162 



Messrs. Carpenter and Jeffreys on [Dec. 8, 



30. During the whole of this Expedition the Temperature of the surface 

 of the Sea was ascertained and recorded every two hours, both by day and 

 by night ; as were also the readings of the Dry and Wet-bulb Thermo- 

 meters, which were placed in a small penthouse on deck, in which they 

 were freely exposed to the surrounding Air, but secluded from direct 

 or reflected Solar heat. — The Temperature of the surface-watery from the 

 time of our leaving the British Channel in Lat. 48° N. to our turning the 

 corner of Cape St. Vincent in Lat. 36° 50' N., increased at a rate which bore 

 a pretty regular proportion to the Southing. Thus, at the " chops of the 

 Channel," it averaged 62° for five days ; whilst by the time we approached 

 Cape St. Vincent it had gradually risen to above 69°. After passing that 

 point, however, we found both the surface- and the 6o^om-temperatures to 

 present certain variations, which, though not considerable in themselves, 

 proved to be of great interest when taken in connection with the peculiar 

 condition of the embouchure of the Strait of Gibraltar. These points, 

 however, will be more fitly discussed hereafter (§ 73 et sea.) ; and we 

 shall now only notice a sudden rise in Surface-temperature of about 3° 

 which showed itself as we turned the corner of Cape St. Vincent and 

 entered the north side of the embouchure, and a sudden fall of nearly 

 6° (to 66°'4) which was encountered when we entered the mid-stream of the 

 narrower part of the Strait as we proceeded towards Gibraltar. 



31. In the course of the First portion of the Cruise between Falmouth 

 and Lisbon (beyond which point Mr. W. L. Carpenter was unable to pro- 

 ceed), thirty-six quantitative determinations were made, by Volumetric 

 analysis, of the amount of Chlorine in as many samples of Atlantic water, 

 taken (1) from the surface, (2) from the bottom at various depths, and 

 (3) from various intermediate depths. The greater part of these, as will 

 be shown hereafter (§ 84), exhibited a very close conformity to a uniform 

 standard of density, as indicated by a Specific Gravity of 1*0268, and a 

 Chlorine proportion of 19"84 per ] 000* ; the chief departures being observ- 

 able in the lower density of the deepest waters, and in the occasional excess 

 of density in the surface-waters. The former is doubtless attributable to the 

 fact that the deepest water is essentially Polar, and therefore derives its 

 more dilute character from that source. The latter we are inclined to 

 attribute to the influence of slight concentration by evaporation. 



Second Cruise. 



32. Leaving Gibraltar early in the morning of Monday, Aug. 15, we 

 steamed out into the middle of the Strait, for the purpose of commencing 

 our experiments on the Gibraltar Current. The point selected by Capt. 

 Calver (Chart of Strait of Gibraltar, Station 39) lay midway between 

 Point Carnero, which forms the south-eastern boundary of Gibraltar Bay, 



* The proportion here adopted, — the number of Grammes of Chlorine to 1000 

 Cubic Centimetres of Water, — is that employed by Prof. Porchhammer in his elaborate 

 Memoir on the Composition of Sea Water (Philos. Transact. 1865). 



