Watertown republican. [volume] (Watertown, Wis.) 1860-1906, 1881-07-06
WHAT IS A COMET?

which now agitate the people and which
even invade the sanctum of the newspa-
per man The local astronomer Of the
Tribune, having devoted his time to the
sun, moon and consultations since the
advent Of the last comet, confesses to a
lack of definite information concerning
these irregular bodies. In order, there
fore, to present to its readers an answer
to a few of the questions asked, a reporter
for the Denver Tribune yesterday called
upon Miss. F. A. Fish, lady Principal and
Professor of Mathematics at Denver Uni
versity, and reproduces here the result of
the interview.
Miss Fish said: 4 comet is a nebulous
body revolving about the sun in an orbit
whose form may be either an eclipse more
or less eccentric, or a paraboIa or an hy-
perbola. In the two latter cases it would
come to its perihelion but once, and on
its return would pass forever from the
the sight of man into the region of illlm-
liable space.
The comets belonging to the solar sys-
tenn must be counted by the thousands.
Eighty have been recorded within the
last fifty years.
The most brilliant comets consist of a
nucleus, cyma and tail, the first appear
ing like star or planet; the nebulosity
surrounding the nucleus is the coma and
the pr0longation of this is the tail The
diameter of the nucleus rarely exceeds
500 miles, and many seem to contract as
they approach the sun and to dilate as
they recede from it. 1t is conjectured that
this effect may arise from the change of
temperature to which the comet is eX-
posed
When a comet first makes its appear
ance it has little or no tail; but it rapid
ly increases in brightness and length as
it comes nearer the sun. The tail Of the
comet of 1S43, which was visible at mid
day, increased at the rate of thirty-five
million miles per day after passing peri
helion.
These luminous trains frequently attain
to great length. One is reported to have
been one hundred millions of miles
in length and fifteen millions of miles in
breadth.
The mode Of the formation of the tail
of a comet is explained upon the suppos-
ition that there exists repulsive force,
which expels certain particles from the
nucleus and these are acted upon by a
still more powerful force, which proceeds
from the'sun; hence the general direction
of the tail is from this luminary.
AS the comet approaches the sun the
tail follows it, but it invariably backs
out from its august presence, the tail be-
ing forced back upon both sides of the
nucleus by this expelling force
The duration of comets visibility
varies from few days to more tEan a
year-usually it is visible for about three
months, this depends upon its intrinsic
brightness and its position in reference to
the sun and earth.
The probable reason why the comet
which is now visible about 3 o'clock in
the morning is not seen earlier is that it
is following closely the suns path.
The amount of matter contained in a
comet is not, so far as is known, sufici-
emily great to cause any apprehensions as
to the result of one coming in contact
with the earth
Whence come and whittier go comets
are questions which perhaps are not so
easily answered. One very plausible the
ory is that they have been expelled from
distant stars or suns, and those that have
been captured and retained within onr
solar system have been forced to travel
on a closed path by the attracting infu-
ence of some planet; and others that ia
vor us with but one visit go back to the
starry depths and wing their flight to
| ether system.
If it be true that the comets which
make their appearance in our system
were expelled from remote stars, what
numberless years some of them may
have been pursuing their journey. For
it would take 100000 years for comet
to come from the nearest star to our sys-
tenn 1t is not probable that these bod
iesss are projected from our sun; such
would either enter other systems, or,
after a short journey would return to the
globe of the sun.
The question is often asked why these
nebulous bodies at their nearest approach
! to the sun do not fall into it? For the
same reason that planet does not At
perihelion these bodies recede from the
sun, partly because Of the increased We
locity, thus increasing the tendency to
fly from it. and partly because Of grad
ual change in the direction.
There is a theory that the interplane-
tary spaces are pervaded by an extremely
thin medium, which does not percepti-
bly, affect the motions of the planets, but
which sensibly obstructs the motion of
such bodies as comets, thus diminishing
their orbital velocity, which would cause
them to be drawn nearer to the sun and
to perform their revolutions in less time.
It may be inferred from this hypothesis
that after many ages have passed comets
and planets will be precipitated upon
the sun. 1t is supposed that some COM
cts are broken into fragments and lose
their cometic form. Comets that move
in the elliptical orbits are classed as pc
riodic. The shortest period of any
known is three and third years, while
the longest, positively verified by its re-
turn, is seventy-fve years. Only eighty