Electro-Magnetic Experiments. 409 
_ Notice of Electro-Magnetic Experiments.* 
[Communicated by Prof. A. D. Bacue, of the University of Pennsylvania.] 
TO THE COMMITTEE ON PUBLICATIONS. 
Gentlemen,—I send you a description of the apparatus for produ- 
cing the spark from a magnet according to the method of Nobili, 
and for other recent and curious experiments on electro-magnetism, 
together with an account of their: repetition. This is done that any 
one who may be desirous 'to repeat or to extend the experiments may, 
without delay, be put in possession of the means of so doing. 
Extract of a letter from J. Saxton,of Philadelphia, to Isaiah Lukens, dated 
London, April 14th, 1832. 
* You may have heard of Faraday’s curious discovery in electro- 
magnetism. He has succeeded in obtaining from a magnet a -spark 
resembling the electric spark. The apparatus consisted of a copper 
plate mounted onan axis, like an electrical machine, and made to re- 
volve between the poles of a large magnet. The plate used was 
about one foot in diameter, and one-eighth of an inch in thickness. 
The rim of the wheel was amalgamated, as well as a ring around the 
axis. ‘Two pieces of copper, shaped to fit, for two or three inches, 
the amalgamated ring and the circle, were attached to either wire of a 
galvanometer. These pieces of copper being applied to the wheel, 
and the latter turned, the needle of the galvanometer vibrates: the 
amount of vibration may be inereased by alternately touching and 
removing one of the plates. The copper plate which touches the 
rim should be between the poles of the magnet. 
‘¢] have made this experiment in a different way and succeeded 
satisfactorily. The method was as follows. A coil of wire wrapped 
with silk, similar to that used in the galvanometer, was attached by 
the ends to the wires of the galvanometer. On passing this roll back- 
ward and forward upon one of the poles of a horse-shoe magnet, or 
placing it upon and removing 1: from either pole, I have made the 
needle of the galvanometer spin round rapidly.” 
* Communicated in a proof for this Journal, with permission of the committee ot 
publication, of the Journal of the Franklin Institute, by Prof. A. D. Bache of Phi- 
ladelphia. 
