F. GEOGRAPHY. 113 



addition to that which the Mediterranean basin previously 

 contained, the density of this water is increased, and a col- 

 umn of it reaching to any given depth becomes heavier than 

 a corresponding column of Atlantic water. Consequently 

 the excess of downward pressure will displace the lower por- 

 tion of the column of water, which will flow outward as an 

 under-current. The withdrawal of a portion of the lower 

 stratum will produce a renewed reduction of the surface lev- 

 el, taken in connection with continued evaporation, and this 

 will occasion a further inflow of Atlantic water, which in 

 turn undergoes concentration. And this interchange will be 

 maintained perpetually, there being, on the one hand, a tend- 

 ency to the restoration of the level lowered by excessive 

 evaporation, and on .the other a tendency to a restoration of 

 the equilibrium disturbed by excess of pressure. The inflow 

 and outflow will thus keep each other in check, so that neither 

 the lowering of the level nor the increase of density will ever 

 exceed a very limited amount. 



This explanation, Dr. Carpenter thinks, received additional 

 confirmation by the phenomena observed by the currents of 

 the Baltic. Here an immense amount of fresh water is re- 

 ceived from the lakes and rivers, which tends to dilute the 

 waters of the sea. An outflow is established from the sur- 

 face, which, of course, being continued without any counter- 

 acting tendency, would in time wash out every particle of 

 salt, were it not for an under-current which brings back into 

 jt the salt water from the North Sea. Thus, while the sur- 

 face current is tending to reduce the level of the Baltic to 

 that of the North Sea, the influx of fresh water into the Bal- 

 tic, and the outflow of a portion of the salt water must tend 

 to diminish the density; and the equilibrium is maintained 

 by the inward passage of a body of salt water from the 

 depths. The case is, therefore, exactly the reverse of that of 

 the Mediterranean, but such as would be expected in view of 

 the hypothesis advanced by Dr. Carpenter. 12 A, November 

 30 and April 6 ; also Contemporary Review. 



CARPEXTER OX OCEAX CURRENTS. 



In a previous article we have given Dr. Carpenter's ac- 

 count of the outward deep-sea current from the Mediterra- 

 nean into the Atlantic, corresponding with the surface cur- 



