1872.] 



e Shearwater 3 Scientific Researches. 



567 



sence of Mediterraneaa water could be detected by an excess in the Specific 

 Gravity of the bottom-water, on the Atlantic side of the slope ; our previous 

 inquiries having shown that no such excess is to be found in the ordinary 

 water of the Atlantic, which appears to be even a little more saline at the 

 surface than below it, — the effect of this excess on Specific Gravity being 

 neutralized by the expansion produced by the more elevated Temperature 

 (Report for 1870, § 84). The average of our determinations of the Sp. 

 Gr. of Atlantic water had been 1*0265, the minimum (bottom) being 

 1*0261, and the maximum (surface) 1*0269; and this agrees very well 

 with the results obtained by Forchhammer, — who, moreover, explicitly states 

 that while the water taken between Lat. 20° and 30° off the western coast 

 of Africa has a Salinity approaching that of Mediterranean water (which 

 he attributes to the great evaporation, and to the absence of river-return of 

 fresh water), the surface-water of the Atlantic embouchure of the Straits, 

 for some distance westward, has the average density of Atlantic water*. 



49. The first sample we obtained of bottom Atlantic water within the 

 influence of the Mediterranean outflow, was by the deep Sounding already 

 mentioned (§ 3) as having been taken on the 19th of August, in Lat. 36° 

 47' N., and Long. 9° 39' W., about 45 miles W.S.W. of Cape St. Vincent. 

 The Sp. Gr. of the surface-water being here 1*0268, that of the bottom- 

 water was 1*0281. — Our next sample was obtained on the 20th of August 

 from a depth of 665 fathoms in Lat. 36° 2' N. and Long. 7° 43' W., in the 

 direct line of the axis of the Strait, and about 90 miles to the west of the 

 " ridge." The Sp. Gr. of the surface-water was here 1*0269, and that of 

 the bottom-water 1*0280. Proceeding eastwards in the direction of Cape 

 Spartel, we took on the following day a succession of samples from the 

 gradually shallowing bottom of the Atlantic slope ; and the Specific Gra- 

 vities of these, as compared with those of the surface-water at the same 

 points, are given (with the preceding) in the following Table : — 



Station. 



North 

 Latitude. 



West 

 Longitude. 



Depth in 

 Fathoms. 



Sp. Gr. at 

 Surface. 



Sp. Gr. at 

 Bottom. 



1. 



36° 47' 



9° 39' 



1560 



1*0268 



1-0281 



2. 



36° 2' 



7° 43' 



665 



1-0269 



1-0280 



3. 



35° 4?i' 



6° 41' 



355 



1*0269 



1*0282 



4. 



35° 43' 



6° 34' 



290 



1*0270 



1*0281 



5. 



35° 40' 



6° 28' 



225 



1-0270 



1*0282 



6. 



35° 38' 



6° 25' 



115 



1 0270 



1*0278 



7. 



35° 47' 



6° 2i 



325 



1-0270 



1-0285 



Thus it appears that along the whole of this line of Soundings there is 

 a most decided excess in the Specific Gravity of the bottom-water over that 

 of the swface-water, and that this excess increases as the "ridge" is 

 approached, — the exception shown at Station 6 being really a proof of the 

 rule ; for at that Station there was obviously a rise of the bottom from a 

 * Phil. Trans., 1865, pp. 220, 223. 



VOL. XX. 2 T 



