In his new work *On some Recent Advances in Physical Science*, Professor Tait has recurred to the subject as follows:[22] “A profound lesson may be learned from one of the earliest little papers of Sir W. Thomson, published while he was an undergraduate at Cambridge, where he shows that Fourier’s magnificent treatment of the conduction of heat [in a solid body] leads to formulæ for its distribution which are intelligible (and of course capable of being fully verified by experiment) for all time future, but which, except in particular cases, when extended to time past, remain intelligible for a finite period only, and *then* indicate a state of things which could not have resulted under known laws from any conceivable previous distribution [of heat in the body]. So far as heat is concerned, modern investigations have shown that a previous distribution of the *matter* involved may, by its potential energy, be capable of producing such a state of things at the moment of its aggregation; but the example is now adduced not for its bearing on heat alone, but as a simple illustration of the fact that all portions of our Science, especially that beautiful one, the Dissipation of Energy, point unanimously to a beginning, to a state of things incapable of being derived by present laws [of tangible matter and its energy] from any conceivable previous arrangement.” As this was published nearly a year after Professor Clifford’s lecture, it may be inferred that Professor Tait adheres to his original opinion that the theory of heat does give evidence of “a beginning.” [22] Pp. 25–26. The parentheses are in the original, and show Professor Tait’s corrections in the verbatim reports of his lectures. The subject is treated again on pp. 168–9. I may add that Professor Clerk Maxwell’s words seem to countenance the same view, for he says,[23] “This is only one of the cases in which a consideration of the dissipation of energy leads to the determination of a superior limit to the antiquity of the observed order of things.” The expression “observed order of things” is open to much ambiguity, but in the absence of qualification I should take it to include the aggregate of the laws of nature known to us. I should interpret Professor Maxwell as meaning that the theory of heat indicates the occurrence of some event of which our science cannot give any further explanation. The physical writers thus seem not to be so clear about the matter as Professor Clifford assumes. [23] *Theory of Heat* 1871, p. 245.