20 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE. 
was difficult to see the planes operate. The planes then crossed hack 
and forth over the cotton fields, flying at about the same level as 
during the daytime earlier in the work (about 15 feet above the 
ground), and a most curious effect was noted. Instead of a white 
dust cloud being swept out behind the plane, almost none was visible, 
although the feed valve was wide open and putting out dust at the 
usual rate. At this elevation the planes were flying inside of the fog 
of ground haze, and they seemed to churn out a channel just slightly 
larger than the propeller. The dust delivered was entirely confined 
by the wall of fog surrounding this channel and did not spread out 
at all, merely coming down in a strip which did not cover more than 
three rows of cotton. 
In the next flights, made just as soon as the hoppers could be re- 
loaded, the planes were operated a few feet above the top of the fog, 
and the behavior of the dust changed entirely. It was blown down- 
ward until it encountered the fog, but instead of immediately 
penetrating through it, it spread out on the top of the fog in a 
layer from 50 to 100 feet wide. It seemed to remain at this point 
without motion, and the observers standing about in the cotton field 
under this fog were puzzled to know what would become of the dust. 
It could be observed on the fog for a few moments and then it 
seemed gradually to disappear. About the same instant, however, 
everyone in the cotton field noted that the air was filled with fine, 
almost invisible, particles of dust falling to the plants. After about 
two minutes the plants, which had been perfectly green before, 
presented the Avhitenecl appearance of a very heavy dusting. 
Unfortunately various difficulties prevented more careful studying 
of this development, so the Avriters really do not yet know whether 
such conditions are exceedingly favorable or exceedingly unfavorable 
for airplane dusting. Certainly it seems useless to fly the plane 
within the ground haze, but when the dust is distributed on top of 
this fog it apparently is spread very thoroughly and settles on the 
plants in an effective manner. Further studies must be conducted on 
this point, however, before any definite conclusions can be reached 
regarding operation under these conditions. A few analyses were 
made of plants treated during the fog, which indicated satisfactory 
arsenical distribution and adhesion, though these can not be taken 
too seriously. The fields treated in this manner showed satisfactory 
worm control, but again no final conclusions are possible because 
these fields were not as heavily infested with worms as many others 
in the experimental area. 
Following these tests, flights were made over a period of several 
days at intervals during the day, from early morning until late even- 
ing, to study the behavior of the dust under the different air condi- 
tions. Immediately after the period of calm in the morning there 
was usually a light breeze of from '2 to 4 miles an hour, which gradu- 
ally increased to from 4 to 10 miles an hour by midday. This per- 
sisted until about 3.30 or 4 in the afternoon, when the 1 morning proc- 
ess was reversed and the air again became calm slightly before dark. 
In these flights it \v;is found that the dust could be blown down 
among the cotton plants at practically any time of day under the 
conditions prevailing through the period of these experiments. 
Considerations of safety indicate, however, that flying for dusting 
should be confined to about seven or eight hours — about four hours 
