268 MANIPULATION. 



even ctit. Mr. Shadbolt has lately done away with the disc 

 of wood, k, and made the tube, h, much larger at that part, 

 and given it an hexagonal figure, like that of D in fig. 172, for 

 the fingers to act upon. This plan answers as well as the 

 disc, and the instrument in consequence can be packed in a 

 much smaller compass. 



An instrument somewhat similar to the above, but less 

 costly, has for a long time been furnished by Mr. Darker, 

 who has also contrived one of a more complete kind, 

 which is fitted to the top of a box, and the central stem 

 is supported by an arm, by which it is kept in a vertical 

 position. The diamond is connected with an adjustable hori- 

 zontal arm, and is made to revolve by means of two pulleys 

 and a connecting band. The glass to be cut is laid upon a 

 piece of plate glass, blackened on its under smrface, which 

 forms part of the cover of the box, and the diamond is kept 

 away from the thin glass by means of a spring ; but in order 

 to render the instrument more effective, an extra finger and a 

 central stem, to keep the thin glass in place, are required. 

 On this account, the apparatus represented by fig. 172, as 

 contrived by Mr. Thomas Ross, wiU be found to perform more 

 readily. A bent arm of brass. A, is supported by means of a 

 square block of wood upon a base, B. Through the collar, 

 C, passes a stem, which is of octagonal figure at D for the 

 fingers, and cylindrical at E. Upon this latter part shdes a 

 spring box, F, having a piece of cork or India rubber at 

 its free extremity. An horizontal arm, G, supporting the 

 spring box, H, through which slides the stem, I, carrying the 

 bar, K, of the diamond, L, is capable of being adjusted for the 

 diameter of the cover by means of a screw. The use of the 

 instrument is obvious ; the glass is laid upon the foot, B, and 

 the proper size having been fixed on by means of the scale, M, 

 the stem, E, is pressed down upon the glass firmly by the 

 fingers applied at D. In order, however, to prevent the 

 prcssm-e from cracking the glass, the spring boxes, F and H, 

 have been employed, so that however much force be applied 

 at D, the diamond and central piece, F, only press upon the 

 glass by the force of the two springs contained in the boxes. 



