Chap. 8] 



MAGNETIC METHOD 



357 



and horizontal, vertical, and total intensity. These applications will also 

 be discussed in detail below. With perfection in earth inductor tech- 

 nique, it is quite possible that the combination of elements selected for 

 magnetic regional surveys may undergo considerable revision. On the 

 other hand, a simple magnetometer based on the balance principle may 

 easil}^ be substituted for the dip circle, so that a complete determination of 

 the magnetic field would consist of measurements of declination, horizontal 

 intensity (as measured at this time), and vertical intensitj^ 



8-35c 



American Aahania Corp. 



836d 



Fig. 8-35c. Magnetic theodolite with oscillation box attachment. 

 Fig. 8-35d. Magnetic theodolite with inductor attachment. 



1. Magnetic theodolites generally consist of a transit base with horizontal 

 circle and horizontal telescope, to which may be fastened an attachment 

 with standards, telescope, and vertical circle for astronomic observations. 

 For the determination of the magnetic meridian, a small case with short 

 magnetic needle, generally suspended in jewels and provided with a re- 

 flecting mirror, is used with the horizontal telescope. For oscillations, a 

 wooden box attachment with torsion tube and thread suspension is substi- 

 tuted for the declinator case. Deflection observations are made with the 

 declinator needle, and two bars with deflecting magnets are attached to 



