Kant asserted that the processes of combination of surrounding

cold materials would generate heat, and, therefore, that the
resulting planetary masses would assume the liquid form; that
Jupiter and Saturn are now in the liquid state; and that all
the planets will ultimately become cold and solid
Kant asserted that the processes of combination of surrounding
cold materials would generate heat, and, therefore, that the
resulting planetary masses would assume the liquid form; that
Jupiter and Saturn are now in the liquid state; and that all
the planets will ultimately become cold and solid. This is in
fair agreement with present-day opinion as to the planets, save
that modern astronomers go further in holding that the outer
strata of Jupiter and Saturn, likewise of Uranus and Neptune,
down to a great depth, must still be gaseous. In 1785, after
the principle of heat liberation attending the compression of a
gas had been announced, Kant supplemented his statement of 1755
as to the origin of the Sun"s heat. He attributed this to
gravitational action of the Sun upon its own matter, causing it
to contract in size: he said the quantity of heat generated in
a given time would be a function of the Sun"s volumes at the
beginning and at the ending of that period of time. This is
substantially the principle which Helmholtz rediscovered and
announced in 1854, and which is now universally accepted--with
the reservation of the past ten years, that radioactive
substances in the Sun may be an additional factor in the
problem.