166 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
It is postulated that the solar system originated from the 
slight disruption of an ancestral sun by the distant approach of 
another star. This resulted in the throwing out of a part of the 
sun’s mass into two opposite; spirally curved arms — a spiral 
nebula was formed. Now it seems to he a well established fact 
that such approaches are not uncommon events, as celestial events 
go, and are recorded by the flashing out of new stars. It is true, 
too, that the spiral nebula is the predominant form in the heavens. 
When it is realized that only T J-g- of the solar system ’s mass is con- 
tained in the planetary bodies it will be realized how compara- 
tively insignificant may have been the event which caused the 
initiation of the system, especially in consideration of the enor- 
mous volumes of matter which are constantly being shot out from 
the sun under ordinary conditions and apparently without any 
external stimulus. 
Reasoning from the analogy of observed spiral nebulge it is 
assumed that the matter contained in the two arms was embraced 
partly in knots or masses of more aggregated matter, between 
which were immense spaces more sparsely occupied.- As the sun- 
substance was shot forth it must have expanded enormously and 
before long much of it passed from the gaseous state through the 
liquid to the solid, though of course it remained in an extremely 
finely divided state. The spectra of the spiral nebulae show that 
they are in this finely divided, chiefly solid condition. Perhaps 
the larger knots, even in their most expanded and cooled state, 
had gaseous centers. The smaller knots doubtless were composed 
of solid particles. 
The attraction of the passing star had imparted a rotatory 
motion to the arms of the nebula, hence the whole mass swept 
around its center of gravity, the knots exerting a secondary pull 
of their own, the more scattered matter controlled directly by 
the central parental body. Some of the matter shot out was 
doubtless drawn back into the sun but the remainder proceeded 
in its evolution to form the planetary system. The knots served 
as the nuclei about which revolved a great swarm of matter, 
most of which was in time gathered into closer relationship to 
form planets, planetoids or satellites. The knots also acted as har- 
vesters of the celestial reaping grounds, if I may use the figure, 
and drew in such of the scattered particles, the planetesimals, 
which had been revolving directly around the sun, as came 
