Encyclopaedia Britannica > Volume 8, DIA-England

ELECTRICITY.
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ed plate of zinc and copper, the zinc will attract the posi¬
tive and the copper the negative electricity.
When the hydrogen issues from a metallic in place of
a glass tube, and a communication is made with the con¬
denser and not with the ground, the metal tube, which
touches the hydrogen without touching the flame, always
takes the negative electricity; and, on the contrary, if the
tube communicates only with the ground, it loses in this
manner the negative electricity which it had before
taken to the condenser, and the product of the combus¬
tion preserves an excess of positive electricity.
In pursuing this inquiry in a similar manner, M. Pouil-
let found that the flames of alcohol, ether, wax, the oils,
fatty substances, and several vegetable bodies, present
exactly the same phenomenon as the flame of hydrogen.
He observed, however, that the particles of charcoal which
float in all these flames, and which, according to Sir H.
Davy, give them the lustre with which they burn, render
them also more fitted to manifest negative electricity.
From these results M. Pouillet has deduced the general
conclusion, that in combustion the molecules of oxygen which
combine disengage positive electricity, which may be com¬
municated to the neighbouring molecules not yet combined ;
and that the combustible body, on the contrary, disengages
negative electricity, which can, in like manner, be communi¬
cated to all the neighbouring combustible parts.
The experiments of M. Pouillet were repeated by M.
Becquerel in 1827, on the flames of hydrogen gas or alco¬
hol ; but he commenced them with some reserve, for, as
they were made by means of platina wires plunged in
the flame, he supposed that the phenomena were not only
owing to the electricity disengaged during combustion,
but also to some property which the metals acquired at a
certain temperature. The following is the general fact,
without entering into any of the details of his experi¬
ments: A platinum wire communicates by one end,
through the intermedium of a band of wet paper, with
one of the plates of a condenser*, the other end being
plunged in one of the envelopes of a flame produced by
the combustion of alcohol, contained in a vessel of cop¬
per, which the observer holds in his hand. The end of
the wire may even be placed without the flame, provided
it is so near it as to become red hot. The wire soon
takes a considerable excess of negative electricity, which
ought not to be ascribed entirely to that which the alco¬
hol carries off1 during combustion. In order to prove this,
let us resume the last experiment but one. As soon as
the end of the platinum wire attains a red heat, let us
withdraw the lamp, and touch this end of the wire with
a band of wet paper, or rather with the end of a tube of
hot glass; the effect is the same as when the wire touched
the flame, or was at a small distance from it. It is very
probable that the disengagement of the electricity is due,
in this last case, in part to the difference of temperature
between the two ends of the wire, and that the flame has
carried off’ the positive electricity of the wire, or the band
of wet paper, as the hot glass tube had done. This opinion
is confirmed by the circumstance that the effect is the
same whether we bring the wire to a red heat in the inte¬
rior or in the exterior of the flame, neither of which pos¬
sesses the same kind of electricity. Notwithstanding this
result, M. Becquerel still admits, that during the combus¬
tion of alcohol and hydrogen, the exterior envelope of the
flame is charged with positive electricity.
M. Becquerel has endeavoured to explain the curious
fact discovered by M. Erman, and already referred to.
Having placed upon an electroscope a lamp without flame,
whose platinum wire was kept at a red heat by the burn¬
ing vapour of the alcohol, he held above the spiral the
negative pole of a dry pile, and the two gold leaves in¬
stantly diverged. He next held the positive pole above Phenome-
tbe spiral, but there was now no divergence of the leaves, na and
Hence the platinum wire afforded a passage only to the Ijaws-
negative electricity. The contrary effect took place when
the electricity passed from an incandescent wire to an¬
other which was not so ; and hence M. Erman found
that the incandescent wire was reciprocally a conductor
and insulator of each fluid.
In order to show that this conclusion is incorrect, M.
Becquerel presented successively to a red-hot platinum
wire the two poles of a dry pile, and it conducted equally
well both kinds of electricity. Besides, as he remarks, it
appears, from our knowledge of the electrical effects pro¬
duced in gaseous combustion, and by increase of tempera¬
ture, that part of the air which surrounds the red-hot
wire of the lamp without flame ought to be in a positive
state of electricity, and the wire which is in the middle
of the alcoholic vapour in a negative state. Moreover, it is
evident, from what has been already stated, that the part
of the wire which is red hot ought easily to yield positive
electricity to contiguous bodies. This being admitted,
when we present to this wire the negative pole of a dry
pile, there are two reasons why the negative electricity
should neutralize both the positive electricity of the sur¬
rounding air, and that of the red-hot wire which tends to
escape from it. The negative electricity of the wire then
becoming free, manifests its action upon the electroscope.
In repeating the experiment in an inverse manner, that is,
by causing each of the two electricities to escape succes¬
sively by the red-hot wire, as this last tends to be nega¬
tive, it neutralizes the positive electricity which arises,
and sets free that of the surrounding air and of the red-
hot end of the wire. It is not therefore necessary to
have recourse to a reciprocity of insulating and conduct¬
ing action in the red-hot wire in order to explain the
phenomenon, for the fact admits of an easy explanation
on the properties above explained.
Sect. IV.—On the Electricity of the Solar Rays.
Our readers are no doubt aware that Dr Morrichini and Electricity
others succeeded in magnetising needles by the action ofof the solar
the blue rays in the solar spectrum. Other philosophersrays*
have failed, even in good climates, in obtaining decided
indications of magnetism, so that accurate researches are
still wanting to remove this opprobrium from our experi¬
mental physics. The very same observations are appli¬
cable to the development of electricity by the influence
of solar light; but still it is necessary, in a work like this,
that we should give some account of the experiments
from which this electrical action has been inferred.
In a memoir on the influence of solar light in the pro-Experi-
duction of electric and magnetic phenomena, Professorments
Saverio Barlocci of Rome relates the following experi-I5ar ocu ’
ments: Having formed the prismatic spectrum by the
solar rays, he caused the red rays and the violet rays to
fall upon two discs of blackened copper, each of which
was attached to a copper wire. Two copper nuts sliding
upon a vertical glass rod, and to which the two wires
were fixed, allowed the discs to be brought near each
other or separated at pleasure. A prepared frog was
then suspended by the body to the upper wire, and the
legs were placed upon the lower one. The red rays being
made to fall on one disc, and the violet on the other, the
extreme parts of the two wires were brought into contact,
and distinct signs of contraction were observed in the frog.
M. Matteucci of Forli has more recently investigated of Mat-
the same subject. Having exposed to the sun a delicate teucci.
condensing electrometer of gold leaf, he soon perceived