National Geographic : 1925 Aug
TOILERS OF THE SKY © International Newsreel Corporation SUN AND SA IIAVE CLOUD-BUILDING RIVALS Not all clouds are composed of vapor alone. Volcanoes send seething masses of ash and smoke and steam upward like towering black cumuli. Even lightning bolts flash from these somber mimic clouds. In arid regions winds may sweep thousands of tons of sand and dust far into the air, building Nature's only "dry cloud." A forest fire or the burning of a great city builds clouds, part smoke, part vapor. And now man, with his smoke screen, builds clouds to order to hide his military, naval, and aeronautical operations. <^^fc'