SEA ICE 
443 
freeze in contact with ice till a fairly low temperature is 
reached, and consequently sea ice when new and thin is 
never hard and rigid like fresh water ice. As a result 
ice even four or more inches thick is for sledging by no 
means safe, wJiereas the same thickness of fresh ice would 
be sufficient to support a regiment of soldiers. 
In cold clear weather about thirty-six hours is required 
to form ice of this thickness, which is then of a dark 
slaty colour, but somewhat mottled owing to differences 
in transparency of the differently oriented crystals. 
If the temperature of the air is below 'zero Fahrenheit, 
as the ice forms and while it is still only a couple of inches 
thick, the extruded salt on tlic surface commences to gather 
moisture from the air and grows upwards in beautifully 
shaped crystals, forming rosettes in almost infinite variety 
of structure, depending chiefly upon tlie conditions of 
temperature and humidity in the air above. 
These ' ice flowers ' have but a fleeting existence, 
however, for should tlic air temperature rise much above 
the temperature at wliich they were formed they melt 
again and collapse. Since the cryoliydric temperature of 
common salt and water is zero Fahrenheit, it follows at 
once that no ice flowers can live above zero tempcralure 
(o° ¥.). 
In the early part of the winter all additions to the 
thickness of the sea ice arc due to conduction by the 
cold air above, but there is every reason to believe that 
later in the winter the sea ice grows to its great thick- 
ness of 8 and 9 feet largely by the deposition of frazil 
crystals from below. 
