Reviews and Notices of Books. 



123 



solar radiation. OF these sources whence heat is derived, it is 

 only necessary for the meteorologist to consider the heat received 

 from the sun's rays, because that received from the other sources 

 is too inconsiderable in amount to be appreciable, except in rare 

 and exceptional cases 



Professor Dove lias calculated the normal temperatures of the dif- 

 ferent parts of the globe ; that is, what would be the temperature 

 of each place provided the earth presented a solid uniform surface 

 everywhere to the sun's rays. These normal lines are of necessity 

 parallel to the equator, or coincident with the parallels of latitude — 

 the temperature increasing on each side of the equator to 10° of lati- 

 tude, and thence decreasing proportionally on either side toward 

 the poles. But, on account of the unequal distribution of land and 

 water, the irregularities of the surface, the prevailing atmospheric 

 and oceanic currents, and other concurrent causes modifying the 

 climates of particular localities, few places possess what may be 

 called their normal temperatures, some falling short of it, but a 

 still greater number exceeding the temperature assigned. Thus 

 London, in latitude 51°-30j ought to have a mean temperature of 

 39° 0, whereas observation assigns to it one of 50°-8, or ll°-8 

 higher. Everywhere on the Atlantic shore of North America the 

 temperature is lower than in Europe. The respective mean tem- 

 peratures of Nantes in France and St John's in Newfoundland, 

 both in corresponding latitudes, are 54^-9 and 38° 4, — the differ- 

 ence in favour of the former being 16°-5. If the temperature of 

 different places be compared for the seasons, it will be found that 

 the discrepancy is still more striking. Thus, whilst the winter 

 temperature of Drontheim, lat. 63°, is + 23°-3, that of Yakoutzk, 

 lat. 62°, is — 36°4, showing an enormous difference of 60°-0 ; 

 whilst the winter temperature of Quebec is 14°*2, that of Penzance, 

 4° nearer the pole, is 44°'2, or 30"* 0 higher than that of Quebec. 

 Again, the summer temperature of Edinburgh is 57°'2, while in 

 Moscow, in the same parallel of latitude, it is 65°*4, or about 8°*0 

 higher. 



" Climates, then, may be divided into equable and excessive, 

 according to the degree in which the mean temperature of the 

 summer and winter differs from that of the entire year ; and with 

 reference to the growth of vegetables, far more importance must 

 be attached to the heat prevailing during summer than to the 

 mean temperature of the climate collectively taken. 



Thus even in Russia and Siberia fine crops of wheat and 

 other kinds of corn are obtained, because the summer temperature 

 rises to the requisite point for ripening the seed, whilst in the 

 north of Scotland, the Orkneys, and the Faroe Islands, although 

 the mean temperature of the year is higher, these crops do not 

 succeed. 



