Cassinis, G.

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PROGRESSI E TENDENZE NEI PROCEDIMENTI PER DETERMINAZIONI DI GRAVITA RELATIVA.(PROGRESS AN D TEN D EN CIES IN T H E  METHODS OF D ETERM IN IN GR E L A T IV E  GRAVITY)by P r o f . G. CASSINISProfessor G. C a s s in is  has written a very interesting article in Nos 5 and 6 of the Bolletino del Comitato Nazionale Italiano per la Geodesia e la Geofisica, which are appended to Nos 5 and 6 of Universo. This deals with the various appliances which, within recent years, have caused the determination of gravity to make great progress.The following is a summary of this article1) Improvements introduced into the method of R . V . S t e r n e c k  by investigating the influence of the elasticity of the support, to which the Italians A. V e n t u r i , G. L o r e n z o n i,G. S il v a  and V . R e i n a  have contributed; the employment of appliances in rarefied air and the employment of invar or of non-magnetic bronze.2) Determination of the duration of the oscillations. The method consisting of appreciating the coincidences by eye and ear has been replaced by various self-registering systems which greatly increase the accuracy : by photography (V e n i n g -M e i n e s z , C o n y n g h a m , O. M e is s e r  and H. M a r t in ), by photo-electric cells and by hertzian waves. One of the most interesting of these appliances, which may also be used for measuring other time intervals, is that which was invented by Father L e  j a y  and investigated by H. M a h n k o p f  and H. S c h m e h l . It consists of a triode valve connected as reaction, followed by a low frequency amplifier. The aerial consists of a horizontal wire, about one metre long, the free end of which is immediately under the pendulum when at rest. The pendulum has, at its lowest part, a short horizontal filament which is parallel to the aerial and very close to it in the position of rest. The valve is so constructed that a very small variation m the capacity of the grid circuit starts oscillation. The signals thus produced by the pendulum at each oscillation are very sharp and can be recorded in the usual way.3) Minimum pendulums, i. e. pendulums the dimensions of which are so combined that the variation in the duration of oscillation, due to irregular variations in distances between the knife edge and the centre of gravity of the pendulum, are made as small as possible. The rule laid down by J. W il s i n g  has been applied to pendulums of cylindrical form by K o h l s c h u t t e r . Various metals and alloys have also been tested.4) The precautions taken by M e is s e r  to introduce great accuracy in the new Jena apparatus, measurement of temperature and pressure, and differential observations.5) Short description of the V e n i n g -M e i n e s z  apparatus intended for gravimetncal measurements at sea. It consists of three pendulums oscillating in the same plane, together with a fourth pendulum which is free to move in a plane at right-angles to the other. M e in e s z  carried out experiments with his apparatus in submarines which were submerged to such depth that the movement of the sea was no longer appreciable. He has obtained several hundred determinations in the Atlantic, the Pacific and the seas of the East Indian Archipelago. It is to be hoped that observations will shortly be taken in the Mediterranean, where comparison with the results obtained on land will be particularly easy and instructive. The investigation of gravity at sea, which this ins­trument has made possible, is quite new and may lead to the corroboration or to the modification of our ideas on the subject of the constitution and equilibrium of the terrestrial crust, on isostasy, on earthquakes etc.6) Investigation of elastic pendulums with which the Swedes, I s in g  and U r e l i u s  have carried oat experiments. These two have adopted a torsion pendulum in which the small quartz bar (about 25 millimetres long) is in an upright position. It sets itself into a position of equilibrium which is determined by the equality of the contrary momentsexerted by gravity and the torsion of a horizontal quartz thread. B y this method the sensitiveness of small variations of g may be practically increased enormously.This static method, which is intended for the measurement of the variation of g from one point to another, has the advantage of being quite independent of timemeasurement. . . ., 1 j-7) A system which has the same object and which is not dissimilar to the preceding one, but which is dynamic, has been used with great success by Father L e j a y . H is  pendulum consists of a shaft of quartz A B , about 10 centimetres long, which stands vertically and which is connected to its support /  by a blade of elinvar K ,  the elastic force of which very nearly counterbalances the weight of the shaft. The pendulum thus has a very long period and is very sensitive to variations in g.A  recent communication by Father L e j a y , which ap­peared later than Professor Ca s sin is ’ article and was included in the Comptes Rendus de I’Academic des Sciences, Paris, of 4^b May, 1931, page 1116, contains a description of the latest model (see figure) and the results obtained in France and Switzerland. Time is measured by an auxiliary free pendulum of quartz, the duration of the oscillation of which (about %  second) is compared by direct stroboscopic observation with that of the gravity pendulum. For this purpose the free pendulum causes a spark at each passage through the vertical and this illuminates the filament L  which is attached to the upper end of the gravity pendulum. To obtain g with an error less than a unit of the second place of decimals, an observation lasting 15 minutes is required. The apparatus stands transportation very well.8 ) H. H a a lc k  has constructed and carried out experi­ments, during 1930, with a static measurer of gravity for deducing the variations in gravity between two stations from the variation in the height of a column of mercury which is held in equilibrium b y the pressure of a gaseous mass enclosed in a suitable receptacle.P. V.The bibliography appended to his investigation by Pro­fessor Ca ssin is  is given below. This will allow full informa­tion on these questions to be obtained.BIBLIOGRAPHY.Ph. F u r t w a e n g le r , Sitzungsber. d. Beri. Akad. 1912. P- 245-A. V e n t u r i, “ Gli integrali generali del moto del bipendolo in relazione a movimenti orizzontali intrinseci ed estrinseci del supporto”. A tti della R. Accad. di Palermo, X, 1911.F. A. V e n in g -Me in e s z , “Observations de pendule dans les Pays-Bas . Delft, ig23 —  “ Theory and Practice of Pendulum observations at Sea” . Delft, 1929-G. L o renzoni & G. S il v a , “ I l  supporto bipendolare M ioni a recipienti pneumatici”. Pubbl. della R. Commissione geodetica italiane. Padova, 1912G. Sil v a , “ Relazione della osservazioni gravimetriche compiute nell’estate 1913 con il Bipendo M ioni". Memorie del R. Istituto Veneto, X X V III, 1914- $ee a*so • B erroth  A., Zeitsch. f. Geoph. I, 1924-25, p. 89 ; Sch m ehl, Zeitsch, f. Geoph., I li,  1927, p. 157 ; P. D o r è , Rendiconti Lincei, X, 1929, p. 62.V. R e in a  and C. Ca s sin is, “Determinazioni di gravità relativa compiute nel 1912. Pubbl. della R. Commissione geodetica italiana, Roma, 1913-L e n o x -C o n y n g h a m , “ The Cambridge Pendulum Apparatus". The Geogra­phical Journal, 63, 1929, p. 326.O. M e is s e r  and H. M a r t i n , “Zur Registrierung von schnell verlaufenden Vorgängen...” Zeitsch. f. Geoph. II, 1926, p. 269— “Erhöhung der Beobachtungs­genauigkeit bei relativen Pendelmessungen". Zeitsch. f. Geoph. V, 1929,p. 145.O. M e i s s e r . “E in  neuer Vierpendelapparat für relative Schweremessungen'1'. Zeitsch. f. Geoph. VI, 1930, p. 1.C. A. H e i l a n d , “Bemerkungen..." Zeitsch. f. Geoph. VI, 1930, p. 479.B. L a n g e , 11 Photozellen in Wissenschaft und Technik". Naturwissenschaften, *9 , 1931. pages 103 and 128.P. L e j a y , “Die genaue Bestimmung der Schwingungsdauer eines Pendels". Deutsche Uhrmacher - Zeitung. 52, 1928, pp. 899 and 981.H. M a h n k o p f , “Die Registierung von Pendelschwingungen mittels kapazitiver K o n t a k t e —  H. S c h m e h l , “Die Registierung der Schwingungen...'" Zeitsch. f. Geoph. V, 1929, pp. 49 and 53.J. W iLsiNG, “ Ueber eine besondere Form invariabler Pendel”. Zeitsch. f: Instrumentenkunde, 17, 1907, p. 109.M. S c h u l e r , “E in  neues Pendel mit unveränderlicher Schwingungszeit". Zeitsch. f. Physik, 42, 1927, p. 547.E. K o h l s c h u e t t e r , “ Ueber Pendelformen". C. R. de la Troisième Séance de la Commission Géod. Baltique. Helsinki. 1928, p. 83 —  “Die Invariabilität und Abstimmung von Minimumpendeln". Zeitsch. f. Geoph., VI, 1930, p. 466.H . N a g a o k a , “ Invariable Pendulum of Tungsten for relative Measurements of Gravity". Proceed, of the Imperial Academy, II, p. 198, Tokio, 1926.A. B e r r o t h , “ Referenzpendelmessungen am Salzhorst Oldau-Hambüren". .Zeitsch. f. Geoph. III, 1927, p. 1.F. A. V e n i n g -M e i n e s z , “ Gravity at Sea", Report presented to the Commis­sion for the Gravity at Sea. Stockholm, 1930, containing the complete biblio­graphy of the argument.F. A. V e n i n g -M e in e s z , “Maritime Gravity Survey in the Netherlands East Indies : Tentative Interpretation of the Provisional Results". Proceed, of the Konin. Akad. van Wetenschappen. X X X III, p. 566. Amsterdam, 193°- — ' “ Relevé gravimétrique maritime de l ’Archipel Indien". Publ. de la Commission Géodésique Néerlandaise, Delft, 1931.G. I s in g  and N. U r e l i u s , “Die Verwendung astasierter Pendel für Relative Schweremessungen". Kungl. Svenska Vetenskapsakademiens Handlingar, 3 a Serie, Bd. 6, num. 4 Stockholm, 1928.P. L e j a y , “ Recherches sur les pendules élastiques”. Bull. géod. N ° 25, p. 16.—  “ Instruments transportables pour la mesure de la gravité", (lithogr.) Paris, Août 1930.H. H a a lc k , “E in  statischer Schwerkraftmesser", Zeitsch. f. Geoph. VII, i 93x> P- 95 -Part I of Vol. VI of the “Handbuch der Geophysik", directed by B. G u t e n b e r g , (Berlin, Bomtraeger, 1931) contains two important chapters on the measurement of Gravity : E .-A . A n s e l , “ Theorie der gravimetrischen Aufschlussmethoden" and O. M e i s s e r , “Instru­mente der gravimetrischen Aufschlussmethoden".The second part of Volume X X V  (“ Geophysik") (Geophysics), directed by C. A n g e n - h e is t e r  of the “Handbuch der Experimentalphysik", Leipzig, Akadem. Verlagsgesellschaft, 1931, contains an article: “ Figur, Schwere und Massenverteilung der Erde", drawn up by H. S c h m e h l  & K. J u n g  (pp. 141-360).

Progressi e tendenze nei procedimenti per determinazioni di gravita relativa

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Progressi e tendenze nei procedimenti per determinazioni di gravita relativa

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