542 



Captain Spratt on the Undercurrent [June 15, 



it was in the depth of 108 feet, so considerably below the skimming surface- 

 current of lighter water flowing from the Baltic. The denser and warmer 

 water thus found in 108 feet was therefore a continuity of the warmer 

 and denser waters of the deeps of the Kattegat and German Ocean. 

 But the Kattegat being shallow, with a wide entrance between it and the 

 German Ocean, it has no deep trough so much below the separating barrier 

 for retaining still water as in the Sea of Marmora ; its waters would, there- 

 fore, fluctuate in density throughout, between the densities of the Baltic 

 and German Ocean. 



As Dr. Carpenter has made the fallacy regarding the Baltic conditions on 

 the authority of Prof. Forchhammer's statements and opinions the strongest 

 reason and basis of his enlarged theory of universal undercurrents, I must 

 refer to another circumstance, another error of the late Professor in as- 

 suming the existence of an undercurrent at the Sound flowing into the Baltic 

 when the surface-current was running out, viz. the fact often observed in the 

 Sound, that ships of deep draught are frequently carried past the lighter 

 draught ship when sailing together into the Baltic through the Sound*. 



There is, however, another and more probable explanation of the phe- 

 nomenon, namely, that the deep-draught ships are, by the lowness of 

 their keels in comparison with that of the light-draught craft, under a 

 lesser influence of the outward surface-current, through the whole strength 

 of the current not descending to the depth of their greater draught, as 

 surface-currents always diminish in descent. The mean strength of a 

 current felt by a vessel drawing twent}^ feet of water would consequently 

 be less than the mean strength felt by one drawing only eight or ten feet ; 

 this will be evident, especially as the surface-current from the Baltic can- 

 not descend much below the depth of sixty feet, viz. that of the Barrier 

 ridge across the Sound and Great and Little Belts, moreover there is no 

 tidal influence there to force or confuse the outflowing surface-current from 

 the Baltic. 



Judging from these explanations and facts there appears to be really 

 no evidence, from the observations of Prof. Forchhammer, that an under- 

 current is a real necessity for the restoration of the lost salinity of the 

 Baltic any more than in the Black Sea ; but, on the contrary, that the 

 evidences and facts are confirmatory of there being no such undercurrent, 

 and no such necessity for one in either case. 



Therefore, finding the undercurrent theory fallacious in both instances, 

 I have no faith in its application to the Ocean as a grand law of inter- 

 change between surface and deeps, pole and equator, as the great universal 

 movement advocated by Dr. Carpenter. I am therefore induced here, 

 from the apparent importance of some views and facts bearing on the 

 question, to reiterate the following arguments in support of this opinion, 

 which were given elsewhere f, commencing the discussion with the inter- 

 esting facts regarding the high normal temperature of the deeps of the 

 * Phil. Trans. 1865, p. 231. t Crete, vol. ii. Appendix. 



