42 
IOWA ACADEMY OF SCIENCE Voi, XXIX, 1922 
“From the philosophic standpoint a discussion of the subject 
which is of such weight that in the history of thought it must be 
assigned a place above all others is that of Kant in his Kritik. 
Here we, find two opposing propositions — the thesis that the 
universe occupies only a finite space and is of finite duration ; the 
antithesis that it is infinite both as regards extent in space and 
duration of time. Both of these opposing propositions are shown 
to admit of demonstration with equal force, not directly, but by 
methods of reductio ad absurdum” 
I cannot agree fully with the reductio ad absurdum method of 
proof, especially in astronomical science, admittedly true for cer- 
tain lines of logic. But who is to determine when a proposition 
regarding the nature and extent of the cosmos has been reduced 
to absurdity? In my opinion this depends upon the experience 
of the one who judges the argument. What is absurd in the 
scientific world today becomes a method for investigation of new 
truths tomorrow. 
In 1720 Halley argued that “the light would diminish more 
rapidly than the distance between the stars increased and therefore 
space would not be equally illuminated if the stars were infinite 
in number.” He further suggested that light from the stars at 
a great distance would not reach the earth. It would seem that 
Halley had in mind an infinite universe. The main argument that 
is constantly being used against an unlimited universe is that 
space would be equally and brilliantly illuminated if the stars 
were infinite in number. Practically all the older methods of 
dealing with the extent and form of the universe were based upon 
the principle of equal distribution of the stars (uniform density of 
matter) and their apparent luminosity. About the only observa- 
tional data upon which to base this principle was the observed 
stellar density and the ratio of the number of stars of any given 
apparent magnitude to the number of stars in the next lower mag- 
nitude, together with the pitifully small number of stars whose 
distances had been determined by direct trigonometric methods. 
From such inductive studies, astronomers, notably Wolf of 
Germany, Eddington of England, and Newcomb of America, 
have postulated a fairly accordant concept of the extent and 
structure of our stellar universe, the general characteristics of 
which are (1) that the stars are limited in number and not uni- 
form in distribution; (2) that the “Milky Way” or “Great Gal- 
axy” constitutes the major part of our system and is about thirty 
thousand light years in its longest diameter and something like 
