Some recent discussions of the constitution of the sun have turned in
part upon what is known as the sun's proper motion in space. This is
one of the most surprising and interesting things that science has
ever brought to light, and yet it is something of which comparatively
few persons have any knowledge. It is customary to look upon the sun
as if it were the center of the universe, an immovable fiery globe
around which the earth and other planets revolve while it remains
fixed in one place. Nothing could be further from the truth. The sun
is, in fact, the most wonderful of travelers. He is flying through
space at the rate of not less than a hundred and sixty millions of
miles in a year, and the earth and her sister planets are his fellow
voyagers, which, obeying his overpowering attraction, circle about him
as he advances. In other words, if we could take up a position in open
space in advance of the sun, we should see him rushing toward us at
the rate of some 450,000 miles a day, chased by his whole family of
shining worlds and the vast swarms of meteoric bodies which obey his
attraction.
The general direction of this motion of the solar system has been
known since the time of Sir William Herschel. It is toward the
constellation Hercules, which, at this season, may be seen in the
northeastern sky at 9 o'clock in the evening. As the line of this
motion makes an angle of fifty odd degrees with the plane of the
earth's orbit, it follows that the earth is not like a horse at a
windlass, circling around the sun forever in one beaten path, but like
a ship belonging to a fleet whose leader is continually pushing its
prow into unexplored waters.
The path of the earth through space is spiral, so that it is all the
time advancing into new regions along with the sun. She is on a
boundless voyage of discovery, and her human crew are born and die in
widely separated tracts of space. Think of the distance over which the
travels of the sun have borne the earth only since the beginning of
human history! Six thousand years ago the earth and sun were about a
million millions of miles further from the stars in Hercules than they
are to-day. Columbus and his contemporaries lived when the earth was
in a region of the universe more than sixty thousand millions of miles
from the place where it is now, so that since his time the whole human
race has been making a voyage through space, in comparison with which
his longest voyage was as the footstep of a fly.
Thus the great events in the history of the world may be said to have
occurred in different parts of the universe. An almost inconceivable
distance separates the spot which the earth occupied in the time of
Alexander from that which it occupied when Cæsar invaded Gaul. The sun
and the earth have wandered so far from their birthplace that the mind
staggers in the attempt to guess at the stupendous distance which now
probably separates them from it. It may be that the motion of the
solar system is orbital and that our sun and many of the stars, his
fellow suns, are revolving around some common center, but if so, no
means has yet been devised of detecting the form or dimensions of his
orbit. So far as we can see, the sun is moving in a straight line.
Since space is believed to be filled with some sort of ethereal
medium, curious consequences are seen to follow from the motions that
have been described. A solid globe like the earth rushing at great
speed through such a medium will encounter some resistance. If the
medium be exceedingly rare, as it must be in fact, the resistance will
be correspondingly small, but still there will be resistance. If the
sun stood still, the earth, owing to the inclination of its axis to
the plane of its orbit, around the sun, would encounter the resistance
of the ether principally on its northern hemisphere from summer to
winter, and on its southern hemisphere from winter to summer. But in
consequence of the motion of the sun shared by the earth, this law of
distribution is changed, and from summer to winter the earth plows
through the ether with its north pole foremost, while from winter to
summer, although the resistance of the ether is encountered more
evenly by the two hemispheres, yet it is still felt principally in the
northern hemisphere, and the south pole remains practically protected.
It follows that the southern hemisphere, and particularly the south
polar regions are more or less completely sheltered the whole year
around. It might then be supposed that the impact of the particles of
the ether shouldered aside by the earth in its swift flight and the
compression produced in front of the advancing globe would tend to
raise the temperature of the northern hemisphere as compared with the
southern hemisphere, while the south pole, being more or less directly
in the wake of the earth, and in a region of rarefaction of the ether,
would constantly possess a remarkably low temperature.
Now, it is known that the south polar regions are more covered with
ice and snow than those of the north, and that the temperature there
the year around is lower. Whether this difference is owing to the
effects of the earth's journey through the ether, is a question.
The sun, too, moves with his northern hemisphere foremost, and it is
worthy of remark that it has been suspected that the northern
hemisphere of the sun radiates more heat than the southern.
But whatever effect it may or may not have upon the meteorological
condition of the earth, the fact that the solar system is thus
voyaging through space is in itself exceedingly interesting. Not the
wildest traveler's dream presents to the imagination such a voyage as
this on which every inhabitant of the earth is bound. A glance at a
star map shows that the direction in which we are going is carrying us
toward a region of the heavens exceedingly rich in stars, many, and
perhaps most, of which are greater suns than ours. There can be little
doubt that when the sun arrives in the neighborhood of those stars, he
will be surrounded by celestial scenery very different from and much
more brilliant than that of the region of space in which he now is.
The inhabitants of the globe at that distant period will certainly
behold new and far more glorious heavens, though the earth may be
unchanged.--_N.Y. Sun._
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