8 Faraday's Researches

and exalted magnetic powers. If common electricity be
identical with it, it ought to have the same powers. In render-
ing 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, common
electricity has been found deficient, so that sometimes its
power has been denied altogether, and at other times distinc-
tions have been hypothetically assumed for the purpose of
avoiding the difficulty.1

25. 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 on this head;
and in a memoir read to the Academic des Sciences in i826,2
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 other one has come forward in confirmation, MM.
Arago, Ampere, and Savary, not having themselves published
(that I am aware of) their admission of the results, and as some
have not been able to obtain them, M. Colladon's conclusions
have been occasionally doubted or denied; and an important
point with me was to establish their accuracy, or remove them
entirely from the body of received experimental research. I
am happy to say that my results fully confirm those by M.
Colladon, and I should have had no occasion 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 (96, 102, 103,
113, etc.).

26. 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
conductors. Each turn of the machine, when worked moderately,
occupies about four-fifths of a second.

1 Demonferrand's Manuel d? Electricite dynamique, p. 121.

2 Annales de Chimie, xxxiii. p. 62.e volume of Transactions is Dr. Ritchie's paper, from