Reviews and Notices of Books. 



125 



is 36° 37' below zero, the thermometer in July rises to nearly 

 69° of Fahr. 



" In islands, on the contrary, situated in northern parallels, 

 the radiation of heat in summer exerts a much feebler influence; 

 so that Stromness, in lat. 68° 57', has a summer temperature of 

 only 54°; and Unst, the most northern of the Shetland Islands, 

 in lat. 60°, one only of 52°. 



"Hence whilst at Christiania, in lat. 59° 55', fine timber 

 abounds, and crops of wheat and other grain ripen, inasmuch as 

 the mean summer temperature rises nearly to 60°, none but the 

 hardiest kind of barley will grow in the Hebrides, between the 

 parallels of 56° and 58°; and the trees are there reduced to a few 

 of the robuster species, which are both stunted and uncommon. 



" In winter, however, the case is reversed. The extreme cold 

 of extensive continents, such as Russia and Siberia, is caused in 

 part by the radiation of heat from their surface during the long 

 nights of these northern latitudes, and still more through their 

 participation in the climate of regions more northerly than them- 

 selves, owing to the winds which commonly come from that quar- 

 ter in the winter season, and which, bringing with them the 

 temperature of the Arctic circle, first condense the moisture into 

 snow, and afterwards impart to the countries they pass over the 

 dry and cutting cold which characterises them. 



" But on the sea the circumstances are different, owing to a pro- 

 perty peculiar to water, which would seem specially designed as a 

 provision for mitigating the intensity of cold. 



" This is its arriving at its greatest density, not at the point at 

 which it freezes, but 8° above, so that whilst it goes on progres- 

 sively contracting in volume down to 40°, it afterwards again 



expands, until it falls to the temperature of 32° 



" Hence owing to this constant circulation of the lighter and 

 heavier portions of the water, the whole must attain the tempe- 

 rature of 40° before any ice is formed upon its surface, and accord- 

 ingly it is hardly possible that a deep lake should be frozen over 

 even by the longest and most intense frost that can occur. 



" The eff'ect of this constant circulation throughout all portions 

 of a body of water in mitigating the severity of insular climates 

 is sufficiently apparent. 



The ocean may, in fact, be regarded as a store-house of heat, 

 which it dispenses to the air passing over its surface, thus render- 

 ing it impossible that the latter should ever attain the same 

 extreme degree of cold which it acquires on a continent. 



" Hence the equable character of the climate in insular situa- 

 tions, which has been pointed out as prevailing during the summer, 

 holds good also, for the reasons just given, in the winter likewise." 

 Again, the currents of the atmosphere and of the ocean exer- 



