CLIMATE. 1^9 
tropical. The proximity of the Sierra Madre, whose summits 
are always enveloped in clouds, tends to lower the temperature 
of the upland district very remarkably. 
On the Pacific plains, and about Tehuantepec, the thermom- 
eter ranges as high as 92° ; but this temperature is softened 
down by the breezes which blow off shore and from the moun- 
tains. Sefior Moro states, that when the thermometer on the 
plains ranges about 85° Fahr., it is not more than 56° at Chivela 
or Tarifa. 
The altitude of the table-lands of Guatimala and Mexico has 
a more powerful effect in determining the climate of the Isthmus, 
than what the mere latitude, or its own elevation, could lead to 
believe. This table-land has an average elevation of from 6500 
to 8200 feet above the sea, which would give a mean tem- 
perature of 20° throughout the year, less than that of the sea- 
board : thus, if the temperature of the coast be 85°, that of the 
table-land would be 65°, which is a truly temperate climate, 
although within tropical latitudes. This is proved by the growth 
of oak, cypress, pine, and fern trees, which are inhabitants of a 
temperate clime ; and most of the cerealia of northern latitudes 
grow in luxuriance. The average height of the table-land of 
Guatimala gives a mean temperature of 60° through the year, 
and the lands are called Tierras frias. JSTow, it must be recol- 
lected that the Isthmus of Tehuantepec, though in itself possess- 
ing only an elevation calculated to lessen the temperature at the 
sea-board by a few degrees, is subject to the influences of the 
land in its neighborhood, and its own warmth is very much 
reduced by the cool air descending from the high table-lands 
and from the Sierra Madre, spreading over the lowland by its 
density, cooling the surface of the ground, and mixing with the 
warm air of the Pass. 
The climate of the northern division of the Isthmus is damp, 
but as it is not so warm as that of the south, it is not of neces- 
sity unhealthy. 
During the prevalence of northers on the more elevated sec- 
tions to the east, as the Ghimalapas, for example, the atmosphere 
is damp and heavy, with a chilly mist like that experienced on 
the northern coast of Ireland. But otherwise the climate is 
