342 



MAGNETIC METHOD 



[Chap. 8 



The double prism in it admits light from the outside and reflects the reading 

 up to the eyepiece, with which an ocular micrometer is used. The case is 

 provided with a copper mantle and is highly polished on the outside. In 

 the Ostermeier balance the arrangement is essentially the same as in the 

 Schmidt balance, except that the telescope is mounted horizontally on the 

 side of the box. Thi,^ places the instrument at greater distance from the 

 ground and minimizes terrain effects. The case is Ukewise highly polished 

 to reduce temperature interference. Watt's and Toepfer's balances differ 

 from the original Schmidt only in construction but not in principle. 

 Koulomzine's balance has a temperature-compensated magnetic system. 



In Koenigsberger's and Angen- 

 heister's balances, wire suspension 

 instead of knife edge support is used. 

 If Di is the magnetic, D2 the gravity, 

 and Ds the torsional couple, two 

 constructions are possible: (1) D2 

 may be so adjusted as to nearly 

 compensate Di , and the residual 

 may be compensated by the torsion 

 of the wire. In such cases the wire 

 needs to have only a small torsional 

 coefficient (1/6 to 1/10 of g). 

 (2) D2 may be made very small 

 and then may be additive or sub- 

 stractive to Di . In such a case, 

 Dz compensates Di — D^ or Di + D2 

 and the wire has to be fairly strong. 

 Koenigsberger has used the first, 

 Angenheister the second possibility. 

 The latter suspended a very light 

 magnetic system from heavy 

 tungsten monocrystalline wires. 

 The advantage of wire instruments 

 is that they may be used as 

 universal magnetometers if the 

 suspensions are strong enough. 



5. The Hoichkiss superdip^ is in- 

 tended primarily for measurements 

 of the total intensity and secondarily 

 for dip determinations as shown in 

 Figs. 8-27 and 8-28. A magnet rotates about a horizontal steel axle on 

 agate bearings in the plane of the magnetic meridian. It may be adjusted 



" N. H. Stearn, A.I.M.E. Geophysical Prospecting, 169-186 (1932). 



Fig. 8-27. Hotchkiss superdip. 



