THE NEW SCIENCE OF METEOROLOGY 



irregular course, joining together places having the 

 same mean annual temperature, and thus laying the 

 foundation for a science of comparative climatology. 



It is true the attempt to study climates compara- 

 tively was not new. Mairan had attempted it in those 

 papers in which he developed his bizarre ideas as to 

 central emanations of heat. Euler had brought his 

 profound mathematical genius to bear on the topic, 

 evolving the " extraordinary conclusion that under the 

 equator at midnight the cold ought to be more rigorous 

 than at the poles in winter." And in particular Rich- 

 ard Kirwan, the English chemist, had combined the 

 mathematical and the empirical methods and calcu- 

 lated temperatures for all latitudes. But Humboldt 

 differs from all these predecessors in that he grasps the 

 idea that the basis of all such computations should be 

 not theory, but fact. He drew his isothermal lines not 

 where some occult calculation would locate them on an 

 ideal globe, but where practical tests with the ther- 

 mometer locate them on our globe as it is. London, 

 for example, lies in the same latitude as the southern 

 extremity of Hudson Bay ; but the isotherm of London, 

 as Humboldt outlines it, passes through Cincinnati. 



Of course such deviations of climatic conditions be- 

 tween places in the same latitude had long been known. 

 As Humboldt himself observes, the earliest settlers of 

 America were astonished to find themselves subjected 

 to rigors of climate for which their European experience 

 had not at all prepared them. Moreover, sagacious 

 travellers, in particular Cook's companion on his sec- 

 ond voyage, young George Forster, had noted as a gen- 

 eral principle that the western borders of continents in 



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