The Express.
London, England, 1855-04-25 00:00:00

ROYAL INSTITUTION.

Yesterday Dr. Tyndall delivered the second of his cootie
of lectures on voltaic electricity. He commenced by ex-
plaining the arrangements of different metals that serve to
mite electricity by contact, and the combination of those
arrangements in the voltaic battery. The decomposition of
water, and the evolution of the two gases of which it is
composed from sine and platinum plates when immersed
in that fluid slightly acidulated, were illustrated in a variety
of ways. The hydrogen and the oxygen thus evolved,
when mingled together, ere much lighter than atmospheric
air, as was exemplified by filling a small *balloon, made of
collodion, with the two gases, which rapidly ascended to the
ceiling. The film of collodion forming the balloon was
so light that a very small quantity of hydrogen gas was suffi-
cient to give it ascending power; and the experiment was
I varied by igniting the string that tied the opening, so that
soon after the small balloon arrived at the top of the lecture.
room it exploded with a loud report. Hydrogen,
though it is only known as a gas, is suspected by
chemists to be a metal, and several of the experiments
of Professor Faraday on the compression and condensation
of gases had for their object to give metallic form to hydro-
gen. The metallic character of that gas is apparent in its
voltaic actions, for two plates of platinum which have served
for conductors of a voltaic battery exhibit voltaic action in
consequence of their being covered over with the two gases,
hydrogen and oxygen, even alter the connexion with the
battery has been broken. Ibis curious fact, of two plates of
the same metal becoming voltaic though detached from any
voltaic arrangement, was shown in several experiments; and
to make the phenomenon appear the more remarkable, the
plates were taken out of the fluid in connexion with the bat-
tery and were immersed is a vessel of water without
losing their electrical condition. The secondary current,
as it is called, which is thus established by the
evolution of hydrogen from the surface of the negative
plate of the battery, interferes with the action of ordinary
voltaic arrangements, and to overcome that obstacle Mr.
Grove and Professor Bunsen contrived their nitric acid bat-
teries, which are much more energetic than the common
arrangements. Dr. Tyadall, after explaining some of the
different kinds of voltaic batteries which have been found
most generally useful, proceeded to consider the varying
conducting powers of substances for voltaic electricity, and
he elucidated this branch of his subject by some striking
illustrations. The effect of beat in increasing the
resistance of metals to the transmission of electricity
was shown by two well arranged experiments. Two coils
. . . . .

of platinum wire were placed in the circuit, and when both
were glowing with heat one of them was plunged in cold
water, the effect of which was ready to increase the in-
candescence of the other coil, in consequence of the greater
quantity of electricity that passed through the coil that
wee cooled. The reverse of that experiment was shown by

giving greater heat to one of the coils by a spirit lamp,
when the resistance to the passage of the rlectrieity being
increased, the other coil, which was before glowing brightly,
became dim. At the conclusion of the lecture, Dr. Tyndall
exhibited the decomposition of water by throwing the
shadow of the voltaic wires on a screen by means of the
electric light.