Impressions of the Desert 193 
clear and windless days at the same season, the 
desert never appears twice alike, for it is 
exceedingly sensitive to the gradations of light 
due to subtle changes in the atmosphere— 
its humidity, temperature, and proportion of 
dust particles, as well as to the effect of clouds; 
so that at times certain ranges, buttes, mesas, 
or desert plains are emphasised and at times 
almost obliterated from the picture by the 
play of light. A range that yesterday ap- 
peared washed in rose-madder may to-day 
appear a deep purple because of a grey sky. 
So also is the difference very great as one looks 
towards the sun or away from it. It thus 
happens that a gateway in the ragged moun- 
tains at times appears unusually prominent, 
while beyond it lies a wonderful desert shim- 
mering in the sunlight, which before had not 
attracted the attention. It may happen, too, 
when you look again for that gate of pearl and 
that region of light, they have vanished. 
Day after day, looking between the green 
columns of the saguaro, afar off towards the 
MacDowell Peaks, I have felt the spell of the 
desert. It has seemed to draw me like some 
entrancing mirage—a beautiful region, ethe- 
real and opalescent and changeful. Thereisa 
sense of the desert as there is a sense of the 
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