72 
Sir Humphry Davy on the 
probably the heat) generated in electrical discharges depends 
principally on some properties or substances belonging to the 
ponderable matter through which it passes ; but they prove 
likewise that space, where there is no appreciable quantity of 
this matter, is capable of exhibiting electrical phenomena : 
and, under this point of view, they are favourable to the idea 
of the phasnomena of electricity being produced by a highly 
subtile fluid or fluids, of which the particles are repulsive, 
with respect to each other, and attractive of the particles 
of other matter. On such an abstruse question, however, 
there can be no demonstrative evidence. It may be assumed, 
as in the hypothesis of Hooke, Huygens, and Euler, that an 
ethereal matter, susceptible of electrical affections, fills all 
space; or that the positive and negative electrical states, 
may increase the force of vapour from the substances in 
which they exist; and there is a fact in favour of this last 
idea which I have often witnessed — when the voltaic dis- 
charge is made in the Boylean vacuum, either from platinum 
or charcoal, in contact with mercury, the discharging sur- 
faces require to be brought very near in the first instance ; 
but the electricity may be afterwards made to pass to consi- 
derable distances through the vapour generated from the 
mercury or charcoal by its agency ; — and when two surfaces 
of highly fixed metal, such as platinum or iron are used, the 
discharge will pass only through a very small distance, and 
cannot be permanently kept up. 
The circumstance, that the intensity of the electrical light 
in the mercurial vacuum diminishes as it is cooled to a cer- 
tain point, when the vapour must be of almost infinitely small 
density, and is then stationary, seems strongly opposed to 
the idea, that it is owing to any permanent vapour emitted 
