246 



THREE CRUISES OF THE " BLAKE." 



between Norway and Iceland. The same temperature, 0.9° C, 



occurs under the equator at a depth 

 ?, . „ „ „ s of about 2,300 fathoms, while 5° 



C. is found at a depth of 300 

 fathoms. As early as 1859 the 

 Coast Survey had recorded in the 

 Straits of Florida a temperature 

 of 40° F. (4.4° C.) at a depth of 

 300 fathoms, while at the surface 

 the temperature was 80° F. (26.7° 

 C). Beyond 1,000 fathoms the 

 temperature diminishes very slowly. 

 The "Challenger" also found a 

 temperatiu'e somewhat below zero 

 off the Rio de la Plata, at a depth 

 of about 2,900 fathoms. 



The temperature of the oceanic 

 basin depends upon the dei)th, the 

 latitude, the currents, and the 

 seasons ; that of mediterraneans 

 (land-locked seas) is controlled by 

 other causes, which ■will be more 

 fidly discussed when we come to 

 treat of the temperature of the 

 Caribbean and of the Gulf of Mex- 

 ico. The constants are the depths 

 and latitude, while the disturbing 

 elements are represented by the 

 varying atmospheric and oceanic 

 currents and the seasons.^ The 

 effects of seasonal differences of 

 temperature do not extend to great 

 depths, yet act mth sufficient 

 power greatly to modify the force 



1 Dr. J. J. Wild has given in " Thalassa " 



an excellent diagram, showing at a glance the 



general relations of the temperature in the 



liquid envelopes to the earth's crust. It is 



Fig. 171. here reproduced (Fig. 171), slightly modified. 



