74 Royal Society : — Anniversary Address of the President : 



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 was 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 ibr very important suggestions and ob- 

 servations respecting the celebrated comet of Encke, but still more 

 for having developed 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 f, 

 and has described the simple apparatus \yhich 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 DoUond 

 of S^ inches aperture, with a circular micrometer (which he used in 

 the observation of the small planets), a five-foot reflecting telescope 

 by Schroter, a quadrant by Bird, an admirable sextant by Troughton, 

 and a clock by Castens of Bremen. He possessed no transit instru- 

 ment or fixed instruments of any kind ; yet he speedily availed him- 

 self of the circumstances of his locality to determine his time with 

 great accuracy, as well as nearly every element which the peculiar 

 character of his observations rendered necessary ; so fertile are the 

 resources of genius and enterprize to overcome difficulties, which 

 by ordinary men would be abandoned as altogether insuperable. 



Simeon Denis Poisson, one of the most illustrious men of sciencfe 

 that Europe has produced, was born at Pithiviers on the 2]st of 

 June, 1781, of very humble parentage, and was placed, at the age 

 of fourteen, under the care of his uncle, M. L'Enfant, surgeon, at 

 Fontainebleau, with a view to the study of his profession. It was 

 at the central school of this place that he was introduced to the no- 

 tice of M. Billy, a mathematician of some eminence, who speedily 

 discovered and fostered his extraordinary capacity for mathematical 

 studies. In 1793 he was elected a pupil of the Ecole Polytechnique, 

 which was then at the summit of its reputation, counting amongst 

 its professors Laplace, Lagrange, Fourier, Monge, Prony, Berthollet, 

 Fourcroy, Vauquelin, Guyton Morveau, and Chaptal. The pro- 



* Abhandlung ueber die lechteste und bequemste methode die Bahn 

 eincs coraeten aus einigen beobachtungen zu beiechnen. 

 t Monatlichc Corrcspondenz for Feb. 1801. 



