186 



Messrs. Carpenter and Jeffreys on 



[Dec. 8, 



the general average of our observations. — Having thence crossed the em- 

 bouchure of the Strait of Gibraltar, so as to approach the coast of Africa, 

 the three following days were passed in Latitudes averaging about a degree 

 further south than those in which the previous observations had been 

 noted ; yet the surface-temperature of the Sea then fell again to an average 

 of 72°, whilst that of the Air averaged 73°* 7, thus nearly restoring the 

 usual ratio between the two. — 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 66°'4, whilst the temperature of the Air rose to 76°* 6, thus showing the 

 then unprecedented difference of 10 0, 2 between the two. 



74. These remarkable phenomena caused us to give particular attention 

 to the Surface-temperature in the mid-stream of the Strait, and on the 

 northern side of its embouchure, on our return voyage ; when our first series 

 of observations derived full confirmation from another series taken with 

 the greatest care nearly two months afterwards. For when we left Gibraltar 

 Harbour on the morning of September 30th, we found, on proceeding into 

 the mid-stream, that the surface-temperature fell from 70°' 7 to 65°- 6, al- 

 though the latter observation was made towards noon ; that it remained at 

 nearly the same point through the remainder of that day and the succeed- 

 ing night, during which we were slowly proceeding eastwards, — still in 

 the mid-current ; and that it stood as low as 63° at six o'clock on the fol- 

 lowing morning (Oct. 1), when we had reached Station 65, in the deepest 

 part of the channel over the ridge not far from the African coast. Having 

 thence moved towards the Spanish coast, we found the surface-temperature 

 at Station 66 to have risen to 69° ; and a little further, at Station 67, it 

 was found to have risen to 73°. — These observations make it clear that in 

 the line of the strongest surface-mset, the temperature of the current is 

 several degrees lower than that of the surface-water of the Atlantic from 

 which it is directly derived ; and the fact would seem to indicate either that 

 the water of which this current consists is drawn from a part of the Atlantic 

 at least as far north as Lisbon, or (which may be thought more probable) 

 that it is derived from a stratum of the neighbouring ocean somewhat beneath 

 the surface, so as to have received less of the solar superheating than the 

 actual surface-water. — It would be a matter of much interest to trace this 

 colder current to its source, and thus to ascertain how it makes its way 

 through a sea at least five degrees warmer than itself. 



75. Our second series of observations upon the Surface-temperature of 

 the Northern side of the wide embouchure of the Strait were also quite con- 

 firmatory of the inference to which the first seemed to point, — that there 

 is a surface-outflow of Mediterranean water along the Spanish coast, by 

 which the Temperature is kept up above the ordinary standard of Atlantic 

 water in that latitude ; for during the remainder of Oct. 1, the following 

 night, and the greater part of the next day, the surface-temperature was 

 between 70° and 72°' 5, being a degree or two higher than the temperature 



