PREFACE TO THE SECOND EDITION. xxxi 



that I should take Professor Tait's iuterpretion of its 



meanng. 1 



In his new work On some Recent Advances in Physical 

 Science, Professor Tait has recurred to the subject as 

 follows : 2 " 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 con- 

 duction of heat [in a solid body] leads to formulae 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 



1 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 tempera- 

 ture which has previously existed." There is no limitation iii 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 ex- 

 pressed limitation. 



2 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. 



