BESSEL, Friedrich Wilhelm, German as tronomer: b. Minden, Prussia, 22 July 1784; d. 17 March 1846. An astronomical tract which he had drawn up brought him into communica tion with Olbers, who encouraged him in his labors and procured for him the appointment of inspector of astronomical instruments to the University of GOttingen. In 1810 he removed to Konigsberg, and in 1812-13 superintended the construction of the observatory of this town. From 1824 to 1833 he completed a series of 75,011 observations on the celestial zone con tamed between 15° N. and 15° S. declination. These observations included all the stars in the zone as far as the ninth magnitude. A disserta tion which he published in 1844 contains im portant investigations on the variability of the movements of the fixed stars. An important share in the discovery of the new planet Nep tune belongs to him, as in a paper read in 1840 he called attention to the existence of a plane tary mass beyond Uranus, founding on consid erations which were afterward happily proved to be correct. Few contributed as much to the
advancement of astronomy in the first half of the 19th century. He was the inventor of
Functions.' His principal works are an (Essay on the Path Traversed by the Comet of 1807'; (Astronomical Observations' during various years; 'Determination of the Length of the •Pendulum Which Beats Seconds at Ber lin';