XX x PREFACE TO THE SECOND EDITION. 



present order of nature at some definite point of time, 

 which might be calculated." 



Professor Clifford proceeds to explain that Thomson's 

 formulae 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 farther 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 melecules, 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 Ther- 

 modynamics, 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 distribu- 

 tion 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 



