16 
SURVEY OF THE PROBLEM 
the same at all parts of the star. It does not depend on the density nor 
on the opacity of the star*. It depends only on the mass and molecular 
weight. Moreover, the physical constants employed in the calculation 
have all been measured in the laboratory, and no astronomical data are 
required. We can imagine a physicist on a cloud-bound planet who has 
never heard tell of the stars calculating the ratio of radiation pressure to 
gas pressure for a series of globes of gas of various sizes, starting, say, with 
a globe of mass 10 gm., then 100 gm., 1000 gm., and so on, so that his 
nth globe contains 10 n gm. Table 2 shows the more interesting part of his 
results. 
Table 2. 
No. of Globe 
Radiation Pressure 
Gas Pressure 
30 
•00000016 
•99999984 
31 
•000016 
•999984 
32 
•0016 
•9984 
33 
•106 
•894 
34 
•570 
•430 
35 
•850 
•150 
36 
•951 
•049 
37 
•984 
•016 
38 
•9951 
•0049 
39 
•9984 
•0016 
40 
•99951 
•00049 
The rest of the table would consist mainly of long strings of 9’s and 0’s. 
Just for the particular range of mass about the 33rd to 35th globes the 
table becomes interesting, and then lapses back into 9’s and 0’s again. 
Regarded as a tussle between matter and aether (gas pressure and radia 
tion pressure) the contest is overwhelmingly one-sided except between 
Nos. 33-35, where we may expect something interesting to happen. 
What “happens” is the stars. 
We draw aside the veil of cloud beneath which our physicist has been 
working and let him look up at the sky. There he will find a thousand 
million globes of gas nearly all of mass between his 33rd and 35th globes— 
that is to say, between \ and 50 times the sun’s mass. The lightest known 
star is about 3 . 10 32 gm. and the heaviest about 2 . 10 35 gm. The majority 
are between 10 33 and 10 34 gm. where the serious challenge of radiation 
pressure to compete with gas pressure is beginning. 
15 . It is remarkable that the units into which the matter of the universe 
has aggregated primarily are so nearly alike in mass. The stars differ 
* The independence of the opacity seems paradoxical at first, since for given 
flow of radiation transparent matter offers less obstruction and experiences less, 
force than opaque matter. But this is compensated because the flow of radiation 
increases with the transparency of the material.