ELECTRIC LIGHTING.
14
badly-conducting bodies rendered incandescent, and we shall
have occasion to speak of a system of illumination of this kind, devised by Jablochkoff, who makes use of thin plates of kaolin. But in order to obtain these various results a source of electricity must be available, which not only supplies sufficient electricity to produce energetic calorific actions, but possesses a tension sufficiently powerful to
overcome the
resist-
ances offered by the intermediate bodies that are to develop the luminous effects ; and besides this the source of electricity
must be
suitable to the conditions of the experiment.
if the gaseous interval interposed between the conductors of the discharge or current is considerable, it will be necessary for the generator of the electricity to
It is
obvious that
tension especially, whilst to produce a powerful between two rather large carbons, separated by a narrow interval of air, quantity will especially be needed, possess effect
since the calorific effects required to make the carbons incandescent are in proportion to the quantity of electricity
produced by the generator. These two different effects of electric generators may be readily explained by the way in which they operate in settingIf the generator has a very great tension, action. such as occurs with Holtz's machine and the induction
up the
machines, the discharge may take place directly between the which in a manner serve to determine it, leaping
electrodes,
from one to the other ; but as the enormous resistance presented by this gaseous interval very much diminishes the produced is very feeble, and it can be increased only by decreasing the resistance of the The gaseous medium, which may be done by rarefying it. electric intensity, the light so
discharge then spreads itself in the vacuous vessel, and if the quantity of electricity be increased by means of a condenser
a light of some intensity may be obtained. But this intensity be considerable only when the discharge carries with it
will
those material particles heated to reddish-whiteness, which, as we have already stated, constitute the whole brilliancy of