390 MEMORIAL OF JOSEPH HENRY. 



Note D. {From p. 230) 

 henry's mutiple-coil magnet. 



Professor M. Faraday, in the first series of his "Experimental 

 Researches in Electricity," commencing in the latter part of 1831, 

 employed for the magnet by which he made his most important dis- 

 covery — that of magneto-electricity, — the multiple coil of Henry. 

 He thus describes it : "A welded ring was made of soft round bar- 

 iron, the metal being seven-eighths of an inch in thickness, and the 

 ring six inches in external diameter. Three helices were put around 

 one part of this ring, each containing about twenty-four feet of 

 copper wire one-twentieth of an inch thick : they were insulated 

 from the iron and each other, and superposed in the manner before 

 described.* They could be used separately or arranged together. 

 On the other part of the ring about sixty feet of similar copper wire 

 in two pieces were applied in the same manner. - - - There is 

 no doubt that arrangments like the magnets of Professors Moll, 

 Henry, Ten-Eyck, and others, in which as many as 2,000 pounds 

 have been lifted, may be used for these ex])eriments."t 



Henry's warm friend — Dr. Robert Hare of Philadelphia, (Pro- 

 fessor of Chemistry in the University of Pennsylvania,) who early 

 repeated his magnetic experiments, says in a letter to Mr. Sturgeon, 

 dated April 5, 1832: "As soon as I heard of the wonderful mag- 

 net of Professor Henry, I repeated his experiments with copper 

 wire varnished as above described; and I have recently made a 

 magnet by means of copper wire, shellac varnish, and paper sur- 

 rounding the iron, — which in proportion to its weight, holds more 

 than his. It Aveighs 17 pounds, and has held 783 pounds. It is 

 furnished with fourteen coils, of sixty feet each."| 



Professor N. J. Callan, of the College of ]\Iaynooth, Ireland, in 

 1836, giving an account of his "new galvanic battery" remarks 



* [In his preceding electrical induction coils, Professor Faraday employed 

 "twelve helices superposed, each containing an average length of wire of 27 feet, 

 and all in the same direction." Of these, six were connected by their extremities 

 witli the battery — for the primary current, and the alternate six were gatliered 

 by their extremities, for testing the secondary or induced current.] 



t P}nl. Trans. Roy. Soc. Nov. 2t, 1S31, vol. cxxii. sects. 27 and 57; pp. 131, 138.— Also 

 ExpcrimcnUd Researches, etc. 8vo. London, is:i9, vol. i. pp. 7, lo. At the time this 

 was written, the only electromagnet in existence — even aiiproacliing the lifting 

 power stated, was the Yale College magnet of Hknky. Nor had any other experi- 

 menter approximated within a tenth of this magnetic attraction. And it is note- 

 worthy that Professor Faraday adopted very precisely the character of coil 

 originated and recommended by Henry, and did not adopt the single coil 

 employed by Professor Moll. 



{Sturgeon's Annals of Electricity, etc. Oct. 1836, vol. i. p. 10. 



