66 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 17, 



independently of the Gulf-stream, on the mean January temperature 

 about these parts of the coast of western Europe. The actual tem- 

 perature of the west coast of Brittany for January is about 42° F., 

 instead of 32° F., as it would be in the absence of the Gulf-stream, 

 according to the position of my imaginary isothermal for that case. 

 I am, therefore, thus assigning an amount of 10° F. for the influ- 

 ence of the Gulf-stream on the January temperature of the coast of 

 Brittany. The whole effect, therefore, of the Atlantic with the Gulf- 

 stream on that coast is thus estimated at 18° F. 



In traversing North America, the extensive mass of land to the 

 north brings down the winter isothermals again to almost as low lati- 

 tudes as in eastern Asia. The actual isothermal of 32° F. meets the 

 American coast a little south of Philadelphia, and then pursues a 

 very nearly western course until it reaches the meridian of about 

 106° W. long., where it begins to be affected by the Pacific Ocean 

 and to deviate considerably to the northward. To complete my hy- 

 pothetical line of 32° F., I join the point to which we have already 

 traced it on the coast of Brittany with that at which the actual iso- 

 thermal meets the coast of Philadelphia as just mentioned, the con- 

 necting line being slightly convex towards the north on the coast of 

 Europe, and to the south on the coast of America, as is required by 

 the continuity of its curvature. Across America, and to the west of 

 it, the isothermal must manifestly be beyond the influence of the 

 Gulf-stream, and our hypothetical line must consequently coincide 

 with it. 



It would appear from the existing isothermals, that the Gulf-stream 

 produces little effect on the temperature, even in winter, on the east- 

 ern coast of America, as compared with its efl'ect on the western 

 coast of Europe. There are several causes which may be assigned 

 for this difference. After the stream has passed the straits of Ba- 

 hama, it passes into an ocean of which the temperature is not much 

 inferior to its own, and more northerly its influence must be in some 

 degree counteracted by the cold current proceeding southward 

 through Davis's Straits. To the influence of these causes may be 

 added that of the west winds which appear to prevail on the eastern 

 coast of America as well as on the western coast of Europe. These, 

 coming from the land in the former case, and from the ocean in the 

 latter, tend to lower the winter temperature on the American, while 

 they raise it on the European coast. 



The deflection of the actual January isothermal of 32° to the 

 northward on the western coast of N. America is considerably more 

 rapid than that of my hypothetical line on the western coast of Eu- 

 rope. It also exceeds that of the lines of 41° and 50° more than any 

 mere law of continuity would seem to require. A considerable por- 

 tion of the deflection is attributable, I doubt not, to local causes. In, 

 fact, a considerable current is described as setting northward along 

 that coast from about the 45th degree of latitude, which may proba- 

 bly account for this extra deviation. The remainder must be attri- 

 buted to the influence of the Pacific Ocean, and would probably ac- 

 co|:d with the similar deflection which I have given to my hypothe- 



