23G 



DIFFERENT TEMPERATURES 



[Oh, XII. 



parallel to the equator nor to each other.* It is also known 

 that the mean annual temperature may be the same in two 

 places which enjoy very different climates, for the seasons 

 may be nearly uniform, or violently contrasted, so that the 

 lines of equal winter temperature do not coincide with those 

 of equal annual lieat or isothermal lines. The deviations of 

 all these lines from the same parallel of latitude are deter- 

 mined by a multitude of circumstances, among the principal 

 of which are the position, direction, and elevation of the 

 continents and islands, the position and depths of the sea 

 and the direction of winds and currents. 



On comparing the two continents of Europe and America 

 it is found that places in the same latitudes have sometimes 



mean 



some 



in a few cases to 17° Fahr. 

 continents, which have the same mean temperature, differ 

 from 7° to 17° in latitude. Thus, Cumberland House, in 

 North America 



as the citv of 



having the same latitude (54° N.) 



city of York in England, stands on the isothermal 

 line of 32°, which we have to seek in Europe at the North 

 Cape, in lat. 71°, but its summer heat exceeds that of Brussels 



or 



t The principal cause, says Humboldt 



greater intensity of cold in corresponding latitudes of North 

 America, as contrasted with Europe, is the connection of 

 America with the polar circle, by a large tract of land, some 

 of which is from three to five thousand feet in height ; and, 

 on the other hand, the separation of Europe from the arctic 

 circle by an ocean. The ocean has a tendency to preserve 



* We are indebted to Alex, von Hum- lished by Humboldt and Dove in 1848, 



(re-edited by Dove in 1853, from which 

 9, is extracted), supplies a large 



fio* 



boldt for having first collected together 

 the scattered data on which he founded 



an approximation to a true theory of body of well-established 'data for such 

 the distribution of heat over the globe. investigations, of which Mr. Hopkins 

 Many of these data were derived from availed himself in an able essay ' On 

 the author's own observations, and many the Causes which may have produced 



Changes in the Earth's Superficial Tem- 

 perature/ — Q, Journ. Geol. Soc. 1852, 

 p. 56. 



t Sir J. Richardson's Appendix to 

 Sir G.Bach's Journal, 1843— 1845, p. 

 478. 



from the works of M. Pierre Prevost, of 

 Geneva, on tho radiation of heat, and 

 from other writers. -See Humboldt on 

 Isothermal Lines, Memoires d'Arcueil, 

 torn. iii. translated in tho Edin. Phil. 

 Journ. vol. iii. July, 1820. 



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