the Circulation of the Atmosphere. 363 



ward course to throw off branches to the southward, which, as 

 violent gales in the Gulf of Lyons, or under the various names of 

 mistral, tramontana, bora, gregaglia, and levanter, are well known 

 to Mediterranean cruisers. These, again, there is fair reason to 

 suppose, form the eastern wind which so largely prevails over 

 the deserts of North-western Africa, and the hot wind charged 

 with red sand so often felt near the Cape de Verde Islands, 

 where it mingles with the trade, and is lost iu the general system 

 of circulation. 



In comparison with the North Atlantic, other oceans may be 

 considered as but little known, or not at all except in those parts 

 where a quick-witted experience has mapped out the roads to 

 distant ports. But examining the logs of ships making long 

 voyages (and there can scarcely be a more valuable collection 

 than that given in the ' Sailing Directions '), we find a mass of 

 evidence amounting almost to satisfactory proof that the calm 

 region in the South Atlantic is confined to the neighbourhood of 

 Tristan d'Acunha, and towards the north-west quarter from that 

 island, that in the western part of the ocean the south-east 

 trade, in a comparatively low latitude (in 18° or 20°), very com- 

 monly changes to a north-easterly, and so, through north, to a 

 north-westerly breeze, whilst on the eastern side the southerly 

 or south-easterly wind frequently, and in the southern summer 

 generally, carries homeward-bound ships from the Cape into the 

 trades without hindrance from any intermediate calms. From 

 the accounts of travellers in South America there is reason to 

 believe that the trade- wind also recurves over the continent. 

 The northern part of this huge mass of land is so flat that the 

 influence of the tide is felt on the great rivers very far into the 

 interior; the trade-wind blows as nearly as possible due east up 

 the lower Amazon for a great part of the year, but on the upper 

 Amazon it is never felt, whilst on the other hand it blows daily 

 and with remarkable force up the Tapajos, a large tributary of 

 the Amazon which flows from the south. (Bates, ' Naturalist on 

 the Amazons/ vol. ii. pp. 143 et seq.) 



Captain Maury represents the trade-wind as passing over the 

 tops of the Andes and descending on Peru as a wind intensely 

 dry. (Sailing Directions, vol. i. p. 25.) This is scarcely borne 

 out by evidence. There is no proof that the trade reaches so far 

 inland as even the foot of the mountains ; these are, moreover, 

 on that side exceedingly steep, and present a barrier to the pas- 

 sage of the wind which, in the absence of proof to the contrary, 

 I believe to be insuperable. The force required to raise such a 

 mass of air to such a height would be enormous ; the necessary 

 horizontal force acting against a very steep and very rough in- 

 clined plane would be almost beyond conception. But in point 



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