The Express.
London, England, 1855-03-14 00:00:00

ROYAL INSTITUTION.

Yesterday Dr. Tyndall delivered the ninth Ischia
of his course on magnetism and electricity at the Rerei
Institution. The nature of the electric spark was one of
the points of most interest which he undertook to examine,
and he prefaced his observations on the subject by noticing
the difficulty which all original investigators experience
from having to overcome the preconceived notions of pope.
lar hypotheses, and the erroneous views which the tans
often given to phenomena convey. Thus the word " laid,"
as applied to electricity, though it seems to convey a
generally correct idea of the action of the force excited, is
calculated to mislead investigators into the nature of tbs
force itself, as there is no proof that it partakes of the che•
ratter of fluid bodies. Dr. Tyndall attributes the lit
of the electric spark not to the appearance of
electricity itself, but to the incandescence of particles of
matte: interposed in the interval in which the disruptive
discharge of en electrified body takes place. He await the
peculiar action of electric sparks in converting oxygen pa
into ozone, and as ozone fa by some chemists considered to
be a modification of oxygen, by which its active powers are
greatly exalted, Dr. Tyndall seemed inclined to believe that
the matter ef the electric spark would be found to be that
peculiar state of oxygen, though he said he had notyst
made sufficient experiment on the subject to enable him te
arrive at a definite opinion. He then explained the pheno.
mena of the Leyden jar, commencing with the exhibition of
a similar electrical eondition in plates of glass, which had
metallic plates on both sides. Thus when positive demi.
city is communicated to the metallic plate on one side of

the glue, the negative electricity is attracted to the
plate on the other aide, and the positive electri-
city is repelled to the earth. In that condition the glue
with its metallic coatings may be highly charged, though,
being neutralised, it does not part with its electricity to
surrounding bodies until a communication is made between
the two coatings. In the same manner the action of the
oondensee was explained. The two metal plates, when
brought near to each other, and one of them is feebly
charged, give no indication of electricity, because the pool•
tive and the negative electricitin of the two plates an nn-
Lunged. But when ono of the plates is removed, the
electricity on the other becomes directly manifest; and is
this manner the feeblest traces of electricity may be indi-
Gated. The phenomena of the electrophorus were also es•
plainad on the hypothesis of the separation of two dis-
tinct eleetricities by their mutual attractions and repulsion.
The slab of wax, when excited by fire, becomes negative,
and when an insulated metal disc is placed upon it, the
positive electricity in the metal is supposed to be attracted
to the side nearest the wax, end the negative electricity to
be repelled to the top. On allowing the negative electricity
of the disc to escape, by touching it, the disc remain, pod-
threly electrified. Dr. Tyndall concluded by exhibitiog
some of the powerful effects of electricity, by muss of a
battery consisting of fifteen large jars, with which fine
wires of different metals were defiagrated and dissipated
into powder.