350 



MAGNETIC METHOD 



[Chap. 8 



'^^,-^0 



Fig. 8-31. Action of Kohlrausch deflection 

 magnetometer. 



field will turn the needle in the E-W 

 direction. After this adjustment 

 has been made in a normal field, 

 everything is left so adjusted, and 

 at another locality, after the merid- 

 ian has been determined without 

 the deflectors, the angle which the 

 needle makes with the E-W position 

 is observed. If the field of the 

 deflectors is F and if its component 

 in the S direction is Hi and in the 

 E direction H2 , (see Fig. 8-31), 

 then — Hi = F cos (p and H2 = F 

 sin if. If, at a base station, the — 

 needle is so adjusted that the 

 needle points directly E-W, Ho = 

 — Hi , or Ho = F cos (p. There- 

 fore, H2 = Ho tan (p. At a locality 

 where Hi 5^ Ho , the deflection 77 

 from the E-W direction is given by 



tan 7j = 



Hi — Ho 



Hq tan (p ' 



(8-41) 



Schmidt's compensation magneto- 

 meter is likewise designed for the de- 

 termination of horizontal intensity 

 by deflection, and the deflection 



in position. The pedestal car- 

 ries two deflecting magnets 

 which may be rotated horizon- 

 tally on a turntable into posi- 

 tions 30° west or 30° east of 

 north. The north poles of the 

 magnets are toward north, and 

 the distance of the compass 

 from these deflectors is so ad- 

 justed that the north-south 

 component of the deflector 

 field compensates the normal 

 horizontal intensity of the 

 earth's field. Then the E-W 

 component of the deflector 



CompeJiiator 



Fig. 



Compensator 



8-32. Action of Schmidt compensa- 

 tion horizontal magnetometer. 



