72 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 17, 



and winter temperatures of the tract in the vicinity of the European 

 portions of these hues, but probably without producing any material 

 changes in its mean annual temperature. This tract may be consi- 

 dered as comprising the whole of central Europe, together with its 

 western portion from the Pyrenees to the southern shores of the 

 Baltic. It is the region in which the geologist is more especially 

 interested in tracing the climatal influences of changes in the con- 

 figuration of the earth's surface. I shall therefore endeavour to ascer- 

 tain from more general considerations the probable eifect of an ex- 

 tended ocean on the winter, the summer, and the mean annual tem- 

 peratures of the region in question. 



17. For this purpose I have deduced from Dove's map the follow- 

 ing results respecting these temperatures for the 20th, 30th, 40th, 

 and 50th parallels of latitude in both hemispheres. Each result 

 given for January is the mean of the January temperatures for all 

 places situated under the corresponding parallel of latitude ; and each 

 result for July is a similar mean for the July temperatures. The 

 mean of these is assumed to be the approximate value of the mean 

 annual temperature of the different parallels respectively. 



Mean Annual Temperatures of different Parallels of Latitude. 



Lat. = 20° N. 



DifF. 



9** 



12*' 



35° 



Lat. = 20° S. 



o 



January mean temp 78F. "1 



July „ „ 71 / 



Mean annual temp 74*5 



Lat. = 30° S. 



January mean temp 75 F. "I 



July „ „ 63 J 



Mean annual temp 69 



Lat. = 40° S. 



January mean temp 58F. "1 q© 



July „ „ 49 / 



Mean annual temp 53'5 



Falkland Islands.* Lat. = 50° S. 



January mean temp 34 F. "I -.qo 



July ,, „ 52 / ^^ 



Mean annual temp 43 



We may first remark the striking equality of mean temperatures 

 in corresponding parallels north and south of the equator as far as 

 the 40th degree of latitude. The small differences indicated by the 

 above numbers are not to be regarded, because they lie within the 

 limits of error to which the numbers themselves must necessarily be 

 subject. In the latitude of 50° N. the severe winter cold of eastern 

 Asia and that of the central portions of the North American conti- 

 nent reduce the mean temperature to more than 4° lower than that 



* The isothermal lines for this southern latitude on Dove's map are continued 

 only for short distances to the E. and W. of the Falkland Islands, so that the 

 temperatures here given must not be depended upon for the mean temperatures 

 of the parallel of 50° S. They are probably not far v^rong, on account of the great 

 regularity of the neighbouring isothermals. 



Diff. 



January mean temp 68F. \ ,.o 



July „ „ 82 / ^* 



Mean annual temp 75 



Lat. = 30° N. 



Januarv mean temp 58 F. "I ^^.o 



July • „ „ 78 / ^" 



Mean annual temp 68 



Lat. = 40° N. 



January mean temp 37F. 



July „ „ 72 _ 



Mean annual temp 54*5 



Lat. = 50° N. 



January mean temp 16F."1 .pc 



July „ „ 62 / ^^ 



Mean annual temp 39 



