46 
IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
the fact that we are situated in its center, Dr. Shapley’ suggests 
that we have been misled due to our restricted methods of measur- 
ing distances and by chance position of the sun near the center 
of the subordinate system, into thinking that we are in the midst 
of things. In much the same way the ancient man was misled by 
the rotation of the earth, with its consequent apparent daily motion 
of our heavenly bodies around the earth, into believing that even 
this little planet was the center of the universe and that his earthly 
gods created and governed the whole. 
If I were summarizing the world concept of adherents of this 
school, I would say that our stellar system (the galaxy) is a cloud 
or star cluster of about three hundred thousand light years in 
its longest diameter and about one-tenth of this distance in the 
shortest, which is passing through a spiral nebula about at right 
angles to its plane. This was probably first definitely postulated 
by Dr. Comstock of the University of Wisconsin. I quote him: 
“There is here presented the concept of a definite group of stars 
moving through a much more widely extended chaos, as the best 
working hypothesis at present attainable with reference to our 
stellar system.” The globular clusters are typical galaxies or 
remote systems and the spiral nebulae are not island universes 
but are purely nebulous in character and probably a part of our 
own system. The other camp of astronomers reject the prac- 
tically unlimited dimensions assigned to our stellar system and 
support what is known as the Island Universe theory. The un- 
conformity of the characteristics assigned to the spirals forms the 
principal basis for the hypothesis. Their distribution (clustered 
at the poles of the galaxy) is extremely difficult to account for in 
any theory of stellar evolution. Why should we find no spirals in 
the plane of the galaxy if they are part of our own system? By 
what peculiar law of nature do they all recede from the galactic 
plane, Andromeda excepted? If they are surrounded by rings of 
absorbing material as the dark markings on typical spirals seem to 
indicate, their absence in the plane of the “Milky Way” is simply 
accounted for on the theory that they are obscured by our sys- 
tem. The extreme difference in their size^ is difficult to under- 
stand if they are all within approximately the same distance from 
our system. If, on the other hand, they show a great variety 
of distances, say from about twenty thousand light years for 
the Andromeda spiral to say a hundred million light years for the 
smallest ones which can barely be detected as spirals on photo- 
