91 



Mr. Graves, Fellow of Trinity College, mentioned the fol- 

 lowing theorem of his own, relative to confocal surfaces : — 



" If there be two confocal surfaces of the second order, 

 one of which is circumscribed by a cone whose plane of 

 contact touches the other surface in a certain point, the 

 normal at this point will pass through the vertex of the cone." 



A new rain-gauge was exhibited to the Academy, con- 

 trived by the Rev. Thomas Knox. 



The object of this instrument is to register the amount 

 of rain that falls when the wind is in different points. Its 

 construction is very simple. The water, — instead of descend- 

 ing from the reservoir directly into the tube of registry, — 

 passes through a lateral tube into an annular-shaped vessel, 

 divided into eight compartments, each of which terminates 

 below in a graduated glass tube. It is obvious, then, that 

 if the eight tubes be set to correspond with the cardinal and 

 intermediate points, and that the reservoir be made to re- 

 volve on a vertical axis by means of a vane, the direction of 

 which corresponds with that of the lateral tube, the object 

 proposed will be attained. Mr. Knox has preferred to make 

 the reservoir fixed, and the system of tubes moveable ; but 

 the result is obviously the same. 



The Academy then proceeded to consider the amend- 

 ments of the by-laws, proposed by the Council ; and, after 

 some discussion, it was resolved that there be an adjourned 

 meeting at two o'clock, on Friday the 30th of June, for the 

 further consideration of the subject. 



DONATIONS. 



A Copy of the Ordnance Survey of the County of Lei- 

 trim, in 40 sheets. Presented. by Lieutenant-Colonel Colby. 



Proceedings and Ordinances of the Privy Council of Eng- 

 land, Vols. VI. and VII. Presented by the Commissioners 

 of the Public Records. 



