424 Proceedings of the Royal Physical Society. 
in the northern and southern parts of a temperate zone 
for acclimatisation purposes. Individuals and nations are 
not only influenced by the climatology of their original 
residence, but also by their habits and customs and their 
psychical peculiarities. It has been found, as was pointed 
out long ago by Mr Ravenstein, that the peoples of Southern 
Europe, such as the Italians and southern Frenchmen, can 
withstand the climate of sub-tropical Africa better than can 
northern Europeans. “A steady stream of migration is in 
fact setting in in that direction. Germans and Belgians are 
pouring into France; Frenchmen are going to Algeria; the 
Arabs from the shores of the Mediterranean have found their 
way into the Soudan; whilst the Soudanese are pushing 
forward into Bantu Africa. A similar movement is going on 
in South Africa. The descendants of those Dutchmen who, a 
couple of hundred years ago, first settled at the Cape have 
made their way to the Transvaal; and European migration, 
favoured by geographical features, is being pushed even 
within the Tropics towards the Zambesi.” 
This agrees with my own opinion, that wholesale immediate 
acclimatisation for Europeans in Tropical Africa is entirely 
out of the question. 
But it may be said, What about the high African table- 
land? What about the mountainous regions? As it is 
customary to speak of three climatological zones—the hot, 
the temperate, and the cold—between the equator and the 
poles, so in like manner we can say that in the Tropics there 
are three vertical zones of climate. (1) A zone extending up 
to a height of 3000 feet, having a mean annual temperature 
of from 72° F. to 83° F.—the hot zone; (2) a zone from 
3000 to 12,000 feet, with a mean annual temperature of from 
41° to 72° F.—the temperate zone; (3) a zone from 12,000 
to 16,000 feet or above, with a mean annual temperature of 
from 30° to 41° F.—the cold zone. Each zone has peculi- 
arities of its own with regard to the presence or absence of 
_ disease, and the higher the altitude of the region within 
certain limits, the more nearly it approaches the climate of 
Europe. As we proceed, however, north or south of the 
equator, the boundaries of those: zones are found at gradually 
