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 
14and 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. 
Minimum. Maximum. Minimum. Maximum. 
Day of month. Day of month. 
M.L.| D. L.|M.L.| D. L. M.L.| D. L. | M.L.| D. L. 
°F, | CR. | oF. | oF. oF, | °F. | OF. | oF. 
June 7....... 46 |...... (Cae June 13....... 43 74 68 101 
Beasts eos 46 psweces “i. beeenee Wesevnes 43.5} 71 66 104 
| ree 45 |.s.e4 12 \anouns Lbs ecunne 45 76 69 105 
WO sentie se AO 8) i wie.c ie 67 102 16s osunasx 44 78 71 102 
Tacs dex 42 70 69 101 Wassaaaa 41 V7 70 102 
WD ce arereua.s 41.5} 71 69.5; 100 TSisccaved 41 72 69 106 
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 equality between the apartness of maxima and minima—which 
is to say that there is an equality of daily mean range of temperature 
between desert and mountain—it would indicate that the minima are 
