CHANGES^ OF THE SEASONS. ICfil 



Recals the first. All, to reflourish, fades ; 



As in a wheel, all sinks, to reascend : 



Emblem of man, who passes, not expires. — Thomson. 



The orbit in which the earth revolves in his annual 

 course round the sun is not a circle but an ellipse or oval ; 

 and we are more than three millions of miles nearer to the 

 sun in December about the time of the winter solstice, than 

 we are in June about the time of the summer solstice. Now 

 as heat and l>ght from the sun are greater as the distance is 

 less, it is manifest that this circumstance would occasion a 

 variation in the temperature of the air, like that of our sea- 

 sons, if the equator always coincided with the ecliptic. But 

 the seasons with us, in north latitude, are not in the least de- 

 gree occasioned by this circumstance, but by the direction 

 in which the sun's rays fall upon us. When they fall per- 

 pendicularly, or most nearly so, the season is warmest ; and 

 when they fall most obliquely, or in a slanting manner, the 

 season is coldest. The cause of the difference in the obli- 

 quity of the sun's rays is the obliquity of the ecliptic. The 

 effect of obliquity, in regard to rays will be evident, if ai 

 board be held perpendicularly before a fire. It will then re- 

 ceive a body of rays equal to its breadth. But if it be placed 

 obliquely, at an angle of forty-five degrees, then only half 

 the rays will fall on its surface, arid the other half will pass 

 over it ; so it is with the surface of the earth in summer and 

 winter. The circumstance also, that the days are longest, 

 whether in north or south latitude, when the sun's rays fall 

 in the greatest quantity and most directly at any place, con- 

 tributes much to the warmth of summer and the cold of win- 

 ter. In northern countries, where the days are eighteen or 

 twenty hours long, or where the sun is above the horizon for 

 any number of days together, the heat of summer is equal to 

 that of any part of the world. 



Since the degree of heat from the sun increases as the 

 earth's distance diminishes, and this distance is least when 

 it is summer in south latitude, and greatest v/hen it is sum- 

 mer in north latitude, a greater degree of heat, therefore, 

 must be received in summer in south latitude, than in sum- 

 mer in north latitude. But to compensate for a less degree 

 of heat, the inhabitants in north latitude have longer sum- 

 mers than those in south latitude. For as the sun is not in 



