28 



UNIVERSITY OF COLORADO STUDIES 



limit of the plains. In fact the campus, though now planted with trees, 

 was originally an arid plain. The mesa station is at the lower limit 

 of timber. Both stations are exposed to the unobstructed sun at all 

 times. 1 



Climate of Mesa and Plain. — In Table VI are given the maximum, 

 minimum and range for each day during which the thermograph was 

 kept in operation on the mesa. The figures show the differences in the 

 climate of the two places. The campus has higher maxima and 



TABLE IX 

 Daily Means* for May, 1908, at University Campus and Horse Mesa 



Day of Month 



Mean 



Temperature 



at Campus 



Day of Month 



Mean 



Temperature 



at Campus 



Mean 



Temperature 



on Mesa 



3- 



4- 

 5- 

 6. 



7- 



8. 



9- 

 10. 

 11. 

 12. 



13- 

 14. 



IS- 



16. 



53 -o 

 63- 5 

 37-2 

 28.2 

 30. 2 

 45 -o 

 5i° 

 53° 

 47.2 



45-7 

 55-5 

 52.5 

 43 -° 

 54-o 



59-5 

 65-5 



17- 

 18. 

 19. 

 20. 

 21. 



22. . . . 



23 



24 



25 



26 



27 



28 



29 



3° 



3i 



Month . 



* Mean temperatures were calculated according to the formula recommended by Harm: 7 A. 11. + 2 p. m. 

 + 9 p.m. + 9 p. M.-i-4 = mean. The formula: maximum + minimum-*- 2= mean, differed from the above con- 

 siderably for individual days but for the month the mean differed only o . 5 degree for the campus and one 

 degree for the mesa. See Table VII. 



lower minima than the mesa. In other words, the plain has a more 

 severe climate than the mesa. Days are hotter and nights are colder. 

 The mean temperatures, however, do not differ greatly (Table VII). 

 No observations have been made on the rainfall of the mesas but they 

 probably have a slightly greater precipitation than the adjacent plain. 

 Inversion of Temperatures. — It is ordinarily the case that increased 

 altitude is accompanied by lower temperature, but low hills surrounding 



1 The only published data dealing with the climate of this area in reference to plant formations are given 

 by Young, Bot. Gaz., 44:334, 337, 339, 1907. Dr. Young's observations, while interesting, are so frag- 

 mentary that they cannot be used in the present study. 



