n's inquiries that six of
Bessel's stars are exempt from the general drift of the group. They
are being progressively left behind. The inference is obvious that
they do not in reality belong to, but are merely accidentally
projected upon, it; or, rather, that it is projected upon them; for
their apparent immobility (which, in two of the six, may be called
absolute) shows them with tolerable certainty to be indefinitely more
remote--so remote that the path, moderately estimated at
21,000,000,000 miles in length, traversed by the solar system during
the forty-five years elapsed since the Konigsberg measures dwindles
into visual insensibility when beheld from them. The brightest of
these six far-off stars is just above the eighth (7.9) magnitude; the
others range from 8.5 down to below the ninth.

A chart of the relative displacements indicated for Bessel's stars by
the differences in their inter-mutual positions as determined at
Konigsberg and Yale accompanies the paper before us. Divergences
exceeding 0.40" (taken as the limit of probable error) are regarded as
due to real motion; and this is the case with twenty-six stars besides
the half dozen already mentioned as destined deserters from the group.
With these last may be associated two stars surmised, for an opposite
reason, to stand aloof from it. Instead of tarrying behind, they are
hurrying on in front.

An excess of the proper movement of their companions belongs to them;
and since that movement is presumably an effect of secular parallax,
we are justified in inferring their possession of an extra share of it
to signify their greater proximity to the sun. Hence, of all the stars
in the Pleiades these are the most likely to have a measurable annual
parallax. One is a star a little above the seventh magnitude,
distinguished as _s_ Pleiadum; the other, of about the eighth, is
numbered 25 in Bessel's list. Dr. Elkin has not omitted to remark that
the conjecture of their disconnection from the cluster is confirmed by
the circumstance that its typical spectrum (as shown on Prof.
Pickering's plates) is varied in _s_ by the marked character of the K
line. The spectrum of its fellow traveler (No. 25) is still
undetermined.

It is improbable, however, that even these nearer stars are
practicable subjects for the direct determination of annual parallax.
By indirect means, however, we can obtain some idea of their distance.
All that we want to know for the purpose is the _