788 



PEEPAKATION OF FOSSIL SECTIONS 



also a fitting mortar. The mortar should be made of an old steel die, 

 if accessible ; if not, a mass of steel, slightly conical, the base of which 

 ought to be 2 inches in diameter, and the upper part 1^ inch. A 

 cylindrical hole is now to be turned out in the centre, of f ths of an inch 

 diameter, and about 1 inch deep. This, when hardened, is the mortar; 

 for safety it may be annealed to a straw colour. The pestle is merely 

 a cylinder of steel, fitting the hollow mortar but loosely, and having 

 a ledge or edging of an eighth of an inch projecting round it, but 

 sufficiently raised above the upper surface of the mortar, so as not to 

 come in contact while pounding the diamond. The point of the pestle 

 ought only to be hardened and annealed to a straw colour, and should 

 be of course convex, fitting the opposing and equal concavity of the 

 mortar. The purpose of the projecting ledge is to prevent the smaller 

 particles of diamond spurting out when the pestle is struck by the 

 hammer. 



Mr. Bryson has contrived an instrument for slitting fossUs. The 



instrument is placed on the table of a common lathe, which is, of 

 course, the source of motion. (Fig. 955.) It consists of a Watt's 

 parallel motion, with four joints, attached to a basement fixed to the 

 table of the lathe. This base has a motion (for adjustment only) in 

 a horizontal plane, by which we may be enabled to place the upper 



Kg. 955. Mr. Bryson's Instnunent for slitting fossils. 



