Understanding the Weather [ 439 



Washington. Similar forecasts are made for other sections of the 

 country and a radio station in the Weather Bureau broadcasts 

 them, while teletype sends them to airports, newspapers, and com- 

 mercial organizations. A daily weather map is also printed and 

 widely distributed. 



Yet, despite all the skill and care of the experts in reading signs, 

 it is not always possible to be certain about the coming weather. 

 An unexpected shift of winds may blow storm clouds from an area 

 that was prepared for rain, and drench another where sunshine 

 was expected! 



The Weatherman's Tools: The observers who report to the 

 Weather Bureau depend on a variety of instruments. The weather 

 vane, which indicates wind direction, is the one with which most 

 children are familiar. More complicated are the barograph which 

 writes down the pressure of the air, the anemometer which mea- 

 sures the speed of wind, thermometers (of course!), a very precise 

 barometer, an instrument to measure moisture, and another to 

 record sunshine. These tools, and many others, help the observers 

 to prepare their account of weather conditions close to earth. 



Studying the Upper Atmosphere: Besides assembling this informa- 

 tion, weathermen have become increasingly interested in ascertain- 

 ing the condition of the upper atmosphere. To obtain this data 

 the Weather Bureau sends aloft equipment attached to a large 

 balloon. A radio device called a radiosonde is attached to a para- 

 chute carried in the balloon. This instrument is a small radio 

 station in effect, telling, as it rises, about the temperature, winds, 

 and other conditions. 



The information supplied by the radiosonde is recorded on a 

 complicated receiver at the Weather Bureau. The parachute car- 

 ries a small balloon which both prevents the larger one from going 

 up too fast and also helps to steady it. When they reach fifteen 

 hundred feet, the smaller balloon bursts, causing the remaining 

 balloon to rise faster which it does for about thirteen miles. Then 

 the larger balloon bursts the parachute opens and the radio- 

 sonde descends safely. 



