87.Climate. -The average succession of weather changes through-out the year, considered for a long period of years, constitutes the climate. Thus, if the average temperature of a place throughout the year has for a long period been found to be high, and the rainfall largeand uniformly distributed, the place is said to have a hot and humid climate. The climate is a generalized statement of the weather. Two places may have the same average temperature throughout the year without having the same climate, as in one the temperature may be quite uniform and in the other very high at one season and very low at another. Many factors enter into the making up of a comprehensive statement of climate.
88.Effect of Climate upon Animals and Plants. -Plants aregreatly affected by climate. The ornamental palm and orange trees, which are sometimes cultivated in the north, have to be protected fromt h e w i n t e r c o l d w i t h great care, whereas in southern climates they grow and flourish as the apples and pears do in the north. Corn and w h e a t a r e t h e s t a p l e agricultural products of the northern part of the United States, while cotton, rice and orangesA SOUTHERN COTTON FIELD.
are of the southern part.
If plants are to flourish, the heat and cold and amount of moisture must be such that the seeds can ripen and find suitable conditions for preservation and growth in succeeding years. Plants like the cactus and the Yucca Palm which thrive in the dry and desert regions of New Mexico and Arizona would soon die in the moist climate of Louisiana.
As animals live upon plants or upon other animals, the plants must supply the food of the plant-eating animals and through these of the animal eaters. Thus, the distribution of plants has a great effect upon the animal life. Animals that eat grass will not live in a desert, neither will animals that eat nuts live in a prairie, where there are no nut- bearing plants.
YUCCA PALM.
Temperature and moisture also affect animals as well as plants, although animals can hide away from the scorching sun and move about for water as plants cannot. Ananimal like the polar bear, whose coat has become thick to protect him from great cold, would soon pine away and die, if transferred to the jungles of Africa, where his fellow flesheater, the lion, revels in joyful existence. To the camel of the desertthe damp, grassy savannas would be,
CAMEL.
indeed, a dreary waste and verdant cemetery. Thus, when once plants and animals have become adapted to certain climatic conditions, they cannot flourish if placed under very different conditions.
89.Effect of Climate upon Man. -Since man can change his out-er covering of clothes whenever he desires and is able to carry with him and store for long periods his necessary food, and by artificial means raise or even lower the temperature of the space in which he lives, he is not nearly so dependent upon climate as are either plants or animals.
The same man can, for a time, live in arctic regions or in the tropics. Men can, moreover, by centuries of effort become accustomed to the climate of almost any part of the globe. The Laplander and the South Sea Islander both flourish in their adopted homes. Neither of these, however, has attained to the highest development of which man is capable. The rigorous severity of the climate saps the energies of one and its uniform geniality lulls the ambition of the other.
In temperate latitudes, where there is need of providing for the winter when plants do not grow and when food is hard to find, where the blood is stirred by the invigorating cold, and where nature in her ever changing mood gives zest to living, is the place where man has attained his highest achievements. Here the fight for existence does not require all man"s energy, and the bounty of nature does not free him from strenuous effort.
A LAPLANDER.
Thus it is seen that even upon man the
influence of climate is great. How great, it is impossible fully to realize,so complex are his relations.
Summary. -The atmosphere is just as important to life upon the earth as are energy, light, heat, water and land. Air contains oxygen from which we get heat and energy, carbon dioxide, from which plants build up their tissues, and nitrogen which dilutes these two.
The weight of air is not usually realized because it presses uniformly in all directions. Air expands when heated; so a cubic foot of warm air weighs less than a cubic foot of cold air. Warm air will also hold more moisture than cold air.
The pressure of air, due to its weight, may be measured by abarometer. The heights of mountains may also be measured by this instrument, as there is less air above a high mountain than above a low one. The winds are caused by changes in atmospheric pressure; theirprevailing direction is affected by the earth"s rotation. Certain winds common to all Planets are called planetary winds; when modified by certain peculiarities of the earth they are called terrestrial winds. Because of their constancy and their aid to traffic, some of these winds are called trade winds. South of Asia there are winds called monsoons.
When very moist air cools, it cannot hold as much moisture as when it is warm, so this falls as rain, hail, sleet or snow. The rainfall varies from nothing at all in some places to over fifty feet a year in others. In the United States the north Pacific slope has a rainfall of about seventy inches a year; the south Pacific slope about fifteen inches; the eastern slope of the Rockies is very dry; and the Mississippi valley and the country to the east of it have a rainfall of from thirty toA SOUTH SEA ISLANDER.
sixty inches.
Rainstorms when accompanied by thunder and lightning are called thunder-storms. Thunder and lightning are caused by certain clouds having a higher charge of electricity than others. The higher charge bursts across to the lower charge, making a flash of lightning and a roll of thunder.