On the general Causes of the Ocean-Currents. 35 



On another occasion I poured into the box a sohition of common 

 salt to about half its dejsth and then filled up carefully with fresh 

 water. I then let it stand for some hours to allow strata of different 

 saltness, but in perfect equilibrium, to form themselves, and then re- 

 peated the above experiment with the weak stream. At the aperture of 

 the partition I thus obtained four opposite streams, viz: at the top one 

 outflowing-, under which was one flowing inward; under this was on 

 outflowing and then again an inflowing stream. The diff'erence between 

 this and the preceediug experiment is easily accounted for by what I 

 have above said about the shallowness of surface-currents, when the 

 diff'erence of specific gravity is great; in this case both the surface-cur- 

 rent and its reaction-stream were so shallow, that the remaining depth 

 of the orifice was sufficient for the latter to produce its own pair of 

 reaction-currents. This phœnomenon will no doubt be met with in 

 nature. 



Before quitting the question of the reaction-streams, I beg to re- 

 capitulate partly the result of this special research, and to examine from 

 my point of view some circimistances, which may be of importance in 

 forming a clear notion of the ocean-currents properties and movements. 



If a free ocean-current be supposed to move under such circum- 

 stances, that the loss of vis viva, which it suffers from the resistance of 

 friction at every point of its course be always compensated from some 

 constantly active source, the mass of water, which the stream carries by 

 in a imit of time, would continually increase; for the streams velocity 

 then decreases more slowly than its mass increases (pag. 18). Although 

 I might not try to calculate the influence on the velocity of an ocea- 

 nic stream, arising from the conversion of a part of its vis viva into 

 heat, nevertheless it seems probable, that the state of the case not 

 will be entirely changed by this little loss of vis viva. At all events 

 the mass of the moving water will be considerably enlarged by the me- 

 canical reaction of the stream on the neighbouring water-strata, and in 

 general I think we may say, that effusions of lighter water on the Ocean 

 produce much more powerful and more lasting currents^ than ivhat from 

 their original mass one woidd have exjjected. — This circumstance has 

 without doubt been too much overlooked, thus e. g. by Maury, when 

 from the section and velocity of the Gulf-stream at the Florida pas- 

 sage, compared with those at Caj)e Hatteras he endeavours to calculate 

 the inclination of its under surface '). 



') Mauuy, Phys. Geogr. of the sea, 1872 p. 27. 



