122 A CENTURY'S PROGRESS IN ASTRONOMY. 



Two independent investigators, David Peck 

 Todd (born 1855) in America and George 

 Forbes in Scotland, have since undertaken to 

 find the planet. Todd, utilising the "residual 

 perturbations" of Uranus, assigned a period of 

 375 years for his planet. Forbes, on the other 

 hand, working from the comet theory, stated 

 his belief in the existence of two planets with 

 periods of 1000 and 5000 years respectively. 

 In October 1901 he computed the position of 

 the new planet on the celestial sphere, fixing 

 its position in the constellation Libra, and 

 computing its size to be greater than Jupiter. 

 A search was made by means of photography, 

 in 1902, but without success. Nevertheless, 

 astronomers are pretty confident of the exist- 

 ence of one or more trans -Neptunian planets. 

 Lowell is very definite on this subject when 

 he says in regard to meteor groups, " The 

 Perseids and the Lyrids go out to meet the 

 unknown planet, which circles at a distance of 

 about forty-five astronomical units from the Sun. 

 It may seein strange to speak thus confidently 

 of what no mortal eye has seen, but the finger 

 of the sign-board of phenomena points so clearly 

 as to justify the definite article. The eye of 

 analysis has already suspected the invisible." 



