An account of a large Electro-Magnet,'^ made for the Laboratory of 

 Yale College ; by Joseph Henry and Dr. Ten Eyck. 



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



The magnet is constructed on precisely the same principles as 

 that described in the last number of the Journal. It weighs 59^ lbs. 

 avoirdupois, (exclusive of the copper wire which surroilnds it,) and . 



* 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 ex- 

 periments and fixtures were satisfactorily made by Mr. C. U. Shepard, (Chera. 

 Assis.) and Dr. Titus W. Powers, of Albany, who was so obliging as to bring the mag- 

 net 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. t He has the honor of having construct- 

 ed by far, the most powerful 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 seveil 

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

 der his direction. The length of the wires being agreed upon, the winding was 

 done by Dr. Ten Eyck, and the experiments were mutually performed. — Ed. 



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

 to learn the chemical effects of this instrument. As its magnetic flow vras so pow- 

 erful, I had strong hopes of being able to accomplish the decomposition of water by 

 its means. My experiment, however, which was made as follows, proved unsuc- 

 cessful. The battery being immersed, to the extremities of the magnet were applied 

 two broad, polished plates of iron, terminating in flattened wires, which were united 

 with the wires of the ordinary apparatus for decomposing water, and the contact heigh- 

 tened by the use of cups of mercury: not the shghtest decomposition was, however, 

 observable. Aware, that had any chemical effect been produced, this arrangement 

 could have decided nothing, (except perhaps from the degree of energy in the de- 

 composition) as respects the point whether simple magnetism is adequate to decom- 

 pose water, since it might under these circumstances be attributed to the electricity 

 from the battery, I had determined in a second experiment, had the first proved suc- 

 cessful, to have interrupted the galvanic flow by a non-conductor; in which case, 

 had the decomposition ensued, pure magnetism might have been considered as the 

 decomposing agent. But as my preliminary experiment was unsuccessful, I pro- 

 ceeded no farther; I hope, however, to resume the research hereafter, under more 

 favorable circumstances. C, U. Shepard, 



Vol. XX.— No. L 26 



