CORE ORIENTATION 



89 



an inertia motor is adopted. This is a heavy solid lead 

 rotor 36 on a vertical shaft 37 suitably borne in bearings 

 38 and 39. It is so made that it will lag behind the rotation 



FiG.l 



Plate VI. — Hanna's inertia-rotor apparatus. 



speed of the drill, thus continuing to rotate some time after 

 the latter, owing to its momentum. On shaft 37 a worm 

 gear 40 is engaged by a toothed projection 41 on a verti- 

 cally movable rod 42 supported in frame 19. As worm 

 gear 40 rotates, with respect to rod 42 and its lug 41, rod 42 



