222 MEMORIAL OF JOSEPH HENRY. 



of iron covered with several strands of wire,) excited by a galvanic 

 pair of one-sixth of a square foot of zinc surface, sustained 39 

 pounds, or more than fifty times its own weight; while Moll's mag- 

 net of about double the dimensions, employing eleven square feet 

 of battery, lifted only 75 pounds, or fifteen times its own weight. 

 That is, Henry's magnet while about only one-seventh of the weight 

 of Moll's (without their wrappings) supported more than half the 

 load of the latter. Or comparing their larger magnets, — while 

 Moll's twelve and a half inch magnet (of two and a quarter inch 

 iron) lifted as its greatest eifort 154 pounds, (a result with which 

 the author justly felt elated,) Henry's nine and a half inch magnet 

 (of about the same sized iron) lifted 750 pounds; or about five 

 times its maximum load. But the most surprising contrast between 

 the two series of experiments, resulting from their different systems, 

 was the enormous difference of battery-power respectively applied; 

 — Moll pusliing his up to seventeen square feet, — Henry reduc- 

 ing his in the first case to one-sixth of a square foot, andin the 

 latter case obtaining his five-fold duty with one-eleventh of the 

 quantity of galvanic current. The philosopher of Utrecht, though 

 he evidently realized with him of Albany, the importance of close- 

 winding, employed but a single layer of coil. The latter, by means 

 of well-considered trials had ascertained the great increase of mag- 

 netic force resulting from a considerable number of coils. On the 

 theoretical grounds assigned by Henry therefore, Moll's single 

 conducting wire of one-eighth inch diameter, while electrically 

 equivalent to some half a dozen of Henry's conducting wires (of 

 ' the same length and collective weight) would be magnetically inferior 

 thereto — for equal iron cores. 



Notwithstanding that Henry's successes were thus both earlier 

 and more brilliant than those of Moll, the two names are usually 

 associated together by European writers in treating of the develop- 

 ment of the magnet.* 



♦Faraday in subsequently investigating the conditions of galvanic induction, 

 referred with approbation to the magnets of Moi.l, and Henry as best calculated 

 to produce the ellects sought. In constructing his duplex helices for observing 

 the direction of the Induced current, he however adopted Hknry's method by 

 winding twelve coils of copper wire each twenty-seven feet long — one upon the 

 other. (Pttil. Trans. Roy. Soc. Nov. 24, 1831, vol. cxxil. (for 1832,) pp. 12C, and 138. Ex- 

 perimental Researches, etc. vol. 1. art. 6, p. 2; and art. 57, p. 15.) 



