MAGNETIC METHODS 



145 



the standard field balance. The recording mechanism is located in the 

 upper part of the cylindrical housing and comprises : plate holder, flash- 

 light bulb, prism, moving plate holder, clock-drive mechanism. A re- 

 movable brass plate carries the magnetic system which is similar to that 

 of the standard magnetometer except that a prism is employed for deflect- 

 ing the light beam instead of a mirror. 



(A) (B) 



Fig. 60. — Askania continuous recording magnetometer. A, exterior view; B, interior view, a, plate 

 holder; b, flash-light bulb; c, prism; e, clock drive; /, support; g, lens; p, prism. 



The light from the bulb passes through a diffusing glass and a dia- 

 phragm with a point aperture. The image of the aperture is projected on 

 the photographic plate by means of the objective lens, the prism on the 

 moving magnetic system, and the fixed mirror. The fixed mirror receives 

 a portion of the light beam and reflects a continuously moving light spot 

 in a plane perpendicular to the plane of vibration of the magnetic system. 

 Like the fixed mirror which records the base-line, the counter-mirror is 

 fixed to a pivot rotated from a clockwork by a long arm carrying a 

 toothed segment. After the lapse of a given time interval, the toothed 

 segment is thrown out of gear and returns to its starting position. 



