28 Baron N. Schilling on the Constant Currents 



equatorial water would stand 14 feet higher than the water of 

 the polar seas, if it could not flow off. It has been thought 

 that this tendency of the equatorial water- surface to rise would 

 serve to account for the Gulf-stream, which accordingly would 

 flow down hill. But this inconsiderable elevation of the surface 

 of the equatorial sea would not give a fall of even \ inch in a 

 German mile, which, in relation to the velocity, is much too 

 little. Even the assumed elevation of the surface, however, can 

 never actually be produced ; for as soon as any particles of 

 water become a little lighter, they must, in obedience to the law 

 of gravitation, immediately spread uniformly over the entire 

 surface. Thereby is necessarily produced a flow of the warmer 

 and therefore lighter superficial water to the colder regions, and 

 of the heavier cold water at the bottom to the warmer regions. 

 Such an exchange of the waters of the warmer and colder seas 

 exists in reality. A proof of this is furnished by the tempe- 

 ratures of the ocean diminishing with increasing depth — the 

 temperatures of the greater depths being very low, even in the 

 equatorial regions. An exception to this rule is formed by 

 those seas which are divided from the ocean by a ridge over 

 which the water is considerably less deep. In such seas the 

 temperature sinks merely to a depth corresponding to the height 

 of the water above the ridge, and below that remains nearly 

 unaltered, because the colder water, cut off by the ridge, can 

 have no influx. We have an example in the Mediterranean, 

 united with the ocean by the Straits of Gibraltar, the depth of 

 which is only a little over 100 fathoms, — and in the Skagerrack 

 and some Norwegian fjords, for which the bottom of the pro- 

 portionally much shallower North Sea forms a ridge. It is 

 therefore unquestionable that water flows at the surface of the 

 sea out of warmer into colder, and in its depths out of colder 

 into warmer regions ; so that there only remains to get an idea 

 of the velocity of these currents. 



Water, as a bad conductor of heat, is warmed only very 

 slowly, and expands just as slowly. Now, as this expansion is 

 moreover very trifling, the streaming produced by difference of 

 temperature must likewise be only an extremely slow, creeping 

 motion. 



In order to give an idea of the origination of the meridional 

 currents from difference of temperature, Dr. Carpenter showed, 

 on the 9th January 1871, at the Royal Geographical Society in 

 London, the following experiment. He filled a glass tank, 

 several feet long, with water, which at one end of the tank he 

 cooled with ice, and at the other end, by means of a special 

 arrangement, he heated at the surface. The cooled water was 

 coloured red ; the heated, blue. At the close of the lecture, 



