EVOLUTION OF THE SOLAR SYSTEM. 
517 
Then being the attraction between unit masses at unit distance, M being sun’s 
mass, and 365'25 being the earth’s periodic time, we have 
2tt 1 o 8 ' 23558 
^= 86556 = 15 =- 
The momentum of orbital motion of any one of the planets round the sun is given 
by m. v 7 [xM. \/c. 
With the above data I find the following results.* 
Table I. 
Planet. 
Orbital momentum. 
Mercury. 
.... -00079 
Venus . 
.... -01309 
Earth 
.... -01720 
Mars .... 
.... -00253 
Jupiter . 
.... 13-469 
Saturn . 
.... 5-456 
Uranus . 
.... 1-323 
N eptune 
.... 1-806 
Total 
22-088 
We must now make an estimate of the rotational momentum of the sun, so as to 
compare it with the total orbital momentum of the planets. 
It seems probable that the sun is much more dense in the central portion, than near 
the surfaced Now if the Laplacian law of internal density were to hold with the 
sun, but with the surface density infinitely small compared with the mean density, 
we should have 
If on the other hand the sun were of uniform density we should have C—%McC u \. 
* These values are of course not rigorously accurate, because the attraction of Jupiter and Saturn on 
the internal planets is equivalent to a diminution of the sun’s mass for them, and the attraction of the 
internal planets on the external ones is equivalent to an increase of the sun’s mass. 
t I have elsewhere shown that there is a strong probability that this is the case with Jupiter, and 
that planet probably resembles the sun more nearly than does the earth.—See Ast. Soc Month. Not-., 
Dec., 1876. 
X These considerations lead me to remark that in previous papers, where the tidal theory was applied 
numerically to the case of the earth and moon, I might have chosen more satisfactory numerical values 
with which to begin the computations. 
It was desirable to use a consistent theory of frictional tides, and that founded on the hypothesis of a 
homogeneous viscous planet was adopted. 
The earth had therefore to be treated as homogeneous, and since tidal friction depends on relative 
3x2 
