though moving in an orbit more than three times as much inclined to the plane of the ecliptic. The discovery of two planets, in the po- sition where one of them had been so anxiously sought for*, induced Dr. Olbers to conjecture that they were fragments of a larger planet, which had been scattered by some great catastrophe, and that many others probably existed at nearly the same* distance from the sun, and possessing common nodes : he therefore earnestly recom- mended astronomers to observe most carefully those spaces of the heavens in which the nodes of these planets are placed ; a practice which he himself observed for many years. His exemplary dili- gence was rewarded by the discovery of Vesta on the 29th of March, 1807, nearly in the precise position in which he had conjectured that it was most likely to be found f. This was the last of those remark- able discoveries whose history illustrates in so striking a manner that union of profound, yet somewhat visionary speculation, with uncon- querable perseverance, which is so characteristic of the German nation.
His well-known method of calculating the orbits of comets, which has been so generally used by German astronomers, was published at Weimar in 1797^:, with a commendatory preface by his zealous friend the Baron de Zach. This memoir, independently of its other merits, is sufficient to show that its author was a mathematician of very considerable powers, and perfectly acquainted with the works of contemporary astronomers.
Dr. Olbers w^as a diligent observer of comets ; and there are few astronomers who have contributed so much to our knowledge of these singular bodies. He was the discoverer of several comets, in- cluding the celebrated comet of long period of 1815; and we are indebted to him, not merely for very important suggestions and ob- servations respecting the celebrated comet of Encke, but still more for having de ^'eloped the taste for astronomical calculations and observations of that great astronomer, who for many years served him in the capacity of assistant in his observatory.
The Baron de Zach visited this observatory in September, 1800 §, and has described the simple apparatus which enabled him to make so many important discoveries. It was placed in the upper part of his house in the midst of the town of Bremen, and afforded openings or platforms sufficient to afford a command of nearly every point of the heavens. His instruments were an excellent five-foot Dollond of Sf inches aperture, with a circular micrometer (which he used in the observation of the small planets), a five-foot reflecting telescope
and that of Palias 2*7676 : the difference is less therefore than 19,000 miles.
- Their essays on this subject were generally headed, " On the long-expected Planet between Jupiter and Mars."
t The longitude of the ascending node of Pallas is 172° 32' 35"; that of Vesta is 171° 6' 37".
I Abhandlung ueber die lechteste und bequemste methode die Bahn eines cometen aus eiaigen beobachtungen zu berechnen.
§ Monatlichfe Correspondenz for Feb. 1801.
