allured and eluded him to the end, and he died
in 1822 without seeing it even in prospect of solution.
His estimate of the minimum distance of the nearest
star, based though it was on the fallacious test of apparent
brilliancy, was a singularly sagacious one, but it
was at best a scientific guess, not a scientific measurement.


The Distance of the Stars

Just about this time, however, a great optician came
to the aid of the astronomers. Joseph Fraunhofer perfected
the refracting telescope, as Herschel had perfected
the reflector, and invented a wonderfully accurate
"heliometer," or sun-measurer. With the aid of
these instruments the old and almost infinitely difficult
problem of star distance was solved. In 1838 Bessel
announced from the Konigsberg observatory that he
had succeeded, after months of effort, in detecting and
measuring the parallax of a star. Similar claims had
been made often enough before, always to prove fallacious
when put to further test; but this time the announcement
carried the authority of one of the greatest
astronomers of the age, and scepticism was silenced.

Nor did Bessel's achievement long await corroboration.
Indeed, as so often happens in fields of discovery,
two other workers had almost simultaneously
solved the same problem--Struve at Pulkowa, where
the great Russian observatory, which so long held the