OLBERS, Heinrich Wilhelm Matthias (1758-1840), a distinguished astronomer, was born 11th October 1758 at Ar bergen, a village near Bremen, where his father was minister. He studied medicine at Göttingen, 1777-80, attending at the same time Kaestner’s mathematical course; and in 1779, while watching by the sick-bed of a fellowstudent, he devised a method of calculating cometary orbits which made an epoch in the treatment of the subject, and is still extensively used (see Comet, vol. vi. p. 182). The treatise containing this important invention was made public by Baron von Zach under the title Uebeτ die leichteste und bequemste Methode die Bahn eines Cometen zu berechnen (Weimar, 1797). A table of eighty-seven calculated orbits was appended, enlarged by Encke in the second edition (1847) to 178, and by Galle in the third (1864) to 242. Olbers settled as a physician in Bremen towards the end of 1781, and practised actively for above forty years, finally retiring 1st January 1823. The greater part of each night (he never slept more than four hours) was meantime devoted to astronomy, the upper portion of his house being fitted up as an observatory. He paid special attention to comets, and that of 1815 (period seventy-four years) bears his name in commemoration of its detection by him. He also took a leading part in the discovery of the minor planets, re-identified Ceres on the anniversary of its discovery by Piazzi, 1st January 1802, and detected Pallas on the 28th of March following. His bold hypothesis of their origin by the disruption of a primitive large planet (Monatliche. Correspondenz, vol. vi. p. 88), although now discarded, received strong confirmation from the finding of Juno by Harding, 2d September 1804, and of Vesta by himself, 29th March 1807, in the ...