374 THE DEPTHS OF THE SEA. [CHAP, vm 



accepted. Dr. Carpenter believes, however, that the 

 conditions in the Strait of Gibraltar and in the 

 Baltic Sound aptly illustrate the general circulation 

 in the ocean, and confirm his views. 



I quote from the general summary of Dr. Car- 

 penter's address to the Geographical Society : 



" The application of the foregoing principles to 

 the particular cases discussed in the paper is as 

 follows : 



"VIII. A vertical circulation is maintained in 

 the Strait of Gibraltar by the excess of evaporation 

 in the Mediterranean over the amount of fresh water 

 returned into its basin, which at the same time 

 lowers its level and increases its density ; so that 

 the surface inflow of salt water which restores its 

 level (exceeding by the weight of salt contained 

 in it the weight of fresh water which has passed off 

 by evaporation) disturbs the equilibrium and pro- 

 duces a deep outflow, which in its turn lowers the 

 level. The same may be assumed to be the case 

 in the Strait of Babelmandeb. 



" IX. A vertical circulation is maintained in the 

 Baltic Sound by an excess in the influx of fresh 

 water into the Baltic; which at the same time 

 raises its level and diminishes its density, so as to 

 produce a surface outflow, leaving the Baltic column 

 the lighter of the two, so that a deep inflow must 

 take place to restore the equilibrium. The same 

 may be assumed to be the case in the Bosphorus and 

 Dardanelles. 



"X. A vertical circulation must, on the same 

 principles, be maintained between polar and equa- 

 torial waters by the difference of their temperatures : 



