308 SCOTT'S LAST EXPEDITION [June 
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 
A for the reference of future observa- 
tions. He imagines the atmosphere 
* A C in potential equilibrium with 
6 large margin of stability, i.e. the 
WW/////////////////// c difference of temperature between 
A and C being much less than the adiabatic gradient. 
In this condition there is a tendency to cool by radia- 
tion 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 possibly 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. 
Owing to lack of sun heat the effect will be more rapid 
in south than north and therefore the upset will commence 
first in the south. After the first start the upset will 
rapidly spread north, bringing the blizzard. The facts 
