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Rh being terms in a series of combinations of definite factors. Such series are no evidence of contemporary variability. Many of the terms can be separated in the homozygous condition, and there- after may breed perfectly true. Even such an appearance of variability as that seen in polymorphic species is frequently not above suspicion of being the consequence of a cross, more or less remote. Contemporary variation certainly may occur; but of the contemporary origination of new species, or of the occur- rence of genetic changes which can be colourably interpretec as likely to lead to the production of incipient species in a strid sense, no indication has been found. That the forms of life have been evolved from dissimilar precedent forms we know from the geological record, but as to the process by which this evolution has come to pass we are still in ignorance. All that can be said with any confidence is that variation most commonly arises as an error of cell-division, and that conceivably new species have so arisen.

BIBLIOGRAPHY. Text-books : W. Bateson, Mendel's Principles of Heredity (3rd ed. 1913); E. Baur, Einfuhrung in die. experimented Vererbungslehre (4th ed. 1919); T. H. Morgan, Heredity and Sex (1913); The Mechanism of Mendelian Heredity (1915); The Physi- cal Basis of Heredity (1919); R. C. Punnett, Mendelism (sth ed. 1919). Special references: W. Bateson and I. Sutton, "Double Flowers in Begonia," Jour. Gen., viii., 1919; C. B. Bridges, "Non- disjunction as Proof of the Chromosome Theory of Heredity," Genetics, i., 1916; L. Cuenot, " L'Heredite chez les Souris," 4016 Note, Arch. Zoo/, exp. et gen. iii., 1905; E. M. East, "A. Men- delian Interpretation of a Variation that is Apparently Contin- uous," Amer. Nat., 1910; R. P. Gregory, "Experiments with Primula sinensis," Jour. Gen., i., 1911; "Genetics of Tetraploid Plants," Proc. Roy. Soc., B, 1914; J. B. S. Haldane, " Note on a Case of Linkage in Paratettix," Jour. Gen., x., 1920; H. L. Ibsen and E. Steigleder, " Evidence for the Death in uterool the Homozygous Yel- low Mouse," Amer. Nat., 1917; R. K. Nabours, "Studies of Inheri- tance and Evolution in Orthoptera," i., ii., iii., Jour. Gen., Hi., 1913- 4, and vii., 1917-8; H. Nilsson-Ehle, " Kreuzungsunters. an Hafer u. Weizen," Lunds Universitets Arsskrift, 1909 and 1911; A. Pascher, " Uber d Kreuzung einzelliger haploide Organismen," Ber. deut. bot. Ges., xxxiv., 1916; C. Pellew, "Types of Segregation," Jour. Gen., vi., 1917; O. Renner, " Versuche ub. d. gametische {Constitution d. Onotheren," Zeits. f. ind. Abst. u. Vererbungslehre, xviii., 1917; E. R. Saunders, " Further Experiments on the Inheritance of Double- ness and Other Characters in Stocks," Jour. Gen., i., 1911.

The following periodicals are devoted to the subject : The Journal of Genetics (Cambridge); Genetics (Princeton); Genetica (The Hague); Hereditas (Stockholm); Zeits. f. ind. Abst. u. Vererbungslehre (Berlin). (W. BN.) GENOA (see 11.597), the chief port of Italy and capital of the province of Genoa. Pop. (Dec. 1918) of the municipal area of about 12 sq. m. (comune) 272,221, or, with suburbs (circon- dario), 577,449. The latter figure includes the now contiguous industrial quarter of San Pier d' Arena on the west and a growing residential quarter beyond the Torente Bisagno on the south- east to which the Via Venti Settembre gives direct access. Before the World War there was a marked activity in house- building, but the only buildings of note recently erected are the imposing Banca dTtalia in the Via Dante and the Hotel Miramare above the principal station. The improvement of the Piazza de Ferrari, the central square, was begun in 1913: blocks of houses adjoining the 6th-century church of S. Ambrogio were demolished and the area opened up. The historic Palazzo San Giorgio underwent complete restoration and transformation between 1890 and 1914 and became the headquarters of the Harbour Board (Consorzio). A fine new sea-front, the Corso d'ltalia, adds considerably to the attractiveness of the new residential quarter.

The birth-rate in 1913 was 20-6 and the death-rate 17-64; 23-25% of the latter were children below the age of five and n-8 % of these died before the age of one year. Mortality was due mainly to pul- monary diseases, heart affections and infantile diarrhoea. The meteorological station (alt. 147 ft.) records the highest mean annual rainfall of the twelve Italian stations of which statistics are available 52 inches. The average number of rain-days is 117. Themeanannual temperature is 59-6 F. with a mean of 72-6 in summer and 48-1 in winter and an absolute maximum and minimum of 98-4 and 16-7 respectively. During 1916-8 eighteen earthquake movements were recorded.

The total value of the trade in 1916 was 4,581 million lire, or 39 % of that of all Italy. The following table shows the fluctuations of trade in tonnage.

Imports.

Exports.

Total.

1910-1913

(average) 1914

1915 1916 1917 1918 1919

6,210,000 5,930,000 6,560,000 6,870,000 5,090,000 4,530,000 5,210,000

1,230,000 1,080,000 900,000 840,000 430.000 300,000 430,000

7,440,000 7,010,000 7,460,000 7,710,000 5,520000 4,830.000 5,640,000

The marked drop in imports which began in 1917 was due mainly to the great decrease in coal 590,000 tons in 1917 as against a previous yearly average of 3,140,000 tons. About 6,600 vessels (exclusive of sailing craft) of an aggregate tonnage of 6,700,000 entered and cleared in 1919, compared with an average of 12,000 vessels of 14,340,000 tonnage during 1911-3. The British share in shipping in 1913 was 1,260 vessels of 2,900,000 tons. The passenger traffic of Genoa (including emigration) had normally amount.ed to about half a million annually, but it fell to 45,000 in 1916. Emigration decreased from 42,000 in 1914 to 1,500 in 1918.

The port has warehouse and shed capacity for 300,000 tons of general merchandise in addition to coal and cereals. A daily average of 1,000 trucks can be loaded and unloaded. The doubling of the railway track to Pisa and the development of the marshalling station at San Pier d'Arena and of the Genova Brignole station, 3 km. east of the principal station, on the main line to Pisa and Spezia, have aided the improvement of port facilities; also the extension of elec- tric power to the main line towards Turin, and to Savona and beyond on the line along the coast. The power for the latter is supplied by plant of 80,000 H.P. at Cuneo. The new Vittorio Eman- uele basin, equipped with up-to-date plant, was nearing completion in 1920 and the construction of the larger basin of San Pier d'Arena had been begun. Shipbuilding (merchant) is increasing in im- portance; seven steam vessels of 6,900 total tonnage, nine of 7,570 tons and ten of 28,650 tons were built in 1916, 1917 and 1918 respectively.

Woollen factories have been established; the manufacture of felt and straw hats is increasingly important and there is a con- siderable motor-car industry. The construction of an underground electric railway 6J m. in length, with 14 stations, connecting San Pier d'Arena with Quarto, af m. east of Genoa, was proceeding in ' 1920. GEODESY (see 11.607 and 8.801). The term " Figure of the Earth " is sometimes used to denote the form of the sea-level surface or geoid, and sometimes to denote that spheroid of revolution, or three-axial ellipsoid, which most nearly fits the geoid. It is best to confine its use to the latter sense, so that a " determination of the figure of the earth " means the deriva- tion from the results of observation of the lengths of the axes. The values obtained by J. F. Hayford in 1909 (r) were: Equatorial radius of the earth. 6,378,388 18 metres. Reciprocal of flattening. . 297-0 0-5

Polar semi-diameter. . . 6,356,909 metres.

These figures define a spheroid which certainly fits the northern geoidal hemisphere very closely. Helmert (2), examining Hayford's figures, arrived at somewhat larger probable errors, namely 35 metres and 0-8, but even so the uncertainty is small.

In the southern hemisphere, however, there have hitherto (1921) been no determinations of importance; and the extension of the African arc, which now stretches from Port Elizabeth to near the northern boundary of Rhodesia, and its ultimate connexion with the Egyptian triangulation are much to be desired.

In 1915 Helmert (3) deduced a value of the flattening from numerous gravity observations and found i/296-7o-6. This agrees very closely with Hayford's value and is an important corroboration. The advantage over previous determinations of the figure of the earth enjoyed by his solution lies in the fact that the results of the astronomical observations have been corrected by computing the attraction of all the topography up to a great distance from each station under the assumption of isostatic compensation (see below). This procedure undoubtedly frees the astronomical results from a large proportion of the effects of local attraction and so brings the local vertical into much better agreement with the normal to the spheroid than if the correction had not been applied. This solution of Hayford's is in fact so satisfactory that it may almost be said that the problem has been solved.

Geodesy now turns its attention to finding the actual form of he geoid, that is to say, the level or equipotential surface of the earth which corresponds in ocean areas with mean sea level.