PHYSICAL GEOGRAPHY. 107 



In addition to these, there are other causes of a minor 

 import, which it will be unnecessary to enter into, as the 

 action of the rain on mountains, the melting of snows, 

 &c. which have a tendency to alter the Earth's surface, 

 and produce a level. Landslips will occasionally take 

 place, by which means a tract of land will suddenly 

 gink into the earth, as if one of its pillars had given 

 way ; but these occurrences are, providentially, rare. 



OF THE CLIMATE OR TEMPERATURE. 



The general climate or temperature principally depends 

 on two causes, viz., the distance of the place from the 

 Equator, and its elevation above the surface of the sea. 

 There are other causes which may tend to alter the tem- 

 perature, but these are the principal. 



Those parts of the globe which lie within the Tropics, 

 from their having the sun vertical twice a-year, and its 

 receding at no time to a very great distance from their 

 zenith, must necessarily be most favourably situated for 

 the reception of his rays ; while in proportion as any 

 place is distant from the Equator, the Sun's rays will fall 

 obliquely, aud such place will receive proportionately a 

 smaller portion of them. Another cause for increased 

 heat within the Tropics is the Sun's being below the hori- 

 zon for so short a time, never much more than 12 hours ; 

 while in the Temperate Zones during the winter half year, 

 the Sun is absent for a time varying from between 12 and 

 13 hours to 24 hours ; and in the Frigid Zones he keeps 

 below the horizon from 24 hours to six months, in pro- 

 portion to the distance of the place from the Arctic 

 Circle. Geographers have, therefore, arbitrarily divided 

 each hemisphere into 30 different degrees of temperature, 

 called climates, each climate comprising a zone parallel 

 with the Equator, and of an extent depending on the 

 length of the longest day. Thus at the Equator, where 

 the day is uniformly 12 hours long, ihejirst climate is said 

 to commence, and to extend to that parallel where the 

 length of the longest day is 12 hours and a half, when 

 the second climate begins, and continues to where the 

 longest day is 13 hours : half an hour in the length 

 of the longest day thus forming a new climate. This 



