156 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
into the sun forever, or the sun would already be of infinite mass; 
in actual fact it was shown that meteorites could not have been fall- 
ing into the sun at the requisite rate for more than about 20,000,000 
years, or the sun would by now have become more massive than it 
actually is. Similarly as regards the Helmholtz theory—the sun 
can not have been contracting to the requisite extent for more than 
about 20,000,000 years, or it would have shrunk already to less than 
its present dimensions. 
Such periods of time are impossibly small for the sun’s life. 
Geologists find evidence that things have been much as they now 
are on our earth for periods of at least hundreds of millions of 
years, while physical research on the radioactive contents of certain 
Canadian rocks fixes their age at 1,400,000,000 years at the least, 
and analysis of other rocks gives confirmatory evidence. If, as is 
generally accepted, the sun is the parent of our earth, the sun must 
at least be older than the oldest of terrestrial rocks. It was at one 
time thought possible that radioactivity could provide our sun with 
energy for an almost unlimited span of radiation, but the possibility 
did not materialize. Sir Ernest Rutherford calculated that even if 
the sun started life in the most radioactive state possible, namely as 
a sphere of pure uranium, its radioactivity could provide for at 
most 5,000,000 years of radiation at the present rate. It was by now 
abundantly clear that the true source of the sun’s energy must be such 
as to provide the sun with a length of life of a different order of 
magnitude from anything hitherto thought of. 
In 1905 Ejinstein’s first theory of relativity appeared. ‘This 
required that an increase in the energy of any material system should 
be accompanied by an increase in its mass. It had for some years 
been recognized as a special property of electrified bodies that their 
mass increased pari passu with their energy; the theory of relativity 
now showed this to be a general property of matter in all states and 
conditions. The converse must of course also be true, so that a body, 
such as our sun, which is losing energy by radiation must also be 
losing mass. When the rate of loss of energy of any body is known, 
it is easy to calculate the corresponding rate of loss of mass; from 
the sun’s known rate of radiation it is found that its mass must be 
diminishing at the rate of about 250,000,000 tons a minute. 
This statement does not necessarily imply that there are fewer 
atoms or molecules in the sun at the end of the minute than there 
were at its commencement. If the sun were merely cooling down, 
like a red-hot cannon ball suspended in space, the heat agitation 
of each molecule would be less at the end of each minute than at 
its commencement, so that, on the average, the molecules would 
be moving more slowly and so have smaller mass. The aggregate 
of the decreases of mass of all the innumerable molecules in one 
le cea OT Sa Nf A ee Ee 
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