Mr. Ivory's Remarks on M. VoissovlS Memoir. 331 



recedes from the axis, the rotatory velocity will decrease ; and 

 whenever it returns in a contrary direction, the same velocity 

 will increase; and ultimately, in the state of equilibrium, the 

 rotation actually remaining, will depend upon the nature of 

 the figure of equilibrium, and the proportion of the two forces 

 urging the particles. Although we suppose that the rotation 

 in equilibria is small, yet we cannot infer that the rotatory ve- 

 locity originally imprest, was likewise small. On the contrary, 

 ii the rotation were very small, and at the same time the figure 

 very oblate, we must conclude that the primitive rotatory force 

 was just within the limit required to dissipate the fluid. What 

 particular figure the fluid i7i equilibrio will have, we do not 

 now inquire ; but we are entitled to infer that there is only 

 one such figure for every degree of rotatory force originally 

 communicated to the fluid sphere. This is incompatible with 

 the usual theory ; and it refutes M. Poisson's argument. But 

 it is very consistent with my system ; nay, it can be consistent 

 with no other ; for, if there be but one figure, that, it is cer- 

 tain, must be an oblate elliptical spheroid. 



But perhaps all this concurring evidence may not be sufti- 

 cient to overcome the prejudice in favour of a spendid theory, 

 very powerfully upheld from various motives. I hope soon to 

 lay other more direct demonstrations before the public. But 

 I have observed on a former occasion that this branch of 

 science is discouraged and undervalued ; and a passage in the 

 last Quarterly Journal of Science*, written by a modern F.R.S. 

 corroborates what I ventured to allege. The theory of the 

 figure of the planets originated with Newton and Huygens : it 

 has been the subject of incessant discussion for a century ; it 

 has been attended with greater difficulty, and has occasioned a 

 greater number of memoirs, than any other branch of the system 

 of the world. It has occupied the attention of Clairaut, Mac- 

 laurin, D'Alembert, La Grange, Legendre, Laplace, and Pois- 

 son : and I shall not easily be brought to think slightly of the 

 speculations of such men, even when compared with the bust- 

 ling activity in philosophical pursuits that now prevails. One 

 can hardly help thinking that, in order to make amends for 

 past remissness, the indefatigables of the present day are now 

 determined to take Nature by storm. In allusion to what is 

 said, in the passage cited, respecting the studies to which I 

 have been attached, but in allusion to that only, I shall close 

 these remarks with declaring, that I am prouder of the stric- 

 tures of such a critic, than I should have been of his praise. 

 April 4, 1827. J. IvoRY. 



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