CLIMATE OF THE SANTA CATALINA MOUNTAINS. 



77 



Some estimate of the error involved in basing the gradient only on 

 minimum readings may be made by the figures presented in tables 

 14 and 15. These tables exhibit the only daily records of maximum and 

 minimum temperatures for the Catalinas for any period longer than 

 a few days. The average maxima and minima for Marshall Gulch for 

 the months of June, July, and August have been contrasted in table 14, 

 with the average maxima and minima for the Laboratory. During 

 June the apartness of the minima was 30.5°, of the maxima 25.0°. In 

 July this relation was reversed, the apartness of the minima being 

 24.1°, that of the maxima 29.4°, while for August the two were more 

 nearly the same, the apartness of maxima being 26.1°, of maxima 27.3°. 

 The facts that the minimum temperatures of valley and mountain 

 were further apart than the maxima were during June, and not so 

 far apart in July and August, may be connected in some manner with 

 the clear dry weather of June and the rainy, cloudy character of July 

 and August. However, the data in table 15, showing the maximum 



Table 15. — Daily record of maximum and minimum temperatures for a portion of June 

 1912, at summit of Mount Lemmon, with corresponding data for the Desert Laboratory. 



Average difference of maxima, 33.9; of minima, 31.1. 



and minimum temperatures on Mount Lemmon in June 1912, indi- 

 cate that there was a greater apartness of maxima than of minima 

 when these data are averaged and contrasted with those for the Desert 

 Laboratory. 



It would require a much fuller mass of figures than are in hand to 

 make any attempt at an explanation of the differences that exist in 

 the apartness of desert and mountain maxima and minima in different 

 localities and different months. For the present purpose it is instruc- 

 tive to average the entire set of apartnesses for Marshall Gulch for 

 June, July, and August 1911, which gives an average difference of 

 minima of 80.7°, and of maxima of 81.7°. In other words, throughout 

 a series of several months there is doubtless a swamping of the irregu- 

 larity of the apartnesses for individual months. If, then, there is an 

 average equahty between the apartness of maxima and minima — which 

 is to say that there is an equahty of daily mean range of temperature 

 between desert and mountain — it would indicate that the minima are 



