1871.] 



Theory of the Ocean. 



547 



the barrier-ridge to the westward that separates the deeps of the Atlantic 

 from the proper Mediterranean deeps. 



Therefore, as there is here a great convergence or concentration of 

 the Atlantic inset, here there would naturally be a deeper tendency of the 

 inflowing current, as well as of an uprising of the lower part of it, where 

 this concentration produced a more rapid commingling of converging 

 waters, and a sort of boiling-up of parts of the deeper waters would be the 

 natural result of this convergence and constriction. Colder waters would 

 therefore come towards the surface, and vice versa. 



Now Dr. Carpenter shows this to be the result here, although he does 

 not recognize what appears to me to be the natural and simple explanation 

 of the phenomenon as above given. He says in regard to this : — "It was 

 not a little perplexing to find, when we had fairly entered the Strait and 

 were proceeding along the mid-channel towards Gibraltar, that the surface- 

 temperature of the sea fell still further to 06 o, 4, whilst the temperature of 

 the air rose to 76°*6, thus showing the then unprecedented difference of 

 10°' 2 between the two ;" and on his return to the same part about two 

 months afterwards, viz. at Station 64, he found the surface-temperature 

 there 66°. 



Now, if this be the true and simple explanation of the low surface-tem- 

 perature over the position of greatest intermixture or boiling-up of the 

 currents there, as I suggest and believe, we should expect the same thing 

 to occur in some parts over the ridge which extends across the western 

 entrance to the Straits, where the Atlantic current or inflow is also some- 

 what concentrated, or first meets it as an obstruction, and thus causes an 

 uprise of the cold water from below to the surface. And, curious enough, 

 the two surface-temperatures taken by Dr. Carpenter at this part, viz. at 

 Stations 65 and 66, show in proof a much lower temperature, only 63° at 

 the first of these, and 69° at the other. The temperature of 66° at Station 64 

 is therefore clearly a commingling of the uprisen cold waters over the 

 barrier-ridge ; for the mean surface-temperature at 50 miles' distance, on the 

 west side of the ridge, was 72| degrees, and from about 50 miles 5 distance 

 from Gibraltar on the east of the Strait it was 73 J degrees, that is, the mean 

 of seven observations taken about the former distance by Mr. Gwyn 

 Jeffreys, and of seven about the latter by Dr. Carpenter. Deductions 

 from temperature and density in such positions as the narrows and over 

 the barrier-ridges are therefore, to my mind, not reliable ; I experienced 

 the same at the narrows of the Dardanelles, near the two Castles, and 

 so carried out my observations in more normal conditions or tranquil 

 areas, and in parts free of local disturbing influences that might tend also 

 to divert the direction of the lower currents, as well as of those near the 

 surface, and lead to erroneous conclusions favouring a bias for any theory 

 or prediction. 



As Station 65 was one of Dr. Carpenter's positions for trying for the under- 

 current he asserts to exist, and as he has drawn some inferences in favour of 



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