ESE NOLO TLE NEO A fe Lf VPO DALE STIS 61 
1. Comparison of the moment of momentum of the nebular system 
with the moment of momentum of the present system.—\t is a firmly 
established law of mechanics that any system of particles of any 
kind whatever rotating about an axis retains a constant moment 
of momentum whatever changes of form or arrangement the 
matter may undergo by virtue of its own interaction. To make 
this law rigorously applicable to the solar system evolving along 
Laplacian lines, the influence of external and of incoming bodies 
must be excluded. Foreign meteoroidal matter has doubtless 
been added constantly to the system during its evolution, but 
the amount of this is assumed to be negligible; and if it were not, 
the law of probabilities would render its effect upon the rotation 
of the system an essentially balanced one, and hence immate- 
rial. The following argument proceeds upon the Laplacian 
assumption that the system evolved through the operation of its 
own inherent dynamics. On this assumption the sum total of 
rotational and revolutionary momentum must have been the 
same at all stages of the system’s evolution. 
The following table gives the masses. and the present moments 
of momenta of the several members of the solar system and of the 
whole system. They are taken from Darwin’s paper, ‘‘On the 
Tidal Friction of a Planet attended by several Satellites and on 
the Evolution of the Solar System,’ * and are employed in the 
subsequent computations. The masses assigned the planets 
embrace those of the attendant satellites. 
Body Masses (Earth r) Moments of Momenta (Darwin) 
; Laplace’s density law (Min. 
oun ‘ SED ys 20008 ae ) euaceerane ee ees 
Mercury - .06484 .00079 
Venus - -78829 .01309 
Earth - - 1.00000 ,01720 
Mars - .10199 .00253 
Jupiter - 301.09710 1 3.46900 
Saturn - g0.10480 5.45600 
Uranus - 14.34140 1.32300 
Neptune - 16.01580 1.80600 » 
Solar System 315,934.51422 eee ae 
t Phil. Trans. Roy. Soc., Part II, 1881, pp. 516, 517. 
