392 THE DEPTHS OF THE SEA. [CHAP. vm. 



caused by a ' modified case ' of the general oceanic 

 circulation, and neither by the Gulf-stream nor by 

 the anti-trade drift. 



Although there are, up to the present time, very 

 few trustworthy observations of deep-sea tempera- 

 tures, the surface temperature of the North Atlantic 

 has been investigated with considerable care. The 

 general character of the isothermal lines with their 

 singular loop-like northern deflections, has long 

 been familiar through the temperature charts of the 

 geographers already quoted, and of late years a pro- 

 digious amount of data have been accumulated both 

 abroad and by our own Admiralty and Meteoro- 

 logical Department. 



In 1870, Dr. Petermann, of Gotha, published 1 an 

 extremely valuable series of temperature charts, 

 embodying the results of the reduction of upwards 

 of 100,000 observations, derived chiefly from the 

 following sources : 



1. Prom the wind and current charts of Lieu- 

 tenant Maury, embodying about 30,000 distinct 

 temperature observations. 



2. Prom 50,000 observations made by Dutch sea- 

 captains, and published by the Government of the 

 Netherlands. 



3. Prom the journal of the Cunard steamers be- 

 tween Liverpool and New York, and of the steamers 

 of the Montreal Company between Glasgow and 

 Belleisle. 



4. Prom the data collected by the secretary of the 



1 Der Golf-Strom und Standpunkt der thermometrischen Kenntniss 

 des Nord-Atlantischen Oceans und Landgebietes im Jahre 1870. 

 Justus Perthe's ' Geographische Mittheihmgen/ Band 1 6. Gotha, 1 870. 



