Earth's Superficial Temperature. 



21 



gular forms of the known isothermals of the southern hemisphere, 

 extending to about the latitude of 50°, may be seen to be attri- 

 butable to similar causes, more especially, perhaps, in this case to 

 well-known ocean-currents ; and a knowledge of these causes 

 enables us to draw the isothermals in such hypothetical cases as 

 those above stated with approximate accuracy. This is what I 

 have first attempted to do in the memoir before us. 



Taking the first case, I arrive at the results embodied in the 

 following table : — 





At present, 



with the 

 Gulf Stream. 



Differ- 

 ence. 



Without the 

 Gulf-Stream. 



Differ- 

 ence. 



The Alps. 











Temperature for January, . . . 



July, .... 



Mean annual temperature, . . . 



38 F.\ 

 73 I 

 55-5 J 



o 



35 



34 F. ) 

 73 1 

 53-5 / 



39 



Snowdon. 











Temperature for January, . . . 



July, .... 



Mean annual temperature, . . . 



38 F. ^ 

 61 

 49-5 J 



23 



23 F.I 



61 



42 J 



38 



Northern Extremity of Scotland. 











Temperature for January, . 



... July, .... 

 Mean annual temperature, . . . 



36-5 F. 1 

 56 \ 

 46-25 J 



19-5 



12 F. ) 

 56 \ 

 34 ) 



44 



Centre of Iceland. 











Temperature for January, . 



July, .... 



Mean, 



30 F. 1 

 52 J 

 41 

 39 



22 



-4F. \ 

 46 J 

 21 



50 



Mean annual temperature,* . . 



In the case in which the Gulf Stream is supposed to exist, but 

 its progress into the North Sea to be arrested by a continuous 

 barrier of land, I have shewn that the winter temperature of the 

 coast of Iceland would probably be increased 6° or 7° F., and that 

 the January isothermal would probably run nearly north and 

 south from Iceland to the latitude of Central France. You will 

 recollect that a former littoral or sub-littoral communication be- 

 tween the western coasts of Europe and the eastern coasts of 

 America is rendered probable by a certain community of specific 

 forms in those localities. My object in considering the effect of 



* This is deduced from the mean of the monthly temperatures. The mean 

 annual temperatures above given for the other cases are almost identical with 

 those deduced from the monthly temperatures. The discrepancy of 3° in the 

 case of Iceland may be attributed to local peculiarities. 



