CLIMATE. 



153. As the earth turns upon its axis N s, all the places upon 

 the equator E o, are brought successively to the point E, directly 

 under the sun. In other words, at all such places the sun is 

 vertical daily at noon. 



154. At all other parts of the earth between E and N, or 

 between E and s, the sun is seen at noon obliquely, or what is the 

 same, it is at a distance greater or less from the zenith. And 

 the more distant the place is from the equator, the more distant 

 will the sun be from the zenith at noon. 



155. But since the thermal influence of the sun depends in a 

 great degree upon its proximity to the zenith at noon, it follows 

 that this influence will gradually decrease in going from E to K, 

 or from E to s. The temperature, therefore, of the climate at the 

 time of the equinox will gradually diminish as the latitude 

 increases. 



But since any two places at equal distances from the equator, 

 north and south, would be presented towards the sun at noon with 

 equal obliquities, it follows that so far as depends on this circum- 

 stance, the thermal influence of the sun at places having equal 

 latitudes north and south, will be the same at the time of the 

 equinoxes. 



156. The position of the earth with relation to the sun on the 

 21st of June is shown in fig. 9. The equator E in the interval 

 between the 21st of March and the 21st of June, has gradually 

 declined to the south. The north pole N has consequently been 

 turned more and more towards the sun s', and the south pole s has 

 been turned more and more from it. In this position, therefore, it 

 is evident that the sun shines more fully on the northern, and less 

 so on the southern hemisphere. The point T, to which it is 

 vertical at noon, is now, not as in the former case upon the 

 equator, but at the distance of 23^ north of it. Places in the 

 northern hemisphere above this point are shone upon by the sun 

 at noon with much less obliquity than places having equal lati- 

 tudes in the southern hemisphere. 



157. The circle which bounds the hemisphere of the earth 

 enlightened by the sun, divides all the parallels of latitude 

 unequally, the larger part of those in the northern hemisphere 

 being enlightened, and the larger part of those in the southern 

 hemisphere being dark. 



It follows, therefore, that at this time the days are longer than 

 the nights in the northern, and the nights longer than the days in 

 the southern hemisphere. 



158. Now the temperature of the seasons, in any given place, 

 -depends conjointly on the altitude to which the sun rises, and on 

 the length of the day ; for the greater the altitude is, the more 



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