1396 JOHN H. WILSON 
of about 70 gammas from the mean. In practice it has been found that 
the instrument does not give satisfactory results on anomalies of less 
than 250 or 300 gammas. 
The instrument is, therefore, applicable to investigation of larger 
anomalies. It gives fair results over the larger anomalies found in oil 
work, over basic dikes, and over magnetic ore bodies. 
The instrument is so designed as to work in a range from 5,000 to 
100,000 gammas absolute horizontal intensity. Without use of magnets 
of different strength, the instrument could not be used in regions where 
the intensity fell below 5,000 gammas or rose above 100,000 gammas. 
It is not recommended that petroleum geologists use the instrument 
for regular reconnaissance work. It is best adapted to horizontal inten- 
sity work on large vertical anomalies which have already been located 
and to the investigation of igneous intrusions. 
Mining geologists should find the instrument of aid in the tracing 
of some types of dikes, the limits of intrusive bodies, and the investiga- 
tion of iron ore deposits. However, the instrument can not be expected 
to work on sulphide ore bodies not associated with magnetic minerals. 
The instrument is well adapted to illustrate methods of measuring 
the intensity of magnetic fields, the moments of magnets, magnetic 
couples, and other magnetic phenomena. It would be of considerable 
use to a teaching physicist. 
SOME RESULTS OBTAINED 
In Figure 2 are shown the results of a survey across a small dike of 
basaltic rock near Boulder, Colorado. The dike could readily be traced 
with this instrument. Calculation of results by equations (1) and (2) 
are shown. It may be observed that for location work the simplified 
equation could be used satisfactorily. 
In Figure 3 are shown the results of a horizontal intensity survey 
across the Mankato “‘high”’ in Jewell County, Kansas, which had a ver- 
tical anomaly of approximately 900 gammas. Below the profiles are 
shown the vectors calculated from the horizontal and vertical anomalies. 
It should be noticed that the vectors are calculated in the magnetic 
meridian, whereas the section was surveyed in true north and south 
directions. The results indicate that survey with this instrument is 
satisfactory on anomalies of this size and that they may give valuable 
information as to whether polarization is present, and if so, whether 
the magnetic axis is vertical or inclined, and whether the magnetic axis 
of the disturbing body should be regarded as of finite or infinite length. 
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