They constitute an undoubted cluster; that is to
say, they are really, and not simply in appearance, grouped together
in space, so as to fall under the sway of prevailing mutual
influences. And since there is, perhaps, no other stellar cluster so
near the sun, the chance of perceptible displacements among them in a
moderate lapse of time is greater than in any other similar case.
Authentic data regarding them, besides, have now been so long garnered
that their fruit may confidently be expected at least to begin to
ripen.
Dr. Elkin determined, accordingly, to repeat the survey of the
Pleiades executed by Bessel at Konigsberg during about twelve years
previous to 1841. Wolf and Pritchard had, it is true, been beforehand
with him; but the wide scattering of the grouped stars puts the filar
micrometer at a disadvantage in measuring them, producing minute
errors which the arduous conditions of the problem render of serious
account. The heliometer, there can be no doubt, is the special
instrument for the purpose, and it was, moreover, that employed by
Bessel; so that the Konigsberg and Yale results are comparable in a
stricter sense than any others so far obtained.
One of Bessel's fifty-three stars was omitted by Dr. Elkin as too
faint for accurate determination.
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