American citizen. [volume] (Canton, Miss.) 1864-1890, 1874-10-10

| Translated from the French of La Nature.l
SINCE the beginning of this century
our idea of the universe has undergone q
complete metamorphosls, though but few
persons appear to recognize this fact
Less than century ago the sdrdnts who
admitted the earth's motion (some still
| rejected it) pictured to themselves the
system of the universe as being bounded
by the frontier of Saturn's orbit, at dis
lance from the central sun equal to 1O9,
600 the diameter of the earth, or about
500, 600, 900 miles. The stars were fred
specifically distributed at distance but
little greater than that of Saturn. Be
yOnd this limit vacant space was sup
posed to surround the universe. The
discovery of Uranus, in 1885, did away at
once with this belt, consisting of Sat
nation was pushed out to a distance of
1000, 100000 miles from the center of the
system, that is to say, beyond the space
which was vaguely supposed to be occu-
pied by the stars. The discovery of
Neptune, in 1846, again removed these
limits to distance that would have ap-
palled our fathers; the orbit described
by this planet being 1862, 100000 miles
from the sun.
But the attractive force of the sun ex-
tends further still. Beyond the orbit of
CIduuS, UC4Ouo JAC TOutC SlOWIy
traversed by Neptune, the frigid wastes
of space are travelled over by the comets
in their cratic courses. OF these, some,
being controlled by the sun, do not leap
from system to system, but move in
closed curves, though at distances far
greater than those of Uranus and Nep-
tune. Thus Halley's comet recedes to
distance of over 1900, OOO, 900 miles from
the sun; the comet of 1911, $4,000, 600 600
and that of 1850 5,OO0,OOO,OOO. The
period of the last-named comet is $500
years.
Still these figures can scarcely be CON-
pared to those which represent the dis
tances of the stars. What means have
we of measuring these distances? Here
the diameter of the earth will not serve
as the base of the triangle, as when we
measure the moons distance; nor can
we, as in the case of the sun, get any as
sistance from another planet. However,
fortunately for US, the arrangement of
our system affords us a means of meas
uring these distant perspectives; and
this, while demonstrating over again the
earth's motion round the sun, turns that
motion to account for the solution of the
greatest of astronomical problems.
In revolving round the sun at the dis
lance of ~, 100000 miles, the earth an
nually describes an ellipse of about 50O,-
DOC, 900 miles. The diameter of this orbit
is 1874, 100000 miles. As the carths rev.
olution round the sun is performed in
year, the earth at any given instant will
be opposite to the point where it stood
SIX months before, as alse to the point
where it will stand six months later.
Here is a line Of sufficient length to serve
as base of a triangle the apex of which
shall be a star
The process, then, for measuring the
distance of a star from the earth consists
in minutely observing this star at an in
terval of six months, or better for a whole
year, noting whether it remains fixed or
whether it undergoes some little appre-
ciable displacement of perspective, owing
to the annual displacement of the earth
around the sun. If it remains fixed, this
Is because it is an infinite distance from
us-at the horizon of the heavens, SO to
speak-and our base-line of $4,000, 900
miles is as nothing in comparison with
this remoteness. But if it is displaced,
then we know that it annually describes
IA small ellipse, corresponding to the
annual revolution of the earth. Every
one has remarked, while travelling by rail,
how the trees and other objects near at
hand move in direction contrary to
our own, their speed being greater in
to their nearness; whereat
distant objects on the horizon remain
fixed. The same effect is produced in
space, in consequence of our annual
motion round the sun. But though we
move incomparably swifter than an
express train, our rate being l ,632 900
miles per day, and $4,000 per hour, the
stars are SO distant that they scarcely
bulge. Our 1884, 100000 miles of dis
placement are almost nothing as con
Germs even the nearest of them. The in
babitants of Jupiter, Saturn, Uranus, or
Neptune with their orbits five, nine,
and thirty times as large as ours,
could determine the distance of far
greater number of stars than we.
This mode of measuring the distance
of the stars by the perspective effect
produced by the earth's annual displace-