32 
M. DE LA RIVE’S RESEARCHES ON THE VOLTAIC ARC. 
current, the reduction of matter to the molecular state, and the form and nature of 
the deposits resulting therefrom, are so many phenomena capable of throwing light 
on the obscure subject of molecular physics. 
The few preceding remarks suffice to give some idea of the extent of an investiga- 
tion embracing the whole range of experimental research on the voltaic arc under its 
various aspects, which I am far from pretending to have attempted. I shall confine 
myself at present to a few details, and especially to such as exhibit the action of 
magnetism on the voltaic arc, and on those bodies which transmit interrupted currents. 
I shall begin by describing some particular phenomena which I observed during my 
study of the voltaic arc under various circumstances, while employing different sub- 
stances as electrodes, both in the air and in a vacuum ; I shall then proceed to exa- 
mine the action of a powerful electro-magneton this voltaic arc, and I shall conclude 
by describing some remarkable experiments also illustrating the influence of magne- 
tism on conducting bodies, of whatever nature, traversed by interrupted currents. 
§ 1. Some Phenomena concerning the Voltaic Arc. 
Davy was the first who produced the phenomenon of the voltaic arc with two 
points of charcoal. More recently, Messrs. Grove* and Daniell^ employed with 
success the points of different metals, and arrived at interesting results : I also 
published some experiments I made on the voltaic arc^; in 1841. Subsequently^ 
MM. Fizeau and Foucault observed some remarkable facts of the same kind on the 
occasion of an investigation into the intensity of the light emitted by charcoal in the 
experiment of Davy §. The researches made up to the present time, have already led 
to many results, of which I shall consider only the most important. 
1. That the voltaic arc may be produced, a pile of greater tension is required than 
that which is necessary for the ordinary calorific and electro-chemical phenomena. 
The necessity of this condition proves the great resistance presented to the passage 
of the electric current by the minutely divided matter, whatever it may be, which 
connects the two poles. 
2. The luminous arc cannot exist, unless contact be previously made between the 
electrodes, and unless these, or at least one of them, be terminated at the point of 
contact by points fine enough to produce in them an increase of temperature. When 
this increased temperature is once produced, we may, by separating the electrodes 
gradually and with precaution from each other, obtain the luminous arc, the length 
of which will depend on the intensity of the pile. Daniell discovered the important 
fact, which was confirmed by M. Van Breda in a very recent investigation inserted 
in the Comptes Rendus de l’Academie, that without contact having taken place, the 
luminous arc may be produced between two electrodes placed very near together, 
by causing the discharge of a Leyden jar to pass between them : this is owing to the 
* Bibl. Univ. June 1840, i. 27. p. 387. 
I Arch, de l’Elect. tom. i. p. 262. 
f Arch, de l’Elect. tom. i. p. 462. 
§ Ibid. tom. iv. p. 311. 
