A CAPTIVE COMET. 351 



passing notice from the daily newspapers ; even astronomers, at 

 first, thought very little of it, as the discovery of a new comet is 

 now a matter of almost monthly occurrence. It was not long, 

 however, before this body began to attract the attention of the 

 scientific world, and it was soon recognized as a permanent mem- 

 ber of the solar system ; and now, through the researches of Dr. 

 Chandler and others, it has become the most famous comet of 

 this century. It has been identified with the lost comet of Lex- 

 ell, which disappeared one hundred and twenty years ago. 



Upon what grounds do we base this conclusion ? A comet 

 was seen for but a few months during the summer of 1770, another 

 one is observed during the summer and fall of 1889, and it is as- 

 serted that these two bodies are identical. There are no physical 

 means by which they can be identified, for comets have no perma- 

 nent characteristics which, when once seen, can always be recog- 

 nized. Indeed, to all appearances, these two bodies were utterly 

 unlike: the comet of 1770 was large and bright, with a well- 

 marked tail ; while the comet of 1889 was hardly visible even 

 with powerful telescopes, and then appeared but as a small patch 

 of haze against the dark sky. If, then, we rely on similarity of 

 appearance to establish the identity of these two comets, we 

 should fail to do so, and would be forced to conclude that they 

 are not the same. But by a study of the movements of the two, 

 especially of the latter, it can be shown that they must have 

 occupied, at one time, the same position in space — their identity is 

 then self-evident. 



At present the comet is moving in a small ellipse of about seven 

 years' period. This path is shown in the diagram. The smallest 

 circle represents the annual orbit of the earth around the sun. 

 Just outside of this circle is a heavily drawn ellipse with one of 

 its foci at the sun. This is the present orbit of comet V, and on 

 it are marked three positions of this interesting body. The first, 

 July G, 1889, marks its position on the night of discovery ; the 

 second, September 30th, at its perihelion passage, or nearest ap- 

 proach to the sun ; the third, that of December, 1890, the position 

 it occupied when last seen. For months before this last date, 

 however, the comet could only be seen by means of the great 

 thirty-six-inch Lick telescope. Between the two extreme positions 

 above mentioned, there are scattered along the curve some two 

 hundred and fifty other observations ; and on this small part of 

 the comet's path rest all the conclusions as to its movements for 

 over a hundred years. 



The first step in the problem was to deduce from these ob- 

 served positions the orbit of the comet, or the ellipse shown in 

 the diagram. This curve should be clearly understood — it is not 

 the actual path of the comet through the heavens, but that path 



