COMETS. 127 



in cometary astronomy by another great German 

 astronomer, his friend and pupil Encke. The 

 son of a Hamburg clergyman, Johann Franz 

 Encke was born in that city in 1791, and 

 died in 1865 at Spandau. After taking part 

 in the war against Napoleon, he was in 1822 

 appointed director of the Gotha Observatory, 

 being called to Berlin in 1825. In early life 

 he was the pupil of Olbers and Gauss, and 

 his investigations and discoveries formed an 

 epoch in astronomy. His most famous dis- 

 covery related to the little comet which bears 

 his name. The comet was discovered by J. L. 

 Pons (1761-1831) at Marseilles, although it had 

 previously been seen by Mechain and Caroline 

 Herschel. In 1819 Encke computed the orbit 

 of the comet, and boldly announced that it 

 would reappear in 1822, its period being about 

 3 years, or 1208 days. In 1822 the comet, 

 true to Encke's prediction, returned to peri- 

 helion, and was observed at Paramatta in Aus- 

 tralia, the perihelion passage taking place within 

 three hours of the time predicted by Encke. As 

 Miss Clerke remarks, " The importance of this 

 event will be better understood when it is re- 

 membered that it was only the second instance 

 of the recognised return of a comet ; and that 

 it, moreover, established the existence of a new 



