SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 65 
surm'sed by some to be due largely if not entirely to radiuam— 
that most remarkable of known substances, discovered less 
than eight years ago by Mme. Curié. Proofs of its properties 
are ably presented in Rutherford’s ‘‘Radio-Activity.’’ It 
is not only self-luminous, but it is also self-heating, giving out 
every hour enough heat to melt more than its own weight of 
ice, a fourth more. It seems to be a very rare element. Tons 
of pithehblende yield only a few grains of radium. As radium 
evolves helium, and helium is known to be a chief component 
of the Sun’s chromosphere, it is suggested that the Sun con- 
tains much radium. 
Reeall that the Sun radiates from its entire surface in one 
minute enough heat to melt eneasing ice sixty-four feet thick. 
With this measure of the Sun’s heat, and radium’s heat emis- 
sion per minute—melting one forty-eighth of its own weight 
of ice—as data, we readily find that the Sun’s heat equals 
the heat emitted by a mass of pure radium weighing nearly 
as much as ‘the whole Earth weighs. That much of this rare 
and peculiar element in the Sun— our world’s weight of rad- 
ium—would yield its known output of heat. 
The surmise that such a quanity of radium is there, rather 
segregates the Sun from common matter. Moreover, the pro- 
perties of radium are none too well known. At present there- 
fore, attributing the Sun’s heat to radium, is simply an in- 
teresting speculation. 
4. The Mechanical Theory. 
There remains for consideration the mechanical origin of 
solar heat—that is, the conversion of force, or the energy of 
moving matter into heat energy. There can be no doubt that 
many millions of metorie bodies are hourly falling into the Sun. 
We know that something hke twenty million so-called shoot- 
ine stars plunge into our atmosphere daily. heir checked 
energy of mot’on reappeares in the air as light and heat. But 
the heat thus imparted to our Earth in a year has been shown 
to be less than we receive from the Sun in one second! In- 
comparably more of such metoric bodies are continually plung- 
ing into the solar atmosphere. Nevertheless, they must eon- 
tribute comparatively little to the Sun’s heat, for while inter- 
planetary space, at least as far out as the Earth’s orbit, is 
threaded by a veritable maze of meteorids, if sufficiently more 
numerous throughout inner space to produce by their incessant 
impacts on the Sun a large part of its heat, the Comparative 
density of the outlying myriads would affect perceptibly not 
