1869.] 



on the Scientific Exploration of the Deep Sea. 



483 



Specif c Gravity. — The Specific Gravity of Surface-water was found to 

 diminish slightly as land was approached ; but the average of 32 observa- 

 tions upon water at a sufficient distance from land to be unaffected by local 

 disturbances was 1*02779, the maximum being 1*0284 

 and the minimum .... 1*0270. 



It was almost always noticed that, during a high wind, the specific gravity 

 of surface-water was above the average. 



The average of 30 observations upon the Specific Gravity of Interme- 

 diate water was 1*0275, 



the maximum being 1*0281, 



and the minimum 1*02/2. 



The Specific Gravity of Bottom-waters at depths varying from 77 to 

 2090 fathoms, deduced from an average of 43 observations, was 



1*0277, 



the maximum being. . , 1*0283, 



and the minimum 1*0267. 



It will be noticed that the average Specific Gravity of Bottom-water 

 is slightly less than that of Surface-water. In several instances the Specific 

 Gravities of Surface- and of Bottom-waters taken at the same place having 

 been compared, that of the Bottom-water was found to be appreciably less 



than that of the Surface-water. Thus 



At 1425 fathoms depth (Station 17) it was . . 1*0269 



Surface at the same 1*0280 



And 



At 664 fathoms depth (Station 26 b) it was . . 1*0272 



Surface at the same 1*0280 



According, however, to a Series of observations made at the same spot 

 (Station 42) at intervals of 50 fathoms, from 50 to 800, the Specific Gra- 

 vity increased with the depth from 1*0272 at 50 fathoms to 1*0277 at 

 800 fathoms*. 



Several series of Sp.-Gr. observations were made near the mouths of 

 rivers and streams ; showing the gradual mixture of fresh and salt water, 

 and the floating of lighter portions above the denser sea- water, as well as 

 the reverse effect produced by the influence of tidal currents. Thus out- 

 side Belfast Lough a rapid stream of water of Sp. Gr. 1*0*270 was found 

 above water which at a depth of 73 fathoms had a Sp. Gr. of 1*0265. 



Gases of Sea- water. — The analyses of the Gaseous constituents of sea- 

 water may be divided into two groups : (1) Analyses of Surface-waters. 

 (2) Analyses of waters below the surface ; and these last may be again 

 subdivided into (a) Intermediate, and (b) Bottom-waters. 



The total quantity of dissolved gases in sea-water, whether at the surface 

 or below it, was found to average about 2*8 volumes in 100 volumes of water. 



* My own experience of the difficulty of making accurate Hydrometric determinations 

 when the ship was rolling prevents me from attaching much value to the above results. — 

 W. B. C. 



