570 Scientific Intelligence — Geology and Hydrography. 



into the house at high tide. Dr Pingel says, that no aboriginal 

 Greenlander builds his house so near the water's edge. The 

 points mentioned above, the writer of the letter had visited ; 

 but he adds, on the authority of a countryman of his own, 

 highly deserving of credit, that at Napparsok, ten Danish miles 

 (forty-five English) to the north of Ny-Sukkertop, (lat. QB" 20' 

 N.), the ruin's of ancient Greenland winter-houses are to be seen 

 at low water. Dr Pingel is not aware of any instance of sub- 

 sidence in the more northern districts ; but he suspects that the 

 phenomenon reaches at least as far as Disco Bay, or nearly to 

 69'' north latitude. 



2. Quantity and Proportion of the constituent Parts of At- 

 mospheric Air in Water. — Dr Thomson finds that 100 cubic 

 inches of Clyde water contain 3,113 inches of air. This air, 

 extracted from the water by boiling, afforded 70,9 volumes of 

 azotic gas, and 29,1 volume of oxygen gas ; = 100,0. Thus the 

 air extracted from water by boiling is much richer in oxygen 

 gas than common air, containing rather more than 29 per cent., 

 while common air contains only 20 per cent, by volume. But 

 this excess of oxygen diminishes so rapidly when the air thus 

 obtained is inclosed in a vessel over water, that after four days 

 it does not contain more than common air. 



3. Use of NicoTs Calcareous Spar Prism in discovering 

 Shoals in the Ocean. — M. Arago remarks, that the bottom of the 

 sea, or the surface of a shoal at a given distance from the ship, is 

 more distinctly seen from the masthead, or, generally speaking, 

 from a considerable height, than from the deck. This pheno- 

 menon he explains by remarking, that the reflected light from 

 the surface of the sea, which is always intermixed with that 

 from the bottom, or the shoal, possesses a less and less degree of 

 intensity in proportion as the angle of reflection, reckoned from 

 the surface, is larger. In order fully to remove this reflected 

 light, he proposes, when it is wished to look into the sea to dis- 

 cover cliff's or shoals, &c. to observe them by means of a tour- 

 maline, in which the axis is held horizontally, if possible, under 

 a polarizing angle of 37°, reckoning from the surface. The 

 entire and absolute obstruction of the light reflected from the 

 surface of the water cannot possibly take place under a smaller 



