50 WRITINGS OF JOSEPH HENRY. [1831 



AN ACCOUNT OP A LARGE ELECTRO-MAGNET,* MADE FOR THE 

 LABORATORY OF YALE COLLEGE. 



{Extract of a letter to Prof. Silliman, accompanying the Magnet.) 

 (Silliman's American Journal of Science, April, 1831, vol. xx. pp. 201-203.) 



The magnet is constructed on precisely the same princi- 

 ples as that described in the last number of the Journal. It 

 weighs 59| lbs. avoirdupois, (exclusive of the copper wire 

 which surrounds it,) and was formed from a bar of Swede's 



* [This magnet is now arranged in its frame, in the laboratory of Yale Col- 

 lege. Being myself out of town when the instrument arrived, the necessary 

 experiments and fixtures were satisfactorily made by C. U. Shepard, (Chemical 

 Assistant) and Dr. Titus W. Powers, of Albany, who was so obliging as to 

 bring the magnet to New Haven. There has not been time (as the magnet 

 came just as this No. was finishing) to do any thing more than make a few 

 trials, which have however fully substantiated the statements of Prof. 

 Henry. He has the honor of having constructed by far, the most power- 

 ful magnets that have ever been known, and his last, weighing, armature 

 and all, but 82|^ lbs., sustains over a ton. It is eight times more powerful 

 than any magnet hitherto known in Europe, and between six and seven 

 times more powerful than the great magnet in Philadelphia. We under- 

 stand that the experiments described in the last No. of this Journal, (except 

 those ascribed to Dr. Ten Eyck) were devised by Professor Henry alone, 

 who (except forging the iron) constructed the magnet with his own hand. 

 The plan of the frame, and the fixtures, and the drawing in the last No., 

 were done by Dr. Ten Eyck. In the Yale College magnet, the plan was 

 drawn by Professor Henry, and the iron forged under his direction. The 

 length of the wires being agreed upon, the winding was done by Dr. Ten 

 Eyck, and the experiments were mutually performed. — Editor of Journal."] 



[It may be worth while to state a single experiment, which I made with 

 a view to learn the chemical eflfects of this instrument. As its magnetic flow 

 was so powerful, I had strong hopes of being able to aacomplish the decom- 

 position of water by its means. My experiment, however, which was made 

 as follows, proved unsuccessful. The battery being immersed, to the ex- 

 tremities of the magnet were applied two broad, polished plates of iron, 

 terminating in flattened wires, which were united with the wires of the ordi- 

 nary apparatus for decomposing water, and the contact heightened by the 

 use of cups of mercury : not the slightest decomposition was, however, ob- 

 servable. Aware, that had any chemical effect been produced, this arrange- 

 ment could have decided nothing, (except perhaps from the degree of energy 

 in the decomposition) as respects the point whether simple magnetism is 



