SUMMER HOT WINDS ON THE GREAT PLAINS. 345 
the plateau region from a northerly direction, and flows 
down over the eastern slope from a westerly and then a 
southerly direction, depending on the trend of the isobars. 
The mass of air, in moving down the slope, loses a great 
deal of the warmth derived dynamically, by radiation to the 
earth and the surrounding atmosphere, and also by inter¬ 
mixture, and it reaches the lower altitudes with dryness 
and increased temperature, but with less warmth than if 
the descent had taken place rapidly. The dry air is carried 
forward in the upper strata more rapidly than in the layers 
near the earth’s surface, and when thus carried out over 
moister and less dense air its tendency is to descend here 
and there through that air to the earth’s surface, while the 
moist and less dense air ascends at neighboring points and 
forms the scattering clouds often noted in connection with 
these winds! Similar descending currents, on a small scale, 
have often been observed by the writer to descend on dusty 
roadways and blow the dust out in all directions, then move 
off a short distance with the surface wind and die out. 
These currents (or masses of air) in descending rapidly from 
great elevations gain a great deal of warmth, and reach the 
earth with their initial dryness. In order, however, to be¬ 
come so intensely hot they must descend rapidly or the 
warmth gained dynamically is lost by radiation. After the 
earth’s surface is reached, both radiation and intermixture 
become rapid, and each individual current, except in the 
case of a very large one, is of short duration. This expla¬ 
nation accounts both for the general heating of the atmos¬ 
phere and for the intensely hot currents, and also accounts 
for the occurrence of these hot winds at any time of the day 
or night, from any direction, and without regard to the con¬ 
ditions of the soil, whether wet or dry. 
In these descending currents or masses of air evidently 
very little intermixture with the general atmosphere takes 
place until the earth’s surface is reached. They appear to 
retain their identity with sharply defined boundaries, to 
reach the earth with almost extreme dryness, and with 
