Gravity expeditions at sea 1923-1930. Vol. I
The expeditions, the computations and the results
F.A. Vening-Meinesz
Nederlandse Commissie voor Geodesie 3, elft, 1932. 109 pages.
ISBN-13: 978 90 6132 003 6. ISBN-10: 90 6132 003 8. € 13.50
Preface
This volume contains the report of the maritime gravity expeditions
of the Netherlands Geodetic Commission during the years 1923-1930. The
results are reduced to sea-level without further reduction; they are put
together in the list on pages 101 et seq.
A second volume will contain the isostatic reductions of the results and
the discussion of their interpretation.
During the Gravity Survey of Holland in the years 1912-1921, the
mobility of the soil in the Northern and Western part of the country
caused difficulties, which have led ultimately to the development of a
new method for determining gravity at sea. In the swampy parts of
Holland, no fixed base could be found for the pendulum apparatus, and it
was, therefore, necessary to take special measures for ensuring the
accuracy of the observations notwithstanding these macro-seismic
movements of the apparatus. This end was reached by a method of swinging
two pendulums at the same time in the same swinging plane; in this way
the principal effect of the mobility of the apparatus, the effect of the
horizontal accelerations, could be eliminated. The observations were
made with the ordinary Stückrath apparatus, in which four pendulums
swing two by two in planes, perpendicular to each other. For further
details we may refer to the publication of the Netherlands Geodetic
Commission: 'Observations de Pendule dans les Pays-Bas', Waltman, Delft.
The success of this method of eliminating the effects of disturbing
movements of the apparatus led to a further investigation of its
possibilities in order to see if it could also be applied on board of
ships. After developing the method and adapting the equations to the
greater movements, which could be expected, this proved to be possible,
provided the ship's movements do not exceed a certain limit. This
condition can be satisfied by making the observations on board of
submarines during submergence; in this way the ship gets below the wave
disturbance and the rolling and pitching is reduced to a small and very
gradual movement. Even during rough weather it is easy to reach a depth,
where the ship is sufficiently quiet: for an ordinary wave movement, a
depth of 20 meters is usually enough, for long ocean waves it may be
necessary to submerge to 30 meters or more. A further advantage of the
submarine is the fact that during submergence it is moved by
electromotors, which do not bring about vibrations. The idea of making
the observations on board of submarines was first mentioned to the
writer by Prof. Dr. Van Iterson. Director of the Dutch Government Mines.
Some preliminary experiments having been made during the summer of 1923
o/b a submarine of the Netherlands Navy in the neighbourhood of the
Dutch Naval Base, Helder, and these experiments having proved
satisfactory, it was resolved to put the method to a thorough test
during a longer voyage. A good opportunity was offered in the autumn of
1923 by the voyage from Holland to Java of three Dutch submarines, Hr.
Ms. K 11, K V11 and K VIII, accompanied by a mother ship, Hr. Ms.
Pelikaan. The Netherlands Geodetic Commission, President Prof. Dr. J. J.
A. Muller, Secretary Prof. Ir. Hk. J. Heuvelink, asked permission for
the writer to embark with the necessary apparatuses o/b of one of these
submarines and to make experiments during the voyage. The permission was
granted by
the Minister of the Navy, his Exc. Mr. E. P. Westerveld.
Before the beginning of this voyage the apparatus had to be adapted to
the projected method. The principal alteration to the Stückrath
apparatus was the making of a photographic recording device; the
elimination method, applied during the observations in Holland, had been
carried out with the old visual method, but this would be impossible for
the newly developed method, which had to cope with the greater
disturbances, caused by the ship's movements. Details about this method
are to be found in the publication of the Netherlands Geodetic
Commission: 'Theory and Practice of Pendulum Observations at Sea' and
details about the apparatuses used during this first voyage are given in
the next chapter.
The observations have been carried out o/b Hr. Ms. K 11, Lieut. L.A.C.M.
Doorman commanding. Besides 26 gravity determinations at sea,
observations have been made in the harbours, Gibraltar, Tunis.
Alexandria, Suez, Colombo and Sabang.
Contents
I. Historical 5
II. Voyage of Hr.Ms. K II from Holland via Suez to Java, September 18 - December
24, 1923 11
III. Voyage o/b Hr. Ms. K XI from Holland to Alexandria, October 15-November 12,
1925 31
IV. Voyage of Hr.MS. K XIII from Holland via Panama to Java, May 27 - December
13, 1926, with investigation of the Java Deep in February 1927 41
V. Expeditions of Hr . MS . K XI11 through the Netherlands East Indies. Nr. 1.
June 12 - August 12, 1929. Nr. 2. October 8 - November 14, 1928. Nr. 3. January
2 - February 15, 1930. 67
Combined Table of the Positions and the Gravity Results reduced to Sea-Level of
all the Expeditions 100