SUMMER HOT WINDS ON THE GREAT PLAINS. 347 
from the eastern slope eastward over the lakes and down 
the Saint Lawrence valley. Low pressure areas, when 
moving very slowly and accompanied by brisk to high 
winds, will, when the high pressure areas occupy the posi¬ 
tions referred to above, draw the atmosphere after them 
from some distance in the rear, while those moving east¬ 
ward rapidly would soon leave the atmosphere, crossing the 
divide uninfluenced by their action. 
Apparently the conditions on which the development of 
hot, dry winds over the eastern slope of the Rocky moun¬ 
tains and eastward depends are the presence of nearly 
stationary or slow moving low T pressure areas along the 
eastern slope and then eastward, with a relatively high 
pressure over the Pacific off the coast of Oregon or in that 
vicinity. In no instances are hot winds noted with a low 
pressure area which moves eastward with any degree of 
rapidity. 
Although the development of these hot winds is entirely 
independent of drought conditions, yet they will, of course, 
become much more intense, will extend over more territory, 
and be more injurious to crops when they occur during the 
prevalence of a drought than when they occur with season¬ 
able weather, as vegetation in the former case will be the 
principal source from which they must draw their moisture, 
and the excessively dry winds can injure crops generally 
in a very short time. When the earth is moist crops are 
not likely to suffer seriously during the prevalence of a 
generally warm, dry wind, but principally suffer where the 
intensely hot winds occur, resulting from the rapidly de¬ 
scending currents; and the areas affected by these, while 
they make considerable show, are but a small amount when 
compared with the entire crop of a state. Occasionally one- 
sixth, or even one-fourth, of two or three counties are com¬ 
pletely burned up, but such cases are rare. In fact, after a 
careful consideration of this subject, I have arrived at the 
conclusion that while these winds are often very intense and 
striking in their nature and damage crops to a considera- 
