§ 318, 319. RED FOGS AND SEA BREEZES. I35 



a desert — a rainless country, upon which the rays of the sun play 

 with sufficient force not only to counteract the trade-wind power 

 and produce a calm, but to turn the scale, and draw the air back 

 from the sea, and so cause the sea-breeze to blow regularly. 



818. On the coast of Africa, on the contrary, a rank vegetable 

 Influences which reg- growth scrccus the soil from the scorching rays of 

 uiate their strength. ^^^ ^^^^ ^^^ ^■)^q rarcfactiou is not every day suffi- 

 cient to do more than counteract the trade- wind force and produce 

 a calm. The same intensity of ray, however, playing upon the 

 intertropical vegetation of a lee shore, is so much force added to 

 the sea-breeze ; and hence, in Brazil, the sea-breeze is fresh, and 

 strong, and healthful ; the land breeze feeble, and therefore not so 

 sickly. Thus we perceive that the strength as well as regularity 

 of the land and sea breezes not only depend upon the topography 

 of a place, but also upon its situation with regard to the prevail- 

 ing winds ; and also that a given difference of temperature be- 

 tween land and water, though it may be sufficient to produce the 

 phenomena of land and sea breezes at one place, will not be ade- 

 quate to the same effect at another; and the reason is perfectly 

 philosophical. 



819. It is easier to obstruct and turn back the current in a slug- 

 Land breezes from msh than in a rapid stream. So, also, in turning a 



the west coast of Af- ' < o 



rica scorching hot. currcut of air first upon the land, then upon the sea 

 — very slight alternations of temperature would suffice for this on 

 those coasts where calms would prevail were it not for the land 

 and sea breezes, as, for instance, in and about the region of equa- 

 torial calms ; there the air is in a state of rest, and will obey the 

 slightest call in any direction ; not so in regions where the trades 

 blow over the land, and are strong. It requires, under such cir- 

 cumstances, a considerable degree of rarefaction to check them 

 and produce a calm, and a still farther rarefaction to turn them 

 back, and convert them into a -regular sea-breeze. Hence the 

 scorching land-breeze (§ 817) on the west coast of Africa : the 

 heat there may not have been intense enough to produce the de- 

 gree of rarefaction required to check and turn back the southeast 

 trades. In that part of the world, their natural course is from the 

 land to the sea, and therefore, if this view be correct, the sea-breeze 

 should be more feeble than the land-breeze, neither should it last 

 so long. 



