ON CUTTING GLASS. 



269 



As soon as a complete circle is marked by the diamond point, 

 the fingers are removed, and the stem is lifted from the glass 

 by the heliacal spring. By this instrument, as by Mr. Shad- 

 bolt's, the glass to be cut is firmly fixed in the centre, and on 

 this account a piece a little larger than the circle to be cut is 

 only required. 



Fig. 172. 



