35Q THE POPULAR SCIENCE MONTHLY. 



A CAPTIVE COMET. 



By CHARLES LANE POOR. 



ON the night of June 14, 1770, the great French astronomer Mes- 

 sier first saw the captive comet. It then appeared as a small 

 patch of haze against the cloudless sky, but it rapidly grew larger 

 and more brilliant, until, on July 2d, when it passed nearer to the 

 earth than any other known comet, it was as bright as the North 

 Star, and its diameter was twice that of the full moon. From 

 that moment its brilliancy faded, it grew fainter and fainter, and 

 was seen for the last time on October 2d. 



While this comet of 1770 is one of the most famous in the 

 annals of astronomy, it owes its celebrity not to the spectacular 

 effects it produced, for it was not one of those magnificent objects 

 that stretch across the heavens, exciting the wonder and admira- 

 tion of the intelligent, the fear and dread of the ignorant. Its 

 fame is due to its mathematical history, to the path it was then 

 traveling, and to the path it has since traveled. Only twenty 

 years had elapsed since Halley had made his great discovery of 

 the existence of periodic comets, and this comet of 1770 was shown 

 by Lexell to belong to this interesting class of bodies, to be then 

 revolving around the sun in an ellipse of five and a half years. 

 To the conclusions of Lexell it was at once objected by other 

 mathematicians that if this comet revolved about the sun in an el- 

 lipse, like the planets, it should have been seen six years before, and 

 again, six years before that ; at least, some record of its former 

 appearances ought certainly to be found. As there were no such 

 records, as it could be shown that there was no comet that had 

 appeared regularly every five and a half or six years, LexelFs 

 opinions were for the moment discredited. However, he soon 

 conclusively proved that he was right, that the comet was moving 

 at the moment in an ellipse such as he had described, but that it 

 had not always traveled in that same path. He showed that in 

 1767, or only three years previously, the comet had passed very 

 close to the giant planet Jupiter, and that then its path had been 

 greatly altered, so completely changed, indeed, that never before 

 had it passed near enough to the earth to be seen. He also pre- 

 dicted a second close approach of these two bodies in 1779, and 

 said that this circumstance might prevent the reappearance of 

 the comet after that date. This prediction of Lexell's was ful- 

 filled, for the comet was never again seen, unless it prove that 

 the comet discovered by Brooks on July G, 1889, is the lost body. 



On that summer evening, at Geneva, N. Y., Brooks discovered 

 a faint telescopic comet, since known as comet d and V, 18S9. As 

 this body never became visible to the naked eye, it received but 



