On a new General Equation in Hydrodynamics. 157 



rain general ; stormy in Belgium. 13. Calm and foggy. 14. 

 Air in gentle motion; stormy in Ireland. 15. Stormy on the 

 south coast. 16. Hard wind general. 17. Snow at Shap. 

 18. Variable in strength. 19. Calm and fog at many places. 

 20. Frost general. 21. Calm and rain at some places. 22. Calm, 

 fog and frost. 23. Calm and fog. 24. Calm, fog and rain at 

 many places. 25. Variable in strength. 26. Calm. 27. Calm 

 general ; stormy in Belgium. 28. Air in gentle motion. 29. 

 Calm and fog. 30. Calm and fog. 31. Variable in strength. 



The mean of the numbers in the first column of the adjoining 

 Table is 29"652, and it represents that portion of the reading of 

 the barometer due to the pressure of the air ; the remaining por- 

 tion, or that due to the pressure of water, is 0'271 inch ; the sum 

 of those two numbers is 29*923 inches, and it represents the mean 

 reading of the barometer for the quarter endingDecemberSl, 1850. 



XIX. On the alleged necessity for a new General Equation in 

 Hydrodynamics. By G. G. Stokes, M.A., Fellow of Pem- 

 broke College, and Lucasian Professor of Mathematics in the 

 University of Cambridge. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



THE last Number of youi- IMagazine contains a communica- 

 tion from Professor Challis, which appears to be the com- 

 mencement of a series of articles devoted to the establishment 

 and application of a new general equation in hydi'odynamics. It 

 is now several years since Professor Challis first published this 

 equation. I have hitherto refrained from entering into any con- 

 troversy on the subject, though, having had occasion to refer to 

 Prof. Challis's investigations in a report '^'On recent Researches in 

 Hydi-odynamics*," 1 expressed my dissent from Prof. Challis's 

 ■\'iews,as I felt bound to do, in consequence of the thorough convic- 

 tion which I felt that the equation was inadmissible. The subject 

 has recently been taken up by others, who have attacked the new 

 equation, but I must confess that I have seen nothing in the 

 replies of Professor Challis that has tended to shake my original 

 conviction. 



The ])oints on which I entertain an opinion more or less op- 

 posed to that of Professor Challis are so various, that, were I to 

 enter fully into them all, the controversy thence likely to ensue 

 would occujjy in your pages a space altogether unreasonable, and 

 would probaldy come to nothing from its veiy unwieldincss. I 

 intend therefore to conduct the controversy on which, with youi" 



* Report of the british Association for 184(), p. 3. 



