353 



x^p' sin {(it), (18) 



, , w y (^ + ^1) 



where p' = ^ — - * 



Cn 



These equations (17) and (18) evidently answer to a nutation of the 

 extremity of the axis, not in a circle, as when the rings are left out of 

 consideration, but in an ellipse whose semi-axes are (^) and (^'), and 

 the period of nutation 



MONDAY, MAY 25, 1863. 



The Yeey Eey. Chaeles Geayes, D. D., President, in the Chair. 



The Secretary read the following extract of a letter from E. J. Eoot, 

 Esq., to the Eev. Professor Haughton : — 



''Athlone, 3Iay 13, 1863. 



"On" the evening that I read my botanical paper at the Academy, 

 in reply to a question put to me by Dr. Osborne, I stated positively that 

 digitalis grows on the limestone of Burren. Since then I mentioned, 

 at the JSTatural History Society, of its occurring plentifully in the neigh- 

 bourhood of Mullingar, and also near this. Now, most of the Eloras 

 say of digitalis, that it does not occur in limestone districts. 



I find that candour demands of me to modify my statement a little. 

 Quite true that digitalis grows in Burren and in the midland counties ; 

 but it always grows on cherty limestone, or its dehris. I must allow that 

 I never saw either digitalis or heather growing on pure unsiliceous lime- 

 stone. In Burren there are many very siliceous beds of limestone, and 

 on them, in shady places, digitalis is by no means uncommon. Where 

 it occurs at Mullingar and in this neighbourhood, the beds are what has 

 been caUed calp, i. e. black earthy limestone, with bands of chert and 

 shale. 



" In fact, if one meets digitalis in a limestone district, they may feel 

 pretty certain that they are on, or very near to, the black calpy lime- 

 stone." 



The Pev. Samuel Haughton, M. D., read a paper " On the Chemical 

 and Mineral Composition of the Granites of Donegal." 



