CHAPTER VII. 



COMETS. 



AT the time of Herschel the ancient super- 

 stitions in regard to comets had to a great 

 extent vanished, thanks mainly to the return 

 of Halley's comet in 1758. Yet, although 

 comets had ceased to be objects of terror, no 

 explanation or rational theory of their nature 

 was put forward until the appearance of the 

 great comet of 1811. This comet was visible 

 from March 26, 1811, to August 17, 1812, a 

 period of 510 days. It was one of the most 

 magnificent comets ever seen, its tail being 

 100 millions of miles in length and its head 

 127,000 miles in diameter. This wonderful 

 phenomenon was the subject of much investiga- 

 tion, particularly by Olbers, the great German 

 astronomer. 



Heinrich Wilhelm Matthias Olbers was born 

 at Arbergen, a village near Bremen, October 11, 

 1758. His father was a clergyman who, in 



