NO. 4 TEMPERATURE VARIATIONS IN THE NORTH ATLANTIC 97 



together as a whole, as shown in figures 48 and 49, we conclude 

 that there is scarcely any indication that shows definitely that the 

 variations in the surface temperature are first in point of time, and 

 depend on changes of temperature in water-masses brought on by 

 the ocean current. One, however, obtains the impression that the 

 variations in the air temperature go before the variations in the 

 surface temperature of the water ; because, as we have said, in most 

 cases these are greater in the magnitude both of the positive 

 anomalies and the negative anomalies than the variations of the 

 surface temperatures. A clearer impression of this relation is ob- 

 tained perhaps by the study of the curves in the southern fields, 

 particularly 41° to 45° north latitude in plates 44 and 45 and 

 in figures 50 to 52. 



On the whole we have not obtained in this way a final answer to 

 the question whether the marked minimum in the years 1903 and 

 1904 depends upon the transportation of cold water or not. 



TEMPERATURE VARIATIONS IN THE DECADES AS SHOWN IN 

 OUR ISOPLETH DIAGRAMS 



Considering the variations in the other years, we must first investi- 

 gate whether our isopleth diagrams for the decades (see pis. 17, 

 19 to 41) give indications that these variations are brought about 

 by the transportation of cold or warm water-masses. We must, 

 however, recognize that only variations with short periods could 

 produce true displacements in so few decades (only seven) as are 

 included in our diagram. Variations with longer periods would 

 evidently produce effects diffused over all seven of the decades and 

 only at the beginning or the ends of such variations would it be 

 expected that displacements would appear in our isopleth diagrams. 

 There is still another consideration of perhaps even greater weight 

 which must be kept in mind. If the variations are brought about by 

 the transportation of cold or warm water-masses they should be 

 indicated on our isopleth diagrams by a gradual displacement from 

 the left toward the right, that is, from the west toward the east, from 

 decade to decade, and this would imply that the current moved in 

 an easterly direction along the course of our region of investiga- 

 tion. If it crossed this course at right angles or diagonally thereto 

 there would be no clear displacement in the diagrams. But in fact, 

 as already mentioned, we must assume that the current cuts at least 

 in several places our route from the Channel to New York and does 

 not go along with it. The isopleth diagrams therefore cannot show 



