Weather 121 



Temperature of the Atmosphere Formerly it was believed 

 that the higher we ascend the colder the air becomes. In recent 

 years, through the study of the condition of the upper air, investi- 

 gators have found that this is not always true. The tempera- 

 ture does continue to fall until a height of about seven miles is 

 reached, but above that there is a belt of slightly' warmer air. 



The United States Weather Bureau uses balloons in finding 

 out facts about the condition of the air in the upper layers of the 

 atmosphere. A registering balloon is sent up to which is at- 

 tached an instrument called a meteorograph that records, as it 

 rises, the atmospheric pressure, and the rainfall, as well as the 

 temperature and the humidity. Thus the condition of the upper 

 atmosphere is learned. 



Precipitation. Whenever water vapor in the air condenses 

 in drops sufficiently large to fall to the earth, a precipitation, or 

 a fall of rain occurs. When the water vapor is frozen as it con- 

 denses in the upper atmosphere, we have snow, hail or sleet. 

 If the vapor freezes before much condensation occurs, snow 

 results, forming in beautiful crystals of various shapes. If the 

 raindrops are formed and then freeze into particles of ice in 

 the air, they fall as hail. When snow and rain fall together, 

 we have sleet. The various types of precipitation are rain, hail 

 and snow. 



Hail and Snow. During thunderstorms raindrops sometimes 

 freeze and form pieces of ice, called hailstones. These pieces of 

 ice fall toward the earth but are often caught by strong upward 

 currents of air and carried up again. When this happens, more 

 snow or water freezes on them, adding a layer of ice. This may 

 happen several times, until the hailstones become heavy enough 

 to fall even against the force of the upward air currents. This 

 accounts for the unusually large hailstones which fall during 

 severe storms, since the more severe the storm the stronger the 

 upward currents of air. Hail storms often do a great amount of 

 damage to crops by cutting the foliage. The windows of houses 

 and greenhouses are sometimes broken by hail. 



Snow is formed when the water vapor in the air comes in 

 contact with air at a temperature below 32 F., the freezing point. 



