124 



THE DESERT 



How pro- 

 duced. 



Objects in 

 the water. 



Goitfused 

 mirage.' 



density of the air will give the appearance of 

 waves or slight undulations on the water. In 

 either case the illusion is quite perfect. Water 

 lying in such a bed would reflect the exact color 

 of the sky over it ; and what the eyes really 

 see in this desert picture is the reflection of the 

 sky not from water but from strata of thick air. 



This illusion of water is probably seen more 

 perfectly in the great dry lake-beds of the des- 

 ert where the ground is very flat and there is 

 no vegetation, than elsewhere. In the old Coa- 

 huila Valley region of the Colorado the water 

 comes up very close to you and the more you 

 flatten the angle of reflection by flattening your- 

 self upon the ground, the closer the water ap- 

 proaches. The objects in it which people im- 

 agine look like familiar things are certainly very 

 near. And these objects — wild fowl, bushes, 

 tufts of swamp grass, islands, buttes — are fre- 

 quently bewildering because some of them are 

 right side up and some of them are not. Some 

 are reversed in the air and some are quietly 

 resting upon the ground. 



It happens at times that the whole picture is 

 confused by the light-rays being both reflected 

 and refracted, and in addition that the rays 

 from certain objects come to us in a direct line. 



