Theory and practice of pendulum observations at sea, part I
F.A. Vening-Meinesz · Nederlandse Commissie voor Geodesie eBooks · 1929
T h e difficulties experienced during the penclulum observations in the west and north part of Holland, wllere the ground is so subject to microseisn~s that no satisfactory results can be obtained, gave rise to the elaboratioll of a method which would make it possible to eliminate these disturbances.T h e method is described in : ,,Observations cle pendule dans les Pays Ras, 191 3-192 I ", par F. A. VENING MEINKSZ; J Waltman Jr., Delft; in its simplest form it consists in swinging two pendulums in the same plane on the same support with equal amplitudes and in opposite pllase.T h e mean of the two periods is free from the effect of any small movement of the apparatus.T h e old four pendulum Sterneck apparatus of the Stuckratlr type could be used for carrying out this method.T h e good results obtained, led to a study of the possibility of determining gravity in some analogous way on board a moving ship.Of course it would be llecessary t o eliminate t h e effect of much larger movenlents but it was possible to change the method in such a way that this could be done, provided at least that the ship's movements are small.This method is described in the following publication.Small ship's movements can be obtained by carrying out the observations on board of a submerged submarine; the writer is indebted t o Prof. Dr. F. K. TH.VAN ITERSON for first mentioning this idea to him.Besides reducing the rolling and pitching of the vessel, a submarine has the advantage that during submergence the s l ~i p is not subject to vibrations, acircumstance which is of vital importance for t t ~e possibility of swinging pendulums.For carrying out the method it was necessary to provide the Stuckrath apparatus with a photographic recording apparatus.This was constructed at the Meteorological Institute at de Rilt (Holland) by its chief mechanic L. M. Y A N REST in the surnnler of 1923.In the autumn of 1923 the Dutch Geodetic Commission authorised the writer to make a voyage in a submarine of the Koyal Dutch Navy, theK.11, from Holland to Java by way of the Suez canal, ill order to put the method to a test.T h e voyage gave satisfactory results; it appeared possible t o get an accuracy corresponding to a mean error of r : zoo.ooo-I : 300.000 in the gravity.T h e results of this voyage which were ~ublished in: "Observations de pendule sur la mer, 1923, publication provisoire", gave rise to the devising of a new pendulum apparatus more specially adapted to the method, which was again constructed by Mr. VAN REST.T h e apparatus was put to the test in the autumn of I925 during a voyage on board the D u t c l ~ submarine Hr.Ms. K. XI from Holland to Port-Said.T h e apparatus reduces the time required to compute an obszrvation from several days to a few hours.During tlle spring of 1926 a furtl~er improvement was made by suspending t h e apparatus in gimbals and from May till Dec. 1926 a tliird voyage was carried out, this time on board of Hr.Ms. K. XIII, going from Holland to Java by way of Panama (,,Determination de la pesanteur en mer, publication provisoire").T h e final publications of t h e results of this and t h e former voyage will soon appear.In 1928 a last alteration was made by the construction a t de Bilt of a new recording apparatus, wl~ich brings t h e apparatus to its final shape as described in this publication.Arrangements llave been made witli tlie NEDER-LANDSCHE SEINTOI~STEI,I EN FAI;RIFK at Ililversunl (Holland) for undertaking tht: construction of furtl~er copies of tliis apparatus.Thanks are due to the Netherlands Navy for niaking these extensive investigations a t sea possible, whrch led to the elaboration of method and apparatus.'Tllanl