304 SCOTT'S LAST EXPEDITION 



The process of freezing is a very interesting one to watch in cold, 

 calm weather. As the temperature falls the sea becomes covered 

 with small scale-like plate crystals up to one inch across of a deli- 

 cate fern-like structure. They generally float flat upon the sur- 

 face, but many are imprisoned in an approximately vertical posi- 

 tion. After the surface becomes covered, the ice then grows in 

 the ordinary way by accretion from below. In the initial stages, 

 when the ice is only an inch in thickness, the felt-like mass on the 

 surface has little rigidity, and even up to 3 inches thick moves 

 freely up and down under the influence of a swell without losing 

 its coherence in any way. 



Sea ice is quite different in its properties from the ice formed 

 on a pond or lake of fresh water, owing to the fact that some of 

 the salt in solution in sea water is always imprisoned between 

 the individual crystals in the sea ice. This imprisoned salt be- 

 tween the crystals does not 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, whereas 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 the 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 the conditions of temperature and humidity in the air 

 above. 



These * ice flowers ' have but a fleeting existence, however, 

 for should the air temperature rise much above the temperature 

 at which they were formed they melt again and collapse. Since 

 the cryohydric temperature of common salt and water is zero 

 Fahrenheit, it follows at once that no ice flowers can live above 

 zero temperature (o F.). 



In the early part of the winter all additions to the thickness 

 of the sea ice are due to conduction by the cold air above, but 



