Dr Knox on the Climate of Southern Africa. 285 
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whilst crossing this belt or zone. The calms which constantly 
prevail, are attended with alarming squalls, heavy gales, and al- 
most continual rains. A sultry and intolerable suffocating heat, 
which at no season of the year is absent, occasions fevers 
among the crew, and gives a temporary shock to the strongest 
nerves. This is not to be ascribed altogether to the actual tem- 
perature of the air in this climate, but to its being combined 
with moisture , to which union may fairly be attributed the ori- 
gin of most epidemic fevers. The meteorologist will readily 
imagine the direful effects likely to arise to the human frame, 
when the temperature of the air, and its humidity, are much 
increased beyond what happens at sea, between the latitudes 
of 15® N. and 15° S. But innumerable meteorological obser- 
vations shew, that large continents, or extensive islands, possess 
a climate totally different from that of the great ocean, the tem- 
perature of the air being much increased during summer, and 
diminished in winter ; and moreover, being liable to sudden al- 
ternations from hot to cold, and vice versa ; changes which ne- 
ver happen at sea. The atmosphere also over land, is apt in 
various situations to become surcharged with moisture, which, 
combined with great heat, is the undoubted cause of those fa- 
tal fevers known in various parts of the world, under a variety 
of names, by some supposed to originate in contagion, and by 
others in marsh miasmata. In temperate and cold climates, a 
humid atmosphere gives rise to intermittents or agues *. 
When we examine the great zone comprised between 20® 
N. and 15° S. latitude, we find that nearly all those places which, 
have been rendered famous by the destruction of European ad- 
venturers, are included in it. On the American continent, 
* It cannot surely be necessary to point out to those accustomed to meteorology 
cal enquiries, that the atmosphere resting on the great ocean, by the equability of its 
temperature, and the uniformity of its qualities as to moisture, will, under very 
few circumstances, be found capable of exercising over the human frame the same 
dreadful powers as the inconstant air of a continent or large island, subject to end- 
less variations, from the change of seasons, and even by the alternation of day and 
night. The doctrine of marsh miasmata may fairly be ascribed to an unwillingness 
in the human mind to admit as the sole cause of destructive epidemic fevers a phe- 
nomenon so simple as a change in the constitution of the atmosphere, regarding its 
temperature or moisture ; and one, too, apparently so inadequate to the production 
of such dire effects. Those who cannot explain the origin of remittent and in- 
termittent fevers, without having recourse to marsh miasmata , will find it difficult 
VOL. V. NO, 10. OCTOBER 1821. 
V 
