FEB. 19, 1923 . HUMPHREYS: THE MURMUR OF THE FOREST 55 
not overcome or even reversed, by the tendency of the air along the 
slopes, owing to increased density due to loss of heat to the surface 
which, in turn, had cooled by radiation, to drain, or flow, away to 
lower levels. 
Tempest belt—When the wind across the mountain is strong, which 
it seldom is except in connection with a general cyclonic storm, it 
often beats down heavily on a narrow belt near, or beyond, the foot 
of the mountain—the stronger the wind the farther to leeward the 
tempest belt—while the winds both in the valley beyond and up the 
higher slopes are comparatively light, the latter indeed often being 
up the mountain and hence opposite in direction to that of the cross- 
ing and stronger wind. This tempest belt does not appear until the 
lower air, through the turbulence caused by the upper winds, has 
been brought to the same potential temperature throughout; that is, 
to such condition that each rising mass of air, if cooled by expansion 
only, or falling mass, if warmed by compression only, would, at every 
level, have the same temperature as has the adjacent air at the same 
level. In other words, this belt of driving winds does not form until 
the lower air is, by mixing, brought into a state of neutral equilibrium 
when, of course, convection requires but little work. 
Clearly, then, when the lower air has been brought to this state of 
neutral equilibrium, the decrease of pressure along a mountain side 
owing, as explained above, to crossing winds, may be, and frequently 
is, sufficient to cause these winds to flow down closely parallel to the 
lee slope. The inertia of this descending current carries it on, and 
hence it often beats strongly on a belt near the foot of the mountain, 
where the slope has become gentle, or even somewhat out in the 
valley. Furthermore, just as the wind strikes with a downward 
component onto this belt, so too it rebounds from it with an upward 
component. Hence, beyond the tempest belt the winds are com- 
paratively weak. 
But the above may not explain the worst of these tempest winds. 
Since, as already stated, there are several mountains southeast of, and 
parallel to, Peters Mountain, and since the rains and snows of greatest 
duration come from that general direction, it follows that these 
mountains, and the valleys between them, get more precipitation 
than does the valley and adjacent section northwest of this highest 
ridge. Hence, occasionally, the former region may be snow covered 
and relatively cold while the latter has but little snow and is appre- 
ciably warmer. Under these conditions southeast winds on topping 
