﻿THE 

 LONDON, EDINBURGH, and DUBLINT 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OP SCIENCE. 



[SIXTH SERIES.] 



MARCH 1912; 



XXX. The Asteroids. By Percival Lowell*. 



1. V\7"HEN tbe zone of minor planets circling between the 

 \ T orbits of Mars and Jupiter is tabulated with regard 

 to the mean distances o£ its members from the Sun, certain 

 gaps in the arrangement become apparent. Kirkwood was 

 the first to point out the significance of these gaps by showing 

 that they occurred at just the points where a minor planet 

 would have a period commensurable with that of Jupiter, and 

 he attributed them in consequence to the perturbing action 

 of that great body. The question then arose as to whether 

 the gaps were permanent or effects only of a libratory action 

 due to Jupiter which Laplace had already discovered in 

 the case of Jupiter's satellites I., II., and III. Basing an 

 argument on this principle Newcomb gave it as his opinion 

 that the latter was the case, and that the action was not 

 permanent but merely the pendulum-like swing due to what 

 Laplace had explained. This opinion has been followed by 

 others, and the same argument has recently been advanced 

 as affecting the secular results due to commensurability in 

 the periods of the major planets. It will be proper, there- 

 fore, to begin what we have to say about the asteroids by 

 showing that a more careful consideration of the pendulum 

 argument discloses that it is itself illusory. 



One difficulty in celestial mechanics lies in the fact that 



* Communicated by the Author. 

 Phil Mag. S. 6. Vol. 23. No. 135. March 1912. 2 A 



