362 Coffee Culture on tbe Soutbern Coast of Cbiapas. 



The division of the terrestial globe into five zones, the torrid, the 

 two temperate, and the two frigid, merely gives a general idea of the 

 average temperature of those portions of the earth, because the force 

 of the sun's rays is modified by other diverse causes, which bring 

 about the result that in the same latitude various kinds of temperature 

 may exist. 



In order to determine the climate of a locality, various circumstances 

 must be taken into account, the principal ones being the following : 



1. Latitude. Generally, latitude determines the temperature of the 

 locality, because the nearer it is to the equator the greater will be the 

 amount of heat that it will receive, and such amount will diminish in 

 proportion as the locality may be far away from the equatorial line. 

 For that reason the line of perpetual snow is low as one approaches the 

 poles ; at the equator it is about three miles, and at the poles it is at 

 the level of the sea : at 20 of latitude it is about 14,000 English feet 

 above the sea : within the tropics its altitude is from 15,000 to 20,000 

 feet above the sea ; at 30, about 12,000 ; at 40, about 10,000 : at 60, 

 about 4000 ; at 70, about 2000 : and at 8, is at sea level. 



It is also to be noticed that the line of perpetual snow is higher 

 between the 10 and 20 from the equator than at the equator itself ; 

 this may probably be due to the fact that at the equator the sun only 

 remains 12 hours above the horizon, while near the tropics the 

 longest day is about 13^ hours, and as during that time the sun's rays 

 fall vertically, or nearly so, the heat in summer is greater than on the 

 equator. 



2. Altitude. Temperature becomes colder in proportion to the 

 altitude of a place, and the influence of altitude is felt quicker than 

 that of latitude. If we travel from the equator towards the poles along 

 the sea-level, we have to go many kilometers before a change of tem- 

 perature is noticeable, whilst as soon as we begin to ascend from the 

 level of the sea, a very decided change of temperature is experienced. 

 The ascent of 180 English feet merely, brings about the same change 

 of temperature as travelling one whole degree of latitude, or say, 169^ 

 English miles, from the equator towards the poles. At an elevation of 

 15,000 English feet above the level of the sea, we reach perpetual 

 snow in the equator, that being a climate which corresponds along the 

 sea-level to 70 of latitude. For the first 1000 feet of elevation above 

 the level of the sea the temperature descends more than 7, and higher 

 up about i for every 500 feet on an average, and it continues to de- 

 scend less rapidly in proportion as the elevations become greater. 



3. Location of Mountain Chains. If the mountain chains are situ- 

 ated in the northern hemisphere, from east to west, the side that looks 

 to the north is exposed to cold winds, and that looking to the south is 

 sheltered from them, but has the southern winds ; the former, there- 



