the Hon. J. W. Strutt on Gaseous Pressure, 103 



ia which the law signally fails. One of these is so simple, and 

 to my mind so conclusive, that I shall repeat it here. 



Suppose the tube A B to be filled with air which at the time 

 t is destitute of velocity; the density of the air in AC being at 



the same time uniform and equal to J), while that in B C is uni- 

 form and equal to 2D, the common boundary of the two portions 

 of air being an imaginary plane through C perpendicular to the 

 axis of the tube. Under these circumstances, according to Ma- 

 riotte's law, the pressure at the time t of the fluid in B C on the 

 fluid in A C will be double the pressure of the fluid in A C on 

 B C j i. e, the supposition of the truth of Mariotte's law in this 

 instance contradicts the universally received principle that action 

 and reaction are equal and opposite. 



I can assure Mr. Strutt that I am not so profoundly ignorant 

 of the history of the subject as ever to have supposed that Ber- 

 noulli, Lagrange, or Euler had considered it in the way in which 

 I have done. Beset with the analytical difficulties attendant 

 upon the theory, believing (erroneously) that the law of pressure 

 was beyond the scope of their analysis, and was only capable of 

 being determined by experiment, those great writers adopted 

 tentatively and not unnaturally the only experimental law of pres- 

 sure which any one had ever heard or thought of, or indeed was 

 ever likely to obtain — that, namely, of Mariotte or Boyle. That 

 they did so was fortunate ; and benefit flowed from their processes, 

 notwithstanding the error which they involved. But persistence 

 in that error can only work evil, by closing against mathematical 

 investigation a field of inquiry admirably adapted for its exercise, 

 and from its application to which the most brilliant results may 

 be anticipated. 



In conclusion I ask for some inteUigible reason why the ex- 

 pressions for the pressure, velocity, and density given in my 

 June paper are to be rejected. They satisfy the equation of 

 motion, the only test to which they can be subjected possessing 

 the slightest claim to authority. I must hope that eventually 

 they will satisfy Mr. Strutt. 



6 New Square, Lincoln's Inn, 

 July 4, 1872. 



