M. DE LA HIVE’S RESEARCHES ON THE VOLTAIC ARC. 
33 
discharge being always attended by the transference of highly diffused matter, which 
closes the circuit during the instant of time necessary for the formation of the arc. 
3. The enormous elevation of temperature which accompanies the production of 
the luminous arc, is also manifested in the electrodes, especially in the positive ones, 
which become much more strongly heated than the negative. 
4. Matter is thus transported from the positive electrode to the negative, a fact 
which may be verified with electrodes of all kinds, but particularly with those of 
charcoal. 
5. The various phenomena presented by the voltaic arc, are modified to a greater 
or less extent by the nature of the electrodes and by that of the surrounding medium. 
Thus Mr. Grove adduces facts from which it appears that the presence of oxygen is 
necessary in most cases to produce a very luminous and brilliant arc. It results also 
from his experiments, as well as those of other philosophers, that when two different 
substances are made use of for the electrodes, it is not a matter of indifference which 
of the two is placed at the positive pole. 
I now proceed to my own researches. I commenced by studying the production 
of a luminous arc between a plate and a point of the same material in air, and in 
vacuo. By means of a micrometer screw I was able to make the point recede from 
the plate very gradually, and judge of their mutual distance with great precision. 
The limit of distance beyond which the luminous arc ceases to appear, is constant 
for the same plate and the same point: when, however, the plate communicates with 
the positive pole, it is in general double that which it is when the point communi- 
cates with the same pole. But in proportion as the strength of the pile is greater, 
the difference is so much the smaller. 
With respect to the absolute amount of this distance, it is very variable, depend- 
ing on the strength of the pile, on the nature and molecular state of the electrodes, 
and on the time occupied in the experiment. Thus, with a Grove battery composed 
of fifty pairs of plates sixteen square inches in surface, it is two or three times greater 
than with a pile of seventy elements of two or three square inches. With metals 
easily fused or oxidized, as zinc and iron, it is much greater than with platinum or 
silver. The duration of the phenomenon influences the result, inasmuch as the high 
temperature of the electrodes allows them to be drawn asunder to a greater distance 
without breaking the arc. The same effect may be produced by heating them arti- 
ficially, by means of a spirit-lamp. It is evident from what I have said that the 
length of the luminous arc has a relation to the greater or less facility which the sub- 
stances composing the electrodes possess of being segregated, a facility which may 
depend upon their temperature diminishing their cohesion, upon their tendency to 
oxidize (which produces the same effect), upon their molecular state, and lastly upon 
their peculiar nature. Carbon derives from its molecular constitution, which renders 
it so friable, the property of being one of the substances which produces the longest 
luminous arc. 
MDCCCXLVII. 
F 
