National Geographic : 1922 Mar
Photograph byCaptain A.W. Stevens THE DUST CLOUD INVADING THE GROVE A three-angled battle was waged for the control of the dust after the release of the poison powder from the airplane. Gravity tried topull it down; the "booster currents" (see text, page 337) tried to toss it upward, and the surface stratum of air or wind blowing inthe direction indicated by the arrow endeavored to carry it over and through the grove. The last named of the combatants won, for the entire grove was covered by the dust.