ATOMIC POWER—RICHARDSON 155 
opposite each reaction was written the quantity of energy liberated, 
the rate at which the reaction would proceed at the temperature cal- 
culated for the center of the sun, 20 million degrees, and finally, the 
“mean life” or average time required for the reaction to take place. 
Inspection of the table revealed that only a very few reactions 
would provide energy at the rate emitted by the sun. At 20 million 
degrees some reactions would occur so rapidly that the sun would 
explode, while others were far too sluggish. In fact, it was pretty 
obvious that observations could be satisfied only by a particular series 
of reactions in which hydrogen combining with carbon and nitrogen 
is transformed into helium with the liberation of energy. The unique 
feature about the series is its cyclical character, neither carbon nor 
nitrogen being consumed but serving as true catalysts for the com- 
bination of four protons and two electrons into an alpha particle. 
Thus 85 years after the origin of the contraction theory, astronomers 
finally found in the carbon-nitrogen cycle a reasonably satisfactory 
answer to the question, “What is the force from which the sun draws 
its power?” 
It must not be supposed that astronomers now sit back complacently 
and regard the matter as closed. Although the carbon-nitrogen cycle 
accounts very well for the production of energy in stars like the sun, 
it has not been so successful when applied either to very luminous 
white stars or cool red giants. Thus Y Cygni, which is 32,000 times 
as bright as the sun, must be converting hydrogen into helium so fast 
that it can hardly have been shining at its present rate for more than 
85 million years, and probably has only enough hydrogen left to con- 
tinue for another 170 million years. If the present age of the universe 
is 2,000 million years, then stars like Y Cygni are truly “brief candles” 
blazing for a few cosmic minutes only. At the other end of the 
sequence are stars like Capella which have a central temperature cal- 
culated to be about 6 million degrees, so low that the carbon-nitrogen 
cycle would fail to operate effectively. In order to explain the pro- 
duction of energy in the red giants we are forced to rely on proton 
reactions with deuterium, lithium, and beryllium, which occur at 
relatively low temperatures. But it is hard to see how these light 
elements were built up in the red giants in the first place. 
A question which naturally arises at this time is “Why was not 
subatomic energy used as a source of power in the 30’s?” It would 
seem that if nuclear reactions produce so much heat, and if physicists 
knew how to produce them, then why not harness them for industrial 
use immediately? For example, the energy liberated from the trans- 
formation of a single pound of lithium and hydrogen in the proper 
proportions would release as much heat as can be obtained from the 
combustion of 3,150 tons of coal. 
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