in the Twenty Years before 1895 41 



subject to the variations of temperature and pressure obtaining 



at the different depths. The pressure increases regularly 



with the depth, and produces a sliding scale for the temperature. 



The effect of pressure alone would be determined afterwards 



in an hydraulic receiver. The opportunity for using these 



instruments did not occur, but the mercury piezometer, which 



;i development of them, was successfully used by Professor 



Mohn in his researches in the Norwegian sea. It is usual 



now to use capsizing thermometers, and to overturn them 



a messenger sent down the line when the thermometer 



has arrived at the required depth. Both of these devices 



are very old, and were used by Aime in his remarkable researches 



in the Mediterranean between 1843 and 1846. For the 



investigation of the really deep water of the ocean, we require 



mometers with such a scale that tenths of a degree Fahren- 



or the corresponding portion of a Centigrade degree can 



be determined with certainty. In the course of my researches 



in tin- "Buccaneer," I passed over the point where three 



ridges meet, almost on the equator to the north of the island 



tension. These ridges delimit three basins of the Atlantic, 



re distinguished by the temperature of their bottom 



The temperature at the bottom of the basin lying 



to the south and west of this point is 35-5, in that to the 



i and west it is 36-0, and to the eastward in the Gulf of 



Guinea is 36-4 Fain. It is obvious that, in order to be certain 



of differences of this character, the thermometers must have 



ide and open scale. 



We have already a large number of determinations of 

 ;!>ufi<>n of temperature with depth made at dilh rent 

 locality in the ocean, but we have very few determina- 



i in tin- ^anie I'M ;ilit\ at different seasons and 

 in ditt. r . nt ve.u- In the "Buccaneer," I made a point of 

 repeating the serial t nijtcrature observe t all <>t the 



;i the neighbourhood of tin Gv 

 ulerable differences were found, especially 

 i of IOO fathoms in thirknr^. In the 

 also carried out s\ -trin. iti.alK the determine 



<>f tlir t< ' lit Ill til 



