contradictory to received ideas obtained little credit,
until Peters found, in 1851,[98] that the apparent anomalies in the
movements of Sirius could be completely explained by an orbital
revolution in a period of fifty years. Bessel's prevision was destined
to be still more triumphantly vindicated. On the 31st of January, 1862,
while in the act of trying a new 18-inch refractor, Mr. Alvan G. Clark
(one of the celebrated firm of American opticians) actually discovered
the hypothetical Sirian companion in the precise position required by
theory. It has now been watched through nearly an entire revolution
(period 49.4 years), and proves to be very slightly luminous in
proportion to its mass. Its attractive power, in fact, is nearly half
that of its primary, while it emits only 1/10000th of its light. Sirius
itself, on the other hand, possesses a far higher radiative intensity
than our sun. It gravitates--admitting Sir David Gill's parallax of
0.38" to be exact--like two suns, but shines like twenty. Possibly it is
much distended by heat, and undoubtedly its atmosphere intercepts a very
much smaller proportion of its light than in stars of the solar class.
As regards Procyon, visual verification was awaited until November 13,
1896, when Professor Schaeberle, with the great Lick refractor, detected
the long-sought object in the guise of a thirteenth-magnitude star. Dr.
See's calculations[99] showed it to possess one-fifth the mass of its
primary, or rather more than half that of our sun.[100] Yet it gives
barely 1/20000th of the sun's light, so that it is still nearer to total
obscurity than the dusky satellite of Sirius. The period of forty years
assigned to the system by Auwers in 1862[101] appears to be singularly
exact.

But Bessel was not destined to witness the recognition of "the
invisible" as a legitimate and profitable field for astronomical
research. He died March 17, 1846, just six months before the discovery
of Neptune, of an obscure disease, eventually found to be occasioned by
an extensive fungus-growth in the stomach. The place which he left
vacant was not one easy to fill. His life's work might be truly
described as "epoch-making." Rarely indeed shall we find one who
reconciled with the same success the claims of theoretical and practical
astronomy, or surveyed the science which he had made his own with a
glance equally comprehensive, practical, and profound.

The career of Friedrich Georg Wilhelm Struve il