390 MEMORIAL OP JOSEPH HENRY. 



Note D. i 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 pari of 1831, 

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

 covery — thai of magneto-electricity, — the multiple coil of Henry, 

 lie thus describes ii : "A welded ring was made of soft round bar- 

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

 ring >ix inches in external diameter. 1 hree 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, 

 (in the other part of the ring about sixty feel 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 a- 2,000 pounds 

 have been lilted, may be used for these experiments." f 



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, \ repeated his experiments with copper 

 wire varnished as above described; and 1 have recently made a 

 magnet by means of cupper wire, shellac varnish, ami paper sur- 

 rounding the iron, — which in proportion t < > its weight, holds more 

 than his. It weighs 17 pounds, and has held 783 pounds. It i- 

 furnished with fourteen coils, of sixty feet each.";!; 



Professor N. J. Callan, of the College of Maynooth, Ireland, in 

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



■ In Ilis preceding electrical induction coil-, Professor Faraday employed 

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



lull in the same direction." Of these, sis were connected by their extremities 



with the battery — for the primary current, and the alternate six were gathered 

 by their extremities, for testing the secondary or induce, 1 current. 



f Phil. '/'j. r, ( v Hoy. Soc. Nov. 24, IS31, vol. exxii. seels. L'T and 57; pp. 131, IS. — A No 

 Experimental Researches, etc. Svo. I. on, Ion, [$39, vol. i. pp. 7, 15 At the time this 

 was written, the only electro-magnet in existence— even approaching the lifting 

 power stated, was the Yale College magnet of I! inky. >Tor had anj other experi- 

 menter approximated within :i tenth of this magnetic attraction. Ana it is note- 

 worthy thai Proressor Fata. lav adopted very precisely the character of coil 

 originated ana recommended by Henry, ami did not adopt the single coil 

 employed i>\ Professor Moll. 



: Sturgeon's Annals oj Electricity, etc. Oct. 1S36, vol. i. p. Hi 



