OCR Text |
Show CLOUDS MEASURE SPEED FOR AVIATORS Men have discovered a new use for clouds that float in the blue as wind gauges. Aviators always like to know the speed of the wind at various levels. lev-els. A cloud travels with the wind, and makes visible the speed of the wind at a certain altitude. The Weather Bureau of the United States Department of Agriculture-has devised apparatus by which observers can determine how fast a cloud is moving. They sight the clouds in a black mirror mounted in a frame graduated in degrees. By observing the movement of the image of a cloud as reflected by the mirror for a certain cer-tain period of time, they get one factor fac-tor for a computation. The other factor is the height of the cloud above the earth. The observer determines the distance from the earth to the cloud by releasing a standard stan-dard "ceiling" balloon, and watching it until it disappears into a cloud. These balloons are inflated to a certain cer-tain pressure, and the observer knows how rapidly such a balloon rises. By timing it from the moment it is easy j to make a close estimate of the height of the balloon. With this as a second factor the observer computes the rate at which the cloud is moving, and can tell the pilot whether he will fly against a headwind or have the benefit bene-fit of a tailwind. Frequently it is possible to inform the pilot that he will encounter a fav-oi-able wind at about a certain altitude,' alti-tude,' but will find less favorable flying fly-ing conditions at other altitudes. |