G4 LIGHT SCIENCE FOR LEISURE HOURS. 



the work, and tracked the comet until January 12th. 

 Combining the observations made between December 

 22d and January 12th, he assigned to the body apara- 

 bolic orbit. But he was not satisfied with the accord- 

 ance between this path and the observed motions of the 

 body. "When he attempted to account for the motions 

 of the comet by means of an orbit of comparatively 

 short period, he was struck by the resemblance between 

 the path thus deduced and that of Comet I, 1805. 

 Gradually the idea dawned upon him that a new era 

 was opening for science. Hitherto the only periodical 

 comets which had been discovered except Lexell's 

 the "lost comet" had travelled in orbits extending 

 far out into space beyond the paths of the most distant 

 known planets. But now Encke saw reason to believe 

 that he had to deal with a comet travelling within the 

 orbit of Jupiter. On February 5th, he wrote to the 

 eminent mathematician Gauss, pointing out the results 

 of his inquiries, and saying that he only waited for the 

 encouragement and authority of his former teacher to 

 prosecute his researches to the end toward which they 

 already seemed to point. Gauss, in reply, not only 

 encouraged Encke to proceed, but counselled him as 

 to the course he should pursue. The result we all 

 know. Encke showed conclusively that the newly- 

 discovered comet travels in a path of short period, and 

 that it had already made its appearance several times 

 in our neighborhood. 



