152 ON THE PHYSICAL THEORY OF UNDER-CUERENTS. 



The conditions of the Black Sea were then noticed. Here the 

 river supply and rainfall exceeded the evaporation, and the sp. gr. 

 of its water was from 1-012 to 1*014, or about half that of the 

 Mediterranean. There was a strong surface-current running 

 outwards, and the recent experiments of Capt. Wharton in H.M.S, 

 Shearwater had conclusively demonstrated the existence of a 

 strong under-current ranning inwards (from the JEgean Sea) 

 through the Bosphorus and Dardanelles. In the Ealtic, which 

 received the drainage of ^ of Europe where most rain fell, and 

 the evaporation was least, a similar state of things prevailed, and 

 the inward under-currents had been carefully investigated by 

 Dr. Meyer, Kiel. 



The thermal condition of the Sulu Sea, near Borneo, was then 

 explained. To a depth of 400 fathoms its water had free communica- 

 tion with the surrounding China Sea, but below that it was cut off 

 by reefs and shoals. Captain Chimrao, R.N., had shown that 

 down to 400 fathoms the fall in temperature proceeded at the same 

 rate in the two seas; but that below that depth the temperature con- 

 tinued to fall in the China Sea, reaching 37'' Fah. at 1546 fathoms, 

 while in the Sulu Sea it was 50° at any depth from 500" to 

 1778 fathoms, and this difference was attributed by Captain 

 Chimmo to the exclusion of the deep Polar flow which lowers 

 the temperature of the China Sea. 



Mr. Carpenter then proceeded to expound the doctrine of a 

 General Oceanic Circulation sustained by difference of tempera- 

 ture. He stated that a few months previously Mr. Prestwich had 

 called attention to the fact that this doctrine had been first pro- 

 mulgated by Professor Lenz, of St. Petersburg, as an inevitable 

 deduction from his observations made in the voyage of the 

 Kot%ehue, in 1823-6. His main conclusions, which have lately 

 been amply confirmed by the Challenger' s observations, were *. — 



** (1) The doctrine of a deep underflow of glacial water from 

 each pole to the equator. 



" (2) The ascent of polar water to the surface under the 

 equator. 



