s cooling
been uniform? An affirmative answer to both these questions seems to be
necessary to the validity of the calculations on which Sir W. Thomson
lays so much stress.

Nevertheless it surely may be urged that such affirmative answers are
purely hypothetical, and that other suppositions have an equal right to
consideration.

For example, is it not possible that, at the prodigious temperature
which would seem to exist at 100 miles below the surface, all the
metallic bases may behave as mercury does at a red heat, when it refuses
to combine with oxygen; while, nearer the surface, and therefore at a
lower temperature, they may enter into combination (as mercury does with
oxygen a few degrees below its boiling-point) and so give rise to a
heat totally distinct from that which they possess as cooling bodies?
And has it not also been proved by recent researches that the quality of
the atmosphere may immensely affect its permeability to heat; and,
consequently, profoundly modify the rate of cooling the globe as a
whole?

I do not think it can be denied that such conditions may exist, and may
so greatly affect the supply, and the loss, of terrestrial heat as to
destroy the value of any calculations which leave them out of sight.

My functions as your advocate are at an end. I speak with more than the
sincerity of a mere advocate when I express the belief that the case
against us has entirely broken down. The cry for reform which has been
raised without, is superfluous, inasmuch as we have long been reforming
from within, with all needful speed. And the critical examination of the
grounds upon which the very grave charge of opposition to the principles
of Natural Philosophy has been brought against us, rather shows that we
have exercised a wise discrimination in declining, for the present, to
meddle with our foundations.

FOOTNOTES:

[39] On Geological Time. By Sir W. Thomson, LL.D. Transactions of the
Geological Society of Glasgow, vol. iii.

[40] The Theory of the Earth, vol. i. p. 173, note.

[41] Ibid. p. 281.

[42] Ibid. p. 371.

[43] The Theory of the Earth, vol. i. p. 200.

[44] The Theory of the Earth, vol. i. pp. 16, 17.

[45] The Theory of the Earth, vol. i. p. 223.

[46] Principles of Geology, vol. ii. p. 211.

[47] Principles of Geology, vol. ii. p. 613.

[48] "Man darf es sich also nicht befremden lassen, wenn ich mich
unterstehe zu sagen, dass eher die Bildung aller Himmelskoerper, die
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