29 



publication of these results put at rest, for a time, all attempts to construct 

 an electro-magnetic telegraph. 



The next investigations, in the order of time, bearing on the telegraph, 

 were made by Mr. Sturgeon, of England. He bent a piece of iron wire 

 into the form of a horse-shoe, and put loosely around it a coil of copper 

 wire, with wide intervals between the turns or spires to prevent them 

 touching each other, and through this coil he transmitted a current of 

 galvanism. The iron, under the influence of this current, became mag- 

 netic, and thus was produced the first electro-magnetic magnet, sometimes 

 called simply the electro-magnet. An account of this experiment was 

 first published in November, 1825, in the Transactions of the Society for 

 the Encouragement of the Arts in England ; and was made known in this 

 country through the Annals of Philosophy for November, 1826. 



Nothing further was done pertaining to the telegraph until my own 

 researches in electro-magnetism, which were commenced in 1828, and 

 continued in 1829, 1830, and subsequently ; Barlow's results, as I before 

 observed, had prevented all attempts to construct a magnetic telegraph 

 on the plan of Ampere, and our own knowledge of the development of 

 magnetism in soft iron, as left by Sturgeon, was not such as to be appli- 

 cable to telegraphic purposes. The electro-magnet of Sturgeon could not 

 be made to act by a current through a long wire, as will be apparent 

 hereafter in this deposition. 



After repeating the experiments of Oersted, Ampere, and others, and 

 publishing an account in 1828 of various modifications of electro-magnetic 

 apparatus, I commenced in that year the investigation of the laws of the 

 development of magnetism in soft iron, by means of the electrical cur- 

 rent. The first idea that occurred to me in accordance Avith 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 ever 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 mo was that of using a number 



