The Stourbridge Observer, Cradley Heath, Halesowen & District Chronicle.
Stourbridge, West Midlands, England, 1874-07-18 00:00:00

THE COMET.

Mr. Huggins write to the Athena, um of Saturday :-
" A short account of the examination with the span
troacope of Coggia's comet, now so conspicuous an
object in the northern sky, may not be unacceptable
to your readers, though the observations are as yet far
from complete, and for the present I prefer not to
draw from them the information they Berm to contain
as to the nature of these strange bodies. The exami-
nation I was able to make of some telescopic comets
visible in 1866 and 1868 showed :hat the greater
part of the light of comets was not ordinary re-
flected Slaw light, but light emitted, or, at least, greatly
modified by the matter of the comet. Further, the
exact coincidence of the three bright bands, into
which their light was resolved by the separating
power of the prisms, with the spectrum of SUMO com-
pounds containing carbon, appeared to show that this
element is largely present in the matter of comets.
Some small comets which have appeared since, inelud
ing that of Eneke, exhibited a similar spectrum. The
comet, now visible is the first bright comet which has
appeared since the spectroscope has became an instru-
ment of astronomical irsearch. When the slit of the
spectroscope is placed across the nucleus and coma in
the direction ot the comet's axis, there is seen in the
instrument a broad spectrum, consisting of the same
three bright groups of lines which were exhibited by
the previous fainter comets; the bands are crossed
by a linear continuous spectrum, due to the light
of the stellar nucleus. In this spectrum I have not
been able to distinguish with any certainty any bright
lines other than those which I have already described.
The presence of these bands may be due, in part or
entirely, to the bright conietary matter surrounding
the true nucleus and between it and the eye of the
observer. 'When the spectrum of the nucleus was
made broader by a cylindrical lens and examined in a
spectroscope of greater power, it was found how
1 srgely these groups of lines contributed to the bright-
ness of the linear continuous spectrum, and this cir-
cumstance may explain the apparently small rela-
tive amplitude of the red portion of the continuous
spectrum of the nucleus. When the slit was
moved on to other parts of the coma the
gaseous spectrum predominated, but a faint con-
tinuous spectrum was also present, due in part at least
to reflected solar light. When the slit is brought back
past the nucleus on to the tail, the gaseous spectrum
becomes relatively fainter, until, at a short distance
from the nucleus, the continuous spectrum predomi-
nates so greatly that only the brightest of the three
bands can be detected on it. Observations with a
double-image prism show the presence of polarised light
in every part of the comet : the coma, the nucleus itself,
and the tail, all change in intensity BA the prism is
rotated. I should estimate, at a rough guess, the polar-
ised light not to exceed one sixth of the wholelight. The
nucleus of this comet is intensely bright and very small;
on the 6th it did not exceed 2 seas. in diameter. The nu-
cleus has thrown off a bright envelope, which presents
the curious mottled appearance which has been
Observed in the recently formed envelopes of former
comets. I prefer to reserve for the present any
positive statement on the point of exact coincidence,
or otherwise, of the three bright bands with 'those of
the carbon spectrum, and also on that of the altera-
tion of the spectrum by the comet's motion, and on
some other points."