THE DIAMOND DRILL. 459 



has been invented for cutting holes in granite and other 

 hard rocks. It is called the Diamond Drill, because its tip is 

 armed with uncut diamonds. 



It is necessary that the diamond should not be cut, as the 

 natural edges are needed. A glazier's diamond, for example, 

 is always set as it came out of the mine. The stories that are 

 told about cutting out panes of glass with a diamond ring are 

 all absurd. A diamond, when it has once passed through the 

 hands of the jeweller, cannot cut glass. It can scratch glass, 

 but not one whit better than a flake of ordinary flint. 



It is found that the Diamond Drill works with wondrous 

 rapidity, cutting away the stone with ease, and suffering 



BOBEB OP CE8TBU8. DIAMOND-HEADED BOREB. 



scarcely any damage itself. The tube to the end of which the 

 diamonds are fixed is generally made in telescopic fashion, so 

 as to allow it to penetrate deeply into the rock, without the 

 necessity of shifting the machine by which it is turned. I 

 need hardly say that its rate of speed is very great indeed. 



OUR old friend, the Gad-fly, again affords an example of a 

 parallel. 



The ovipositor is tubular, telescopic, and furnished at the 

 top with five little hard, sharp, scaly knobs, which act the 

 same part as the diamonds of the mining tool. Even the scoop- 

 like shape of the tip, and the telescopic shaft, are almost iden- 

 tical in both instances. 



