STATE AGRICULTURAL SOCIETY. 399 



the influence of southwesterly gales, and extends, more or less, into Novem- 

 ber. The rains do not last in most winters more than three or four weeks, 

 and that not continuously. The rest of the winter, until the spring, is gen- 

 erally dry and fine, under the influence of the northerly winds, with the 

 exception of a few occasional days of rain, when the wind turns to southern 

 quarters. Heavy rain again falls in the latter half of March, with south- 

 westerly or southeasterly gales and storms, as in northern Europe. These 

 rains saturate the earth and renew the springs. 



Under their fostering influence, and with the help of the ardent sun, 

 which shines through the clear dry atmosphere, vegetation then advances 

 with astonishing rapidity. As in England, and in most other regions, the 

 seasons, and more especially the winter, vary in different years, so that it 

 is difficult to form a correct opinion from the experience of any one year. 

 There are winters during which southwesterly winds prevail, often cloud- 

 ing the sky and bringing rain at intervals throughout the winter. Such 

 were the winters of 1864-65, and of 1868-9. 



During the summer but little or no rain falls. In some years the drought 

 lasts, without cessation, for six or seven months, from April or May to 

 October or November. Thence the absolute necessity of tanks for the irri- 

 gation of the lemon and orange trees, which, as we have stated, cannot 

 thrive and bear fruit without irrigation during the dry season. The excep- 

 tional dryness of the summer along the Riviera, in the south of France, 

 in Spain, and in the Mediterranean generally, is explained by the fact that 

 this great inland sea lies on the northern limit of that part of the earth's 

 surface to which, in physical geography, is given the name of the rainless 

 tract. The highest expression of this region is the desert of Sahara, which 

 continues those of Arabia and Central Asia. The principal cause of their 

 existence is, no doubt, the passage of northeasterly winds over Asia and 

 southern Europe during the entire year, either as upper or surface currents. 

 These winds passing over continents and great chains of mountains, gradu- 

 ally lose their moisture, until they have but little to bestow on the regions 

 they attain in the more advanced stage of their progress, and the latter 

 consequently become dry regions or deserts for want of rain. The winds 

 that course over the earth's surface may be divided into two principal 

 currents. 



The one, from the poles to the equator; the other, a return current from 

 the equator to the poles. 



Owing to the earth's diurnal motion of rotation, the wind from the poles 

 to the equator takes a slanting easterly direction; that from the equator to 

 the poles a westerly one. Thus, in the northern hemisphere the wind from 

 the pole to the equator is a northeast wind; that from the equator to the 

 pole a southwesterly one. From the tropic of Cancer, or from about lati- 

 tude 30° to the equatorial region, the northeast wind is always a surface 

 wind, and constitutes the northeast trade. From the pole to the tropic the 

 systemic northeast wind is either an upper current or a surface one, accord- 

 ing to seasons and other influences. 



According to M. de Brea's statistics, omitting the fractions, the annual 

 number of fine days in which the sun shines without clouds is 214; the 

 number of days in which the sun shines with clouds is 45; and the num- 

 ber of days in which the sun is not seen, the sky being completely obscured, 

 without rain, is 24; to which we may add: days of rain, 80, many in part 

 sunshiny. 



The rainy days principally occur between the months of October and 

 May. In summer, as has been stated, there is sometimes not a drop of 

 rain for months together. The winds can then blow from the south with- 



