THE POLAR JOURNEY 503 



It is common knowledge that as you rise in the atmo- 

 sphere so the pressure decreases : in fact, it is usual to 

 measure your height by reading the barometer. Now the 

 air on this last stretch to the Pole was rising, for the wind 

 was from the south, and, as we have seen, the plateau here 

 was sloping down towards the Pole. The air, driven up- 

 hill by this southerly wind, was forced to rise. As it rose 

 it expanded, because the pressure was less. Air which has 

 expanded without any heat being given to it from outside, 

 that is in a heat-proof vessel, is said to expand by adia- 

 batic expansion. Such air tends first to become saturated, 

 and then to precipitate its moisture. These conditions 

 were approximately fulfilled on the plateau, where the air 

 expanded as it rose, but could get little or no heat from out- 

 side. The air therefore precipitated its moisture in the form 

 of crvstals. 



Owing to the rapid changes in surfaces (on one occasion 

 they depoted their ski because they were in a sea of sas- 

 trugi, and had to walk back for them because the snow 

 became level and soft again) Scott guessed that the coastal 

 mountains could not be far away, and we now know that 

 the actual distance was only 130 miles. About the same 

 time Scott mentions that he had been afraid that they were 

 weakening in their pulling, but he was reassured by getting 

 a patch of good surface and finding the sledge coming as 

 easily as of old. On the night of January 12, eight days 

 after leaving the Last Return Party, he writes : "At camp- 

 ing to-night every one was chilled and we guessed a cold 

 snap, but to our surprise the actual temperature was higher 

 than last night, when we could dawdle in the sun. It is 

 most unaccountable why we should suddenly feel the cold 

 in this manner : partly the exhaustion of the march, but 

 partly some damp quality in the air, I think. Little Bowers 

 is wonderful ; in spite of my protest he would take sights 

 after we had camped to-night, after marching in the soft 

 snow all day when we have been comparatively restful on 

 ski." 1 On January 14, Wilson wrote : "A very cold grey 

 thick day with a persistent breeze from the S.S.E. which 



1 Scott's Last Expedition, vol. i. p. 540. 



