EVOLUTION OF THE SOLAR SYSTEM. 
521 
Taking the moons parallax as 3422"'3 (which gives a distance of 60 27 earth’s 
radii), and the sun’s parallax as 8"*8, we have 
8-8 
C “ 3422-3 
Taking the lunar period as 27‘3217 m.s. days we have 
2tt 
f2 = - 
27-3217 
As above stated, m is f |, and m is -^ 3 -; whence it will be found that the moon’s 
181 
orbital momentum is 
10 10 ' 
This is 4‘7 8 times the earth’s rotational momentum. 
The resultant angular momentum of the system, with obliquity of ecliptic 23° 28', 
9-^G 
is 571 times the earth’s rotational momentum, and is — l o- 
Mars. 
The polar diameter at distance unity is 9"'352 (Hartwig, ‘ Nature,’ June 3, 1880). 
With an ellipticity -g^o this gives 4"'6 8 8 as the mean radius. The diurnal period is 
24 h 37 m 23 s . Assuming the law of internal density to be the same as in the earth 
I find 
Cn= 
1-08 
10 10 
The masses of the satellites are very small, and their orbital momentum must also 
be very small. 
Jupiter. 
The polar and equatorial diameters at the planet’s mean distance from the sun are 
35"'170 and 37"'563 (Kaiser and Bessel, ‘ Ast. Nach,’ vol. 48, p. 111). These values 
give a mean radius 5'2028 X 18"'383 at distance unity. 
The period of rotation is 9 h 55^ m , or '4136 m.s. day. 
I have elsewhere shown reason to believe that the surface density of Jupiter is very 
small compared with the mean density. It appears that we have approximately 
C=f ma 2 ='2637 ?na 2 .* 
6 2-528 
The numerical coefficient differs but little from that which we should have, if the 
Laplacian law of internal density were true, with infinitely small surface density 
(f infinite, 0=180°) ; for, as appeared in considering the sun’s moment of inertia, the 
factor would be in that case '26138. 
* Ast. Soc. Month. Not., Dec., 1876, p. 83. 
