638 



Dr. W. B. Carpenter on the 



[June 13, 



their stand upon its prolongation as a " deep, warm, voluminous current." 

 Under no other condition than this, indeed, can it retain its heat for 

 anv considerable duration, beneath an Atmosphere whose temperature is 

 much below that of its surface (§ 155) ; for since, as we have seen (§ 142), 

 the Gulf-stream, even at its deepest and strongest, loses in winter fifteen 

 degrees of surface-heat while passing from the Florida Channel to the south 

 of Nova Scotia, it must part much more rapidly with any excess it may still 

 retain, when its superheated stratum has been thinned out by superficial ex- 

 tension, and when the progressive reduction of its movement to a rate per 

 dag not exceeding its rate per hour in the most rapid part of its course, 

 prolongs its exposure from days to weeks, and from weeks to months. 



164. I conclude, then, that nothing save the general Northerlg movement 

 of a stratum of Water deep enough to retain an excess of heat through a 

 lengthened period, whilst flowing beneath an Atmosphere of lower tempe- 

 rature than its own, can account for the Thermal phenomena indicated in 

 Dr. Petermann's Gulf-stream Charts. Of such a movement it has been 

 shown that the Temperature-soundings taken in the ' Porcupine ' Expedi- 

 tions afford very distinct evidence (§ 13). On the other hand, the very fact 

 of its extension to so great a depth appears sufficient to negative the idea that 

 it is to be accounted for either by the vis a tergo of the Florida current, or by 

 the drift-action of S.W. winds on the surface. 



II. On the Dardanelles and Baltic TJnder-currents. 



165. When discussing, in the Report of the Porcupine' Expedition for 

 1870, the Physical Theory of the Gibraltar Current, I endeavoured to 

 strengthen my case by showing the applicability of that Theory, mu- 

 tatis mutandis, to two other cases in which all the conditions of the 

 Gibraltar Current are reversed together, — an Under-current of the heavy 

 water of the German Ocean having been proved to flow inwards through 

 the Baltic Sound, beneath the outward surface-current of lighter Baltic 

 water ; whilst the existence of a similar inflow from the iEgean into the 

 Black Sea, beneath the outward surface-current of the Bosphorus and 

 Dardanelles, might be predicated (I ventured to affirm, § 123) "on the 

 double ground of a priori and a posteriori necessity." — I much regret that 

 I was not at that time acquainted with the experiments and observations 

 which had been made by Capt. Spratt on the Dardanelles Current some 

 years previously * ; since, if they had fallen under my notice, I should 

 have cited them as affording probative evidence of the truth of my position. 

 For although the conclusion which Capt. Spratt has himself deduced from 

 them is diametrically opposite to my own, yet the fallacy of that conclusion 



* In excuse for my ignorance of Capt. Spratt's inquiries on this subject, I may point 

 out that the ' Travels and Eesearches in Crete,' in which they are published as an 

 Appendix, is not a work into which any one seeking information upon the Dardanelles 

 Current would naturally look. 



