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Rh and the length of i" of meridian in latitude 45 being about 3,100 cm. the change in I cm. is 8-1 X io 9 . Along the parallel there is no change. These are the normal values. The Torsion balance determines the actual rates of change at the point of observation and the direction in which this rate is a maximum. Eotvos calls this maximum rate the " Gravity Gradient," Gr(g). The instrument consists of a light horizontal tubular beam 40 cm. long suspended from its centre by a fine platinum wire about 50 cm. long; at each end of the beam there is a weight of 28 gr., the one inserted in the tube and the other hang- ing from it by a thread about 60 cm. long. The whole is enclosed in a case so constructed as to protect the interior as far as possible from inequalities of temperature. The case is capable of being rotated on a vertical axis into different azimuths, and it is by measuring in each of a series of positions the amount of torsion of the suspending wire that is required to balance the small forces acting on the beam and tending to cause it to take up a position coinciding with the direction of Gr(g), that the direction and magnitude of Gr(g) are determined.

The quantities which the Eotvos balance is capable of measuring are almost incredibly small, I Xicr 9 C.G.S. being rather larger than the average of the differences which it is able to detect. The data furnished by this instrument afford the means of tracing the form of the geoid and, after the effects of the visible topography have been allowed for, of detecting the presence of subterranean irregularities of density. A large number of observations with this instrument have been made in Germany since 1917 under the direction of the Prussian Geodetic Institute, chiefly with the object of studying its applicabil- ity to geological research ; that is to say, for the location of masses of abnormal density.

REFERENCES. (i) J. F. Hayford, Supplementary Investigation in 1909 of the Figure of the Earth and Isostasy, Coast and Geodetic Survey, United States (1910); (2) F. R. Helmert, Sitzungsbericlite der Kon. Preuss. Akademie der Wissenschaften (1911); (3) F. R. Helmert, Neue Formeln fiir den Verlauf der Schwerkraft im Meeres- niveau beim Festland (Berl. Akad. 1915); (4) A. R. Clarke, Philo- sophical Magazine (August 1878); (5) J. de Graaff Hunter, "For- mulae for Atmospheric Refraction," etc., Survey of India, Prof. Paper No. 14 (1913); (6) J. H. Pratt, A Treatise on Attractions, Laplace's Functions, and the Figure of the Earth (1871); (7) C. E. Dutton, " Some of the Greater Problems of Physical Geology," Phil. Soc., Washington, Bulletin, vol. xi. (1888-91); (8) J. F. Hay- ford, The Figure of the Earth and Isostasy from Measurement in the United States (1909) ; (9) J. F. Hayford and Wm. Bowie, The Effect of Topography and Isostatic Compensation upon the Intensity of Gravity, Coast and Geodetic Survey, special publication No. 10 (1912) ; (10) Wm. Bowie, Investigations of Gravity and Isostasy, Coast and Geodetic Survey, special publication No. 40 (1917); (ll) Col. Sir S. G. Burrard, " Investigations of Isostasy in Himalayan and Neigh- bouring Regions," Survey of India, Prof. Paper No. // (1918); (12) Benoit et Guillaume, La Mesure Rapide des Bases Geodesiques (1908); (13) Comptes Rendus de ['Academic des Sciences (Nov. 1920), vol. clxxi.; (14) J. de Graaff Hunter, " The Earth's Axes and Triangulation," Survey of India, Prof. Paper No. 16 (1918); (15) C. Lallemand, Nivellement de Haute Precision; (16) " Levelling of Precision in India," Operations of the Great Trigonometrical Survey, vol. xix. (1910); (17) A. Claude et L. Driencourt, Description et Usage de ['Astrolabe a Prisme (1910); (18) John Ball and H. Knox- Shaw, A Handbook of the Prismatic Astrolabe (1919); (19) Prof. Sampson, Monthly Notices of the Royal Astronomical Society, June 1918, May 1920, Nov. 1920; (20) W. H. Burger, The Measurement of the Flexure of Pendulum Supports with the Interferometer; Report for 1910, Coast and Geodetic Survey, Appendix No. 6; (203) R. Schu- mann, " Cber die Verwendung zweier Pendel," etc., Zeitschrift fiir Mathematik und Physik, 44th year, parts 2 and 3; (21) Capt. H. J. Couchman, "The Pendulum Observations in India and Burma 1908-13," Survey of India, Prof. Paper No. 15 (1915); (22) " Determination of Gravity at Sea," Report of the Committee of the British Association (8gth Report, 1919); (23) "Etude sur les Surfaces de Niveau et de la Variation de la Pesanteur et de la Force Magnetique," Rapports presentes au Congres International de Physique reuni a Paris en 1900; (24) " Bestimmung der Gradienten der Schwerkraft und ihrer Niveauflachen mit Hilfe der Drehwage," Verhandlungen der XV. allgemeinen Conferenz der Internationalen Erdmessung in Budapest 1906; (25) Die Niveauflache des Balatonsees und die Verdnderungen der Schwerkraft auf diesem. Resultate der wissenschaftlichen Untersuchungen des Balaton, vol. i., part I., section II. (G. P. L.-C.; J. DEC. H.)

GEOGRAPHY (see 11.619). The application of geography to matters connected with the World War and the peace settlements took two main directions. The first was concerned with all those special naval and military studies and operations of which the results are expressed principally on maps (see MAP). The other showed geography in what may be termed its encyclopaedic aspect, in which, to a prefatory description of a territory in its topographical and (so far as appropriate) its geological, botanical, and other scientific aspects, there must be appended a discussion of its social, political, and economic conditions, its communications, history, and so forth: in short,

an account of the activities of its inhabitants in whatever direc- tion. For example, much work of this general character was executed by British intelligence organizations such as the geographical section of the Naval Intelligence Department and the historical section of the Foreign Office, the French Service Geographique de I'Armee, and others. Most of this work was carried out by organizations created ad hoc; much of it was of permanent value apart from its immediate military and polit- ical uses; and, generally speaking, it indicated many desirable directions for geographical research and the collection of data, which might have been placed on a permanent footing but for restrictions imposed by financial considerations after the war.

Expressed in the broadest terms, the keynote of geographical study on this side is the relation of man to his geographical environment. A natural corollary is to view the world first in natural regions, as defined by physical conditions of climate, relief, vegetation, etc.; afterwards to correlate ethnographic, linguistic and political divisions with these. The study and definition of natural regions, at any rate on broad lines, is specially associated in Britain with the name of Andrew John Herbertson, professor of geography in Oxford University. This division of the earth into natural regions, and the influence of the conditions of each upon its inhabitants, is obviously ca- pable of application not only on broad simple lines to the world generally, but locally and minutely in special areas. In this last direction there is an almost infinite field for research: it is necessary at all times that its practical application should be kept in view, and trivialities, on the one hand, and too bold generalizations, on the other, avoided.

This relationship between man and his environment as prescribed by natural regions has thus become a leading motive of geography, in research and as an educational subject, in Britain and in Europe, especially among French and German geographers, and elsewhere through the local and individual work of such investigators as Prof. J. Cvijic in the Balkan area. In the United States, too, this view of geography has taken firm hold, though here it did so later, as at first the modern development of geographical study tended rather towards the physiographical side (land forms) alone. In the wider field such workers as Ellen C. Semple, Prof. R. de C. Ward, W. L. G. Joerg, Prof. I. Bowman, and others, turned their attention to many parts of the world, but especially, perhaps, to their own country, and a proposal was made to the Association of American Geographers that, by way of a basis, a map dividing the United States into physiographical provinces should be prepared with the collaboration of all American geographers and institutions interested.

Distributional surveys, whether physical or ethnographical or economic, or of whatever sort, are in fact the chief requirement of this branch of geography, though the prospect of their being put in hand on international or even national lines is remote. In certain special directions international action has been taken, as for example the expression of the need, and the laying down of certain general principles, for a series of international aeronautical maps, which was voiced in the convention for aerial navigation signed by about 30 States in Paris in Oct. 1919. But a proposal for an International Geographical Union, which arose out of the formation of the International Research Council in 1918 by national academies of the principal Allied Powers, was not welcomed with unanimity, although one was formed for geodesy and geophysics. It was not only as regards geography among the sciences, however, that doubt was expressed as to the present possibility of working international unions, in view of the preoccupation of workers with the reorganization of their individual work at home. Such work is largely concerned with the establishment of geography as an educational subject (see below). As a special example apart from this, mention may be made of the work undertaken in 1919 and following years by a permanent British committee representing the Admiralty, the War, Foreign, Colonial, India, and Post Offices, the Boards of Trade and Agriculture, and the Royal Geographical Society, which was charged with the preparation of lists of standard spellings of geographical names, the divergent.