220 Ohservations on the Comet of Halley. 



After its perihelion, the comet was first seen here December 31st. 

 It was then elevated less than 10° above the horizon, and moreover 

 had to contend with the morning twilight ; yet the sky in that quar- 

 ter of the heavens was unusually transparent. It is evident, that 

 under these circumstances, no very exact estimate of the intensity 

 of its light could be made; but it is also certain that if its light had 

 not been considerable, the comet could not have been seen at all. 

 A better judgment can be formed by comparing the times at which 

 the comet was visible to the naked eye. I saw the comet distinctly 

 with my naked eye about a dozen times during the months of Feb- 

 ruary and March. The intensity of its light by theory, may be sta- 

 ted at .16. Before the perihelion passage, the comet was first faintly 

 visible to the naked eye on the 19th of September. This is proba- 

 bly the very earliest date, at which it could have been seen ; and 

 the intensity of its hght at that time, by theory was ,67, four times 

 as great as in February. This leads us directly to the conclusion, 

 that the intensity of the comet's light was -very much increased by 

 its approach to the sun, being nearly four times greater after the 

 perihelion passage than before. On the evening of April 5th also, 

 although the comet could not probably be seen by the naked eye, it 

 was still visible in the finder of Clark's telescope, being itself a small 

 telescope, of less than twelve inches in length. The comet has ap- 

 peared larger and less distinctly defined since its perihelion than be- 

 fore. When first seen in August, the outline of the coma was very 

 regular, being almost an exact circle, and its margin very well defi- 

 ned. Since its perihehon, it has appeared smoky, and Irregular, 

 with its margin so indefinite that it was impossible to estimate its di- 



