56 THE OCEAN WOKLD. 



between land and sea, for water is always present, although in a solid 

 state ; the surface is always at a very low temperature ; snow does not 

 melt as it falls, and the sea is thus sometimes covered with a continu- 

 ous sheet of frozen snow ; sometimes with enormous floating hlocks of 

 ice which are driven by the currents. Meeting with these floating 

 masses of ice is one of the dangers of polar navigation. Captain 

 Scoresby has given a very detailed description of the different kinds of 

 ice met with in the Arctic Seas. The ice-fields of this writer form 

 extensive masses of solid water, of which the eye cannot trace the 

 limits, some of them being thirty-five leagues in length and ten 

 broad, with a thickness of seven to eight fathoms ; but generally these 

 ice-fields rise only four to six feet above the water, and reach from 

 three to four fathoms beneath the surface. Scoresby has seen these 

 ice-fields forming in the open sea. When the first crystals appear, 

 the surface of the ocean is cold enough to prevent snow from melting 

 as it falls. On the approach of congelation the surface solidifies, and 

 seems as if covered with oil ; small circles are formed, which press 

 against each other, and are finally soldered together until they form a 

 vast field of ice, the thickness of which increases from the lower 

 surface. 



The water produced from melted ice is perfectly fresh the result 

 of a well-known physical cause. When a saline solution like sea 

 water is congealed by cold, pure water alone passes into the solid 

 state, the saline solution becomes more concentrated, increases in 

 density, and, sinking to the bottom, remains liquid. Blocks of ice, 

 therefore, in the Polar Seas, are always available for domestic use. 

 There are, however, salt blocks of ice, which are distinguished from 

 fresh-water ice by their opaqueness and their dazzling white colour : 

 this saltness is due to the sea water retained in its interstices. 

 Scoresby amused himself sometimes by shaping lenses of ice, with 

 which he is said to have set fire to gunpowder, much to the astonish- 

 ment of his crew. 



The ice-fields, which are formed in higher latitudes, are driven to- 

 wards the south by winds and currents, but sooner or later the action 

 of the waves breaks them up into fragments. The edges of the 

 broken icebergs are thus often rising and continually changing : these 

 asperities and protuberances are called hummocks by English navi- 

 gators; they give to the polar ice an odd, irregular appearance. 



