SOME FUNDAMENTAL CONCEPTS OF EARTH HISTORY 163 
gravitative control the atmospheric constituents, nor the waters 
of the ocean, nor probably even the much heavier rock sub- 
stances of the future earth. 
(4) In any rotating system the momentum of rotation re- 
mains constant through all changes of state. As the nebula 
contracted it rotated faster and hence assuming the present 
momentum of the solar system, the sun should today have an 
equatorial velocity of 270 miles per second. Its actual velocity 
is about one and one-third miles per second. There seems to be 
no agent competent to have caused this enormous retardation. 
(5) If the mass of the solar system be theoretically converted 
into a gaseous spheroid as postulated by La Place and be given 
all its present momentum, by the time the Neptunian ring is 
ready to be separated the nebula will be found to have less than 
of the momentum necessary for that separation. In like 
manner at the Jupiter stage the momentum of the nebula will be 
only yUg- of the necessary value, at the earth stage T sVo an d 
at the Mercury stage ygVo. Reversing the statement — at the 
time the Neptunian ring was ready to be formed there would be 
required for separation a momentum 200 times as great as the 
actual momentum at that stage. In the Jovian stage the needed 
momentum would exceed that available by 140 times; in the 
earth stage by 1800 times ; in the Mercury stage by 1200 times. 
These figures not only reveal a serious weakness but they show 
alarming discrepancies among themselves. 
(6) Directly in line with these facts is the demonstration that 
if, assuming again the original nebula, the whole mass re- 
mained together until the rate of its rotation became sufficient 
to force the separation of a ring, it would not acquire this rota- 
tion until it had shrunk well within the orbit of the innermost 
planet. 
(7) If again we assume the system to have developed to the 
stage when Jupiter ’s ring was ready to be left behind we can see 
that Jupiter ’s momentum must be proportioned to that of the 
nebular material inside his ring as the masses and velocities and 
radii of the two bodies were proportional. Now the mass of 
Jupiter and his satellites is about Jifc that of the system ex- 
clusive of the planets outside his orbit. But computations by Sir 
George Darwin show that Jupiter and his moons carry 96 per 
cent of the whole momentum of the solhr nebula at that stage. 
