at least by Professor Hare of the University of Pennsylvania, who in a 

 letter of February 24, 1831, published in Silliman's Journal of July 

 1831, stated with reference to wire for magnets, "I used no wrapping, 

 but merely shell lac varnish, applied in winding. ..." The same issue 

 of Sillimans Journal quotes a letter from Professor J. W. Webster of 

 Harvard of February 7, 1831, stating, "In constructing the magnetic 

 apparatus, there is considerable economy in using sealing wax instead 

 of silk." 

 b. Multiple Layer Windings 



In 1831 Henry wrote as follows: 



"At the same time [1829 or 1830], a very material improvement in the formation of 

 the coil suggested itself to me, on reading a more detailed account of Prof. Schweig- 

 ger's galvanometer, and which was also tested with complete success upon the same 

 horse-shoe; it consisted in using several strands of wire, each covered with silk, in- 

 stead of one: — agreeably to this construction, a second wire, of the same length as the 

 first, was wound over it, and the ends soldered to the zinc and copper in such a manner 

 that the galvanic current might circulate in the same direction in both. . . ." ^ 



This is generally acknowledged to be the first publication of the use 

 of this important improvement in magnet construction. 



In Henry's early work the windings were wound directly on the 

 magnet core. It is not clear whether he later wound up coils sepa- 

 rately intended to be applied to the magnet cores after winding. This 

 form of construction, however, was used by Professor Hare as early 

 as 1831 in making the Henry type magnets. In a letter of March 4, 

 1831, he described in detail the process of winding the coil on a mandril 

 and later slipping it over the core, apparently as an improvement in 

 construction detail.^ 



2. Proportioning of Magnet and Battery for Maximum Effect 

 Henry, in a paper published January, 1831, described a series of 

 experiments instituted jointly with Dr. Philip Ten Eyck for the pur- 

 pose of determining how the type of magnet and battery and the length 

 of the interconnecting wires alifected the magnetic force produced. 

 From the results he concluded that: 



"From these experiments, it is evident that in forming the coil we may either use 

 one very long wire or several shorter ones as the circumstances may require: in the 

 first case, our galvanic combinations must consist of a number of plates so as to give 

 ' projectile force'; in the second, it must be formed of a single pair." " 



3. Electromagnetic Motor 



In 1821 Faraday made the first electric motor, the action of which 



was the rotation of a current-carrying wire around the pole of a perma- 



6 SW, Vol. 1, p. 39. 



* Silliman's Journal, July, 1831. 



'SW, Vol. 1, p. 42. 



