CLIMATE AND SOCIAL DEVELOPMENT. 325 



quills ; . . . paper, becoming soft and soppy by the loss of glazing, 

 acts as a blotter ; . . . metals are ever rusty ; . . . and gunpowder, 

 if not kept from the air, refuses to ignite." 



But it is the direct effects of different hygrometric states which 

 must here be more especially set down — the effects on the vital pro- 

 cesses, and therefore on the individual activities, and, through them, 

 on the social activities. There is good reason, inductive and deduc- 

 tive, for believing that the bodily functions are facilitated by atmos- 

 pheric conditions which make evaporation from the skin and lungs 

 tolerably rapid. That weak persons, whose variations of health fur- 

 nish good tests, are worse when the air, surcharged with water, is 

 about to precipitate, and are better when the weather is fine, and that 

 such persons are commonly enervated by residence in moist localities 

 but invigorated by residence in dry ones, are facts generally recog- 

 nized. And this relation of cause and effect, manifest in individuals, 

 is one which we may suspect holds in races — other things being equal. 

 In temperate regions, differences of constitutional activity due to dif- 

 ferences of atmospheric humidity, are less traceable than in torrid re- 

 gions, the reason being, that the inhabitants are subject to a tolerably 

 rapid escape of water from their surfaces, since the air, though well 

 charged with water, will take up more when its temperature, previ- 

 ously low, is raised by contact with the body. But it is otherwise in 

 tropical regions where the body and the air bathing it differ much less 

 in temperature, and where, indeed, the air is often higher in tempera- 

 ture than the body. Here the rate of evaporation depends almost 

 wholly on the quantity of surrounding vapor. If the air is hot and 

 moist, the escape of water through the skin and lungs is greatly hin- 

 dered; while it is greatly facilitated if the air is hot and dry. Hence, 

 in the torrid zone, we may expect constitutional differences between 

 the otherwise-allied inhabitants of the low, steaming tracts and the 

 tracts which are habitually parched with heat. Needful as are cuta- 

 neous and pulmonary evaporation for maintaining the movement of 

 fluids through tiie tissues, and thus furthering molecular changes, it 

 is to be inferred that, other circumstances being alike, there will be 

 more bodily activity in the people of hot and dry localities than in the 

 people of hot and humid localities. 



The evidence, so far as we can disentangle it, justifies this infer- 

 ence. The earliest recorded civilization grew up in a hot and dry re- 

 gion — Egypt; and in hot and dry regions also arose the Babylonian, 

 Assyrian, and Phojnician civilizations. But the facts when stated in 

 terms of nations are far less striking than when stated in terms of 

 races. On glancing over the rain-map of the world, there will be seen 

 an almost continuous area marked " rainless district," extending across 

 North Africa, Arabia, Persia, and on through Thibet into Mongolia; 

 and from within, or from the borders of, this district have come all 

 the conquering races of the Old World. We have the Tartar race, 



