1851.] HOPKINS ON CHANGES OF CLIMATE. 63 



Part II. 



On the Influence of various Configurations of Land and 

 Sea, and Oceanic Currents, on the Earth's Superficial 

 Temperature. 



Having discussed the operation of internal and external causes on 

 the temperature of the surface of the earth, I now proceed to the 

 consideration of the influences of superficial causes depending on the 

 configuration of land and sea, and on the oceanic currents which re- 

 sult from such configuration, or are greatly modified by it. The ad- 

 mirable map of isothermal lines by Humboldt and Dove, embodying, 

 as it does, all the best-established observations on temperature in all 

 the accessible regions of the earth, affords us data for this investiga- 

 tion far superior to all we have hitherto possessed. Every geologist 

 is aware how long and ably Sir Charles Lyell has advocated the effi- 

 ciency of the above-mentioned causes of change of climatal condi- 

 tions ; but before the publication of this isothermal map, the geolo- 

 gist had no adequate means of estimating numerically the effects 

 which these causes were capable of producing. The want of this 

 quantitative evaluation of the intensity of assigned causes has hitherto 

 necessarily given to the theoretical views founded upon them much 

 of a conjectural character, which it is my object, with the improved 

 means we possess, as far as possible to remove. 



Every separate configuration of land and sea which we may sup- 

 pose to have existed at any assigned geological period would require 

 a separate investigation, in order to ascertain its effect on the climatal 

 conditions of that period. In this paper I shall restrict myself to 

 the examination of those hypothetical cases which, according to the 

 general views of different geologists, may have been actual cases du- 

 ring the later periods of geological history ; and my more especial 

 object will be, moreover, to ascertain whether any of these supposed 

 configurations will enable us to account for the cold of the glacial 

 period in our own region of western Europe ; and, if so, which of 

 them must be regarded as most effective for this purpose. 



9. In examining the course of the isothermal lines for the north- 

 ern hemisphere, we are at once struck by their extraordinary devia- 

 tions from parallelism with the equator, which must be considered as 

 their normal type. The most remarkable of these deviations is that 

 which exists in the northern part of the Atlantic and in the adjoining 

 part of the North Sea. (See Map, Plate II.) The isothermals for 

 every month, but especially those for the winter months, have an ex- 

 traordinary deviation and convexity towards the north. Again, in 

 north-eastern Asia the abnormal courses of these lines are almost 

 equally remarkable. For the winter months, the deviation, and con- 

 sequent convexity, of the lines is here to the south ; while the sum- 

 mer lines deviate, on the contrary, to the north. Deviations also 

 exactly similar to those of north-eastern Asia exist in the northern 

 part of the New Continent. The deviations frorii the normal types 

 in the southern hemisphere are much smaller, the principal ones 



