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

for navigation. The clergyman and geographer, P. Plancius (1552-1622), hoped
just as De Castro that the magnetism of the earth would provide a solution to
the problem of determining geographic longitude at sea.
Netherlands physicists like S. Stevin (1548-1620) and Chr. Huygens (1629-
1695) showed interest in the practical nature of geophysical problems. In his
book "Havenvinding" (finding the harbour) Stevin agreed with Plancius concerning
the theory of longitude determination. Huygens contributed to the true
solution of this problem by developing the theory of the pendulum as weil as by
inventing a clockwork suitable for use on ships. By doing so he furthered the
accuracy of the measurement of time and therefore of the determination of longitude
at sea.
In the centuries after the Golden Age (the 17th century) the interest in geomagnetism
was no longer focused mainly on the values of the field components
all over the world, but more on the temporary variations . For years some scientists
determined daily the direction of the geomagnetic field. However, a
continuous study of the earth's magnetism based on measurements at regular
times, began not earlier than the middle of the 19th century.
I. 2. GEOMAGNETISM IN THE NETHERLANDS
In the Netherlands in the 19th century research into geophysics of the solid
earth was closely connected with meteorology and oceanography. When in 1854
the Royal Netherlands Meteorological Institute (KNMI) was founded at Utrecht,
meteorological research was put on a firm footing. The Institute was housed in
the Sonnenborgh, an old castle in the town of Utrecht (now the Astronomical
Observatory of the State University at Utrecht). In this building also ob servations.
of the earth's magnetic field were included in the routine of daily observations.
Three times a day the position of a magnetic needie on a scale was
re ad through a telescope in the cellar of the Sonnenborgh. These daily observations
of the declinations of the compass had started in 1849 (see: KNMI,
Gedenkboek, 1954).
The special interest in geomagnetism was coupled in the Netherlands (and in
other countries) with a general interest in the unknown and mysterious polar
regions , which in the last century were the aim of many expeditions (see: section
IV.l. Polar Years). Arelation bet ween geomagnetic storms and aurora was
known, but geomagnetism as weU as the aurora were not weU understood natural
phenomena. The connection between them and the relation with the polar
regions and with the activity of the sun were very puzzling. Therefore, regular
observations of the magnetic field of the earth we re considered to be worthwhile.
Several times a day two components of the geomagnetic field, the declination
and the horizontal force, were determined. In that way some knowledge
was gained about the regular variations of these quantities; and also of the
variations , later called magnetic storms, which are related to the appearance
of spots on the sun.
Photographic recording of geomagnetic variations began in 1868 in the cellar
of the Sonnenborgh, and since that time absolute measurements of the field
strength were also carried out, in conformity with international methods. In
the Yearbook of the KNMI of 1894 we find for the first time tables of hourly
values of the declination and of the horizontal intensity of the earth 's magtletic
field (KNMI, 1894).
The increased research activity in the field of geomagnetism. as appears from
the extensive KNMI publication of 1894, was due to the work of E. van Rijckevorsel,
who carried out measurements of declination , inclination and horizont al
12