444 Professor Airy in reply to Mr. Ivory. 



which I paid to Mr. Ivory's. This is merely to account I'or 

 the introduction of the note. What foundation Mr. Ivory 

 can find for the charges of " injury on the authority of mere 

 assertion," " flippancy," and " supercihous importance," I 

 cannot imagine. I have simply stated my difference of opinion 

 from Mr. Ivory on a point whicli I was unable, from the na- 

 ture of the paper, to explain at greater length. The note is 

 now before your readers ; and I appeal to them whether I 

 have said any thing which can justify the use of such expres- 

 sions. Upon the whole, I think that I have reason to com- 

 plain of the terms in which Mr. Ivory has mentioned me, as 

 most improper, and most unworthy of the respect which a 

 gentleman ought to have for himself, as well as for any other 

 who claims that title. 



The only probable cause for Mr. Ivory's anger, independent 

 of our difference of opinion, appears to be my omission of 

 the reasons for that difference of opinion. The cause of that 

 omission 1 have explained: but that Mr. Ivory may have for 

 the future no ground of complaint, I shall state here my rea- 

 sons for disagreeing with him. Mr. Ivory's opinion was first 

 published in the Phil. Trans, for 1824, p. 101—108; but he 

 has explained it in nearly the same terms in the Philosophical 

 Magazine for July 1826. I shall request your readers, there- 

 fore, to refer to page 4 of that Number ; and I shall begin 

 my remarks at line 25. By the common theory it is known 

 that if the forces which act on a fluid satisfy a certain equation, 

 any level surface {couclie de niveau) may, by the removal of a 

 part of the fluid, become the external surface of the remaining 

 fluid which is still in equilibrium. But this is true as a general 

 proposition only when the forces are expressed by the same 

 functions of the coordinates, whether the quantity of fluid be 

 great or small. It appears then, from the common theory of 

 fluids, that Mr. Ivory's proposition advanced in the sentence 

 beginning in line 25, is certainly true, if there be no mutual 

 attraction of the particles ; but is not certainly true, if there be 

 such attraction. It may happen, and in the particular case of 

 which he treats it does happen, to be true, when the mutual 

 attraction is taken into account, but this is quite accidental. 

 The two following sentences are elucidations of the preceding: 

 the latter of them is of course to be taken with the same re- 

 strictions as that of which I have treated ; namely, it is to be 

 supposed that the particles have no mutual attraction. With 

 this supposition the reasoning of the next sentence, which 

 depends entirely on the existence of attraction, falls to the 

 ground. And after much consideration I am quite unable to 

 see any force in the reasoning upon which I have commented. 



Whatever 



