Omaha daily bee., 1896-11-08
through space as the photographs show i

through space as the photographs show 1t
actually does.
There is another very interesting circum-
stance brought out by these photographs of
the stars, when we remember that they form
a background with respect to the comet II
will be observed that many of the stellar
streaks are visible right through the tail.
To appreciate all that this implies we should
note that most OF the stars here concerned
are in truth very faint objects. They would,
under any circumstances, be quite invisible
to the naked eye. Yet they are nevertheless
distinctly seen, Notwithstanding the inter
position of this stupendous volume of come
tary matter. Here. then we see that stars,
even though they be faint stars, can never
theless DO discerned through a thickness of
hundreds of thousands of miles, of the ma
terial which forms the substance of the tail
to the comet This enormously thick curtain
is quite unavailng for the purpose of hid
ing the stars. Yet the light from those stars
is so feeble that the slightest film of haze
on a summer sky would suffice to eXtinguish
them This circumstance shows, in very
striking manner how insignificant must be
the quantity Of material which is contained in
a comet. We can admit this without, per-
haps, going quite so far as to agree with
those who assert that the tail of notable
comet may, nevertheless contain no greater
quantity of solid material than could be
packed into a portmanteau.
SPECTRoSCOPIC METHODS USED.
The remarkable movements of all comets,
and the brilliant appearance which many Of
these objects display make every crcum-
stance with regard to them of much interest
1t WILL therefore, not be a matter of sur
prise to learn that the spectroscopic meth
DDS of research, which have already taught
us so much with regard to the sun and the
stars, have been applied to the examination
of comets. The results are very instructive,
and we here give some account of them.
A..
totally different ways in which body may
be rendered visible. In the first case, 1t may
shine by its own light; in the second case
IL may simply show the light reflected from
some other luminous body The illumination
dispensed by a sun or a star is of the first
kind, that shed by the earth or any other
planet is of the second kind. The first ques-
ton which we have to ask with regard to
the light received from comet may be
thus stated. Is this light due to some cause
of luminosity in the comet itself, or is it
merely sunlight reflected from the comet
as from a planet?
If we had been restricted to the use of
telescopes, however powerful, 1t would hardly
have been possible for us to have solved this
problem The spectroscope has. however,
the power of disentanglng the component
rays in beam of light and thus indicating
their character in such a way as enables us
to learn what the source of the light may
have been We thus find that the light
emitted from a comet is, generally speak
ing, of a twofold character. Part of IL Is
undoubtedly reflected sunlight This is dem
onstrated by observations with the spectre
scope, which shows that part of the radia-
ton from a comet exhibits continuous
spectrum, marked by precisely these lines
and groups OF lines which are distinctly char
acteristic OF sunlight. The evidence on this
point is quite convincing. We should, in
deed, have been greatly surprised had IL
been otherwise; for when the comet adven-
lures so near the sun, 1t does In the
course OF its wanderngs, II must be brill
liantly lighted up by the great luminary,
and, of course, some portion of the splendor
thus produced is naturally reflected to us,
COMETS AS LIGHT GENERATORS,
But besides the brightness which comets
possess in virtue OF the sunlight which
they receive, 1t is quite certain that they
are also to be regarded as being in GER
tain sense light generators themselves, In
this respect the comet Is at once per-
ceived TO be a body OF totally different
character from a planet The splendor OF
Venus is due simply to the sunlight which
falls upon II. Nor does the great Jupiter
himself emit any rays beyond those
which he imperfectly reflects from the
sun. The comet is however OF very
different nature from the more robust
planets. Part OF the light which the comet
transmits is unquestionably due to in
candescence in the body itself II the sun
were to be suddenly deprived of light-giv-
ing power while we were surveying the