SUMMER HOT WINDS ON THE GREAT PLAINS. 343 
are lower to the south than over the territory affected by 
these winds. Therefore general southerly winds do not ex¬ 
plain the origin of the special hot winds. Such winds 
would, moreover, be general, and not confined to the narrow 
limits often described in connection with these hot winds. 
Furthermore, this explanation would not be applicable to 
those* hot winds which blow from the north. 
The opinion that the general hot winds over the eastern 
slope of the Rocky mountains in summer are a special class, 
and that their heat and dryness are of dynamic origin the 
same as that of the foehn and chinook, has been advanced 
by a few scientists, and the present study of all the observa¬ 
tions and correlated facts which can be found relating to 
this subject certainly appears to confirm the theory that 
these winds are of such origin. The distribution of pressure 
in each case where these hot winds have been noted is such 
as would augment the generally eastward movement of the 
atmosphere of the middle latitudes. The high pressure off 
the coast of Oregon and Washington tends to give south¬ 
easterly winds between the coast and the divide, and this 
force acting with the general trend of the atmosphere of 
these latitudes causes the winds to become more easterly. 
With these conditions it can readily be seen that an area of 
low pressure remaining nearly stationary over the eastern 
slope of the Rocky mountains for a few days w T ould cause 
the wind to continue its course across the divide toward 
such low pressure area. The atmosphere as it moves east¬ 
ward from the Pacific coast to the crest of the continental 
divide is always accompanied by clouds and more or less 
rain, and at the outset is nearly saturated with moist¬ 
ure. In crossing the divide to reach the low pressure 
area this air must ascend to a height of 10,000 to 15,000 
feet. From the deductions of Dr. Harm,* Prof. Bezold,t Prof. 
* The Laws of the Yariation of Temperature in Ascending Currents of 
Air, etc. Zeitschrift Oest. Met. Gessell., 1874, pp. 321-346, IX. 
f Thermodynamics of the Atmosphere in the Sitzungsb. Ak. Wiss., 
Berlin, 1888, pp. 485-522. 
