132 NAVIGATION. 



Point Turnagain. 



Point Turnagain, from whence Captain Franklin 

 returned, is in latitude 68 34' N., longitude 1 09 25' 

 W. 



Ice Bergs. 



The altitude of one ice berg seen in Captain 

 Parry's Voyage of 1821-22, was 258 feet above the 

 surface of the sea, its total height, therefore, (allow- 

 ing \ to be visible,) must have been 1806 feet. 

 This, however, is on the supposition, that the base 

 under water does not spread beyond the mass above 

 water, but descends perpendicularly, which is impro- 

 bable. An approximation might apparently have 

 been gained by sounding, to discover if the depth 

 actually amounted to 300 fathoms. 



A decrease of wind immediately takes place to the 

 lee of ice, whether as a stream, sheet or in large 

 pieces. In the polar regions, which are encumbered 

 with them, there is a total absence of heavy or dan- 

 gerous squalls of wind, never obliging the seaman to 

 lower his topsail. 



Lieutenant Ross, in Captain Parry's third voyage, 

 tried the thickness of the salt-water ice by digging 

 holes the greatest thickness was 7 feet 2| inches, 

 on the 4th May, 1825. 



Refraction. 



The refractive powers of the atmosphere are so 

 fluctuating as to render it impossible at all times to 

 ascertain correctly, or by any invariable rule, the 

 distances of terrestrial objects by their heights, or 

 their heights from the distances at which they may 

 be visible to the eye. This influence is probably 

 most powerful in the polar regions. The highest 

 land seen by Captain Ross in Baffin's Bay, he esti- 

 mated at only 4000 feet, yet during the voyage it 

 was clearly ascertained, that objects were sometimes 



