the two extreme Seasons in the Temperate Zones. 45 
the earth the same amount of heat while over its north hemis- 
tained by the sun’s increased distance is furnished by the fact 
that it requires about 72 days of the sun’s influence for its com- 
pensation. The north and south hemispheres may therefore be 
regarded as receiving equal shares of heat in the period of a 
complete year, and popular writers on astronomy seem to have 
contented themselves with exhibiting this fact without examin- 
ing, very carefully at least, how the different seasons of the two 
hemispheres respectively are affected by the manner in which 
these shares are distributed ;—an inquiry in some respects more 
Interesting perhaps than that concerning the equality of the 
shares themselves.’ It is the effects of the variations in the 
sun's distance and in its angular motion in the ecliptic upon this 
distribution and consequently upon the extreme seasons in the 
temperate zones, that are now to be considered. 
It will be sufficiently accurate for our present purpose, and 
will tend to simplicity of statement, to suppose the duration of 
the summers and winters of the two hemispheres to be deter- 
mined by the sun’s passage through those two quadrants of the 
ecliptic that have its perigee and apogee for their middle points 
respectively: these limits will assign to them two periods of 
Which one extends from about the middle of May to the middle 
of August, and the other from the middle of November to the 
middle - February, fully including the extremes of both sea- 
ow 
~ gain by the one process exceeds from day to day the loss by 
® other, a gradual elevation of the general or average tempe- 
' “Now the periheli ee Present 
: perihelion of the orbit is situated nearly at the place of the mm 
Winter solstice, so that were it not for t i just described the effect 
isphe ‘4 e difference of summer and winter in the southern hem- 
hee and to moderate it in the northern. . . . As it is, however,no such ine- 
nail Subsists, but an equal and impartial distribution of light and heat is ac- 
to both."—Herschet Outlines of Astrondmy, London, 1849. Stal pened 
extent that the exaggeration and moderation here referred to are pro tosome 
cnt notwithstanding the compensation. : 
“Thaesract cP: Astron, London, 1858), illustrating this compensation, remarks: 
the two warm seasons of our atmosphere (spring and summer) are certainly 
at the seasons of the southern hemisphere, but they are 
Mtcar time of longer duration.” Had he employed cold seasons in the 
Rorth ration it would have run thus —they are certainly somewhat milder at the 
Sation, but they are at the same time” pe freee which, instead of being a compen- 
Would of course make them milder still. ; iJ 
