The Hickman courier., 1882-11-10
COMETS.
rrOf. ProctDr's Views About Come
and Their PeculiaritIes.


rrOf. Proctor's views About Comets
and Their recusiaritIes.
To The Editor Of The Ncto Forlf Herald;
During the last two years many comets,
some OF them bright ones, have been
'sss.sn, and from all sides the question
reaches me, Do we know more about
comets than we did two years 3goP
wish that | could honestly answer. We
know n great deal more; but l cannot.
Still, something has been added to our
knowledge, and, unless l mistake, al
though that something may in itself be
slight, the manner in which it has been
learned is such that the small modicum
Of new truth Is full of promise.
| suppose every one who reads these
lines. knows pretty well what are now
the chief difficulties in cometic science.
We want to know why, as the comet APP
proaches the sun, it throws out all around
it, but chiefly toward the sun, the lum-
nous appendage we call the coma or
hair-really, so far as we can judge,
nebulous or gaseous envelope. We
want next to know why the matter thus
thrown out seems to become subject to
repulsiye force by which it IS strongly
driven from the sun to form what is
called the comets tail. We want to
know how much of the light of the COM
cts nucleus Cor brightest part,) coma or
nebulous surrounding. and tail is due to
the mere reflection of sunlight and how
much is inherent. Also, having ascer-
tanned beyond all possibility of doubt or
cayil that part of the light. in all three
cases is inherent. we want TO know how
sufficient heat is acquired to raise
nucleus, coma and tail TO actual inher-
ent luminosity.
Now, in former years, and especially
during the appearance of the comets of
Winnecke and Brorsen, in 1868, astrOno-
mers recognized that part of the light
of some comets, at any rate, is due TO
the inherent luminosity of certain COM
pounds of carbon and hydrogen. DIR.
William Higgins, of London, is not
very daring scientific speculator; he
usually errs on the side of excessive eau
ton Gndeed have myself been stating
respecting his results for the stfourteen
years. what he now only begins to state
for himself) therefore, when he does
speak positively we may believe that he
has found the evidence overwhelmingly
strong. Well, he says in n lecture very
recently delivered before the Royal In
stitution: 1.-The general close agreement
in the case of some twenty comets of the
bright bands in the cometary light with
those seen in the spcctra of hydrocarbons (
justifies US fully in ascribing the light of |
these comets to matter which contains
carbon in combination with hydrogen"
Until quite recently this has been the |
only matter which has been clearly rec
'ognized by the spectroscopic method as
forming part of the substance of comets. !
And the wonder has been that a substance
so refractory rs carbon--a substance |
which cannot be vaporized in our labor
atories under any ordinary conditions
should thus appear in the form of lumin-
Gus vapor in the case of comets further !
from the sun than our own earth. 1t is
difficult to see where the heat can come
from by which the carbon present in
these bodies can thus give light-evidence
(Which means also heat-evidence) of its
presence. It is not carbon only which
is thus shown to be present, nor even
carbon and hydrogen only; nitrogen
seems also to be indicated. Professors
Liveing and Dewar have found that GER
tain bright lines are only present in the
spectra of certain compounds of carbon
when nitrogen is also present, and that
in fact they indicate the presence of cyan
ogen, well-known nitrogen compound
of carbon. Now these bright lines have
not only been seen. they have been pho
tographed in the spectrum of the bright
est comet of 1881 (by DIR. William Hug
ginsin London, and by DIR. Henry Draper
in New York;. A part, then, of the
light of every comet is inherent, and
comes from a luminous mixture of car
bon, hydrogen, nitrogen and probably
oxygen also. A part of the light, is,
however, reflected sunlight nearly the
whole of the tails light being thus re-
ilected, and great portion of the light
of the coma, with a smaller portion of
the light of the nucleus Even
here, however, we cannot be as
sured that all the light which might be
reflected sunlight is really so. The only
way in which we can distinguish such
light from inherent light coming from
glowing solid or liquid matter, is by
noting that when we analyze reflected
sunlight certain tints thousands of them)
are missing, SO that across the rainbow
tinted streak. into which the spectre
scope resolves such light, there are seen
numbers of dark lines corresponding to
those missing tints. In the case of light
from a self-luminous solid or liquid mass
no such dark lines are seen. But the
faint light of a comet is not very easily
analyzed as closely rs is necessary to
show whether these dark lines exist in it
or not. Until quite recently astronomers
have been content to regard the presence
of acontinuous rainbow-tinted spectrum,
with or without lines. as evidence that
the comet shone by reflected sunlight
Now, however, closer scrutiny has
been made, and in the spectrum of the
brightest comet of 1881 physicists have
succeeded in detecting the dark lines
Ohe so-called Fraunhofer lines) of the
solar Spectrum. These lines have even
been photographed by DIR. Huggins (they
don't show in DR.. III. Draper's photo
graphs-) Now, falling to obtain or see
these dark lines means little or nothing;
seeing them, however. and. still more,
photographing them, is decisive, making
it absolutely certain that part of the
comet lights reflected sunlight. There
must be matter like meteoric dust in the
head and nucleus and probably in the
tail also of comet to enable it to shine
in this way by rejecting the light of the
sun.
But the latest comet which has vet
been observed with the spectroscope has
brought fresh news. l refer to Wells
cSnet, sometimes called, rather affect
edly, Comet Wells. The spectrum OF
sthis comet did not at first show the car
bon bands to which have referred above.
The cyanogen groups" says DIR. Hug
gins, .'are not SEEM and he does not |
seem to have looked for them later. But
in May. 1881, Vogel found that the car
bon bands were present, though faint.
He noticed no other bright bands or
lines. Still later. however. an unex-
pected change took place. Dr. B. Has