D. Kirkwood on Planetary Distances. 67 
piter’s satellites. The differences between the radii of the orbits, 
commencing with the greatest, are, 
11°64811, 5°72677, and 357494. 
But while the first is almost exactly double the second, the sec- 
ond is less than double the third. In other words, as in the case 
of Mercury, the theoretical distance of the innermost satellite is 
somewhat greater than the actual distance. Now, if the original 
intervals constituted an exact geometrical progression, can a 
diminished, and thus the original interval between the first 
and second orbits increased. The same explanation applies to 
ercury.” 
With an interval = 11°64811 between the third and fourth 
Satellites, and a ratio = 4, we find 3°70213 as the limit at which 
the central body separated from the exterior mass. This isa 
little beyond the present circle of equilibrium between the cen- 
ps and the centripetal forces, the radius of this circle being 
299. 
THE SATURNIAN SYSTEM. 
In the primary system* and also in that of Jupiter, we have 
found that the original circle of separation between the nucleus 
and the surrounding mass was a little exterior to the present 
circle of equilibrium between the two central forces. This is 
what ought to be expected, as the contraction of the nucleus. 
would accelerate the rotation. For Saturn, however, we foun: 
the primitive circle of equilibrium /ess than the present ; but in 
this calculation no allowance was made for the contraction of 
Sve ent date geen lg rnc eg 
e Paris Observatory “has found that Mereury’s mean motion -on dimin 
hing; as if the planet were, in the progress of his revolutions, receding ger? 
5 
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| 
ity, & resisting medium which moves round the Sun in the same direction as the 
lanets oeiies W hewell’s Hist, of the Ind. Sci., 3rd ed., vol. i, p. 560.— Perhaps 
> satisfactory determination of the facts can be reached without long continued 
servations. : 
This Journal for J uly 1864, p. 13. * Tb., p. 15. 
CO we Pes 
5 
