chapter 3._

"The effect which an electric current, flowing in a wire, can exercise upon a neighbouring compass needle was discovered by Oersted in 1820. This first announcement of the possession of magnetic properties by an electric current was followed speedily by the researches of Ampere, Arago, Davy, and by the devices of several other experimenters, including De la Rive's floating battery and coil, Schweigger's multiplier, Cumming's galvanometer, Faraday's apparatus for rotation of a permanent magnet, Marsh's vibrating pendulum and Barlow's rotating star-wheel. But it was not until 1825 that the electromagnet was invented. Arago announced, on 25th September 1820, that a copper wire uniting the poles of a voltaic cell, and consequently traversed by an electric current, could attract iron filings to itself laterally. In the same communication he described how he had succeeded in communicating permanent magnetism to steel needles laid at right angles to the copper wire, and how, on showing this experiment to Ampere, the latter had suggested that the magnetizing action would be more intense if for the straight copper wire there were substituted one wrapped in a helix, in the centre of which the steel needle might be placed. This suggestion was at once carried out by the two philosophers. 'A copper wire wound in a helix was terminated by two rectilinear portions which could be adapted, at will, to the opposite poles of a powerful horizontal voltaic pile; a steel needle wrapped up in paper was introduced into the helix.' 'Now, after some minutes' sojourn in the helix, the steel needle had received a sufficiently strong dose of magnetism.' Arago then wound upon a little glass tube some short helices, each about 2¼ inches long, coiled alternately right-handedly and left-handedly, and found that on introducing into the glass tube a steel wire, he was able to produce 'consequent poles' at the places where the winding was reversed. Ampère, on October 23rd, 1820, read a memoir, claiming that these facts confirmed his theory of magnetic actions. Davy had, also, in 1820, surrounded with temporary coils of wire the steel needles upon which he was experimenting, and had shown that the flow of electricity around the coil could confer magnetic power upon the steel needles. ... The electromagnet, in the form which can first claim recognition ... was devised by William Sturgeon, and is described by him in the paper which he contributed to the Society of Arts in 1825."

_S. P. Thompson, The Electromagnet,