48 THE YEAR. 



that from September to March ; that, in each hemi- 

 sphere, they will take place in the summer half year ; 

 will be nearer to each other the nearer that the place 

 is to the tropic ; and that just at the tropic they will 

 meet in one single day. 



From this there follows a very considerable modifi- 

 cation of the solar influence, and consequently of the 

 seasons. The times at which the sun is vertical are, 

 allowing time for the effect to be produced in the 

 manner already mentioned, the times of the greatest 

 heat. They are nearly half a year asunder at the 

 equator, and as the latitude increases, and the average 

 annual heat becomes less, they are nearer to each other, 

 they have more than twelve hours of sunshine each 

 day, and the shortest interval between them con- 

 sists of days on which the sun shines still longer. 

 Thus, in proportion as the equator is receded from, 

 and the whole annual heat becomes less, the very 

 same causes that lessen it, accumulate a greater pro- 

 portion of it into the summer; and thus give to the 

 growing and ripening season a temperature consider- 

 ably above the average. 



At whatever point between the tropics the sun is 

 vertical at any moment of time, that point is always 

 the centre of the illuminated hemisphere, which, with- 

 out taking into the account an effect of the atmos- 

 phere which will be noticed afterwards, is an entire 

 half of the earth's surface, or extends 90 from the 

 centre in every direction. Though the earth be not 

 quite a sphere, and thus the portion of it that is 

 shone upon by the sun be not exactly the same at 

 all times, and though the distance from the sun be 



