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until dangerously close aboard. When the fog is dense but the sun 

 is shining the first appearance of a berg is in the form of a luminous 

 white object ; while if the sun is not shining it is a dark, somber mass 

 with a narrow streak of black at the water line. Diffusion of light in 

 the fog will produce a blink around the berg that augments the appar- 

 ent size of the ice mass. 



Relieving stresses set up by temperature changes, and responding to 

 vibrations from sound or wave action, bergs may at anytime calve off 

 large sections of ice, which after falling into the water may bob up to 

 the surface again with great force, often at a considerable distance 

 away. Bergs are often so balanced that this calving, or merely melt- 

 ing of the under surface, will cause a shift in the center of gi^avity with 

 consequent capsizing and readjustment of the mass to a new state of 

 equilibrium. Vessels and boats should therefore keep well clear of 

 bergs that give evidence of disintegrating or overturning. Bergs may 

 also possess underwater spurs and ledges at a considerable distance 

 from the visible portions, and should be given a wide berth at all times. 



In fair weather, icebergs can be of great assistance to navigation 

 in floating ice. They may mark shoals, break up consolidated pack, 

 and afford reference points to assist in conning through ice. Having 

 a relatively small "sail area" in proportion to their bulk, bergs are not 

 affected by wind to the same extent as pack ice, and with a wind blow- 

 ing the pack past a berg, the optical illusion may arise that the berg is 

 being carried to windward, cutting a channel. Illusion or not, such 

 a lee may be a desirable place for a vessel to lie to avoid heavy ice; 

 there are cases on record of vessels laying out an ice anchor to a berg 

 under such circumstances. A careful watch must be kept for growlers 

 calved off from the berg under these conditions. Navigators are fre- 

 quently alarmed by the presence of icebergs in an anchorage area. 

 Unless the bergs are of mammoth size or disintegrating, there is little 

 to fear. Small bergs that foul a handling area can easily be fended 

 off with ice picks. 



When navigating in fog, the presence of a large number of growlers 

 bunched together may be a good indication of icebergs to windward. 

 In calm weather, growlers may sometimes be found distributed in a 

 curved line, with the berg on the concave side of the curve. 



SEA ICE 



F(h^t ice forms in sheltered bays, gulfs, and fiords, as well as among 

 floating lumps of old ice. Developing along the shore and spreading 

 into the sea, it joins the new ice formed around islands, grounded 



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