1872.] 



1 Shearwater 1 Scientific Resear dies. 



547 



of M. Charles Martins on this point having confirmed those formerly made 

 by Scoresby off the coast of Greenland, in indicating a temperature above 

 32° at 40 fathoms, when the temperature of the surface is below 32°. 

 This is easily accounted for by the inferior salinity of the cold surface- 

 stratum, the reduction of its temperature and of its salinity being alike 

 due to the melting of ice. For if the ice be that of Icebergs formed 

 as Glaciers on land, the water into which it dissolves will be entirely 

 fresh ; whilst if it has been formed by the freezing of sea-water, so large 

 a part of its salt will have been left out in the act of congelation, that the 

 product of its liquefaction will be of comparatively low Specific Gravity ; 

 and thus Sea-water at or even below 32° may float upon water some degrees 

 warmer than itself. That this is really the explanation of many cases of 

 this kind, seems probable from the fact, which I have learned from Capt. 

 Toynbee (of the Meteorolugical Department), that when our American 

 Packet-ships, in crossing the Atlautic, meet with a sudden depression of 

 surface-temperature, they find the Specific Gravity also of the surface- 

 water to be sensibly lessened ; both results being pretty certainly due to 

 the melting of icebergs borne southwards by the Arctic Current. — But the 

 strata of Ocean-water do not always arrange themselves in accordance with 

 their relative Specific Gravities and Temperatures. Two currents may 

 meet, as on the Agulhas Bank, in such a manner that the inclination of 

 the Sea-bed throws up the colder one nearer to the surface than the warmer ; 

 and the former may maintain this superiority of position as long as its force 

 of translation lasts. This agency was doubtless operative in the following 

 remarkable case cited by Dr. Petermann : — "Lieut. Rogers, in 1855, found 

 "in the Asiatic part of the Arctic Ocean a warm surface-current with water 

 "of low Specific Gravity ; beneath it a cold current ; and then, again, a warm 

 "current of heavier water ; and all these strata running in opposite direc- 

 " tions." I am informed by Mr. Leigh Smith, who last summer penetrated 

 to the N.E. of Spitzbergen, that he has encountered a similar succession. — 

 Cases of this kind, however, do not invalidate the general fact, that the glacial 

 stratum in Polar Regions extends from less than 50 fathoms below the surface 

 to the bottom, however deep. Thus Scoresby found the temperature at about 

 120 fathoms to be 29 3 , when it was 34° at the surface. Sir Edward Parry 

 found the surface-temperature off Spitzbergen to vary from 31° to 2S°, and 

 the bottom-temperature at depths down to 100 fathoms to vary from 30° 

 to 28°. Sir John Ross found the temperature in Lat. 72° 33' N. and Long. 

 73° 7' W. to be 35° at the surface, and to decrease gradually to 28?° at a 

 depth of 1000 fathoms. And the recent observations of M. Chas. Martins 

 have shown that from 40 fathoms downwards the temperature constantly 

 undergoes reduction, until the thermometer stands below 29°*. This is 

 confirmed by the still more recent observations of MM. Weyprecht and 

 Payer, which further show that the stratum above 32° becomes thinner as 

 it flows northwards : — 



* The foregoing Temperatures are stated on the authority of ilr. Prestwich. See his 

 Presidential Address for 1871, in the Quart. Journ. of the Geological Society, p. lis. 



