6 
The Colorado Experiment Station 
mountains, and later the wind springs up and the chinook is at 
hand. Chinooks are liable to occur at all seasons of the year, 
but the warmth is relatively greater in winter and therefore 
more noticeable when the mountain region is warmer in com¬ 
parison with the plains than in summer, adding extra heat to 
the descending air. 
RAPID EVAPORATION REDUCES EFFECT OF HIGH AND 
LOW TEMPERATURES 
During the heated period in July and August, high tem¬ 
peratures often characterize the days. However, the periods of 
oppressive heat, sunstrokes and heat prostrations that occur in 
our eastern states, especially in the large cities, are practically 
unknown in Colorado, owing to the mild effect of our tempera¬ 
ture, although the thermometer in this State often registers as 
high as in the eastern states. The prevailing lack of moisture 
in the air is favorable to increased intensitv of the direct ravs 
•• 
of the sun, but owing to the dry atmosphere, which is favorable 
to rapid cooling by radiation and evaporation, even the warm¬ 
est days are comfortable in the shade, and are succeeded by 
cool nights, which prevent a tendency toward the debility inci¬ 
dent to continued heat. Nowhere in Colorado is the air sultry 
or ^ ^ muggy the dryness being marked as shown by the low 
reading of the wet bulb thermometer, which gives the tempera¬ 
ture of evaporation, or sensible temperature, or approximating 
that experienced by the body. In Colorado this temperature 
is not infrequently 20, 30 or 35 degrees lower than the air tem¬ 
perature during the hottest part of the day. The air tempera¬ 
ture as it is commonly recorded does not necessarily indicate 
the sensation of heat experienced by a person, so that an esti¬ 
mation of the pleasantness of two locations, as judged by the 
air temperatures, may give an entirely erroneous impression. 
The term ‘ ‘ sensible temperature ’ ’ is used to describe the tem¬ 
perature felt on the surface of the body. The wet bulb ther¬ 
mometer as used indicates this. It is an ordinary thermometer 
covered with a piece of muslin and immersed in Avater. The 
dryness of the air takes up the water by evaporation, the 
greater the dryness the greater the evaporation, and since this 
is a cooling process, it alfects the temperature shown by the 
thermometer. Evaporation thus atfects, also, the temperature 
experienced by a person. The greater the humidity, or amount 
of moisture in the air, the less the evaporation, and therefore, 
less cooling effect. The wind is also an important factor in 
promoting evaporation, hence the effect of a light breeze is to 
