308 Probable Origin and Age of the Sun . [July, 
outermost planet. The total amount of work in foot-pounds 
performed by gravitation in the condensation of this mass to 
an orb of the sun’s present size can be found by means of 
the following formula given by Helmholtz : — 
Work of condensation = 
5 Rw 
M is the mass of the sun, m the mass of the earth, R the 
sun’s radius, and r the earth’s radius. Taking — 
M =4230 x 10 27 lbs., m = 11,920 x io 21 lbs., 
R = 2,328,500,000 feet, and 7 = 20,889,272 feet, 
we have then, for the total amount of work performed by 
gravitation in foot-pounds, 
3 (20,889,272*5 ) 2 x (4230 x 10 27 ) 2 
5 2,328,500,000 x 11,920 x io 21 
= 168,790 x 10 36 foot-pounds. 
The amount of heat thus produced by gravitation would 
suffice for 20,237,500 years. 
The conclusions are based upon the assumption that the 
density of the sun is uniform throughout. But it is highly 
probable that the sun’s density increases towards the centre, 
in which case the amount of work performed by gravitation 
would be something more than the above. 
At this point, in reference to the age of our globe, 
Geology and Physics are generally supposed to come into 
diredt antagonism. For if it be true, as physicists main- 
tain, that gravitation is the only possible source from which 
the sun could have derived its store of energy, then the sun 
could not have maintained our globe at its present tempera- 
ture for more than about 20 millions of years. “ On the 
very highest computation which can be permitted,” says 
Prof. Tait, “ it cannot have supplied the earth, even at the 
present rate, for more than about fifteen or twenty million 
years.”* The limit to the age of the sun’s heat must have 
limited the age of the habitable globe. All the geological 
history of the globe would necessarily be comprehended 
within this period. If the sun derived its heat from the 
condensation of its mass, then it could not possibly be more 
than about twenty million years since the beginning of the 
Laurentian period. But twenty million years would be con- 
sidered by most geologists to represent only a comparatively 
small portion of the time which must have elapsed since 
organic life began on our globe. 
* Recent Advances in Physical Science, p. 175. 
