118 



EXPLORATION GEOPHYSICS 



Each station reading of a Hotchkiss Superdip magnetometer involves the fol- 

 lowing steps : 



(1) Set up the tripod and level the mounting plate. 



(2) Place the compass on the mounting plate. Orient the plate in its proper 

 relation to the earth's magnetic meridian, and clamp it. 



(3) Remove the compass to a safe distance (20 feet or more) and mount the 

 magnetometer. 



(4) Move the north pole of the magnet to the zero position on the circular scale. 



(5) Carefully lower the swinging assembly to the agate edges and note the end of 

 the swing. (The reading taken is the position of the north pole of the magnet relative 

 to the circular scale at the end of the swing.) 



(6) Clamp the swinging assembly and record the reading, temperature, time, and 

 location of the station. 



Figure 43 also shows the average sensitivity of dip needles. This sensi- 

 tivity is comparable to the Superdip, when S = 18>4°. As the value of 

 ^ is decreased, the sensitivity of the Superdip increases. 



A profile run with a Superdip instrument is given in Figure 44. The 

 line of profile was N 15° W, from a point two miles north of Amarillo, 

 Texas, to the north line of Potter County in the same state. The Potter 

 County fault and the Amarillo buried granite ridge were crossed. The 

 Superdip was set with a value for 2 of about 2°, which gave a working 

 sensitivity about 37 times that of an ordinary dip needle.f 



2z 

 »-o 



3000- 

 2000- 

 1000- 



,,, V ''"red BE'0i",~s'A'LT' 0.\' 



re'd'bVds-,' siLT-\ - / "\' > jd:oy.psVm;:-^ - .\ 



POTTER COUNTY FAULP 



Fig. 44. — Magnetic profile with Hotchkiss Superdip 

 Magnetometer across the Buried Granite Ridge in the 

 Texas Panhandle. (After Stearn.) 



Schmidt-type Field Magnetometers 



The most widely used field magnetometers are those of the general 

 type originally manufactured by the Askania Werke, of Berlin, Germany. 

 It is significant that the beginning of the art of magnetic prospecting as 

 practiced today dates from 1915 with the development, by Adolph Schmidt, 

 of a portable magnetometer with which small magnetic anomalies could 

 be measured rapidly. 



t N. H. Stearn, A.I.M.E. Geophysical Volume, 1932, p. 189. 



