392 THE DEPTHS OF THE SEA. [CHAP. VIII. 
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 has been accumulated both 
abroad and by our own Admiralty and Meteoro- 
logical Department. 
In 1870, Dr. Petermann, of Gotha, published’ 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. From the wind and current charts of Lieu- 
tenant Maury, embodying about 30,000 distinct 
temperature observations. 
2. From 50,000 observations made by Dutch sea- 
captains, and published by the Government of the 
Netherlands. 
3. From 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. From 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 Mittheilungen,’ Band 16, Gotha, 1870. 
