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IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
Other planets show similar disproportions between masses and 
momenta, some of them even greater than this one. The 
planetary system as a whole carries 1/745 of the mass of the en- 
tire solar system but it contains over 97 per cent of the total 
momentum. Tidal reaction between the central and outlying 
bodies might help this difficulty slightly but it is entirely in- 
adequate to fully meet the case. 
(8) It would seem that the rings should have a certain 
symmetry and regularity in masses. But this does not hold good, 
as has always been recognized. The masses of the planets from 
outermost to innermost, taking the earth as unity, are 17, 14.6, 
94.8, 317.7, 0.1073, 1, 0.82, 0.0476. 
(9) The rings should have been circular when formed and 
no great divergence should result during later evolution. Most 
of the planets satisfy this law fairly well, but the orbits of the 
planetoids are neither circular nor concentric, but are singularly 
interlooped. 
(10) If we consider the evolution of the satellites from their 
primaries we will see that the former should revolve in the same 
direction as the rotation of thqunaster spheres, from the very 
mode of their origin, and that these master spheres should 
rotate in less time than the revolutions of their respective 
satellites. But Phobos, the inner satellite of Mars, revolves 
around that planet more than three times while the planet 
rotates once, and the little bodies which form the inner border of 
Saturn’s inner ring revolve in about half the time of Saturn’s 
rotation. 
(11) As additional evidence of the same kind may be cited 
the discovery that Saturn has one moon and Jupiter two wdiich 
revolve in retrograde direction. The necessity of uniformity 
of motion under the Laiplacian hypothesis was so patent that it 
was taught that a single exception would prove fatal to the 
hypothesis. 
It must be remembered that La Place propounded his theory 
at a time when less was known of the heavenly bodies and their 
mechanics, and also of the laws of gases, than is known now. 
For many years the theory seemed to fit the observed facts, 
astronomic, physical and geologic. It would be hard to over- 
estimate its value to advancing science, substituting as it did 
something specific and tangible and reasonable for the wild 
