56 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 4 
Peters Mountain must, because of their comparatively great density 
incident to the low temperature, rush cataract-fashion down the lee 
side and onto the nearer portion of the valley. At such times the 
winds of the tempest belt are abnormally violent, and much like the 
famous Helm Wind along the west side of the Pennine range of 
mountains in northern England. 
It may, perhaps, be worth while to call attention here to the all 
but obvious fact that when the lower air has been brought to neutral 
equilibrium, which it soon is after the surface winds become strong, an 
- aviator can more easily cross a high mountain with the wind than 
against it—more easily when the currents boost him up than when 
they beat him down. 
Smoking of chimneys.—When the wind is from the mountain it 
frequently happens that chimneys near its base, and even many in 
the valley, ‘‘smoke”’ in a most disagreeable, puffy, manner, a phenom- 
enon locally interpreted to imply the approach of bad weather, a 
prediction that usually comes true. The cause of the smoking of chim- 
neys at the time of winds from the mountain is, of course, perfectly 
obvious. As just explained, these winds have marked downward 
components, and some of the gusts are strong enough to drive well 
into an open topped chimney against the heated air, and send smoke 
and ashes whirling through the room. Hence in mountainous regions 
many chimneys are hooded as a protection against both the smoke 
nuisance and its inevitable fire hazard. 
Sounds beyond the mountain.—At the very beginning of a general 
storm and before any other evidence of it is apparent, sounds made 
in a windward valley, or beyond, often are distinctly heard in the 
next valley to the leeward where at other times they are quite inaudi- 
ble. This effect clearly is owing to the fact that the vibrating air, 
transmitting the sound with the velocity of about 1100 feet per second, 
is itself a part of the general wind. Since the velocity of sound has 
been closely determined for certain temperatures, and is known 
to vary as the square root of the absolute temperature, it follows 
that for any given variation of temperature with altitude and given 
corresponding direction and speed of the wind the path of any sound 
ray—any normal to the sound-wave front—can be traced with all 
desired accuracy. Under certain simple conditions, such as uniform 
changes of temperature and wind velocity with altitude, the path 
of a sound ray can be given in terms of a concise equation. However, 
it is not worth while here to indulge in any such mathematical diver- 
SS a? 
