1871.] 



Theory of the Ocean. 



529 



excess of density on the side of the shorter column, there will be a 

 tendency to the restoration of the level by a surface-flow from the higher 

 to the lower, and a tendency to the restoration of the equilibrium by an 

 under-Row in the opposite direction from the heavier to the lighter 

 column.' 5 



Dr. Carpenter then refers to the observations and opinions* of the late 

 Dr. Forchhammer of Copenhagen, for the conditions and facts that are 

 said or assumed to exist between the Baltic and German Ocean in regard to 

 the interchange of a surface and undercurrent between them so as to 

 restore the lost density of the former caused by a supposed continued 

 outward surface- current, and thus maintain the equilibrium or normal 

 conditions between them. 



As I shall be obliged to refer to these opinions as assumed facts here- 

 after, I must here dwell more particularly upon what has been assumed in 

 regard to the Black Sea and iEgean, regarding which Dr. Carpenter states 

 as follows : — f ' The condition of the Euxine is precisely parallel to that of 

 the Baltic ; and a surface-current is well known to be constantly flowing 

 outwards through the Bosphorus and Dardanelles, carrying with it (as in 

 the case of the Baltic) a large quantity of salt. Now, as the enormous 

 volume of fresh water discharged into the Euxine by the Danube, the 

 Dneiper, and the Don would in time wash the whole of the salt out of its 

 basin, it is obvious that its density can only be maintained at its constant 

 amount (about two-fifths that of ordinary sea-water) by a continual 

 inflow of denser water from the iEgean, the existence of which inflow, 

 therefore, may be predicted on the double ground of a priori and a posteriori 

 necessity." 



The first consideration then is, whether these predictions, as necessary 

 premises to his enlarged theory, are true both for the Baltic and Black 

 seas, since upon them the soundness of the theory mainly depends. 



I am therefore induced, as I have been frequently requested to do, to 

 give my experience and knowledge of the conditions of the surface and 

 deeps of the Mediterranean and Black Sea, and next analyze the observa- 

 tions of Dr. Forchhammer to see whether his opinions and conclusions are 

 true in regard to the Baltic, viz. that the density of the Baltic is main- 

 tained by an undercurrent from the denser waters of the Kattegat and 

 German Ocean. For it is through my knowledge and experience of the 

 conditions existing at the Black Sea Straits and iEgean Sea, from repeated 

 experiments in them on temperature and densities, &c, that, with all due 

 deference to the judgment of Dr. Carpenter, I am obliged to regard those 

 advanced by him as fallacious, and to maintain that, in adopting them, he 

 is advocating a theory upon erroneous premises. It is therefore necessary 

 for me to briefly show here the nature and extent of these investigations, 

 either published or unpublished, in support of my reasons for so differing 

 from Dr. Carpenter. 



* Philosophical Transactions, 18G5. 

 VOL. XIX. 2 T 



