RAIN 



RAINBOW 



565 





Rangoon 99, Tavoy 197, Mergui 162, and Port 

 Blair 117. In the north-east angle of the Bay 

 of Bengal, and thence north to Bhutan, where the 

 summer monsoon curves to a westerly course up 

 the valley of the Ganges, the rainfall is great, 

 rising at Cherra-punji, in the Khasi Hills dis- 

 trict, to 472 inches or nearly 40 feet being the 

 largest known rainfall anywhere on the globe. 

 Owing to this diversion in the course of the mon- 

 soon, the valley of the Ganges enjoys a generous 

 rainfall. On the other hand, tlie rainfall is small 

 over the plains of the Punjab, being at Multan 

 6 P 79, and at Kiirrachee ~"25, increasing over the 

 higher parts of the province, at Lahore 21, Um- 

 balla 36, Simla 70, and Dharmsala 122. 



The key to the distribution of the rainfall over 

 the East Indian Archipelago and Australia is the 

 distribution of pressure from south-eastern Asia to 

 Australia, with the resulting prevailing winds. 

 During the winter months pressure diminishes 

 rapidly from Asia southwards, and northerly winds 

 prevail. Now, as these winds have travelled a 

 great breadth of ocean, they arrive in a highly 

 saturated state and deposit a heavy rainfall over 

 these islands and the north of Australia. The 

 degree to which these rains penetrate into Aus- 

 tralia depends entirely on the strength of the 

 winter monsoon. On the other hand, during the 

 summer months pressure increases from Asia south- 

 wards, and southerly winds set in from Australia 

 to Asia, distributing in their course a very large 

 rainfall over the Islands of the Eastern Archi- 

 pelago, rising at several places to 30 inches a 

 month. The small rainfall in such islands as 

 Timor, which are more immediately sheltered, as 

 it were, by Australia during these southerly 

 winds, impresses on the region well-marked dry 

 and wet annual seasons. These marked differences 

 among the climates of this archipelago really 

 depend on the geographical distribution of land 

 and sea in this part of the globe, and must there- 

 fore be regarded as permanent differences, ami its 

 having played no inconspicuous part in the unique 

 distribution of animal and vegetable life which is 

 so characteristic of the archipelago. Since in the 

 summer of the southern hemisphere the winds blow 

 from the sea inland, and in the winter from the 

 laud seaward, it follows that generally the summer 

 is the rainiest season. In the interior, along the 

 Murray Kiver and its affluents, the rainfall every- 

 where is necessarily small. In the north of New 

 Zealand the winter rainfall is the heaviest, but 

 farther south, where the wet westerly winds prevail 

 with some constancy at all seasons, the rainfall 

 is distributed pretty equally through the year, and 

 is of course largest on the western slopes of these 

 islands. Thus, while in the east it is at Dunedin 

 34 and at Christchurch 28 inches, in the west it 

 is at Hokitika 120, and at Beaby, inland, 106 

 inches. 



Europe as regards its rainfall may be divided 

 into two regions the countries bordering on the 

 Mediterranean, and the rest of the continent. A 

 vast ocean on one hand, a great continent on the 

 other, and a prevalence of westerly winds rule the 

 distribution of the rainfall in western and northern 

 Europe. Now, since these westerly winds have 

 traversed a vast extent of ocean before arriving at 

 the land, they distribute a large rainfall, particu- 

 larly on hilly regions opposing their course. Thus, 

 over a large part of the Highlands of Scotland 

 more than 80 inches fall annually, and over fully 

 one-third of the British Islands the annual amount 

 exceeds 40 inches. On the other hand, in eastern 

 districts on the lee side of the great mountain- 

 ranges, the rainfall does not exceed 30 inches over 

 a large portion of England, and in some of the 

 beet agricultural districts of Scotland. In the 



west of Norway it is 72 inches at Bergen, 46 inches 

 at the Lofoden Isles, and 10 inches at the North 

 Cape ; over large portions of Sweden it is 21 inches, 

 and in Russia and Siberia it varies from 20 to 2 

 inches. Spain presents great extremes, from 70 in 

 the north-west to 13 inches at Saragossa. In the 

 plains of France and Germany it varies from 20 to 

 35 inches, rising, however, on approaching the 

 Alps to more than 100 inches. In western Europe 

 the greater part of the rain falls in winter, but in 

 the interior of the continent in summer. The 

 summer climates of the extreme south of Europe 

 and in the north of Africa, situated at compara- 

 tively low levels, are practically rainless, owing to 

 the northerly winds that set in with considerable 

 force at this time of the year towards the heated 

 plains of the Sahara. 



The summer winds in the south-east of the 

 1 Tnited States are southerly ; and, as they have 

 previously traversed a considerable extent of ocean, 

 they arrive well but not super-saturated, and pour 

 down a monthly rainfall of 6 inches or more from 

 Louisiana to Chesapeake Bay. The comparative 

 equableness of the rainfall over the eastern states 

 is the result of no mountain-ridges lying athwart 

 their path and of the winds passing into higher 

 latitudes and therefore cooler regions. Again, 

 the distribution and amount of the summer rain- 

 fall in the west and north of the United States is 

 really determined by the low atmospheric pressure 

 which has its centre in the region of the Kocky 

 Mountains. To the west of this low pressure 

 winds are generally north-westerly, and as they 

 thus pass into hotter regions the summer rainfall 

 in these parts of the United States and Canada 

 is either nothing or very small ; whereas on the 

 east side winds are southerly, and the rainfall con- 

 sequently equals, or even exceeds, that of the finest 

 agricultural districts of Great Britain. 



As regards the rainfall of the two extreme 

 months, January and July, the following show in 

 inches the amounts for various places : Vera Cruz, 

 5-10 and 35-90; Para, 6 "51 and 3"26; Manaos, 7 "33 

 and 1'82 ; Buenos Ayres, 2 - 37 and 1'70 ; Corricntes, 

 5^24 and 2'67 ; and in Africa, Alexandria, 1 !)."> and 

 0-20; Algiers, 4'43 and 0'04 ; Senegal, 0'28 and 

 3-00; Sierra Leone, 0'69 and 24 '20; Capetown, 

 0-28 and 3'83 ; Durban, 5 '00 and 1'70; and Zanzi- 

 bar, 2 '02 and 2'35. The explanation of these and 

 similar differences is found in the seasonal changes 

 of the wind. The South African colonies present 

 the strongest aspects of climate, so far as the rain- 

 fall is concerned, being divided into two totally 

 distinct classes, the climates of the Natal coast 

 and of the inland regions where the rains occur 

 during the summer months, and the climates of the 

 other regions where the rains fall chiefly during 

 the winter months. The driest region of Africa is 

 doubtless the Sahara, and the wettest the region 

 from the Victoria Nyanza northwards, including 

 the gathering-grounds of the Nile. 



See METEOROLOGY, RAIN-GAUGE; also BLOOD-BAIN, 

 and, for showers of frogs and fishes, SHOWERS. For maps 

 of annual rainfall of the globe, see Loomis in Silliman'i 

 Amer. Jour. Sci., Murray in jour. Roy. Scot. Geo. Soc., 

 and I l.-uni in Climatoloi/ical Atta. For particular coun- 

 tries, Symons, and Buchan for the British Islands ; 

 Ranlin for France and Algiers ; Blanford and Elliot for 

 India ; the Dutch for East India Islands ; Tod, Kus*ell, 

 Hector Ellery, and \Vragge for Australasia ; the Siynal 

 Service for the United States ; Carpmael for Dominion of 

 Canada ; the Meteorological Services of the different 

 European countries, \<; 



Rainbow. The rainbow is the best known 

 of all optical meteorological phenomena, consist- 

 ing of a coloured arch formed opposite the sun 

 on falling raindrops, and visible whenever the 

 necessary conditions of a passing shower on one 

 side and a clear and not too high sun ou the 



