Semi-weekly herald., 1910-03-17
COULD THE EARTH COL.
LioE WITH A COMET
-

I5,D00.0D0 miles away. II is but nat
urai that thinking man should ask:
Is there a possibility that the earth
may encounter comet and thus come
TO frightful end?
Curiously enough, Il was HALEY him
self Who first pointed out the possi-
bility. Winston. Newton's successor
IN the Lucasian chair of mathematics
NJ Cambridge, was so alarmed at "a
chariot OF Gre" which flared up in
his day, that HALEY was prompted to
look closely into It's movements. His
work led 10 the startling result that
The comet, when passing through the
descending node, had approached the
oar,hs path within semi-diameter OF
the earth. Naturally. HALEY wondered
what would have happened had the
earth and The comet been actually so
close together In their respective or
bits Assuming the comets mass TO
have been comparable with that OF
ibe earth (an assumption which we
now know TO have been utter beyond
reason) he concluded that their mu-
tual grayitation would have caused a
change In the position OF the earth In
its orbit, and consequently in the
length of year This train OF thought
led him to consider what the result of
an actual collision would have been,
aud he concludes that "if so large "A
body with SO rapid a motion were TO
strike the earth--a thing by no means
Impossible shock might reduce
this beautiful world to its original
chaos"
Hence HALEY not only dispelled the
superstition and the terror which once
followed in a comets wake, but also
pointed ont possibility which The su
perstiiious Dark Ages had never dream
ed of. 1t seemed to HALEY not i'm
probable thar the earth had at some
remote period been struck by comet
which, coming upon 1t obliquely, had
changed The position of the axis of
rotation. The north pole having orig
i00lly, he thought, been al a point not
far from 1iudson's bay. The more re-
cent investigations OF Kelvin and Sir
George Darwin completely upset any
such theory.
Since Halley's time the chance OF Il
collision between the earth and com
ct has engaged the attention of many
astronomical mathematidans. Laplace.
for example, painted the possibility of
collision with the earth so yividly
that he startled his day and genera
lion lie drew picture of comet
whose mass was such that tidal
wave some $4,000 or $4,000 feet high
Inundated the world, with the result
that only the higher peaks of the Hi
malayas and the Alps protruded. La
lande created panic by q similar
consideration of the subject in a pa
per which was intended for presenta-
ton before the Academy of Sciences,
hut which was not read Such was
the popular excitement, that he felt
himself constrained to allay the pub
lie fears as well AS he could in d
soothing article published in the Ga,
zette de France. The masses assumed
by both Laplace and Lalande are So
preposterous that their theories are no
longer seriously considered by any
sane astronomer.
Since the day of Laplace and La
lande there have been several comet
'scares.r Biela's comet crossed the
earth's orbit on Oct. 20. 1882. When
that fact was announced. Europe was
In ferinent. The orbit of the earth
was confused with the earth itself.
Such was the popular excitement, thar
Arago took 1t upon himself to compute
the possibilities of collision. He
reach the exact spot where the comet
had intersected the earth's orbit until
o month later. on Nov 80, on which
date the comet was 100000 miles
away. Incidentally he pointed out that
a collision was always happily remote.
He thought that the chances of a meet
ing were about one In PSI 900 900. Bah
met, on the other hand, thought that
collision WAS likely to take place
once In about 15,000,00O years. More
recently The entire problem has been
considered by Prof w II. Pickering of
Harvard BY collision he under.
stands, first, that any part OF the earth
strikes any part OF the comets head;
second. that any part of the earth
strikes the most condensed point in
the head lthe eore) as distinguished
from the larger nucleus What the
average size of visible comets head
may be. we have no means OF know
ing Young estimates that for tele-
scopio comet IL averages from 10000
to 100000 miles in diameter. The head
of the great comet OF 1911 was 200.
o00 miles; that of Holmes comet in
1892, 100000 miles: and that of naked.
eye comets generally over 100000
miles.
In the last half OF the last century
i2l comets. including returns, pene-
lrated the sphere OF the earth's orbit.
ls.n,., THE D,nr Iog.E,.f,fr tpf,r.g thai