Native Vegetation 
29 
TABLE XIII.—DECREASE OF AIR 
Altitude (feet) 
0 
1640.42 
3280.8 
4921.2 
656i.7 
8202.1 
9842.5 
11482.9 
13123.3 
16404.2 
PRESSURE WITH ALTITUDE. 
Air Pressure (inches) 
30 
28.307 
26.693 
25.157 
23.622 
22.283 
20.905 
19.724 
18.504 
16.339 
Providing other factors remain the same, a decrease in the at¬ 
mospheric pressure increases the rate of evaporation. Further¬ 
more, radiation of heat increases in intensity with an increase in 
the rarity of the atmosphere. Hence, as a result of the increased 
rate of radiation, and of evaporation at high altitudes, objects cool 
off very rapidly, the formation of frost is favored, and the length 
of the growing season is shortened. 
2. Decrease of air temperature.—As a rule, in Colorado, an 
increase in elevation of 1,000 feet decreases the mean temperature 
for the year about 2y 2 °, spring 3^4°, summer 3°, fall 2*4°, and 
winter 1 y 2 °. (Page 7). 
3. Decrease in the difference between the mean temperature 
of the warmest month and that of the coldest month. 
4. Greater difference between sun and shade temperatures 
page 9). 
5. Greater difference between day and night temperatures 
page 9). 
6. Increase in heating effect of the sun (page.9). 
7. Increase in the difference between the temperature of soil 
and plant surfaces and that of the surrounding air (page 10). 
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1 
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8. Increase in the effect of exposure (page 11). 
9. Shortening of the growing season (page 13). 
10. Increase in precipitation (page 24). 
11. Decrease in absolute amount of moisture in the air (page 
27). 
12. Increase in the rate of evaporation (page 27). 
13. Stronger wind movement.—However, the rate of wind 
movement is very dependent upon local topographic conditions, 
such as direction of mountains, and exposure. 
14. I ncrease in the intensity of ultra-violet rays. 
