189 

 inner side ; within this frame the chisel plays, and 

 by it therefore is securely guarded. When the in- 

 strument is used, the chisel is drawn back to about 

 the extent represented in the foregoing wood-cut, 

 and into the space thus created is introduced the 

 projecting tooth, which consequently is encircled on 

 every side, and both before and behind is between 

 two cutting edges. The operator then firmly grasps 

 the handle, and applies to it such force as he cal- 

 culates will be sufficient to counteract the effect of 

 that blow which he is about to deliver. With a 

 hammer of adequate weight he now strikes the head 

 of the chisel, and the tooth flies off. The operation 

 is instantaneous, and so far it is an advantage ; but 

 beyond this is the safety which accompanies it. The 

 softer parts cannot be wounded, for the action is 

 strictly circumscribed in every direction, but the main 

 principle of the invention remains to be pointed out. 

 However great may be the force employed, no sen- 

 sible jar is communicated to the jaw. The writer 

 has held between his fingers a tooth which has been 

 divided with this instrument at a single blow, and 

 the shock was so trivial as to be unworthy of any 

 notice. The concussion is received upon the guard 



