174 



ELEMENTARY SCIENCE 



have heard of equinoctial storms. The equinoxes come 

 at stormy times of year and it was formerly believed that 

 the equinox was the cause of these storms. It is now 

 known that this is not the case, but the term is still 

 used. 



The shortest day of the year in the northern hemisphere 

 is evidently the longest day of the year in the southern 

 hemisphere; and the reverse is also true. But, as you have 

 noted, the equinoxes come at the same time in both hemi- 

 spheres. Also, you should note, that precisely at the 

 equator, days and nights are always of equal length. 

 Variations in length of day and night, and the consequent 

 effects, evidently increase in proportion to the distance 

 from the equator, until at last, precisely at the poles, 

 variation ceases, and day and night are each a half year 

 lon'g. In the tropics, however, day and night are always 

 of nearly equal length, and there is little variation in the 

 angle at which the sun's rays strike the earth. Hence we 

 find in this region much less variation in the seasons than 

 we do to the north or south of them; the farther we go 

 from the equator, the more marked the differences be- 

 tween the seasons become, until we reach the regions of 

 perpetual ice and snow. Toward the poles the seasons 

 become merged in one long winter, while toward the 

 equator they merge in one long summer. 



The Zones. Doubtless you learned hi geography that 

 the earth is measured by two sets of lines which are indi- 

 cated on all maps, and which give a geometrical method 

 of locating places. The lines which run parallel to the 

 equator are called parallels or lines of latitude; the ones 

 which cut these at right angles and converge at the poles 



