168 Dr. Faraday's Experimental Researches in Electricity. 



sion to refer for experimental proof in a future part of this 

 paper (34«4«.). 



288. ii. Magnetism. Voltaic electricity has most extraor- 

 dinary and exalted magnetic powers. If common electricity 

 be identical with it, it ought to have the same powers. In 

 rendering needles or bars magnetic, it is found to agree with 

 voltaic electricity, and the direction of the magnetism, in both 

 cases, is the same ; but in deflecting the magnetic needle, 

 it has been found deficient, so that sometimes the power 

 has been denied altogether, and at other times distinctions 

 have been hypothetically assumed for the purpose of avoid- 

 ing the difficulty*. 



289. M. Colladon, of Geneva, considered that the difference 

 might be due to the use of insufficient quantities of common 

 electricity in all the experiments before made upon this point; 

 and in a memoir read to the Academie des Sciences in 1826f, 

 describes experiments, in which, by the use of a battery, points, 

 and a delicate galvanometer, he succeeded in obtaining de- 

 flections, and thus establishing identity in that respect. MM. 

 Arago, Ampere, and Savary are mentioned in the paper as 

 having witnessed a successful repetition of the experiments. 

 But as no second witness of these effects has come forward, 

 MM. Arago, Ampere, and Savary, not having themselves 

 published (that I am aware of,) their acceptance of the results, 

 and as others have not been able to obtain the effects, M. Col- 

 ladon' s conclusions have been by some doubted or denied ; 

 and an important point with me was to establish their accu- 

 racy, or remove them entirely from the received body of ex- 

 perimental evidence. I am happy to say that my results fully 

 confirm those by M. Colladon, and I should have had no oc- 

 casion to describe them, but that they are essential as proofs 

 of the accuracy of the final and general conclusions I am 

 enabled to draw respecting the magnetic and chemical action 

 of electricity, (360. 366. 367. 377. &c). 



290. The plate electrical machine I have used is fifty inches 

 in diameter; it has two sets of rubbers; its prime conductor 

 consists of two brass cylinders connected by a third, the whole 

 length being twelve feet, and the surface in contact with air 

 about 1422 square inches. When in good excitation, one re- 

 volution of the plate will give ten or twelve sparks from the 

 conductors, each an inch in length. Sparks or flashes from 

 ten to fourteen inches in length may easily be drawn from the 



* Demonferrand's Manuel d? Elcctricite dynamique, p. 121. 

 \ Annates de Chimie, xxxiii. p. 62. 



