I9II] ACTION OF SEA WATER ON ICE 213 



day, but the sky has not been clear since they spread over it 

 except for about two hours in the middle of the night when the 

 moonlight was so bright that one might have imagined the day 

 returned. 



Otherwise the web of stratus which hangs over us thickens 

 and thins, rises and falls with very bewildering uncertainty. We 

 want theories for these mysterious weather conditions; mean- 

 while it is annoying to lose the advantages of the moonlight. 



This morning had some discussion with Nelson and Wright 

 regarding the action of sea water in melting barrier and sea ice. 

 The discussion was useful to me in drawing attention to the equi- 

 librium of layers of sea water. 



In the afternoon I w^ent round the Razor Back Islands on ski, 

 a run of 5 or 6 miles; the surface was good but in places still 

 irregular with the pressures formed when the ice was ' young.' 



The snow is astonishingly soft on the south side of both 

 islands. It is clear that in the heaviest blizzard one could escape 

 the wind altogether by camping to windward of the larger island. 

 One sees more and more clearly what shelter is afforded on the 

 weather side of steep-sided objects. 



Passed three seals asleep on the ice. Two others were killed 

 near the bergs. 



Saturday, June 10. — The impending blizzard has come; the 

 wind came with a burst at 9.30 this morning. 



Simpson spent the night turning over a theory to account 

 for the phenomenon, and delivered himself of it this morning. 

 It seems a good basis for the reference of 



future observations. He imagines the at- ' A 



mosphere A C in potential equilibrium with 

 large margin of stability, i.e. the difference 



of temperature between A and C being « 



much less than the adiabatic gradient. 



In this condition there is a tendency to V//////////////////////y C 

 cool by radiation until some critical layer, 



B, reaches its due point. A stratus cloud is thus formed at B ; 

 from this moment A B continues to cool, but B C is protected 

 from radiating, whilst heated by radiation from snow and pos- 

 sibly by release of latent heat due to cloud formation. 



The condition now rapidly approaches unstable equilibrium, 

 B C tending to rise, A B to descend. 



