4 16 Professor Airy in reply to Mr. Ivory. 



to remind Mr. Ivory, that the equilibrium would not be dis- 

 turbed if the resultant of these attractions were a force ex- 

 jiressed by a function of the coordinates of the attracted point, 

 similar to the function expi^essing the pi'eviously-acting forces 

 (including the attraction), and that there does not therefore 

 appear to be any reason for saying that it must be evanes- 

 cent. 



These are my reasons for not admitting Mr. Ivory's new 

 equation. I have stated them plainly, but I hope not unci- 

 villy : if I am wrong, I shall be glad to have my errors pointed 

 out in the same manner. I trust that I shall not be exposed 

 to the charge of presumption for holding the opinion of La- 

 place and Poisson, in opposition to that of which Mr. Ivory 

 is (I believe) the sole advocate. 



But Mr. Ivory says that I misapprehend his conditions, 

 which he has always limited to the case of homogeneit}'. 

 When 1 wrote the note in question, I was perfectly aware that 

 the algebraical investigations which Mr. Ivory had founded 

 on his equation were confined to homogeneous fluids: but 

 I did not so clearly know that the reasoning was equally re- 

 stricted. I have since examined the reasoning with some at- 

 tention ; and I declare, that I cannot discover any part of it 

 which is not as applicable to heterogeneous fluids as to homo- 

 geneous fluids. Judging from my own feelings, I think that 

 the scientific world would be much obliged to Mr. Ivory, if he 

 would point out the parts of his reasoning which are not ap- 

 plicable to heterogeneous fluids. 



Mr. Ivory " consoles himself because he knows with the 

 certainty of demonstration, that my problem is not solved, and 

 cannot possibly be solved except by his theory." I console 

 myself by thinking that Mr. Ivory has not reasoned with his 

 usual accuracy upon a point which is somewhat abstruse, and 

 by believing that my problem is solved (as far as such a pro- 

 blem can be solved) without the assistance of Mr. Ivory's 

 equation. 



I had intended to confine my remarks to the offensive 

 note in which Mr. Ivory has treated me so unhandsomely 

 But as Mr. Ivory has in the preceding page mentioned an- 

 other point on which we are at variance, 1 will endeavour 

 to lay before your readers a more complete statement of the 

 argument than he has given. I think it proper to say, that I 

 have no reason whatever to complain of the terms in which 

 he has there mentioned my name. 



The first part of my paper (as "Mr. Ivory has correctly 

 stated) is employed in attempting to prove that Laplace's fun- 

 damental equation (il/cr, Cil. liv. iii. No. 10) is exactly de- 

 monstrated, 



