Olbers on Comets. 163 



ii. Extract of a Letter from Dr. Olbers, of Bremen, dated 29th 

 Nov. 1819; received II th Feb. 1820. 



As soon as Professor Encke shall have completed his com- 

 putations of the perturbations of the extraordinary comet, and 

 formed an ephemeris of its apparent orbit for the time of its 

 next re-appearance in 1822, I shall immediately communicate 

 them to you, in order that the best possible use may be made 

 of them. For, since this comet will arrive next at its perihelium 

 in the middle of May 1822, it will be scarcely visible at that 

 time in any part of Europe. Before its arrival at the perihelium 

 it will be too remote from the earth, and afterwards it will be 

 too far to the south to be seen by European observers. But in 

 the southern hemisphere it will be beautifully conspicuous ; and 

 at the end of June, when its latitude will be 77° south, its light 

 will be more than 26 times as strong as when it was discovered 

 by Pons, on the 26th November 1818. It is therefore greatly 

 to be desired that this comet should be watched and properly 

 observed in the southern possessions of Great Britain, in parti- 

 cular at the Cape or at Botany Bay. For this purpose, the 

 ephemeris of its motion should be sent out in good time, with 

 proper instructions for its employment, and an astronomer 

 should be found who might be capable of making the necessary 

 observations. 



For this, and for many other reasons, it is the general wish 

 of all astronomers, who are attached to the science, that an 

 observatory should be established at the Cape of Good Hope, 

 furnished with all the instruments that are required in the pre- 

 sent state of astronomy. In Europe, I imagine, there are a suffi- 

 cient number of observatories, if a proper use were made of 

 them. But, for the still further perfection of astronomy, it is 

 absolutely necessary to compare the observations made in 

 the northern hemisphere, with others made with similar instru- 

 ments beyond the equator. The physical properties of the ma- 

 terials, of which our instruments are constructed, and by which 

 they are supported and surrounded, notwithstanding the per- 

 fection of our artists, and the skill and attention of our astro- 

 nomers, confine the precision of the observations within cer- 

 M2 



