Our country and its resources; . n notation; 5,000 billion, ac-cording to British notation) is about 1 of the en-tire weight of the terrestrial globe. The pressure of the air is meas-ured by means of an instrumentcalled the barometer, and hence isoften referred to as barometricpressure. In this instrument theweight of the air is balanced againsta column of mercury, and the heightof the latter, generally expressed ininches or millimeters, is taken asthe measure of the former. Hence,when we say that the average baro-metric pressure at sea-level is , we are really e
Our country and its resources; . n notation; 5,000 billion, ac-cording to British notation) is about 1 of the en-tire weight of the terrestrial globe. The pressure of the air is meas-ured by means of an instrumentcalled the barometer, and hence isoften referred to as barometricpressure. In this instrument theweight of the air is balanced againsta column of mercury, and the heightof the latter, generally expressed ininches or millimeters, is taken asthe measure of the former. Hence,when we say that the average baro-metric pressure at sea-level is , we are really expressing 414 OUR COUNTRY AND ITS RESOURCES in a roundabout way the weight ofthe air at that level. HOW THE ATMOSPHERE IS HEATED Our life and our weather are bothmaintained by a tiny fraction—lessthan half a millionth—of the heatgiven off by the great luminaryaround which the earth revolves inspace. At any given moment halfthe surface of the globe basks inthe sunshine while the other half isin shadow. Besides rotating on its. \ o<vA THE MARCH OF THE SEASONS8, tlic sun ; V, north pole of tlio earth ;/?. winter in X. hemisphere and summerin s. hemisphere: I), summer in , winter in s. hemisphere; .1,C, equinoxes. axis once a day. the earth revolvesaround the sun once a year, and itsaxis, which always remains parallelto itself, is inclined to the plane ofits orbit. These facts (illustrated inthe accompanying diagram i explainthe alternation of day and night,the march of the seasons, and theopposition of the latter in the twohemispheres. The northern half ofthe globe receives more than itsshare of solar heat at the seasonwhen the southern half is receivingless, and vice versa; hence the north-ern summer coincides with theSouthern winter, and the northernwinter with the southern amount of heat received at aparticular place, at a given time, de-pends chiefly upon the angle atwhich the suns rays reach theground, and this is continuallychanging. The interpo
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyo, bookyear1917
