96 



EXPLORATION GEOPHYSICS 



^ujum auup£/fs 



MACNtr JVf/fCSTING OiVICf 



'/CftOM£T£/f CL4MP 



UICROMSTER SCnCvt 



Fig. 28. — Horizontal and vertical sections of a C.I.W. compass- 

 variometer (Bauer, Peters, and Fleming, Carnegie Institution of Wash- 

 ington, Publication 175, Vol. V.). 



The usual method of measuring variations in H at different stations 

 consists in keeping the distance e fixed and observing the changes in i/^. 

 Ai/r at any station will depend on the initial (base station) value of y\i 

 and on the anomaly A// at the station. For a given variometer and given 

 base station value of y\i, the value of L\\i at any station will depend only 

 on the anomaly A// at that station. 



It is evident that, for a given value of the magnetic moment M of the 

 magnets, the sensitivity of the instrument depends on the value of \\i and of 

 e. For 1/^ = 60°, ^ = 6.5 cm., the sensitivity (AH for Ai/^^ 1°) is of the 

 order of 75 gammas. 



Inclination or Dip Determinations 



Dip Circle. — The dip angle which the total intensity makes with the 

 horizontal intensity is usually determined at magnetic stations by means 



