* THE CURRENTS OF THE ATLANTIC. 391 



But the climate of a place depends upon the ranges of tempera- 

 ture, whether diurnal or annual, no less than upon the mean 

 rallies. It is a well known meteorological fact, that the ranges of 

 temperature on the globe vary within very wide limits, being 

 least of all at sea, and increasing with the distance of the place 

 from the ocean, until in the interior of the continents they become 

 very great. Thus, the difference between the mean temperatures 

 of summer and winter, or the annual range, is, on the average, 

 19 in Great Britain ; 27 in France ; 36 in the eastern parts of 

 Germany ; 40 in European Russia ; 60 in Siberia until at 

 Jakoutsk, in that inhospital clime, it reaches the enormous amount 

 of 101 ! And these differences exist even among places having the 

 same mean temperatures. Thus Dublin, Prague, and Astrakhan 

 on the shores of the Caspian, have all nearly the same mean 

 annual temperature. But the difference between their summer 

 and winter temperatures are respectively, 17'5 for Dublin, 37 

 for Prague, and 57 for Astrakhan. These differences are due to 

 the different effects of solar radiation on water and on dry so/7, 

 already explained ; and climates have been distinguished into 

 marine and continental, according to the amount of this variation. 

 The annual range in Ireland is the smallest in Europe ; on the 

 coasts it falls as low as 14. 



The difference between the mean temperature of day and 

 night, or the diurnal range, follows the same law, being least on 

 the coasts, and greatest in the interior of the continents. I have 

 already adverted to the principal cause of this. A great portion 

 of the solar heat which falls on the water during the day is 

 employed in changing its state into that of vapour, and does not 

 affect its temperature ; and, on the other hand, the heat so 

 employed is, in part, restored and rendered sensible, when the 

 vapours are condensed during the night. Thus the two extremes 

 approach one another. But another reason is, that the vapour 

 itself stops, or absorbs, a large portion of the sun's heat ; and the 

 effect, of course, is greatest when the air is most humid. Dr. 

 Livingstone found a difference of temperature, amounting to 48, 

 between sun-rise and mid-day, on the eastern side of South Africa ; 

 while in the valley of the Zambesi, on the opposite side of the 

 Continent, where the air is loaded with moisture, the difference 

 amounted only to 12. 



In accordance with this, the diurnal rmigo of temperature 



