54 LIGHT SCIENCE FOR LEISURE HOURS. 



higher branches of mathematical calculation. He took 

 the difficult work of determining the orbital motions of 

 newly-discovered comets under his special charge, and 

 Dr. Bruhns tells us that every comet which was detected 

 during Encke's stay at Seeberge was subjected to rigid 

 scrutiny by the indefatigable mathematician. Before 

 long a discovery of the utmost importance rewarded his 

 persevering labours. Pons had detected on Novem- 

 ber 26, 1818, a comet of no very brilliant aspect, which 

 was watched first at Marseilles, and then at Mannheim, 

 until December 29. Encke next took up the work, 

 and tracked the comet until January 12. Combining 

 the observations made between December 22 and 

 January 12, he assigned to the body a parabolic orbit. 

 But he was not satisfied with the accordance 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 LexelPs 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 5, he wrote to the eminent 

 mathematician Gauss, pointing out the results of his 

 inquiries, and saying that he only waited for the en- 



