576 



materials of an older building, which were used in the build- 

 ing of the church now in ruins. In the same way one of the 

 figures in the Museum, from the Dawson collection, appears 

 to have been built into the wall of the church where it was 

 found. Under such circumstances, the actual antiquity of 

 these curious figures is quite problematical. The subject 

 is a new one, and well deserving of the attention of antiqua- 

 ries, to whom this notice is submitted more as a suggestion 

 for consideration than as an opinion. The number of facts 

 known are few, and probably it may be premature to attempt 

 a generalization. 



April 22. 

 SIR Wm. R. HAMILTON, LL. D., President, in the Chair. 



Read, — a letter from the Secretary of the Lord Lieu- 

 tenant, presenting to the Academy the stones containing 

 the inscription from the old bridge of Athlone. 



Resolved, — That the thanks of the Academy be given 

 to His Excellency the Lord Lieutenant for his donation. 



The Rev. Professor Graves read a paper on the Alge- 

 braic Geometry of Curves traced upon given Surfaces. 



Let u = (p {x,y,isi) zzO he the equation of a surface re- 

 ferred to ordinary rectangular coordinates. Its complete 

 differential will be 



vdx -f- Qc?2/ 4- ^ds = 0. 

 Making 



X = -, and Y = -, 



R R 



Mr. Graves denominates x and y the normal coordinates of 

 a point on the surface. When they are known, the x, y, s 

 of the point are determined by the three equations 



