16 D. Kirkwood on certain Harmonies of the Solar System. 
11°6.” This would indicate a value of & for the Jovian system 
ual to 2; 7a) =3; and the possible separation of secondary 
asteroids between the limit 3 and the distance 4°5. 
Our knowledge of the Uranian system is perhaps too imper- 
fect to justify any conclusion in regard to the prevalence of a 
perturbations.” 
Tl—Tue Mean Distances of THE Pertopic CoMETS, AND THEIR 
Retation To THE Sovar SysTEM. 
The celebrated Laplace remarked that, according to the nebu- 
lar hypothesis, ‘the comets do not belong to the solar system.” 
He regarded them as small nebule which, wandering through 
space till they come within the sphere of the solar influence, 
enter our system from without, pass around the sun, and, unless 
influenced by the attraction of the planets, or the resistance of 
the ethereal medium, again pass off in parabolas or hyperbolas. 
Other astronomers believe them to have originated within the 
yr system. Perhaps each view may be partially correct. Sev- 
eral comets, among which we may instance that of June, 1861, 
have moved in hyperbolic orbits. These, together with many 
whose orbits seem to be parabolas, have probably entered the 
system ab extra, On the other hand, a large majority of periodic 
comets are believed to have originated in the system, and to be- 
long properly to it. The author several years since called atten- 
tion to the fact that there is an approximate coincidence between 
the planetary and confetary periods.* There are 13 known 
the 
the radius of gyration of the fifth planetary pair greater than the mean distance of 
Mercury, seemed, it was thought, sufficient ground for its rejection. At the Albany 
ae 
