Chase.] A'Ao [Match 7, 



9. § inertia period of Jupiter and Saturn 4038.49 



10. § " " " Uranus 4060.86 



11. f " " Saturn and " 404G.08 



12. | " " " Neptune 4071.89 



13. J, " " Uranus and " 4027.52 



14. Kirkwood's period 4043.43 



15. Mean 4070.48 



If we substitute J* of Jupiter's year (4043.74) for the fifth number in 

 the above table, the mean will become 4049.85, the time of planetary 

 revolution at Jupiter's mean perihelion being 4057.65 days. The frac- 

 tional coefficients of the exterior planetary years will also be nearly com- 

 mensurable, 2 X ft being nearly equivalent to 5 X '> 14 X t 2 -> anf ^ 

 28 X tV- 



The relations of Uranus to the centre of oscillation of Neptune's radius 

 vector and to the synchronous vibrations of light and gravity, lend in- 

 terest to the following table. The elements introduced are the mean 

 aphelia of the three outer planets, the mean perihelion of Jupiter, and 

 the mean distances of the inner planets. 



Approximate Commensurability of Planetary Distances. 



| Neptune's mean aphelion 20.226 



Uranus' " " 20.043 



2 X Saturn's" " 20. 



4 X Jupiter's mean perihelion 19.913 



13 X Mars 19.808 



20 X Earth 20. 



28 X Venus 20.253 



52 X Mercury 20.129 



Average 20.046 



The almost precise accordance of the general mean with the aphelion 

 of Uranus, the diminution of values towards the centre, and the group- 

 ing by pairs, are all indicative of harmonic laws which may serve 

 not only to explain the sun-spot cycles, but also many of the other phe- 

 nomena of our system. 



RELATIVE VELOCITIES OP LIGHT AND GRAVITY. 

 By Pliny Earle Chase. 



{Bead before the American Philosophical Society, March 1th, 1873.) 



The only approximate estimate of the velocity of gravity that has ever 

 been made, appears to be that of La Place, who showed that it must be 

 at least six million times as great as that of light. The mutual action 

 and reaction of centrifugal and centripetal forces may, perhaps, furnish 

 means for its ultimate satisfactory determination, to which end the fol- 

 lowing considerations may be regarded as preliminary. 



