316 
THE SOURCE OF STELLAR ENERGY 
The frequency is 7*3.10 21 and the corresponding wave-length 
A - *00041 A. 
If there is a succession of processes the frequencies of the quanta will be 
smaller but of the same order of magnitude. 
We may also assume that if an electron and proton annihilate one 
another the released energy constitutes a quantum. This conclusion is not 
strictly justified unless there exists some counter process by which radiation 
can spontaneously generate electrons and protons—an assumption carry 
ing us into realms of speculation that are perhaps better avoided. If the 
counter process exists a state of equilibrium can be reached, and by the 
second law of thermodynamics the distribution of radiation in this state 
must be the same as that given by all other interactions of matter and 
radiation; accordingly Planck’s law holds and the radiation must be bound 
and released in single quanta. But I suppose that those who have imagined 
a reformation of waste radiation into matter have done so rather with a 
view to evading the consequence of the second law of thermodynamics 
that the world is running down, and it is not very logical to apply the 
second law to a process intended to get round it. 
Assuming that the quantum relation holds it gives for the annihilation 
of an electron and proton 9 
1 hc 1 — hv, 
so that A = *0000131 A. 
To justify either of these theories of the source of stellar energy we 
must satisfy ourselves that the star contains the necessary mechanism 
for transforming this high-frequency radiation into a normal form of 
energy. Until recently this constituted a difficulty. Being so far above the 
K frequency of any material its chance of ionising an atom is exceedingly 
small. The second of the two quanta above calculated would probably 
travel right through the star—and to the end of the world—with nothing 
to absorb it and utilise it. This difficulty has been resolved by the dis 
covery of the Compton effect in the scattering of radiation (§ 52). Although 
the scattering coefficient diminishes for radiation of very high frequency, 
it does not fall off with great rapidity as the absorption coefficient does. 
The subatomic radiation will be scattered after a path short compared 
with the radius of the star. The Compton effect increases the wave-length 
by *024 (1 — cos 0) Angstroms whenever the radiation is scattered through 
an angle d, the increase being independent of the original wave-length. 
The first considerable deflection will accordingly bring the energy down 
to y ray status and after that there is no difficulty in its further transmuta 
tion. The greater part of the energy is, however, no longer in the scattered 
ray but has been handed over to the electron which scattered it. This 
recoils with enormous energy, which it proceeds to distribute through the