SEASONAL VARIATIONS. 33 



over head, but a little in the rear of it; and the 

 distance between the two points will be greater in 

 proportion as the apparent motion of the sun is 

 more rapid. For the same reason, the point of 

 greatest solar influence will approach nearer to the 

 point where the sun is vertical, when the appa- 

 rent motion of that luminary is diminishing, and 

 recede farther from it, when the apparent motion 

 is increasing. At all seasons and places, there- 

 fore, when not counteracted by local or temporary 

 causer,, the daily time of greatest heat must be 

 after noon, and the time of sunset always warmer 

 than that of sunrise. One very obvious beneficial 

 effect results from the latter circumstance ; the plants 

 get time to cool more gradually in the evening, and 

 to warm more gradually in the morning. Though, 

 as has been noticed already, plants, in the early 

 stages of their growth, suffer severely when a night, 

 cold enough for converting the dew into hoar frost, 

 is followed by a warm sun, and a dry atmosphere. 



But there is a seasonal as well as a daily effect 

 occasioned, by time being required before the sun can 

 produce its full influence. The seasons are thereby 

 retarded, so that before the most valuable trees be in 

 blossom, and the more valuable species of grain too far 

 advanced for shooting again, even if they are nipt by 

 the frost, the days have become considerably longer 

 than the nights, and thus the cold of the latter is 

 diminished more in proportion than the duration is 

 shortened. That it is so, may be seen either from the 

 fact or from the principle. Unless there has been an 



