= 
TEMPERATURE OF THE SEA. 65 
continents of Asia and Africa, it attains a much 
greater elevation. The difference between the tem- 
perature of the day and night is also less than on 
land. 
Temperature of the Sea.—From Corunna to the 
mouth of the Tagus, the temperature of the sea 
varied little (between 59° and 60°8°) ; but from lat. 
39° to 10° N., the increase was rapid and generally 
uniform (from 59° to 78°4°), although inequalities 
occurred, probably caused by currents. It is very 
remarkable that there is a great uniformity in the 
maximum of heat every where in the equinoctial 
waters. This maximum, which varies from 82° to 
84:2°, proves that the ocean is in general warmer 
than the atmosphere in direct contact with it, and 
of which the mean temperature near the equator is 
from 78°8° to 80-6°. 
Hygrometrical State of the see Tes the 
whole of the voyage, the apparent humidity of the 
atmosphere indicated by the hygrometer underwent 
a sensible increase. In July, in lat. 13° and 14° N 
Saussure’s hygrometer marked at sea from 88° to 
92°, in perfectly clear weather, the thermometer 
being at 75:2°. On the banks of the Lake of Geneva 
the mean humidity of the same month is only 80°, 
the average heat being 662°. On reducing these 
observations to a uniform temperature, we find that 
the real humidity in the equinoctial basin of the 
Atlantic Ocean is to that of the summer months 
at Geneva as 12 to 7. This astonishing degree of 
moisture in the air accounts to a great extent for 
the vigorous vegetation which presents itself on the 
coasts of South America, where so little rain falls 
throughout the year. 
D 
