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X':.] THE MOVEMENTS OF THE EARTH. 355 



fore, that, when the earth is at A, it must be nearer to the 

 sun than when at B. The nearest distance is called the 

 perihelion^ and the greatest distance the aphdion? 



It would, at first sight, seem a very fair assumption that 

 when the earth is at perihelion it should be hottest, because 

 it is then at its nearest point to the sun. As a matter of 

 fact, however, the earth is at perihelion about Christmas^ 

 which is almost the coldest part of the year, in the northern 

 hemisphere ; and it is at aphelion about the beginning of 

 July. There are, indeed, several influences which tend to 

 neutralize the effects of the sun's proximity. ThuS; when 

 the earth is at perihelion, the days with us are short, for the 

 sun is not long above the horizon. Nor does he rise high 

 in the sky, at this season ; and, hence, the rays fall very 

 obliquely upon the earth ; so that they have less heating 

 effect than if they fell more directly upon the surface. 

 Again, it must be remembered that the earth moves more 

 rapidly as it approaches the sun. These influences more 

 than neutralise any augmentation of heat which may be due to 

 increased nearness to the source of heat; hence, the apparent 

 paradox, that the earth is nearer to the sun during our 

 winter than during our summer, becomes easily intelligible. 



It is evident that the temperature of any locality depends 

 chiefly on the duration of its supply of sunshine, and on the 

 direction in which the sun's rays are received^ In this 

 country, for example, the temperature is highest when the 

 sun has been shining during the long days, and when he 

 rises highest in the sky. But the altitude, or height of the 

 sun above the horizon, in England, never exceeds about 

 two-thirds of the distance from the horizon towards the 

 zenith. 



^ Perihelion, from irep), peri, near ; ^Aios, hclios, the sun. 

 ^ Aphelion, from anro, apo, from ; and 'i\Kios, 



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