History of Geophysical Research in The Netherlands ... - DWC - KNAW

netic survey in the East Indian Archipelago. He measured the declination , inclination
and horizontal intensity of the geomagnetic field at about 150 places
on the various islands. This work with maps of the magnetic components, reduced
to 1-1-1876, was published by the Royal Netherlands Academy of Arts
and Sciences (Van Rijckevorsel, 1879).
W. van Bemmelen (1909) repeated the magnetic survey of the East Indies in
the years 1903 to 1907. He studied the secular variation of the earth 's magnetic
field in the western part of the East Indian Archipelago, based on measurements
from the years 1900 to 1918 (Van Bemmelen, 1920). The phenomenon of
secular variation aroused special interest. The speed of the variations is so
great that it is difficult to ascribe them to tectonic movements in the earth 's
crust.
Repeating the geomagnetic measurements with intervals of some years became
therefore a matter of routine. In the years 1917 and thereafter members of the
staff of the KMMO made regular field trips to repeat the magnetic surveys at
many places on the islands . The instruments were not very different from those
used by Van Rijckevorsel, viz. a magnetometer-theodolite for measurements of
declination and horizontal intensity, and a dip circle or inclinatorium for measurements
of inclination. Co-workers of the KMMO who took part in the measuring
program were C. Braak, W. van Bemmelen, J. Voûte and S. W . Visser, and
later H.P. Berlage and M;W.F. Schregardus. Visser (1925) published new isomagnetic
maps of the whole Archipelago based on the measurements of Braak,
Van Bemmelen, Voûte and himself.
During the Geophysical Year 1957 -1958 a geomagnetic observatory was operated
at Hollandia (former Netherlands New Guinea). see Chapter IV, section 2.
Geomagnetic Observatories and Surveys - Netherlands East lndies, 1866 to 1949
Year Location
1866 Batavia
1874 to 1877 About 150 places
1883 Batavia
1899 Buitenzorg
1903 to 1907 Throughout the islands
1917 to 1942 Ditto
1925 Kuyper Island
1942 to 1945 Kuyper Island
1945 to 1949 Kuyper Island
Remarks
First geomagnetic observatory, measurements
several times daily
First geomagnetic survey
Continuous photographic recording
began
Geomagnetic observatory moved from
Batavia
Second geomagneticsurvey
Third geomagnetic survey
Geomagnetic observatory moved from
Buitenzorg
Recordings interrupted by war
Observatory closed in 1949
1.7. GEOMAGNETIC RESEARCH BY DUTCH SCIENTISTS OUTSIDE THE
NETHERLANDS AND THE NETHERLANDS EAST INDIES
Some years af ter his East Indian expedition (see section 1.6) Van Rijckevorsel
left for South America with his instruments. He measured the geomagnetic
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