94 



we can find points and tangent -planes ad libilum, by the follow- 

 ing construction : — Take in the focal conic two diametrically 

 opposite points ; with one as centre, and twice the distance 

 from it to the extremity of the perpendicular axis as radius, 

 describe a sphere. Through the other point draw a plane, 

 normal to the focal conic ; it will cut the sphere in a certain 

 circle. Connect any point in this circle with the two points on 

 the focal conic, and at the middle point of the line connecting 

 it with the second point draw to it a perpendicular plane. 

 This is a tangent plane to the surface, and the point where 

 it cuts the first connecting line is a point on the surface. 



Another mode of generating the surface is easily derivable 

 from (7). 



Mr. Petrie gave an account of some ancient Irish inscrip- 

 tions of the sixth century, found in the island of Arran. 



Dr. Kane made some remarks on the Theory of Types. 



DONATIONS. 



Transactions of the TMerary and Historical Society of 

 Quebec. Vols. I. and II. ; and Parts 1 — 4 of Vol. III. Pre- 

 sented by the Society. 



Report of the Directors of the Chamber of Commerce at 

 Manchester on Import Duties. 1 1th March, 1841 . 



Report of the Select Committee of the House of Commons 

 on the Import Duties. 



Proceedings of a Meeting of Members of the House of 

 Coinmons, held at the Thatched House Tarern, St. Jamcs's- 

 street, on the 20lh February, 1841. Presented by Joseph 

 Hume, Esq., M.P. 



