Chap. 8] 



MAGNETIC METHOD 



339 



(5) Adjust eyepiece and mirror until scale is in focus and evenly lighted. 



(6) Take a number of readings; arrest and release system between read- 

 ings. (7) If necessary, use auxiliary magnets. (8) Read and note time 

 and temperature. (9) Clamp magnetic system. Push in safet}^ lock. 

 (10) Dismantle station; avoid jarring instrument when placing it into 

 case. Calculation forms for the horizontal magnetometer (Table 42) are 

 virtually identical with those for the vertical magnetometer except that 

 readings are entered for one operating position only and that a column for 

 vertical intensity correction is added : 



Table 42 

 FIELD RECORD 



OFFICE RECORD 



3. In Haalck's universal balance the magnetic system consists of a 

 "magnetic cross". Horizontal and vertical blades are attached to an 

 aluminum cube which carries a mirror on its side whose deflections are 

 observed by means of a telescope with an autocollimational system. The 

 magnets are fastened to one side onlj^ for purposes of temperature com- 

 pensation. Declination and vertical and horizontal intensit}^ may be 

 measured with this instrument. For this purpose two additional deflector 

 magnets are provided, one mounted above at an angle of 45 degrees (at 

 right angles to the imaginary magnetic axis of the system), the other 

 below in horizontal position. The oblique magnet is used in horizontal 

 intensity measurements; the horizontal magnet in vertical intensity de- 

 terminations. The latter magnet is permanent while the oblique magnet 

 may be taken out, changed in distance, and reversed in polarity. 



With reference to Fig. 8-26, the gravity couple is the same as in the 

 vertical magnetometer, or Do = —mg sin i (a cos 8 — d sin d). The 

 magnetic couple follows from eq. (8-16) by replacing the magnetic cross 



^^ For illustrations, see H. Haaick, Die magnelischen Verfahren der angewandten 

 Geophysik, Fig. 72, Borntracger (Berlin, 1927). 



