JULY 7, 1899. ] 
5. We are taught that gravity varies in- 
versely as the square of the distance. As 
the distance between any two particles is 
halved, their mutual attraction is raised 
fourfold. Perpetual halving would cause 
the attraction to mount up toward infinity. 
In the sun, then, there seems to bo this 
interesting combination : (1) a gaseous mass 
already above the critical temperature 
growing hotter and hotter by self-compres- 
sion and bound to grow hotter and hotter 
so long as it remains a gas; and it is bound 
to remain a gas until it falls below the 
critical temperature, which it cannot do 
’ while it continues to grow hotter; (2) a 
gravity that increases four-fold with every 
halving of distance and that is bound to 
increase so long as concentration continues, 
and concentration must continue while the 
substance is a gas and the gravitative pres- 
sure increases. 
What is the logical outcome of this kind 
of logic and this sort ofa combination? A 
geologist begins to grow dizzy contempla- 
ting such thermal possibilities. Why 
should not atoms, atomecules, and what- 
ever else lies below, one after another have 
their energies squeezed out of them; and 
the outer regions be heated and lighted for 
an unknowable period at their expense ? 
There was a time when the chemical 
theory of the sun’s heat was fairly satis- 
factory to the scientists of the day, but its 
inadequacy appeared in time. There fol- 
Yowed a period in which the meteoroidal 
theory of the sun’s origin was deemed ade- 
quate, but its defects soon became apparent. 
There has followed the contractional theory, 
the validity of which is perhaps not less 
questioned now than was the validity of 
the chemical and meteoroidal hypotheses in 
their day of acceptance, but, judging from 
the past, it may easily appear in the future 
that the Helmholtzian theory is inade- 
quate in some measure not unlike its 
predecessors. 
SCIENCE. 13 
But assuming, as we are wont to do, that 
the limits of our present knowledge are a 
definition of the facts, has the evolution of 
the sun been worked out with such definite- 
ness and precision as to give a determinate 
and specific history of its thermal stages 
from beginning to end? It is one thing to 
tell us, on the basis of the contractional 
theory, that the total amount of thermal 
energy originally potential in the system is 
only equal to so many million times the 
present annual output, but it is quite a dif- 
ferent thing to give a specific statement of 
the actual time occupied by the sun in the evo- 
lution and discharge of this amount of heat and 
to define its successive stages. It is with 
this actual history that we are specially 
concerned. The distribution of the com- 
puted heat in time may have been such 
hypothetically as to shorten the period of 
its expenditure not simply to 20 or 25 mill- 
ions of years, as indicated by Lord Kelvin, 
but to four or six millions of years as de- 
duced by Ritter.* On the other hand, the 
dealing-out of this amount of heat may 
hypothetically have occupied a period many 
times the 20 or 25 million years postulated. 
It seems altogether necessary to determine 
specifically the distribution of the heat in time 
before any approach to a satisfactory appli- 
cation to geological history can be made. 
The period of 20 or 25 million years named 
can have little moral guiding force until 
this problem is solved. But the literature 
of the subject shows an almost complete 
neglect of this consideration. While cer- 
tain of the physicists and astronomers have 
been instructing us ‘e superiore loco,’ they 
seem, with very rare exceptions, to have 
overlooked this vital factor in the case. 
Even in computing the sum-total of heat 
they have, for the most part, heretofore 
neglected the central condensation of the 
sun and in their computations have sub- 
* Astrophysical Journal, December, 1898 ; Journal of 
Geology, p. 93, No. 1, Vol. VII., 1899. 
