October 7, 1909] 



NA TURE 



427 



We believe that we shall do better to give an account 

 of the principal discussions only, rather than to 

 attempt to mention the name of every report and its 

 author. 



On Tuesday morning', September 21, the chair was 

 taken by Mr. Haldane, Secretary of State for War, 

 who warmly welcomed the association to England on 

 behalf of the British Government. Sir George 

 Darwin, vice-president, welcomed the delegates in 

 the name of the Royal Society, in the absence of 

 .Sir Archibald Geikie, prevented by an accident from 

 being present. General Bassot (president of the 

 .-issociation) then took the chair and delivered his 

 address; the permanent secretary (Prof. H. G. van 

 de Sande Bakhuyzen) presented his report, and much 

 business of a formal character was taken. 



On the Wednesday morning the first business of 

 importance was Prof. Hecker's account of his deter- 

 mination of the lunar earth-tides. Nearly thirty years 

 ago Sir George Darwin and Mr. Horace Darwin tried 

 tV observe the lunar earth-tide in the Cavendish 

 l.aboratorv at Cambridge, but the effect was masked 

 Ijv much larger deviations due to temperature. Prof. 

 Meeker states that the effect of the solar heat was 

 diminished 85 per cent, when his apparatus was trans- 

 f^rred from the cellars of the Geodetic Institute to a 

 chamber in a well shaft 25 metres below the surface. 

 Here, in 1902 December, he installed his horizontal 

 pendulums, and observed, with two small inter- 

 ruptions, until 1909 May. Analysis of the resulting 

 ■curves shows an undoubted periodicity in half a lunar 

 day, and a comparison of the observed with the easily 

 calculated theoretical curve gives the following 

 results : — The yielding is a little larger than would 

 occur if the earth were a ball of steel, and 

 about half the theoretical amount for a perfect fluid ; 

 there is little lag, so that the internal friction caused 

 bv deformation of the earth must be insignificant; the 

 ratio between the major and minor axes of the 

 tUiptical curve does not agree with theory ; this is 

 probablv not caused by local irregularity, but is, 

 )ierhaps, due to the position of Potsdam near the 

 western edge of the European-Asiatic continent ; an 

 investigation, whether the shape of the surface of the 

 earth is changed bv change of barometric pressure, 

 gave inconclusive results. Prof. Hecker concluded 

 'hat the outstanding questions could be settled only by 

 observations at a number of stations, and he asked 

 the association to stand godfather to these investiga- 

 tions. 



In discussion, Sir George Darwin said that the 

 association had in the past devoted much of its funds 

 t 1 the study of the variation of latitude; we may feel 

 quite sure that Newcomb was right in regarding the 

 prolongation of Euler's nutation period as due to the 

 elastic vielding of the earth's mass; and he regarded 

 Hecker's work, therefore, as a second chapter in the 

 \ariation of latitude investigations. He accepted as 

 worthy of consideration Prof. Hecker's explanation of 

 the remarkable absence of symmetry in the path of 

 the vertical, but suggested an alternative possibility. 

 The curve was much compressed in the N.-S. direc- 

 tion, showing that the earth has much greater rigidity 

 E.-W. than N.-S. It is possible to explain this to 

 some extent by the earth's rotation. Lord Kelvin 

 introduced the idea of gyroscopic rigidity, that is, of 

 greater rigidity E.-W. due to rotation. Whether this 

 is a sufficient explanation cannot be said, because no 

 one has succeeded in solving completely the gravita- 

 tional problem of a 'otating elastic globe. Prof. 

 Hecker's examination of the barometric effect had 

 proved abortive ; but he had been pleased to receive 

 lately a letter from Mr. Napier Denison, of the 

 Canadian Meteorological Service, who has succeeded 



NO. 2084, VOL. 81] 



in showing that on the Pacific coast, when the higli- 

 pressure system moves towards Alaska, the mean 

 position of the vertical shifts in the same direction. 



Dr. Backlund (Russia) suggested that in this matter 

 the International Seismological Association might 

 cooperate with the Geodetic Association in providing 

 funds. 



A commission to report on the subject was appointed 

 as follows: — Dr. Backlund (Russia); Sir George 

 Darwin (Great Britain); Baron Eotvos (Hungary); 

 Profs. Haid, Hecker, and Helmert (Germany) ; M. 

 Poincare (France); and Prof. Weiss (Austria). 



On the Thursday morning Sir David Gill presented 

 his report on the progress of the great African arc of 

 meridian. Tlie British portion has been carried nearly 

 to Tanganyika from the south, and a small section 

 has just recently been measured on the Uganda- 

 Congo frontier. The intervening section belongs to 

 Germany. He understood that Prof. Helmert had 

 already taken active steps to ask for money, and was 

 sorry that for the moment the German Treasury had 

 not responded with its usual alacrity. He could 

 only hope that the little piece just completed to the 

 north will act as a hook to which they will duly rise 

 and be caught ni the net of triangulation. We must 

 now think of carrying the arc forward to Egypt, and 

 from Egypt to join Struve's great arc which ter- 

 minates on the Danube. Captain Lyons had travelled 

 over most of the line in Africa, and Sir David Gill had 

 his authority to say that the completion was only a 

 question of money. There are no real geographical 

 difficulties. Much has been made of the sudd, but 

 this occupies only the valleys, and there are hills on 

 each side. He believed, also, that it is possible to 

 find, away from the river, a line more practicable and 

 closer to the 30th meridian. To complete the whole 

 from L'ganda to the Danube would cost about 

 ioo,oooL He wished the association to adopt a resolu- 

 tion expressive of the importance of the work, and 

 hoped that in time the Governments concerned, helped 

 bv private munificence, might be able to provide the 

 money. 



Colonel Close (General Staff) said that when it 

 became necessary to send a party to survey the dis- 

 puted territory on the Congo-Cganda boundary, the 

 Colonial Survey Committee gladly took advantage of 

 the occasion to measure a section of the arc of 

 meridian. The British Government asked the 

 Government of the Congo to approve and coojx'rate, 

 and the latter appointed a commissioner, who observed 

 all the latitudes. The Royal Society, the Royal 

 Astronomical and Geographical Societies, and the 

 British Association had contributed part of the funds. 

 The whole was an admirable example of cooperation 

 between governments and learned societies. 



On the Saturday morning, Prof. Baron Eotvos pre- 

 sented a very encouraging report on the results of his 

 three years' work with his torsion balance. In 1906 

 he had described the plan of this remarkable ap- 

 paratus, which gives a rapid means of determining 

 abnormalities in the direction and intensity of gravity. 

 In response to a recommendation of the association, 

 the Hungarian Government placed an annual sum of 

 60,000 crowns at the disposal of Baron Eotvos, who 

 has been enabled thereby to make many improve- 

 ments in his apparatus, and to complete a gravity 

 survey over 400 square kilometres in the great plain 

 of Hungary. Simultaneous observations with the 

 torsion balance and with half-second pendulums of the 

 standard Potsdam tvpe, combined with determinations 

 of the deviation of the vertical from astronomical and 

 geodetic latitudes, resulted in a complete accordance, 

 and established the accuracv as well as the extreme 

 handiness of the torsion balance. Baron Eotvos' 



