Professor Clifford proceeds to explain that Thomson’s formulæ only give a limit to the heat history of, say, the earth’s crust in the solid state. We are led back to the time when it became solidified from the fluid condition. There is discontinuity in the history of the solid matter, but still discontinuity which is within our comprehension. Still further back we should come to discontinuity again, when the liquid was formed by the condensation of heated gaseous matter. Beyond that event, however, there is no need to suppose further discontinuity of law, for the gaseous matter might consist of molecules which had been falling together from different parts of space through infinite past time. As Professor Clifford says (p. 481) of the bodies of the universe, “What they have actually done is to fall together and get solid. If we should reverse the process we should see them separating and getting cool, and as a limit to that, we should find that all these bodies would be resolved into molecules, and all these would be flying away from each other. There would be no limit to that process, and we could trace it as far back as ever we liked to trace it.” Assuming that I have erred, I should like to point out that I have erred in the best company, or more strictly, being a speculator, I have been led into error by the best physical writers. Professor Tait, in his *Sketch of Thermodynamics*, speaking of the laws discovered by Fourier for the motion of heat in a solid, says, “Their mathematical expressions point also to the fact that a uniform distribution of heat, or a distribution tending to become uniform, must have arisen from some primitive distribution of heat of a kind not capable of being produced by known laws from any previous distribution.” In the latter words it will be seen that there is no limitation to the laws of conduction, and, although I had carefully referred to Sir W. Thomson’s original paper, it is not unnatural that I should take Professor Tait’s interpretation of its meaning.[21] [21] Sir W. Thomson’s words are as follows (*Cambridge Mathematical Journal*, Nov. 1842, vol. iii. p. 174). “When *x* is negative, the state represented cannot be the result of any *possible* distribution of temperature which has previously existed.” There is no limitation in the sentence to the laws of conduction, but, as the whole paper treats of the results of conduction in a solid, it may no doubt be understood that there is a *tacit* limitation. See also a second paper on the subject in the same journal for February, 1844, vol. iv. p. 67, where again there is no expressed limitation.