JOURNAL OF TirE COLLKGK OF SCIENCE. TOKYO IMl'lUflAL ITNIVEUSITY. 



VOL. XL I., ART. 3. 



Researches on the Distribution of the Mean 

 Motions of the Asteroids. 



By 



KiyotSugu HlRAYAMA, Bi(iakuhakiishi, 

 Assistant Professor of Astronomy, Science College, Tokyo Imperial University. 



With 1 plate. 



In accordance with the views of some astronomers the fall of 

 meteors, the zodiacal light and the gegenschein suggest the possi- 

 bility of some kind of resistance to the planetary and satellite mo- 

 tions. It may be exceedingly small for the major planets. But 

 for small bodies like asteroids or satellites'^ it may not be entirely 

 negligible if the interval of time be sufficiently long, say hundreds 

 or thousands of years. 



Last year while at Yale University I considered the theoretical 

 effect of a resisting medium, supposedly motionless, on the libra- 

 tion of asteroids, and tried to explain the gaps of the asteroid dis- 

 tribution on that hypothesis. But I did not succeed. 



Recently I have worked on the supposition of another kind 

 of resistance suggested by Prof. E. W. Brown. ^^ According to this, 

 resisting materials having the size of ordinary meteors are supposed 

 to move around the central body in circular orbits. The result of 

 my study seems satisfactory to explain the gaps in the first approxi- 

 mation. I shall present the course of my investigation in the 

 following chapters. 



The numerical computations throughout this investigation 

 were duplicated by Mr. S. Terada, to whom the writer desires to 

 express his sincere thanks. 



1) For comets see § 8. 



2) Sir G. Darwin seems to have had similar id(-a. See A. N. 184, p. 263. 



