CLIMATE 11 
2. Altitude-—The temperature falls as we rise above 
the sea-level just as it falls as we recede from the Tropics. 
In consequence of this, the succession of vegetation 
up a mountain is much the same as that which we observe 
as we proceed along the earth’s surface from the Equator 
to the Poles. 
II. Humidity. 
Water has a high capacity for heat ; in other words, 
it takes a relatively large amount of heat to raise its 
temperature one degree ; it is slow to get warm and slow 
tocool. This fact has an important bearing upon climate, 
for where there is a great deal of water-vapour present 
in the air, the variations and extremes of temperature 
are not so marked as in the case of a dry atmosphere. 
The climate is more equable, the summers being cooler 
and the winters milder than in drier countries ; nor does 
the night-temperature differ so greatly from the day. 
1. Rainfall.—This is by far the most important factor 
in climate, and as we are here concerned with the 
effects of rain on vegetation, the following considerations 
with respect to the rainfall become very important : 
(a) The actual number of inches of rain falling in a 
year. The effect of this varies with the temperature. 
In a hot country a much larger rainfall is necessary to 
serve the needs of the vegetation than in a cold country ; 
for example, the minimum amount of rain necessary 
to maintain forest will not be the same in all latitudes. 
In dealing with climatic effects, heat and moisture must 
always be considered together. 
(b) The frequency of rainy days. This is more impor- 
tant than the actual quantity of rain which falls in a 
year. Occasional torrents, however heavy, influence 
climate, and therefore vegetation, far less than precipita- 
tions, which, though less in quantity, are more evenly 
distributed throughout the season. 
(c) The season of greatest rainfall. Rain falling during 
the season of vegetative inactivity is largely lost to 
vegetation. Most rain should fall when the vegetation 
needs it most—that is, in summer. 
2. Proximity to the Sea.—Countries near the sea 
generally enjoy a mild and moist climate, especially 
when the winds that reach them come laden with moisture 
