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Published online by Cambridge University Press: 17 January 2013
An argument which I had stated against the Huttonian Theory of the Earth, in so far as it relates to the operation of a central heat, was honoured some time ago with a reply by a distinguished Member of the Society. Respect for the opinion of Mr Playfair led me to consider attentively the reasoning he employed; and still feeling some confidence in the grounds on which the original argument rests, I propose to offer a few observations with regard to it. The question farther involves the consideration of the mode in which heat is distributed at the surface of the globe. This, when minutely investigated, presents a very perfect arrangement, by which the escape of caloric is prevented, while its equal distribution is more effectually attained; and the subject, under this point of view, may have some interest, independent of its relation to any controversial discussion.
page 412 note * I ought to remark, that this view of the constant existence of a central heat is not considered by all the defenders of Dr Hutton's system, as a necessary part of it, nor do they even regard it as a position which he himself maintained. They suppose the existence only of interior local heat, which may cease for a time, and be again renewed; and to this hypothesis the above argument does not so strictly apply. I must only add, that if even this view of the subject be adopted, much of the difficulty will still remain in its original force; it becomes liable, too, if I mistake not, to other objections peculiar to itself, equally important; and by adopting it, much of the beauty and unity of the system are lost. These seem to me to require the assumption of a central heat, or general reservoir of heat capable of extending its action to every part of the circumference, always existing, though not equally active in its apparent effects. It is to this view of the subject, consistent, I believe, with the original statement of the theory by Dr Hutton, that the argument applies. It is this which Mr Playfair admits, and on the admission of which, indeed, his reasoning is founded; and, strictly speaking, it is to his reasoning only that the observations in this paper are directed.
page 414 note * Transactions of the Society, vol. vi. p. 356.
page 418 note * If the sphere from the centre of which heat is supposed to be diffused, be not exposed to an unequal external source of heat, the heat will be communicated equally at its circumference to the incumbent atmosphere, and produce ascent and descent of the air, with little of that circulation of it from one part to another, which is the consequence of inequality of temperature at the surface of the solid. But still the same changes of capacity for heat will accompany the ascent and descent of the aerial mass, and the principal effect will be, to accumulate temperature at the surface. The condition is one, however, which need not to be taken into account, as it is one which has never existed with regard to our planet; and the argument remains as is stated above, while there is inequality in the distribution of heat over the circumference of the globe.
page 429 note * Lettres sur l'Origine des Sciences, p. 329.
page 433 note * Histoire de l'Astronomie Moderne, tom. ii. p. 726.
