352 



MAGNETIC METHOD 



[Chap. 8 



magnetometer is permanently mounted above the magnetometer. The 

 vertical intensity is observed in the customary manner by a telescope 

 mounted on the side of a box; the horizontal intensity is observed as in 

 the Kohlrausch magnetometer; and the declination is determined with the 

 compass alone. 



The Wilso7i compas& attachment is used witli a Brunton compass, at an 

 angle of 30° in the same manner as a Dahlblom sine arm.^^ 



Fig. 8-33. Cardan suspension magnetometer. 



The Cardan suspension magnetometer, designed by the author, is a 

 vertical-intensity magnetometer similar to a Dahlblom pocket magne- 

 tometer, the comparison force beirig the torsion of a helical spring. The 

 magnetic system is so suspended that the axis of revolution coincides as 

 nearly as possible with its center of gravity. One end of the helical spring is 

 attached to the magnetic system, and the other end is fastened to a movable 

 arm which may be rotated about a horizontal axis by turning a pointer on a 



« Illustration in A.A.P.G. Bull., 1392 (Nov., 1931). 



