DUSTING COTTON FROM AIRPLANES. 
19 
period of absolute calm between daybreak and about 7.30 or 8 a. m. 
In a few instances daybreak was accompanied by a light breeze, but 
this did not last long and there were still about two hours of abso- 
lutely calm air. As is generally the case in the Delta country, the 
dews were very heavy in the early morning and usually did not dry 
off until about 6.30 or 7 o'clock, with sometimes a little dampness 
persisting until 8 o'clock. There was also nearly always a heavy fog 
or " ground haze " among the cotton plants for the first hour or so 
after daybreak. 
A short time before daybreak on the day when these particular 
tests were undertaken, this haze extended from 50 to 100 feet in the 
Fig. 17. — Typical dust cloud being laid down in cotton field by plane. Note particularly 
that from the plane to the point marked a the dust cloud is rotating spirally above the 
plants and without touching them. At this point, however, the diameter of the cloud 
becomes large enough to reach into the plants and the cloud very quickly loses its 
spiral shape and flattens out among them. This plane was flying about 35 'feet above 
the plants. 
air in a very irregular form. Just about daybreak it settled into a 
very heavy fog, blanketing the earth in a layer from 20 to 30 feet 
thick. This condition was ideal for the operation of ground dust- 
ing machines, but gave very peculiar results in airplane dusting. 
The planes had been prepared late the preceding evening, and the 
motors were warmed before the first break of day. Just as soon as 
it was light enough to see to fly the planes took off, giving a very 
weird effect in the ground haze. This haze was so heavy that vision 
did not extend far enough down the held to see them when they left 
the ground, and they seemed to simply disappear in the fog. Thirty 
feet above the ground the pilots found that they were out of this fog, 
with perfectly good air and vision for flying, but from the ground it 
