The Sun.
London, England, 1865-04-19 00:00:00

Luminous and Obscure Radiation.

We are so accustomed to associate the idea of
heat with that of light, that the radiation of the for-
mer alone without the latter appears to us very like
an anomaly. We perfectly understand the catching
of the sun's rays in a lens and igniting thereby a
piece of paper held in the focus, because we see the
intense light in that point ; but if we did not, we'
should be astonished to see the combustible mate-
rial catching fire in a place not distinguishable by
the eye from any other. Professor Tyndal, F.R.S.,
having made the radiation of heat the subject of
minus inquiry, has arrived at some curious results.
His appagrus consisted of an electric lamp, so mo-
a.-4* to admit of its receiving, instead of the
charcoal burners, an illuminating gas or a hydrogen
flame at pleasure, while a thereto-electric pile with
its galvanometer was used to find the point of maxi-
mum heat after the light had been decomposed into
a spectrum (consisting of the colours of the rainbow)
by passing through a rock-salt prism. Beginning
with a luminous gas flame, he found the maximum
heat was not contained within the spectrum, but a little
beyond the red or last colour, the first being violet. The
hydrogen flame gave no visible spectrum at all ; the
thereto-electric pile denoted a temperature 2} times
smaller than the preceding one, and still at a point
not reached by the visible spectrum. Such being
his modus operandi, we will state some of his results.
A solution of. iodine.: in bi-sulphuret of carbon,
though perfectly opaque to light, will transmit heat
completely, without absorbing a particle of it. By
means of this substance our author has been enabled
to separate the luminous calorific rays from the ob-
scure ones, as the following experiment will show.
Having filled a hollow lens with the above solution,
and held it to the sun, no luminous focus was visible
to the eye ; nevertheless the sun's obscure rays were
collected in the focus, though the luminous ones
were not ; and a piece of black paper placed there
was instantly pierced and set on fire; and by shift-
ing the paper, aperture after aperture was formed
in quick succession. He thus shows that only one-
24th of heat radiated by an incandescent platinum
wire is luminous, the rest being obscure ; that in the
same way only 1-25th of the heat radiated by the
most brilliant portion of a flame of coal gas is lumi-
nous, and only 1-10th of that emitted by the elec-
tric light excited by a Grove's battery of 40 cells is
luminous.— Galignani.

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Holborn, W.C.—[ADvT.]
PASS GE OF TROOPS THROUGH LlVERPOOL—Yes-
terday the C battery of the B brigade of the Royal
Horse Artillery, under the command of Major D. F. Green,
embarked at the Clarence Dock, Liverpool, en route from
Woolwich to Dublin. The battery consisted of six officers,
145 men, 140 officers, and six guns. They were embarked
on board the steamers Trafalgar and St. Columbia. On
Tuesday next, the 25th inst., the Ist battalion of the 3d
Foot, consisting of 37 officers and 820 men, and accom-
panied by over 200 women and children, will also embark
at Liverpool for Dublin.

THE SEAL Fl SHE RY.--GLASG OW, April 17.
Telegrams received here from St. John's, dated April 4,
state that the screw steamer Bloodhound had returned
from the ice quite full ; and the Osprey, with 6,000 seals,
and having her bows injured. The screw steamer Wolf is
reported with 7,000 seals.