22 



UNIVERSITY OF COLORADO STUDIES 



species which would be killed by the greater heat of the plains. This 

 question will be more fully discussed in a later paper. 



Precipitation Compared with That of Other Parts of the United 

 States. — The mean annual precipitation is eighteen inches at Boulder. 

 Hence the climate may be described as semi-arid, but not as desert. 

 Since evaporation is less rapid at Boulder than on the great plains the 

 eighteen inches of rainfall really goes farther than the same amount 

 would in eastern Colorado or western Nebraska. The precipitation 

 at Boulder is 40 per cent, that at New York and 65 per cent, that at 

 St. Paul, Minn. Fig. 2 shows graphically the mean rainfall by months 



TABLE II 

 Summaries of Relative Humidity Readings at Boulder, Colo., 1908 



Monthly mean, using 6 A. m. and 6p.m 



Monthly mean, calculated from maximum and 



minimum 



Monthly mean, using 2 A. m., 8 A. m., 2 p. m. 



and 8 p. m 



Monthly mean, using 8 A. m. and 8 p. m 



Mean daily maximum 



Mean daily minimum 



Mean daily range 



Greatest daily range 



Least daily range 



Highest maximum 



Lowest maximum 



Highest minimum 



Lowest minimum 



June 



% 

 63-3 



6 5 .8 



63.2 

 65-4 

 84.6 

 47.1 



37-5 

 92.0 

 11. o 

 100. o 

 47.0 

 60.0 

 8.0 



July 



% 

 66.5 



67.9 



86.3 



49-5 

 36.8 

 56.0 

 16.0 

 100. o 

 61.0 

 69.0 

 27.0 



August* 



% 

 78.3 



75-i 



91.8 

 58.5 

 33-3 

 58.0 

 10. o 

 100. o 

 69.0 

 79.0 

 33 -o 



* August, 1908, was unusually wet. The precipitation was 3 . 3 inches, being 2 inches above normal. 



for Boulder, New York, St. Louis, St. Paul and Phoenix, Ariz. The 

 last-named place is included as a representative of desert conditions. 



Wind.— Although Colorado has a reputation for high winds the 

 total wind movement at Denver (twenty-five miles from Boulder) is 

 less than in many parts of the eastern United States. The mean annual 

 movement of wind in Denver is 62,621 miles which is less than that of 

 such eastern cities as Chicago with 136,454 miles, Boston 101,907, 

 New York 96,769, St. Louis 96,016 and St. Paul 63,ooo. 1 Unfortu- 

 nately no wind records are available for Boulder. The wind at Boulder 



1 Edson, Carroll E., "Denver," Wood's Rej. Handb. Med. Sci., Vol. Ill, pp. 408-11, 1001. 



