326 THE POPULAR SCIENCE MONTHLY. 



which, passing the southern mountain-boundary of this rainless dis- 

 trict, peoi:>led China and the regions between it and India — thrusting 

 the aborigines of these areas into the hilly tracts; and which has sent 

 successive waves of invaders not into tliese regions only, but, from 

 time to time, into the West. We have the Aryan race, overspreading 

 India and making its way westward through Europe. We have the 

 Semitic race, becoming dominant through Korth Africa, and, spurred 

 on by Mohammedan fanaticism, conquering parts of Europe. Ihat is 

 to say, besides the Egyptian race, which, seeming by its alliances to 

 have originally been of low type, became powerful in the hot and dry 

 valley of the Nile, we have three races, widely unlike in type, and 

 speaking languages classed as fundamentally distinct, which, from 

 different parts of the rainless district, have spread as invaders over 

 regions relatively humid. 



Original superiority of type was not the common trait of these 

 races : the Tartar type is inferior, as well as the Egyptian. But the 

 common trait, as proved by subjugation of other races, was energy. 

 And when we see that this common trait, in races otherwise unlike, 

 had for its concomitant their long-continued subjection to these special 

 climatic conditions — when we find further, that from the region char- 

 acterized by these conditions, the earlier waves of conquering emi- 

 grants, losing in moister countries their ancestral energy, were over- 

 run by later waves of the same races, or of other races coming frcm 

 this region, we get strong reason for inferring a relation between con- 

 stitutional vigor and the presence of an air which, by its warmth and 

 dryness, facilitates the vital actions. 



A striking verification is at hand. On turning to the rain-map, it 

 will be seen that, of the entire New World, the largest of the parts dis- 

 tinguished by the absence of shade as almost rainless, is that Central 

 American and Mexican region in which indigenous civilizations devel- 

 oped ; and that the only other rainless district is that which formed 

 part of the ancient Peruvian territory — the part, moreover, in which 

 the pre-Inca civilization has left its most conspicuous traces. Induc- 

 tively, then, the evidence justifies in a remarkable manner the physio- 

 logical deduction. 



Nor are there wanting minor verifications. Comparisons among 

 African races are suggestive of similar contrasts in constitution, simi- 

 larly caused. Of the varieties of negroes Livingstone remarks ("Mis- 

 sionary Travels," p. V8) : *' Heat alone does not produce blackness of 

 skin, but heat with moisture seems to insure the deepest hue ; " and 

 Schweinfurth, in his lately-issued "Heart of Africa," similarly remarks 

 on tlie relative blackness of the Denka and other tribes living on the 

 alluvial plains, and contrasts them with " the less swarthy and more ro- 

 bust races who inhabit the rocky hills of the interior" (vol. i., p. 148). 

 There seem, generally recognizable, corresponding differences in en- 

 ergy and social advance. But I note this difference of color arising 



