DIFFUSE MATTER IN SPACE 
393 
To recall Kelvin’s classic phrase, there are two clouds obscuring the 
theory of the structure and mechanism of the stars. One is the persistent 
discrepancy in absolute amount between the astronomical opacity and 
the results of calculations based either on theoretical or experimental 
physics. The other is the failure of our efforts to reduce the behaviour of 
subatomic energy to anything approaching a consistent scheme. Whether 
these clouds will be dissipated without a fundamental revision of some 
of the beliefs and conclusions which we have here regarded as securely 
established, cannot be foreseen. The history of scientific progress teaches 
us to keep an open mind. I do not think we need feel greatly concerned 
as to whether these rude attempts to explore the interior of a star have 
brought us to anything like the final truth. We have learned something 
of the varied interests involved. We have seen how closely the manifesta 
tions of the greatest bodies in the universe are linked to those of the smallest. 
The partial results already obtained encourage us to think that we are 
not far from the right track. Especially do we realise that the transcend 
ency high temperature in the interior of a star is not an obstacle to 
investigation but rather tends to smooth away difficulties. At terrestrial 
temperatures matter has complex properties which are likely to prove most 
difficult to unravel; but it is reasonable to hope that in a not too distant 
future we shall be competent to understand so simple a thing as a star.