Year: 1874

MASS OF THE COMET.


| The fact that comets contain but
small quantities of matter, as compared
with the earth and the larger planets
of the solar spstem, is proven by the
fact that comets do not change the Or
bit of the planet when in such position
that the planet does cause a great
change in the direction of the comets
path. And the spectrOscOpe has re-
Gently led astronomers to infer that
even the head of the comet is only a
volume of glowing gas. But there is
no warrant for the favorite idea of
some astronomers that the weight of q
comet might be carried in ones vest
pocket. A globe of hydrogen gas,
which is the ligbtest gas known to us
(if we except the hypothetical Abaron)
if equal in bulk to the earth and of the
same density as thata which the gas
is measured at the earth's surface,
would contain one part in $1,000 of the
quantity of matter contained in the
earth. Now, we can scarcely conceive
it as possible that density one hun
dred times less than that of hydrogen
gas at the earth's surface would permit
the reflection of the sunlight to your





miles. Yet, even this stretch of the
imagination towards the limits of tam
gible tenuity would give, for globe
of the size of COggia's comet, mass
which would weigh not less than
$4,000, ,000, 900, ,000,0 900 tons, if it could be
brought down to the earth's surface.
This compares with the mass of the
moon, as to 81 900; with the earth, as
to 100000, and with the sun, to
134, 200, 100000. 1t is not improbable,
however, that the mass of the comet is
much greater than this quantity, so
that it would compare favorably with
the largest of the planetoids revolving
between the orbits of Mars and Jupiter.
The largest planetoid is exceeded $50
times ~ volume by the moon; and ifits
density should be the same as that of
the moon, then its mass would be
equal to that of the comet, if the latter
had any average density sixteen times
less than that of hydrogen at the
earth's surface.


Henry M. Parkhurst, in revising his
calculations ur to July 6, writes The
Tribune as to the Comet striking US
with its tail:


The motion of the earth is 1850, 600
miles per day; that of the comet about
1000, 900 miles per day, and will con-
tinue about the same so long as it re-
mains visible. The motion of that
part of the tail nearest us is nearly
100000 miles per day; that is, 20
miles per second, which is 5000 times
faster than the motion of an express
train. The thickness of the tail as
sumo at about 100000 miles at the
distance of $4,000, 600 miles from the
head, when it shall have reached that
length. If the earth were to pass GEN.
trally through it, the passage would oc-
cupy about .wenty-four hours. Pass
ing through the extreme edge, as l at
first thought possible, would not occu-
py more than four to six hours. My
computations indicate that the nearest
approach to the centre of the tail will
be not less than 1900, 600 miles, which
would be a distance from the edge of
the tail of 1,500,0 900 miles, which is six
times the distance of the moon. But
this will be sufficiently near to cause it
to appear enormously large, If it can be
seen at all, of which hope to be able
to speak more definitely within few
days. One thing is certain, it will be
there whether we can see it or not.