D. Kirkwood on Certain Analogies in the Solar System. 217 
members of which are nearly equal in diameter. Thisis exhib- 
ited in the second column o 
; TABLE Il. 
» Planets. Mean diameter. Density. 
i § Neptune, 4739 187 
*( Uranus, 4-498 153 
Ty § Saturn; 9-205 133 
Jupiter, 11-255 243 
tr § Ast. Planet, ‘584 7 14721 
a 519 1-032 
Iv Earth, 1-000 1-000 
*) Venus, 991 9 
v4 Mercury, » 891 1-980 
Remarks on the foregoing Table.—1. Encke’s mass of the 
Farth is zzagz1} that of the Earth, and Moon together, 55;4;55- 
It is scarcely necessary to observe that the former is to be used in 
determining the density, and the latter in estimating the diame- 
ter of the sphere of attraction. By applying the other masses in 
Table I, and the diameters in Table III, we obtain the densities 
in tolumn third of the latter. 
2. In each pair, the densities of the members are to each other 
as the volumes ; or, what is the same thing, as the square roots 
of the masses ; whence also it follows that the masses are to each 
other as the sixth powers of the diameters. 
Thus if D, d = the respective diameters of the members of any pair ; 
/ 4, 5 = the densities ; 
M, m = the masses 3 
then D2 .d® -: 4:6, 
resulting value 
in each instance falling between those of id a 
* Cosmos, vol. i 517. Hind’s Solar System, pp. 24, 103, 138. A 
remarkable error ae bes a yee diameters of Uranus and ‘Mephane occurs in the 
latter work, pp. 120 138. The apparent diameter of the former, reduced to the 
’s tla tratan is put for that of the latter, and vice versa; and hence it is 
ie concluded that the true di of Neptune is rather less than that of 
is Szconn Sunms, Vol. XIV, No. 41—Sept, 1852. 
2 
28 
