MIRAGES—GORDON 339 
reaching up to a common level; next comes the effect of feeler tops 
flattening out and extending to meet others to form windows, and 
then to fill in the windows. The completed flattop seems to be a 
climax, the highest point of development the inversion layer and lens 
can reach. In the unbuilding, these steps are reversed. The mirage 
has furnished us with some idea of what has been going on in the 
lens and has made it visible, somewhat as the colored algae in Yel- 
lowstone Park outline the course of each little stream in the brook. 
The Flattop seen some 35 miles southeast from Yuma is a late 
starter, rarely seen before 7:30 a.m. As a rule, about sunrise is the 
best time to see such mirages. 
A very unusual development of this Flattop building technique was 
observed at Naco, in southeastern Arizona, one morning in the late 
winter of 1916-17. Five or six miles to the east is a barren, sawtooth 
line of hills, rising perhaps 250 to 300 feet. A bit before sunrise rising 
feelers were noted on those hills, followed by the usual routine; tops 
of feelers flattened out, streamers met, and windows filled in, to form 
a flattop. Out of this was built up again the jagged skyline which de- 
veloped into a second flattop, and a third story was built on top of 
that. Two or three minutes later, the unbuilding began, unhurriedly, 
following the rules exactly, top story, second, and finally superstruc- 
ture of the first, to leave only the bleak, dark profile of the hills. All 
this, fitted in between setting-up exercises and breakfast call, was 
observed by hundreds of men of the First Arizona Infantry and others 
of the 10th U.S. Cavalry, camped next to us, on border duty following 
Villa’s raid on Columbus. 
In this case, evidence offered by the mirage points to the fantastic 
conclusion that there were three nearly identical temperature-inver- 
sion layers cooperating with beautiful precision. When the lens of 
the first reached its climax, the lens of the second took over, and the 
third after that, and they worked the same way with the unbuilding. 
The inversion layers may have formed some little distance apart at 
slightly different levels and drifted together; this is by no means im- 
possible to imagine. Use of lenses in these layers to do the building 
and unbuilding is however, quite beyond our imagining, as are many 
of the phenomena in Operation Distortion. This three-story effect is 
completely without precedent in my collection of mirage lore. Of the 
watching company, a good proportion of them ranchers, cowboys, 
prospectors, outdoor men, no one I talked to had seen anything of 
the sort before. 
I understand that in certain recent atmospheric studies radiosonde 
equipment was sent up by a captive balloon to work at any desired 
level and send back much fuller information on that level than a 
regular run could provide. It would be most interesting to make such 
