. The Americana : a universal reference library, comprising the arts and sciences, literature, history, biography, geography, commerce, etc. of the world . from the earth ist equal to that gained during the day from the sun. This, as previously stated, occurs sev-eral weeks after the sun is well on its waysouthward. About September 21 the autumnalequinox occurs, when the sun crosses the equa-tor, and, as at March 21, the days are of equallength at all latitudes of both hemispheres. Onor about December 21 — the winter solstice —the sun is farthest south, and the same con-ditions prevail in the
. The Americana : a universal reference library, comprising the arts and sciences, literature, history, biography, geography, commerce, etc. of the world . from the earth ist equal to that gained during the day from the sun. This, as previously stated, occurs sev-eral weeks after the sun is well on its waysouthward. About September 21 the autumnalequinox occurs, when the sun crosses the equa-tor, and, as at March 21, the days are of equallength at all latitudes of both hemispheres. Onor about December 21 — the winter solstice —the sun is farthest south, and the same con-ditions prevail in the southern hemisphere thatprevailed in the northern hemisphere on June21. North of the equator the sun is now leasteffective; its rays reach the earth at the low-est angle through the greatest depth of air, andthey are operative for the fewest hours duringeach day, of any portion of the year, but thegreatest cold does not occur. This comes aboutfour weeks later, when the increasing heat re-ceived each day by the earth from the sun isjust equal to that lost by radiation. The effect of latitude will be understood byreference to the following figure:. As the latitude increases, the rays of thesun will fall with increasing obliquity, andthey lose in power by being spread over alarger surface, and by traversing a greaterdepth of air, which absorbs more of their heat. The same beam A, <(when the sun is vertical,is spread over a surface such as CC. When thesun is inclined at an angle as shown in the fig-ure, the beam is spread over a surface, C C,which is somewhat greater than the first, and itpasses through a column of air, B B C C,greater than that of BBCC. The intensity ofinsolation at midday decreases approximatelyas the cosine of the latitude.* Near the equator the suns rays at middayfall perpendicular to the surface of the earth,and there is virtually no change in the lengthof the day, and consequently there is little va-riation in the daily or seasonal the v
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectencyclo, bookyear1903
