175 



Tlie numbers in the last column should vary as the cubes of those 

 in the first, or be as 1, 8, 27. If we deduct 10 grains from each 

 of them for the action of the weight of the wire depressing itself, we 

 shall have these numbers — 



90 710 2390 



dividing respectively by 1,8, and 27, 



90 89 SB'S 



Hence the mean result for M /'-^ for D = -25, or - = j};^, 



is nearly 89 grains, consequently, 



(100)3 

 and M = 89,000,000 grains. 



But a foot in length of the wire in question weighs 11 grains. 

 The equivalent modulus of elasticity is therefore very nearly 

 8,000,000 feet of the wire in question, which agrees closely with 

 the received numbers for steel-wire. 



2. On the Anthracite of the Calton Hill. By Dr Fleming. 



The occurrence of anthracite in this locality has been noticed and 

 recorded by several observers, who seem to have overlooked some of 

 its more remarkable peculiarities. At present, this mineral may be 

 detected in a series of anastomosing vertical veins of calcareous spar, 

 including, at the same time, angular poi-tions of the claystone 

 porphyry in which they are situate, on the upper north walk on the 

 north side of the Observatory. The anthracite occurs, 1. In 

 rounded, drop-like pieces, on which the calcareous spar has been 

 moulded, not unlike the colophonite of Norway. 2. In masses with 

 plane surfaces, apparently produced by the laminae of the surround- 

 inof spar. 3. In angular masses, with sharp edges, and a conchoi- 

 dal fractured surface. The drop-like pieces must have been solid 

 previous to the solidification of the spar, while the flattened masses 

 have yielded to the pressure of its crystallization. The angular 

 masses, however, which are the most numerous, occur crowded to- 

 gether, of different sizes, while the neighbouring fragments unequi- 

 vocally indicate, by their corresponding shape, that they had been 

 broken when in a hai-d state, and separated in the very spot they 

 now occupy, being suspended in the calcareous parts which afterwards 



