378 
ATMOSPHERIC HEAT. 
heated by the radiant caloric which the perpendicular rocks 
emit from the time the sun sets. The examination of the 
thermometric observations made during nine months at La 
Gruayra by an eminent physician, enabled me to compare the 
climate of this port, with those of Curnana, of the Havannah, 
and of Vera Cruz. This comparison is the more interesting, 
as it furnishes an inexlmustiblo subject of conversation in 
the Spanish colonies, and among the mariners who frequent 
those latitudes. As nothing is more deceiving in such 
matters than the testimony of the senses, we can judge of 
the difference of climates only by numerical calculations. 
The four places of which we have been speaking are con- 
sidered as the hottest on the shores of the New World. A 
comparison of them may serve to confirm what we have 
several times observed, that it is generally the duration of a 
high temperature, and not the excess of heat, or its absolute 
quantity, which occasions the sufferings of the inhabitants of 
the torrid zone. 
A series of thermometric observations shows, that La 
Gruayra is one of the hottest places on the earth ; that the 
quantity of heat which it receives in the course of a year is 
a little greater than that felt at Cumana; but that in the 
months of November, December, and January (at equal 
distance from the two passages of the sun through the 
zenith of the town), the atmosphere cools more at La 
Gluayra. May not this cooling, much slighter than that 
which is felt almost at the same time at Vera Cruz and at 
the Havannah, he the effect of the more westerly position of 
La G-uayra ? The aerial ocean, which appears to form only 
one mass, is agitated by currents, the limits of which are 
fixed by immutable laws ; and its temperature is variously 
modified by the configuration of the lands and seas by which 
it is sustained. It may be subdivided into several basins, 
which overflow into each other, and of which the most 
agitated (for instance, that over the gulf of Mexico, or 
between the sierra of Santa Martha and the gulf of Darien) 
have a powerful influence on the refrigeration and the motion 
of the neighbouring columns of air. The north winds some- 
times cause influxes and counter-currents in the south-west 
part of the Caribbean Sea, which seem, during particular 
months, to diminish the heat as far as Terra Pinna. 
