Dip Meter (Hand held)

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Item Dip Meter (Hand held)
Item code
Description Randy Keller
Manufacturer Gurley Model 1GC 974B
Circa 1920
Donor Randy Keller
Location HGC
Serial number
Taxonomy IMG5039

(IMG5039) The Thomson-Thalen magnetometer is similar in construction to the Schmidt vertical balance. Anomalies in vertical intensity are not read in terms of deflection angles; they are compensated by changing the position of a deflecting magnet beneath the magnetic system. The differences in the inverse cubes of the observed readings are, therefore, proportional to the differences in intensities. The instrument shown in (Fig. 8-3028), contains a magnetic system consisting of two parallel cylindrical magnetic needles, mounted in a brass ring with like poles in the same direction. This ring is supported in agate, cup-shaped bearings by two pointed hardened steel screws. The arresting mechanism consists of another brass ring below the magnetic system. This ring carries four forks which lift the system off its bearings and press it firmly against two pillars, mounted to the upper part of the circular case. The compensating magnet is slightly below the system, North Pole up, and is attached to a long spindle, which ends at the top of the case. The spindle may be moved up or down by turning a keyed thumb-nut at the top of the case. This nut is graduated in centimeters, part of the threads being faced off for the divisions. The readings indicate the distance of the upper pole of the magnet from the magnetic system. The instrument is used at right angles to the magnetic meridian, placed in this direction by a compass mounted permanently on a long staff above the instrument. The deflection of the magnetic system is given by eq. (8-20), or tan 11 = (MZ – mga/mgd. Contrary to the Schmidt balance, 11 in this equation is very large, since mga is too small to compensate MZ. Compensation is effected by a magnet producing, in its normal position, a field which is only approximate for this instrument, as the magnet is very close to the magnetic system.

GSH IMG5039.jpg