CLIMATE. 
Under the term climate are comprised the results of the influ- 
ences of geographical position, of prevailing winds, elevation 
of country, and the disposition of the mountains and seas of any 
particular latitude. These result in producing a certain mean 
temperature, a certain annual fall of rain, and the stimulant 
effects of light and electricity ; so that when the climate of any 
latitude is spoken of, all the circumstances enumerated above 
are supposed to be taken notice of. 
A slight review of these circumstances as affecting the Isth- 
mus is given here ; at the same time it may be stated, that the 
data upon which this portion of the report is based has been 
necessarily limited, the time of those engaged in the survey not 
allowing of occupation in experiments devoted to this object. 
The facts stated here, however, have been derived from obser- 
vation, and the inferences drawn are trustworthy. 
As a regular mountain-chain the Andes may be said to de- 
scend suddenly at Panama, and are merely continued northward 
to join the Rocky Mountains by a mass of elevated ground, with 
an irregular mixture of mountains and table-land. This table- 
land occupies the greater part of Mexico or Anahuac. It com- 
mences at the Isthmus of Tehuantepec, and passes northwest to 
latitude 42°, an extent of 1600 miles. This land is narrow at 
its southern limit, and widens northward to the latitude of the 
city of Mexico, where it is 300 miles across its greatest breadth, 
and where also its elevation is greatest ; from this point north- 
ward the plateau again descends. Southward this elevated 
plain borders on the table-land of Guatimala, which is much 
more elevated above the ocean level, except in certain passes 
