Page:Popular Science Monthly Volume 89.djvu/56

 The War in the Clouds

���A battle in the air. An allied monoplane (on the left) rising to attack a German biplane among the clouds over the war front in France. The photograph was taken in mid-air by a third aeroplane, and shows clearly the trenches over which the machines are battling

���An Austrian pilot balloon being inflated from a gas cylinder. These small pilot balloons arc Fcnt aloft just before a Zeppelin foray in order to determine the direction and velocity of the air currents. In time of peace they are employed to obtain temperature read- ings of the upper air for the use of meteorologists

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