PROCEEDINGS OF THE REGENTS. 109 



maojnetic apparatus, I commenced in that year the investigation of 

 the laws of the development of magnetism in soft iron, by means of 

 the electrical current. The first idea that occurred to me in accord- 

 ance with the theory of Ampere, with reference to increasing the 

 power of the electro-magnet, was that of using a longer wire than 

 had before been employed. A wire of sixty feet in length, covered 

 with silk, was wound round a whole length of an iron bar, either 

 straight or in the form of a U, so as to cover its whole length with 

 several thicknesses of the wire. 



The results of this arrangement were such as I had anticipated, 

 and electro-magnets of this kind, exhibited to the Albany Institute 

 in March, 1829, possessed magnetic power superior to that of any 

 before known. 



The idea afterwards occurred to me that the quantity of galvanism, 

 supplied by a small galvanic battery, might be applied to develop a 

 still greater amount of magnetic power in a large bar of iron. On 

 experiment, I found this idea correct. A battery of two and a half 

 square inches of zinc, developed magnetism in a large bar sufficient to 

 lift fourteen pounds. 



The next suggestion which occurred to me was that of using a 

 number of wires of the same length around the same bar, so as to 

 lessen the resistance which the galvanic current experienced in pass- 

 ing from the zinc to the copper through the coil. To bring this to 

 the test of experiment, a second wire, equal in length to the first, 

 was wound around the last mentioned magnet, and its ends soldered 

 to the plates of the same battery. 



The magnet with this additional wire lifted twenty-eight pounds, 

 or, in other words, its power was doubled. 



A series of experiments was afterwards made, to determine the re- 

 sistance to conduction of wires of different lengths and diameters, and 

 the proper lengths and number of wires for producing, with different 

 kinds of galvanic batteries, the maximum of amount of magnetic de- 

 velopment with a given quantity of zinc surface. For this purpose a 

 bar of soft iron, two inches square and twenty inches long, weighing 

 twenty-one pounds, and much larger than any before used, was bent 

 in the form of a horse-shoe. Around this were wound nine strands 

 of copper wire, each sixty feet long, the ends left projecting so that 

 one or more coils could be used at once, either connected with a bat- 

 tery or with each other, thus forming several coils with several battery 

 connexions, or one long coil with single battery connexions. The 

 greatest effect obtained with this magnet, using a battery of a single 

 pair, with a zinc plate of two-fifths of a square foot of surface, and all 

 the wire arranged as separate coils, was to lift a weight of six hun- 

 dred and fifty pounds ; with a large battery the effect was increased 

 to seven hundred and fifty pounds. In a subsequent series of experi- 

 ments, not published with the preceding, the same magnet was made 

 to sustain one thousand pounds. When a compound battery was 

 employed of a number of pairs, it was found that the greatest effect 

 was produced when all the wires were arranged as a single long coil. 

 I subsequently constructed electro-magnets on the same plan, which 

 supported much greater weights. One of these, now in the cabinet 

 of Princeton, will sustain three thousand six hundred pounds with a 



