iichich Jiave been discovered since Jnhj IS-tl-. 413 



-0T> Old T>^^^^' I^ecember 13'68294'. Gfeenwich mean tim?. 



ft ... 118 23 24 1 '^^^^^q-^^^^^^- 



,c y-iBU'tds...... 45 36 3*riiUoU,M yd Lh 



^rn«il') i08?9toiM iKifi ,}; '[Motion direct. 



WHfert'Mt'.'M^ahlfi'^'bbservations are finally reduced, a more 

 complete investigation may be made, and perhaps we shall 

 then learn something respecting the nature of the conic sec- 

 tion described by the comet. From some sextant observa- 

 tions taken in Ceylon, and the positions furnished by later 

 observations in Europe, I found an elliptical orbit, as pub- 

 lished in the Astronomische Nachrichten of Prof. Schumacher, 

 and also in the Compfes Rendiis of the Royal Academy of 

 Sciences at Paris. The period in this ellipse was about forty- 

 eight years, but on receiving Mr. Caldecott's observations, it 

 became evident that the earlier observation employed was 

 jttiikch'in^ error, and that the probable orbit would be hyper- 

 -bolic. It is somewhat singular, that about the same time M. 

 Clausen, misled by an erroneous observation at Rome, found 

 an ellipse of thirty-three years' period for De Vico's second 

 comet; thus affording in a short time a double proof of the 

 necessity of extreme accuracy in cometary observations, and 

 likewise of the adxmntage arising from the jpublication of the ori- 

 ginal measures, in cases where there is no check to be expected, 

 from corresponding observatioiis : by original measures may be 

 understood the mean differences in right ascension and decli- 

 nation of the comet and comparison star, which affords the 

 practical astronomer an important means of checking the de- 

 duced place of the comet, and likewise the accuracy of the 

 star's assumed position. 



i,.u-^ui<^.'.uii)r Comet of di^ Kwest. 



On the 28th of December 1844-, M. d' Arrest perceived a 

 nebulosity in Cygnus, which proved to be a telescopic comet. 

 Cloudy weather prevented general observation until the second 

 week in January, when it was seen at most of the observato- 

 ries. About the middle of February the comet was within 

 20,000,000 miles from the earth : at this time it was distinctly 

 visible with the smallest optical aid ; I saw it frequently with 

 a telescope one foot in length and about one inch aperture. 

 The exact determination of the elements was attended with 

 more than usual difficulty, from the comet being so nearly in 

 opposition. M. Sievers of Altona computed the orbit by 

 Gauss's general method, and obtained hyperbolic elements : 



