314 
THE SOURCE OF STELLAR ENERGY 
stars; but nothing very favourable or unfavourable to the theory has been 
found, except that it predicts correctly that the mass ratio progresses 
towards unity as the evolution advances. 
6. The uniformity of the main series comprising the great majority 
of the stars suggests that there is a simple mode of liberation of energy 
tapping an enormous store, in contrast to the rapidly exhausted supplies 
used during the giant stage. 
7. Great difficulties arise in relating the rate of liberation of energy 
to temperature, density, and exhaustion of the source; but since these 
affect every proposed source of subatomic energy there must presumably 
be some way out of them. 
Transmutation of Hydrogen. 
221. We sum up similarly the reasons for and against the transmutation 
of hydrogen into helium or higher elements as the main source of stellar 
energy. 
(1) It is the only process known to occur or to have occurred which 
would be capable of providing sufficient energy, and is therefore less 
speculative than other suggestions. 
(2) Unless the initial proportion of hydrogen in a star is unduly large 
the length of life of the star is only barely sufficient. 
(3) If the low value of e in the sun as compared with Capella and 
V Puppis is held to be due to exhaustion—and it seems impossible to 
explain it otherwise—the sun must very nearly have exhausted its stock 
of hydrogen and its future life will be short. The hypothesis thus extends 
the Kelvin time-scale where extension is least needed, viz. in the early 
infrequent types, and does not extend it sufficiently for the dwarf G to M 
stages which include the great majority of the stars. 
(4) The transmutation of elements is virtually a single source of 
energy, since there is very little further release of energy after helium has 
been formed. The phenomena of giant stars and the main series seem to 
indicate that at least two sources are tapped successively. 
(5) Part of the attraction of the hypothesis is lost if it is not accepted 
in its complete form—that the formation of the elements (hydrogen nuclei 
being reckoned as unformed primordial matter) begins with the condensa 
tion into stars. Besides the occurrence of advanced elements (Ti, Zr, etc.) 
in very early stars and of light elements (He, C) in the diffuse nebulae, 
the evidence of the theory is strongly against admitting a large proportion 
of hydrogen in early stars. 
(6) We should say that the assemblage of 4 hydrogen nuclei and 
2 electrons to form the helium atom was impossible if we did not know