90 Transactions of the Academy of Science of St. Louis 
the astronomer Laplace proposed the nebular hypothesis of the 
earth’s origin, which was probably suggested by the rings of 
Saturn. According to this hypothesis the solar system was origin- 
ally a vast nebula of highly heated gas, extending beyond the 
orbit of the outermost planet and rotating in the same direction 
us the planets now rotate. As this nebula, which was more than 
five billion miles in extent, lost heat, it contracted. Due to con- 
traction, the speed of rotation increased and resulted in flatten- 
ing at the poles and a bulging at the equator. As further con- 
traction continued, the speed of rotation increased until the cen- 
trifugal force at the equator of the spheroid was equal to the 
force of gravity and a ring of particles was left behind. The 
process continued until successive rings were formed and the 
central mass became the sun. Each ring rotated as such for a 
time and then broke up to form a planet and its satellites. Ac- 
cording to this hypothesis the earth was first a globe of highly 
heated gas, then it became liquid and later a crust formed over 
the liquid interior. For more than one hundred years this was 
accepted as the most satisfactory explanation of the origin of 
the earth. During this time unexplainable objections accumulated 
and in 1905 Chamberlin and Moulton offered as a substitute the 
planetesimal hypothesis. In this hypothesis it is assumed that 
our solar system originated as a spiral nebula composed of finely 
divided solid or liquid material. Each knot-like mass in the arms 
of the spiral nebula grew by capture of material into a planet 
or a satellite, and the central mass became the sun. At first the 
nucleus of the earth was too small to retain an atmosphere, but 
later the heavier gases accumulated to form the initial atmos- 
phere and when saturation occurred the condensed water vapors 
formed the oceans. {The planetesimal hypothesis removed many 
of the difficulties which were unexplainable under the Laplacian 
hypothesis, but also it introduced new problems. In the effort to 
solve these problems, modifications of the current theories and 
new ones were advanced. Among the hypotheses which have re- 
ceived wide publicity is the Tidal Theory of Jeans and Jeffreys. 
But, the same objection applies to each, namely, it is not com- 
plete in itself, for it does not explain the original matter of 
the universe from which the planets evolved. Therefore, the 
