MIRAGES—GORDON 3a5 
the asphalt street surface and the cement guter, it stopped short. 
The air forming the lens was colored by the transmitted light so as 
to be clearly visible. ‘The lens seemed to be formed of a scurrying, 
shimmering blue blanket of heat waves about 2 inches thick. In 
the brisk wind the air forming the lens must have been changed 
every 3 or 4 seconds. Moving across the south cement-asphalt 
dividing line, it became instantly visible, a part of the functioning, 
mirage-forming lens, passed out of it, and vanished at the north 
line. Cars and trucks passing through it in a steady stream had no 
visible effect; there seemed to be no piling up against the windward 
side of tires. The lens arched up over the crown of the road, fully 
a foot higher than the gutter. 
What mysterious force within that lens maintained it as a func- 
tioning entity amid all those disruptive forces? It was composed 
of air that was changed every few seconds, surrounded by air except 
where it rested on the ground, and yet it was completely set apart, 
doing things the surrounding air could not do until it moved into 
the lens, and could no longer do the second it moved out. The 
assumption of the mirage-making power the instant the air crossed 
the south cement-asphalt line was something to see and wonder at. 
Earlier in this paper reference was made to the two laws most 
deeply involved in mirage making and their two rather mysterious 
junior partners. One of these two junior partners would seem to 
be concerned with the forces that set the lens apart and keep it that 
way; the other with the need to select the location in which a lens 
will operate. How they carry out these functions we do not yet 
know. Because of the wind, the effects shown in this mirage were 
almost miraculous, but its lessons were borne out in other locations. 
There is an almost comic side to these hard-fighting, long-lasting 
street mirages—they cannot stand competition from real water. <A 
brisk shower or even a sprinkling cart can bring an end to them in 
seconds. 
At this point it is well to consider the extreme contrast between 
what we have been watching and the lenses that operate for only 
a fleeting moment to give us the filmiest of pictures, sometimes recur- 
ring, sometimes not. In my experience these momentary showings 
are not common. My most impressive example was the appearance 
of a great towering block of mesa, seeming quite near, reaching 
much above my little watchtower hill, completely unreal, without 
substance, and yet easily seen. It probably lasted more than a 
minute. It was impossible to say what real object might have been 
so distorted. 
Related to the little mirages in particular, but having also to do 
with mirages in general, is the following fairly typical case. At a 
distance of 200 yards or more the seeming water will appear and will 
