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quently the power of those rays in heating it, varies with the 

 exposure of the soil relatively to the sun. Countries in the 

 northern hemisphere will be rendered warmer by having large 

 tracts of low land to the south and sea to the north, and cooler 

 when the relative position of these two is reversed. This fact 

 is exemplified by a comparison of the climate of Europe with 

 that of America and Asia. The western parts of the old conti- 

 nent derive considerable warmth from Africa. On the contrary, 

 the north-eastern extremity of Asia experiences in the same lati- 

 tude extreme cold ; for it has land on the north between the 

 sixtieth and seventieth parallel, while to the south it is separated 

 from the equator by the North Pacific. The whole of Europe, 

 compared with the eastern parts of America and Asia, has an 

 insular climate. If lines be drawn round the globe through all 

 those places which have the same winter temperature, they are 

 found to deviate from the terrestrial parallels much more than 

 the lines of equal mean temperature. 



When we compare the climate of the northern and southern 

 hemispheres we find a great difference in the corresponding 

 parallels. There is no accurate information as to the mean tem- 

 perature of any place beyond 50° of south latitude ; but there is 

 every reason to suppose that it differs considerably from that of 

 places in the same degree of north latitude. In Sandwich land, 

 according to Cook, in 59° of south latitude, the perpetual snow 

 and ice reach to the sea beach ; and in the island of Georgia, 

 which is in 54° of south latitude, the line of perpetual snow 

 descends to the level of the ocean. We therefore observe that 

 latitude is one only of many powerful causes which determine 

 the climate of particular regions of the globe. The coldness of 

 the southern hemisphere in countries situated under similar cir- 

 cumstances as those in the north, has frequently been attributed 

 to a cause quite inadequate to explain it, namely that of the sun 

 being a shorter time (said to be 7| days) on the south than on 

 the north side of the equator. As the variable diameter and ve- 

 locity of the sun has been already alluded to as optical decep- 

 tions, w^e need not dwell on the inadequacy of such an hypothesis 

 to account for the difference, but simply state, that w r e believe 

 the lower degrees of temperature of the southern zones as com- 

 pared to those of the north, placed under equal circumstances, 



