SURVEY OF THE PROBLEM 
25 
ccurring in the 
l Thus we can 
anta at a very 
id mouthful it 
n. But in the 
id cannot take 
p is ready it is 
i traps are in 
fficient is pro- 
for the stellar 
m of Table 3. 
ire the atom’s 
to measure its 
>y the hungry 
Lption by the 
attention not 
:tron capture), 
on coefficients, 
emission must 
. It is only a 
V- 
ie emission or 
hysical theory 
ar weight, the 
large influence 
Lid extend the 
lim to predict 
l density with 
ch seems most 
lictions pretty 
3. This part of 
p feeling that 
3 waiting just 
ie discordance 
y factors and 
n a star. The 
•mpared with 
results which 
l observation, 
m the mathe 
matical investigations we may be equipped with a general knowledge 
of the conditions to be studied and of the interplay of the various 
factors. 
Other problems will arise in the course of our work. The Cepheid 
variables, considered to be pulsating stars, give opportunities for develop 
ment and test of the theory. Of special interest is the theory of the 
White Dwarfs—incredible but apparently true. The problem of the source 
of a star’s energy will be considered; by a process of exhaustion we are 
driven to conclude that the only possible source of a star’s energy is 
subatomic; yet it must be confessed that the hypothesis shows little 
disposition to accommodate itself to the detailed requirements of 
observation, and a critic might count up a large number of “fatal” 
objections. 
Those portions of thermodynamics and the quantum theory which are 
essential for our astronomical investigations are developed ab initio in 
Chapters n and nr. It is not expected that these Chapters can take the 
place of a regular treatise; nor has it been our aim to give a particularly 
elementary exposition suitable for a first approach to the subject. It can 
probably be assumed that everyone interested in astrophysical problems 
has picked up sporadically the leading ideas of atomic structure and 
quanta, and is familiar with some of the numerous experimental applica 
tions. The systematic outline here offered may help him to arrange these 
ideas and fill up the gaps in their sequence. Although the discussion is 
given in the form of mathematical deduction, it must be understood that 
when, as in these two Chapters, the results at every stage are subject to 
close test by experiment, the purpose of the argument is to exhibit the 
inner connection of the various phenomena and not to persuade the sceptic 
that the phenomena must occur. Consequently, although a reasonable 
degree of rigour is required, the laborious exploration and closing of every 
possible loophole is of secondary importance and would be out of place 
in a brief survey. 
Chapters iv-xi contain the main theme of investigation—the study of 
the internal condition of a star. The culminating point is Chapter vn, 
where the comparison with observation is made. Roughly speaking, the 
mechanics of the problem is placed before this, and the physics is placed 
afterwards. That is because the study of absorption, ionisation, electrical 
energy, etc., in the light of atomic physics would if undirected lead us 
far away from astronomical problems; and it is necessary first to ascertain 
what are the points of special astronomical importance, the doubts to be 
settled, and the difficulties to be discussed. We need to have a clear idea 
of how our results will react on observable properties of the stars. I do 
not think that any order of development would have avoided the numerous 
cross-references forward as well as backward. 
/