42 



'LAPIDARY 



seen separate mfy. 1322, -which serves for turning the wheel i. This bar is formed of 

 three iron plates n, o ; p, q ; and q, r (fig. 1322). The first is bent round at the point 

 'ii, to embrace the stud s; the second p q, is of the same breadth and thickness as the 

 first ; and the third, is adjusted to the latter with a hinge joint, at the point q, where 

 they are both turned into a circular form, to embrace the crank M. When all these 

 pieces are connected, they are fixed at the proper lengths by the buckles or square rings 

 1 1 1, which embrace these pieces, as is shown in fig. 1322. 



The stud s, seen \nfig. 1322, is fixed to the point v, by a wedge-key upon the arm p, 

 represented separately, and in perspective, in Jig. 1323. The labourer seizes the two 

 upright pegs or handles x x ; by the alternate forward and backward motion of his 

 arm, he communicates the same motion to the crank-rod, which transmits it to the 

 crank of the arbor M, and impresses on the arbor, and the wheel which it bears, a 

 rotatory movement. 



1323 1324 



Fig. 1324 shows piece-meal and in perspective a part of the lapidary's wheel-mill. 

 There we see the table c c, the grind plate i, whose axis is kept in a vertical position 

 by the two square plugs a a, fixed into the two summers by the wedges b b. On the 

 two sides of the wheel-plate, we perceive an important instrument called a dial, which 

 serves to hold the stone during the cutting and polishing. The instrument has received 

 lately important ameliorations, to be described in fig. 1325. The lapidary holds this 

 instrument in his hand, he rests upon the iron pins u u, fixed in the table lest he should 

 be affected by the velocity of the revolving wheel-plate. He loads it sometimes with 

 weights e e, to make it take better hold of the grinding-plate. 



Fig. 1325, shows an improvement made by one of the most expert lapidaries of 

 Geneva, whereby he cuts and polishes the facet with extreme regularity, converting it 

 into a true dial. Each of the two jaws bears a large conchoidal cavity, into which is 

 fitted a brass ball, which carries on its upper part a tube e, to whose extremity is 



"fixed a dial -plate ff, engraved with several concentric circles, divided into equal parts, 

 like the toothed-wheel cutting engine-plate, according to the number of facets 

 to be placed in each cutting range. The tube receives with moderate friction 

 the handle of the cement-rod, which is fixed at the proper point by a thumb-screw, not 



, shown in the figure, being concealed by the vertical limb d, about to be described. 



1325 1326 1327 



A needle of index g ti placed .with a square fit on the tail of the cement-rod, marks by 

 Jts points the divisions on the dial-plate /./. On the side m n, of the jaw A, there 

 is fixed by two screws, a limb d, forming a quadrant, whose centre is supposed to be 

 at the centre of the ball. The quadrant is divided as usual into 90 degrees, whose 

 highest point is marked 0, and the lowest would mark about 70 ; for the remainder of 

 the arc down to 90 is concealed by the jaw. The two graduated plates are used as 

 follows : 



When the cement-rod conceals zero or of the limb, it is then vertical, and serves 

 to cut the table of the brilliant; or the point opposite to it, and parallel to the table, 



