On the Formation of Bottom Ice. 409 



According to Chydenius, the above described process of 

 ice formation is common, and known to all the fishermen 

 off the coast of the islands of Aland, in the Baltic. The 

 sounds and the bays between these islands often freeze in 

 this manner, according to their accounts, i. e., by round 

 plates of ice coming up from the bottom in large quantities, and 

 freezing together on the surface. 



This surface freezing often takes place in so short a time 

 that a boat which is not well out to sea, in water altogether 

 free from ice, can hardly come into harbour before the surface 

 of the sea is covered with ice. Martin compares the appear- 

 ance of the sea ice in Spitzbergen with the bottom ice in the 

 German rivers. According to Scoresby, the first formation of 

 ice in the Polar Seas is in the shape of crystals, which resemble 

 snow-flakes dropped into water at freezing-point. These 

 crystals then freeze together into small pieces of ice of about 

 two inches in diameter ; these again freeze together into large 

 cakes of ice, which become round by coming into collision with 

 each other through the working of the waves. Sailors give 

 these round cakes of ice the name of "pancakes." The ice 

 formation in the Polar Seas takes place often in an incredibly 

 short time. Chydenius, who accompanied the Swedish Spitz- 

 bergen Expedition in 1857, has related, that on one occa- 

 sion the sea, which was quite clear of ice, in the space of a 

 single half hour was so covered over the whole surface with ice 

 that they could with difficulty force the boat through it. The 

 temperature of the air during the day had not been lower than 

 — 4° Cent.,* and no wind or stream had driven these masses of 

 ice together, but they were formed where they first appeared. 



The formation of ice cakes during the freezing of sea water 

 is no rare phenomenon, but, on the contrary, seems to be the 

 usual manner in which the sea freezes up. As has been before 

 stated, the sea water becomes chilled, and the first ice forma- 

 tion takes place at some distance below the water's edge, or 

 even at the very bottom, and the small round plates of ice 

 which are the characteristics of such a formation grow together 

 in their passage up through the cold water to the surface, and 

 thereby attain the size of which they are generally seen. It is 

 impossible in any other manner to explain how the sea can 

 often become so quickly frozen over. As we have before 

 shown, when the temperature of the air is 4° Cent., the whole 

 surface of the sea can be frozen over in the short space 

 of half an hour; if, on the contrary, the temperature of 

 the water is below freezing point, the freezing, after it has 

 once begun, goes on with the same haste, just as when we 



* — 4° Cent, corresponds with. 24- 8 Fahr. 



