60 Prof. Stokes on the Principles of Hydrodynamics. 



second memoir " On the Symbols of Logic/' &c. (Camb. Phil. 

 Trans., vol. ix.), with which I was not before acquainted. It 

 contains some investigations on certain applications of the theoiy 

 of probabilities, to which I ought to have referred. On the 

 subject of the credibility of testimony, my remarks appear to be 

 entirely consistent, so far as they go, with those of Professor De 

 Morgan. But from what he has said in p. 46 of his Memoir, I 

 am uncertain how far he would agree with my account of the 

 surprise excited by the accidental occurrence of a symmetrical 

 event. I shall not, however, enter further into that subject, as 

 enough has been said to make it intelligible what the question 

 is ; and any reader who shall have taken the trouble to follow 

 the reasoning of these papers and of Professor De Morgan's, 

 will be in a position to form his own judgement upon it. 



X. On the Principles of Hydrodynamics. 

 By Professor Stokes. 



To the Editors of the Philosophical Magazine and Journal:. ,\ 



Gentlemen, 



AS I do not see the remotest prospect of agreement between 

 Professor Challis and myself respecting the principles of 

 hydrodynamics, I think it time to fulfill the promise which I 

 have already made you of discontinuing the controversy. 



As, how^ever, I have seen nothing to shake the fii'mness of my 

 conviction, which I have already expressed, that the new equa- 

 tion is both unnecessary and untrue, I request that you will have 

 the goodness to record my protest against it. ( 



As I do not mean to continue the controversy, it would not 

 become me to discuss the contents of Professor Challis's last 

 communication. There is, however, one point in a former article 

 which I will briefly notice. In alluding to the experiments by 

 which it is (as I conceive) shown that compression does directly 

 raise the temperature of air, Professor Challis speaks of the heat 

 developed by compression as " being in the first moment of its 

 generation in the state of radiant heat.'' (Phil. Mag., S. 4. vol. i. 

 p. 407.) I do not know what Professor Challis's notions re- 

 specting the nature of radiant heat may be ; but according to my 

 own, I cannot understand how the heat developed by compres- 

 sion can be in the first instance in the state of radiant heat, or 

 if it were, how the observed effects could be produced. 

 I remain, Gentlemen, 



Yours sincerely, 

 Pembroke College, Cambridge, G. G. Stokes. 



June 12, 1851. 



