102 Mr. R. Moon's Reply to some Remarks of 



If we have three relations^ 



p=Moct), 



where the forms o^f\,f^,f^ are utterly unknown to us, the pre- 

 sumption is that 



p= funct. [p,v). 



This is the rule, to which there may possibly be exceptions; but 

 those who rely on the exceptions must prove them to exist. 



The only restriction upon the forms of f^, /g, /a is that they 

 shall satisfy the equation 



0-4!^ 4.1 ^ 



where oo is the ordinate of the point of rest of a particle, y the 

 ordinate at the time t, and D the density of equilibrium. Can 

 my opponents prove, what Mr. Strutt in effect affirms that they 

 maintain, viz. that the forms of/^/g, /g are so moulded by this 

 condition "that, when you eliminate o: and t, v will disappear 

 with them'' ? 



That they have never attempted to do so, analytically, is cer- 

 tain ; and that any attempt of the kind must have resulted in 

 failure is equally so. The only experimental proof upon which 

 my opponents can rest their conclusion is Mariotte's, or, as Mr. 

 Strutt prefers to call it, Boyle's law. Let us see, therefore, the 

 degree of support which this affords them. 



Mr. Strutt has " never heard " that the law " was regarded 

 otherwise than as a clear result of experiment.'"' 



Surely Mr. Strutt must be aware that Boyle's law only pre- 

 dicates the rate of pressure in an elastic fluid when in equili- 

 brium, that every experiment upon which the law rests, down 

 to those of Begnault, is a statical experiment and that neither 

 Mariotte, Boyle, nor any one else has ever so much as attempted 

 to prove experimentally the law which prevails when the fluid 

 is in motion. That the law holds when the fluid is in motion is 

 a pure assumption, and one which, with deference to Mr. Strutt, 

 I must continue to characterize as gigantic. 



That the law does not hold outside the limits within which it 

 was originally proposed I have proved irrefragably by the adduc- 

 tion of instances* (which might have been multiplied indefinitelv) 



* See Phil. Mag. S. 4. vol. xxxvi. p. 27. In a paper of mine, an abs- 

 tract of which appeared in the Proceedings of the Royal Society for 1862, 

 the subject is treated in considerable detail. I regret that in the case fir.-t 

 discussed the argument is so incorrectly stated in the abstract as scarcely 

 to be intelhgible. A further case of failure is pointed out in my Julc 

 paper. 



