w miles out, and crossed over to the back of
Valparaiso, which was soon captured.--_The Graphic._

* * * * *

THE SUN'S MOTION IN SPACE.

By A.M. CLERKE.

Science needed two thousand years to disentangle the earth's orbital
movement from the revolutions of the other planets, and the
incomparably more arduous problem of distinguishing the solar share in
the confused multitude of stellar displacements first presented itself
as possibly tractable a little more than a century ago. In the lack
for it as yet of a definite solution there is, then, no ground for
surprise, but much for satisfaction in the large measure of success
attending the strenuous attacks of which it has so often been made the
object.

Approximately correct knowledge as to the direction and velocity of
the sun's translation is indispensable to a profitable study of
sidereal construction; but apart from some acquaintance with the
nature of sidereal construction, it is difficult, if not impossible,
of attainment. One, in fact, presupposes the other. To separate a
common element of motion from the heterogeneous shiftings upon the
sphere of three or four thousand stars is a task practicable only
under certain conditions. To begin with, the proper motions
investigated must be established with _general_ exactitude. The errors
inevitably affecting them must be such as pretty nearly, in the total
upshot, to neutralize one another. For should they run mainly in one
direction, the result will be falsified in a degree enormously
disproportionate to their magnitude. The adoption, for instance, of
system of declinations as much as 1" of arc astray might displace to
the extent of 10 deg. north or south the point fixed upon as the apex of
the sun's way (see L. Boss _Astr. Jour._, No. 213). Risks on this
score, however, will become less formidable with the further advance
of practical astronomy along a track definable as an asymptote of
ideal perfection.

Besides this obstacle to be overcome, there is another which it will
soon be possible to evade. Hitherto, inquiries into the solar movement
have been hampered by the necessity for preliminary assumptions of
some kind as to the relative distances of classes of stars. But all
such assumptions, especially when applied to selected lists, are
highly insecure; and any fabric reared upon them must be considered to
stand upon treacherous ground. The spectrographic method, however,