3i 8 Probable Origin and Age of the Sun , [J uly, 
quence, as is generally supposed, that this store of energy 
must have been limited to the amount obtained from gravity 
in the condensation of the sun’s mass. The utmost that 
any physicist is warranted in affirming is simply that it is im- 
possible for him to conceive of any other source. His inability, 
however, to conceive of another source cannot be accepted as 
a proof that there is no other source. But the physical argu- 
ment that the age of our earth must be limited by the 
amount of heat which could have been received from gravity 
is in reality based upon this assumption — that, because no 
other source can be conceived of, there is no other source. 
It is perfectly obvious, then, that this mere negative evi- 
dence against the possibility of the age of our habitable 
globe being more than 20 or 30 million years is of no weight 
whatever when pitted against the positive evidence here 
advanced, that its age must be far greater. 
Now, in proving that the antiquity of our habitable globe 
must be far greater than 20 or 30 million years, we prove 
that there must have been some other source in addition to 
gravity from which the sun derived his store of energy ; and 
this is the point which I have been endeavouring to reach by this 
somewhat lengthy discussion. 
Are we really under any necessity of assuming that 
the sun’s heat was wholly, or even mainly, derived from 
the condensation of his mass by gravity ? According to 
Helmholtz’s theory of the origin of the sun’s heat by con- 
densation, it is assumed that the matter composing the 
sun, when it existed in space as a nebulous mass, was not 
originally possessed of temperature, but that the temperature 
was given to it as the mass became condensed under the 
force of gravitation. It is supposed that the heat given out 
was simply the heat of condensation. But it is quite con- 
ceivable that the nebulous mass might have been possessed 
of an original store of heat previous to condensation. 
It is quite possible that the very reason why it existed in 
such a rarefied or gaseous condition was its excessive tem- 
perature, and that condensation only began to take place 
when the mass began to cool down. It seems far more 
probable that this should have been the case than that the 
mass existed in so rarefied a condition without temperature. 
For why should the particles have existed in this separate 
form when devoid of the repulsive energy of heat, seeing 
that, in virtue of gravitation, they had such a tendency to 
approach one another ? 
It will not do to begin with the assumption of a cold 
nebulous mass, for, the moment that the mass existed as 
