WEDNESDAY, APRIL 15TH. 
THE EVOLUTION OF THE SOLAR 
SYSTEM, 
BY 
Mane]. PETITPOURT, B.& 
Assuming the Solar System to have originally existed as a 
nebulous mass of vast extent, how far would the evolution of the 
Nebula in accordance with the laws of nature produce the com- 
plex aggregate of phenomena now exhibited by the Sun and its 
attendant planets? The answer may be summarized as follows :— 
In the first place the Nebula was subject to radiation of heat 
and to contraction, with the almost inevitable accompaniment of 
a rotatory motion which increased in velocity as contraction pro- 
ceeded. A spheroidal form was thus imparted to the mass, and a 
maximum of centrifugal force was developed at the equator, 
likewise increasing with time, until, overbearing the central 
attraction of the Nebula, it checked the further contraction of 
the equatorial parts, and a ring became detached and left behind. 
A series of nebulous rings was thus formed, until contraction had 
so far advanced that the centripetal force could no more be over- 
come, and the nucleus, settling down, ultimately became our 
luminary, the Sun. These rings meanwhile coalesced to form 
the planets, all following the same direction of revolution as that 
originally imparted, and with increasing velocity from the outer 
to the inner planets. 
These considerations, together with the augmented density of 
the Nebula at cach successive stage and the differences in the 
magnitudes of the orbits, lead to the conclusion that a series of 
large planets, ascending in magnitude, followed by a descending 
series, should be formed, which is fairly the case in the Solar 
System ; and there seems to be a similar tendency in that of the 
moons of Jupiter and Saturn, which may be considered as having 
originated from rings on the same principle as above. 
The densities of the planets can be deduced from the follow- 
ing principles :—1. The inner rings were of denser materials. 
2. Radiation and contraction were more rapid in the smalier 
planets. We should therefore expect to find an ascending series 
of densities. This is the case, except (a) Saturn. This is perhaps 
