnetic bell, first exhibited five years previously in 

 the hall of the Albany Academy. It has already been noticed, 

 that contrary to all the antecedent expectations of physicists, 

 Henry had established the fact that the most powerful form of 

 magnet (designated by hira the "quantity" magnet) is not the 

 form best adapted to distant action through an extended cir- 

 cuit. The ingenious idea occurred to him that notwithstand- 

 ing this fundamental fact, it would be quite easy to combine 

 the two systems so as to enable an operator to produce the most 

 energetic mechanical effects, at almost any required distance. 



* Trans. Am. Phil. Soc. vol. v. n. fl. art. x. pp. 223-231. 



+ Joimicil of the Franklin Institute, March, 1835, vol. xv. pp. 169, 170. 



t M Becqnerel in his elaborate Treatise on Electricity, in the chapter 

 on " The influence of an electric current on itself by induction," says with 

 re'ra.rA to the increase of tension in a feeble current when passing through 

 along spiral conductor, " The effects observed in these circumstances 

 appear to have been noticed for the first time by Professor Henry. 

 ( Traite experimental de VEIectricite et du Magnetisme, 8vo. 7 vols. Pans, 

 1824-1840, vol. v. art. 1261, p. 231.) 



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