140 A CENTURY'S PROGRESS IN ASTRONOMY. 



for, says Miss Clerke, " If it would be a violation 

 of probability to attribute to one such agglomera- 

 tion a period of an exact year or sub -multiple 

 of a year, it would be plainly absurd to suppose 

 the movements of two or more regulated by such 

 highly artificial conditions." Accordingly Erman 

 suggested in 1839 the theory that meteors re- 

 volved in closed rings, intersecting the terrestrial 

 orbit ; and that when the Earth crossed through 

 the point of intersection, it met some members 

 of the swarm. The subject now remained in 

 abeyance for thirty-four years, if we except some 

 wonderful ideas put forward in 1861 by Daniel 

 Kirkwood (1813-1896), an American astronomer, 

 who stated his belief in the disintegration of 

 comets into meteors ; but little attention was 

 paid to his opinions. In 1864 the subject was 

 taken up by Hubert Anson Newton (1830- 

 1896), Professor at Yale, who undertook a search 

 through ancient records for the thirty-three-year 

 period of the Leonids or November meteors. His 

 search was highly successful, and having demon- 

 strated the existence of the period, Newton set 

 himself to determine the orbit. He indicated 

 five possible orbits for the swarm, ranging from 

 33 years to 354J days. Newton was unable to 

 solve the question mathematically ; but here 

 Adams, the discoverer of Neptune, came to the 



