/ 
c 284 Dr Knox on ike Climate of Southern Africa . 
occult qualities the healing powers of marine air in several dis- 
eases, and more particularly in pulmonary consumption. Ei- 
ther not understanding, or not believing in the extraordinary 
equability of temperature which prevails in the air over exten- 
sive oceans, they have ridiculously ascribed the effects arising 
from this alone to the u saline humidity of marine air; to its 
greater density and elasticity ; and to its being more agitated 
by winds.” Nearly all the facts which the Annals of Medicine 
contain, tend to prove, that, to the mildness and equability of 
marine air, is to be ascribed its extreme salubrity in consump- 
tive diseases ; and by reflecting on this fact, we may see the ab- 
surdity of directing consumptive patients to sail along a coast, 
or in an inland-sea, where the temperature of the marine air dif- 
fers but little from that of the neighbouring continent or island. 
It is, for example, well known to Greenland whalers, and sea- 
faring men trading to the North Seas, that the Baltic is often 
frozen, when the great ocean, ten degrees farther north, is open, 
and the weather mild. Seamen are made aware of the vicinity 
of land, by the sudden cooling of the air and of the sea ; and 
this, indeed, is reckoned an almost infallible test of their ap- 
proaching the coast. 
The effects of the sun’s declination on the temperature of the 
great ocean situated within the Tropics, or of its atmosphere, are 
inconsiderable. This is sufficiently proved by tables of the 
temperature, which have been kept by some individuals, and 
by the uniform weather experienced whilst crossing these fatal 
climates. Yet there would seem to exist a certain difference be- 
tween the climate of the northern and southern hemispheres, 
even within the tropics. The very peculiar climate called by 
sailors the Rains , is found to exist only to the north of the 
Line, between the Equator and the 13th degree of north lati- 
tude. These Rains extend nearly across the ocean, in a belt, 
varying in breadth, but having generally about ten degrees of 
latitude. They are felt in every degree of longitude between 5° 
and 30° W., nor are they experienced more severely at any one 
point than at another. Formerly, when the art of navigation 
had not reached that perfection which it has now attained, ves- 
sels bound to the southern hemisphere were wont to make dis- 
astrous voyages, attributable often to delays of many weeks 
