450 Mr. W. Sturgeon on the Theory of Magnetic Electricity. 



discs, however, can drive off through wires the whole force 

 excited. 



Cylinders properly mounted, with respect to the exciting 

 magnetic li?ies 9 offer a much more efficient apparatus than discs 

 for driving a continuous current through conducting wires. 

 I have made some apparatus upon this principle, but must de- 

 fer the description till another opportunity. 



When a sudden and momentary current is to be exhibited, 

 no mode of excitation hitherto discovered can be employed 

 with greater advantage than that of suddenly making and anni- 

 hilating a temporary magnet of soft iron, inclosed in a spiral of 

 copper wire, — a mode which I believe was first introduced 

 by Mr. Faraday in some of his experiments for deflecting the 

 magnetic needle ; and which, in the experiments of M. Nobili, 

 and afterwards, in this country, in those of Mr. Saxton and 

 Mr. Forbes, has been so successfully employed in exhibiting 

 the electric spark. 



By this mode of excitation the whole of the exciting polar 

 magnetic lines are called forth simultaneously, and with a ve- 

 locity not easily accomplished any other way; and in directions 

 the most suitable to produce the greatest effect. 



I have only to add in this place, that whatever claims may 

 have been made by others to the first discoveries of this branch 

 of science, I apprehend that the experiments and explanations 

 hitherto produced in this series of communications can leave 

 very little difficulty in placing those discoveries in the proper 

 quarter. My vibrating disc (Phil. Mag. and Annals, N.S. 

 vol. xi. Plate III. fig. 3.) has, I perceive, already been recog- 

 nised as the first instrument which exhibited phaenomena 

 which could not be reconciled to the hypothesis advanced 

 upon the experiments of Arago. And my rotating disc is 

 not only the first " machine" of this class that was ever made, 

 but is at this time the most efficient of its kind. The deflec- 

 tions of the needle exhibited by the former apparatus led to 

 the construction and employment of the latter. And although 

 I did not, in my first communication, advance a direct asser- 

 tion that the excited force in the discs was the electric; my 

 statements, to say the least of them, were favourable to the 

 supposition, — perhaps as much so, as the nature and results of 

 my experiments, and a due regard to propriety, would permit. 

 My drawings, however, amply testify that my real views of the 

 character of the force were perfectly correct. It is however 

 due to other experimenters that I should state, that I never 

 employed wires in my experiments in magnetic electricity until 

 I heard of them being employed by Mr. Faraday. And the 



