few, and were frequently
interrupted. The parallax, accordingly, of about a quarter of a second
(0.2613") which he derived from them for Alpha Lyrae, and announced
in 1840,[74] has proved considerably too large.[75]

Meanwhile a result of the same kind, but of a more striking character
than either Bessel's or Struve's, had been obtained, one might almost
say casually, by a different method and in a distant region. Thomas
Henderson, originally an attorney's clerk in his native town of Dundee,
had become known for his astronomical attainments, and was appointed in
1831 to direct the recently completed observatory at the Cape of Good
Hope. He began observing in April, 1832, and, the serious shortcomings
of his instrument notwithstanding, executed during the thirteen months
of his tenure of office a surprising amount of first-rate work. With a
view to correcting the declination of the lustrous double star Alpha
Centauri (which ranks after Sirius and Canopus as the third brightest
orb in the heavens), he effected a number of successive determinations
of its position, and on being informed of its very considerable proper
motion (3.6" annually), he resolved to examine the observations already
made for possible traces of parallactic displacement. This was done on
his return to Scotland, where he filled the office of Astronomer Royal
from 1834 until his premature death in 1844. The result justified his
expectations. From the declination measurements made at the Cape and
duly reduced, a parallax of about one second of arc clearly emerged
(diminished by Gill's and Elkin's observations, 1882-1883, to O.75");
but, by perhaps an excess of caution, was withheld from publication
until fuller certainty was afforded by the concurrent testimony of
Lieutenant Meadows's determinations of the same star's right
ascension.[76] When at last, January 9, 1839, Henderson communicated his
discovery to the Astronomical Society, he could no longer claim the
priority which was his due. Bessel had anticipated him with the parallax
of 61 Cygni by just two months.

Thus from three different quarters, three successful and almost
simultaneous assaults were delivered upon a long-beleaguered citadel of
celestial secrets. The same work has since been steadily pursued, with
the general result of showing that, as regards their overwhelming
majority, the stars are far too remote to show even the slightest trace
of optical shifting from the revolution of the ea