40 METEOROLOGY 



up to their bellies. When the sun was hot the travelling would be much better, for 

 the surface snow got near the luelting-point, and formed a slippery layer not easily 

 broken. Then again a fall in the temperature would produce a thin crust through 

 which one broke very easily." * 



On consulting the thermometer readings of the Southern party, we find that 

 the highest temperatures recorded for their journey over the Great Ice Barrier 

 were 22° Fahr. at 8 A.M. on December 3, 1908, and 21° Fahr. at 1 p.m. on 

 December 2. The shade temperature for noon on December 3 was not taken. On 

 December 2 the shade temperature at 8 a.m. was 14° Fahr. There was a rise there- 

 fore on December 2 of 7° Fahi'. between 8 A.M. and 1 p.m. If there was a similar 

 rise in temperature on December 3, the shade temperature on that day may liave 

 been about 29° Fahr. at 1 p.m. December 3 was the last day of the Southern party's 

 journey over the Great Ice Barrier. Previous to these two days the shade temperature 

 had been considerably below freezing-point. It was probably the case that the 

 softening of the snow surface, described by Shackleton as preceding the formation of 

 the crust on the snow surface, was due to actual microscopic thawing partly caused 

 by minute j^articles of rock dust, spread over the snow by the blizzards. 



Granular Ice Crystals from Snoiv. On relatively warm bright days in summer 

 it seemed as though crops of granular ice crystals were growing on the surface of the 

 snow. On the Barrier near latitude 83° 16' S., Shackleton states:* "The surface 

 of the Barrier still sparkles with the million frozen crystals which stand apart from 

 the ordinary surface snow." Again {op. cit. vol. ii. p. 12) he says, speaking of the 

 surface of the barrier : " The snow generally was dry and powdery, but some of the 

 crystals were large, and show in reflected light all the million colours of diamonds." 



At an altitude of over 7000 feet on the plateau on which the South Magnetic 

 Pole is situated, these crystals are much in evidence. These ice crystals on January 

 14, 1909, were found to be about half an inch in width and about one sixteenth of an 

 inch in thickness. They form a layer about half an inch in thickness over the top of 

 the neve. In the bright sunlight the snow surface covered with these sheets of bright 

 reflecting ice crystals glitters like a sea of diamonds. 



Probably these crystals M'ere not being freshly developed each sunny day at the 

 surface of the snow, but were crystals originally formed an inch or so below the snow 

 surface and subsequently exposed through the removal of the former covering by 

 evaporation. If this is so, their presence shows that there is considerable evaporation 

 taking place on these high Antarctic plateaux. 



The snow surface of thisjalateau was never up to thaw point, and almost certainly 

 never is. The hottest temperature that the Northern party experienced on the part 

 of the plateau near to the Magnetic Pole area, where the above observation was made, 

 Avas about 15° Fahr.t on the noon of January 5, 1909, at an altitude of about 7000 



* " The Heart of the Antarctic," vol. i. p. 303. 

 t Not corrected for instrumental error. 



