12 Mr Glaisher, On a formula of Cauchys. [Nov, 6, 



is due to Professor Cayley, and was communicated by him to the 

 Meeting after the reading of this paper, 



We have 



Put 



and the integral 



1 1 



= - fiy) dx, + \ f{y) dx^ 

 Jo Jo 



f(y){dx^ - dxj = / /(v/) dy, 



for X, + x„ = 0, 



so that 1 — XjX^ = 0, 



whence x^ — Xj^ = y, and dx^ — dx^ = dy. 



(2) Professor T. M^K. Hughes, On a Series of Specimens 

 illustrating the Formation, Weathering, and Fracture of Flint: 

 with Note hy Professor Stuart. 



Peofessor Hughes exhibited three series of specimens in 

 illustration of the mode of (1) formation, (2) weathering, ■ and 

 (8) fracture of flint, the first two being selected chiefly with a 

 view to the last. 



He produced proofs that the supposed faulted and re-cemented 

 flints were generally only flint that had irregularly replaced jointed 

 chalk, the formation of the flint being arrested by the joints. In 

 the case of the banded flints he exhibited and distinguished two 

 kinds — one in which infiltration had taken place all round the 

 outside, often a good test of the drift origin of certain fragments ; 

 and the other in which a difference of texture, due generally 

 to some included organism, had determined and limited the 

 area over which infiltration had produced bands of colour. He 

 pointed out that these differently coloured included portions, whe- 

 ther banded or not, affected the fracture, as they also depended 

 upon the texture of the flint, but that the bands themselves had 

 little or no influence upon the fracture. 



