264 
SUMMARY OF CURRENT RESEARCHES. 
screw, lias in it a long cutting-slot, one edge being sharp, the ether 
rounded off. The slot is opened or closed by means of a handle A 
attached to a rod passing down the interior of the bore to a hollow 
plunger 0. When A is pulled up, 0 is raised and the cutting-slot H 
opened. 
Fig. 59. 
A transverse section of the cutter is shown in F. E is a projection 
attached to the plunger for clearing the cutting-slot of any earth got 
during the sinking of the borer. In using the instrument, the slot is 
opened by pulling up A, the boring is resumed, and when the cavity 
contains sufficient earth, the slot is closed by pushing dow r n A and 
firmly fixing it by means of the thumb-screw B. 
