2S REPORT—1905. 
Thus far we do not find anything which renders the tidal theory of evolu- 
tion untenable. 
But the physicists have formed estimates in other ways which, until 
recently, seemed to demand in the most imperative manner a far lower 
scale of time. According to all theories of cosmogony, the sun is a star 
which became heated in the process of its condensation from a condition of 
wide dispersion. When a meteoric stone falls into the sun the arrest of 
its previous motion gives rise to heat, just as the blow of a horse’s shoe on 
a stone makes a spark. The fall of countless meteoric stones, or the 
condensation of a rarefied gas, was supposed to be the sole cause of the 
sun’s high temperature. 
Since the mass of the sun is known, the total amount of the heat 
generated in it, in whatever mode it was formed, can be estimated with a 
considerable amount of precision. The heat received at the earth from 
the sun can also be measured with some accuracy, and hence it is a mere 
matter of calculation to determine how much heat the sun sends out in a 
year. The total heat which can have been generated in the sun divided 
by the annual output gives a quotient of about 20 millions. Hence it 
seemed to be imperatively necessary that the whole history of the solar 
system should be comprised within some 20 millions of years. 
This argument, which is due to Helmholtz, appeared to be absolutely 
crushing, and for the last forty years the physicists have been accustomed 
to tell the geologists that they must moderate their claims. But for 
myself I have always believed that the geologists were more nearly correct 
than the physicists, notwithstanding the fact that appearances were so 
strongly against them. 
And now, at length, relief has come to the strained relations between 
the two parties, for the recent marvellous discoveries in physics show 
that concentration of matter is not the only source from which the sun 
may draw its heat. 
Radium is a substance which is perhaps millions of times more 
powerful than dynamite. Thus it is estimated that an ounce of radium 
would contain enough power to raise 10,000 tons a mile above the earth’s 
surface. Another way of stating the same estimate is this : the energy 
needed to tow a ship of 12,000 tons a distance of six thousand sea miles 
at 15 knots is contained in 22 ounces of radium. The ‘Saxon’ probably 
. burns three or four thousand tons of coal on a voyage of approximately the 
same length. Again, M.and Mme. Curie have proved that radium actually 
gives out heat,' and it has been calculated that a small proportion of 
radium in the sun would suffice to explain its present radiation. Other 
lines of argument tend in the same direction.? 
‘ Lord Kelvin has estimated the age of the earth from the rate of increase 
of temperature underground. But the force of his argument seems to be entirely 
destroyed by this result. See a letter by R. J. Strutt, Vatw7e, December 21, 1905. 
* See W. HE. Wilson, Nature, July 9, 1903; and G. H. Darwin, Wature, Septem- 
ber 24, 1903. 
