Mr. Forbes on an Electric Spark from a Natural Magnet. 49 



duce an action, which is as it were continuous*. From the 

 little I have done, and from what 1 have said, it follows that 

 being able by this method to sum up the simultaneous action 

 of an indefinite number of electric currents, this my battery 

 may become fulminating. 



I hope I have said enough to enable my readers to com- 

 prehend the mode of constructing this electro-motive battery. 

 Hereafter, and by the help of a figure, I will describe the most 

 useful and convenient distribution of the elementary pairs, 

 and the mode of obtaining the maximum effect when employ- 

 ing the smallest possible number of elements, or of pairs of 

 spirals. 



Errata relative to Signori Nobili and Antinori's paper. 

 At page 402 of the last Number of Phil. Mag. and Annals, 

 line 23, — for electromo read electrotomo ; and in the correspond- 

 ing note, for electronic read electrotonic. 



XII. Account of some 'Experiments in "which an Electric Spark 

 was cUcitedfrom a natural Magiiet, By James D. Forbes, 

 Esq. F.R.S. L. 8f E. F.G.S.\ 



T^HE recent discovery of Mr. Faraday has conclusively de- 

 -*- monstrated, that in every case where a magnetic current 

 is created (to use the word current in its ordinary acceptation, 

 as indicative of a peculiar condition, and without reference to 

 any theory whatever), a momentary electric current is induced 

 at right angles to it. The experiment may be shown in two 

 ways : either by mechanically causing a magnetic bar to tra- 

 verse the axis of a helix of copper-wire of considerable length, 

 — or by causing a piece of soft iron, placed in the axis of such 

 a helix, to connect the poles of a horse-shoe magnet, and thus 

 temporarily acquire polarity. 



The second method is that which in my late experiments 

 I have entirely employed ; and the subject of them has been 

 a very fine natural magnet, capable of supporting 1 70 lbs. 

 presented to the University by Dr. Hope. I willingly avail 

 myself of this opportunity to express my obligations to that 

 gentleman for the numerous and important facilities which 

 have been afforded to my researches, in his laboratory, where 

 the magnet still is. 



My preliminary experiments demonstrated, by the action 



[• See the note at page 46. — M. F.] 



t Read before the Royal Society of Edinl)ui{;h, April 16, 18.S2, and 

 abriilgcil from the fortliconiing volume of their Transactions: Sec Phil. 

 Maj;. and Annals N. S. vol. xi. p. .^SI). 



Third Series. Vol. 1. No. 1. Jutjj lb32. H 



