6 The Colorado Experiment Station. 
warmth is relatively greater in winter and therefore more noticeable 
when the mountain region is warmer in comparison with the plains 
chan in summer, adding extra heat to the descending air. 
During the heated period in July and August, high tempera¬ 
tures often characterize the days. However, the periods of oppres¬ 
sive heat, sunstrokes and heat prostrations that occur in our eastern 
states, especially in the large cities, are practically unknown in Colo¬ 
rado, owing to our low, sensible temperature, although the tempera¬ 
tures in this State are often as high as those reached in the eastern 
states. The prevailing lack of moisture in the air is favorable to 
increased intensity of the direct rays of the sun, but owing to the 
dry atmosphere, which is favorable to rapid cooling by radiation 
and evaporation, even the warmest days are comfortable in the 
shade, and are succeeded by cool nights, which prevent a tendency 
toward the debility incident to continued heat. Nowhere in Colo¬ 
rado is the air sultry or “muggy,” the dryness being marked, as 
shown by the low reading of the wet bulb thermometer, which gives 
the temperature of evaporation, or sensible temperature, or approxi¬ 
mating that experienced by the body. In Colorado this temperature 
is not infrequently 20, 30 or 35 degrees lower than the air tempera¬ 
ture during the hottest part of the day. The air temperature as it 
is commonly recorded does not necessarily indicate the sensation of 
heat experienced by a person, so that an estimation of the pleasant¬ 
ness of two locations, as judged by the air temperatures, may give 
an entirely erroneous impression. The term “sensible temperature” 
is used to describe the temperature felt on the surface of the body. 
The wet bulb thermometer as used indicates this. It is an ordinary 
thermometer covered with a piece of muslin and immersed in water. 
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 affects the temperature experienced by one. The greater 
the humidity, or amount of moisture in the air, the less the evapora¬ 
tion, and therefore, less cooling effect. The wind is also an import¬ 
ant factor in promoting evaporation. Hence the effect of a light 
freeze is to make it seem cooler than the temperature of the air 
would indicate, especially on a cold day. 
We often hear the statement made that the climate is changing, 
and the popular belief that such is the case can only be explained by 
the generally short and defective memories of people who through 
exposure to them, or inconvenience, or perhaps loss from a few 
severe storms in the past, unintentionally exaggerate the severity 
and frequency of the event. Although large fluctuations occur in 
different years with some indication of periodical term, especially in 
Coloiado where the range of temperature is great, there seems to 
