84 Miracles Ahead! 



oxygen even though he is breathing pure oxygen. This hap- 

 pens because the pressure above thirty-three thousand feet is 

 so low that the lungs cannot breathe in enough oxygen even 

 from a pure supply. At thirty thousand feet the air pres- 

 sure is only 30 per cent of what it is at sea level, and only 19 

 per cent of the pressure at forty thousand. At sixty thousand 

 feet the boiling point is so low that blood boils. 



At around 35,300 feet (the tropopause) the temperature 

 becomes fixed at 67 degrees below zero. This upper region of 

 the atmosphere is known as the stratosphere. It is a "weather- 

 less" region, free from clouds and with no strong vertical air 

 currents. 



In 1936 Squadron Leader Swain of the R.A.F. conquered 

 the stratosphere. He reached an altitude of 49,144 feet, wear- 

 ing a pressure suit made of rubberized fabric with a rubber 

 helmet. A pump kept the suit inflated with pure oxygen at the 

 proper pressure. Flight Lieutenant Adam of the R.A.F. later 

 flew to 53,937 feet using the same suit, and in 1938 an Italian 

 aviator set a world record of 56,047. 



The pressure suit has the advantage of adding little weight 

 to the plane; but the suit still does not supply adequate pres- 

 sure with full efficiency, and the pilot is so bundled up that 

 his movements are awkward. 



In 1937 the United States Army developed the first success- 

 ful pressure cabin and took attention away from the pressure 

 suit. The pressure cabin is ideal for the crew. An aviator's 

 movements are not hampered by a bundlesome pressure suit. 

 The Boeing Stratoliner a commercial adaptation of the 

 Flying Fortress was equipped with a pressurized cabin for 

 transcontinental flights at twenty thousand feet and for Pan 

 American's fast flights over the Andes in South America. 



The pressurized cabin did, however, have a serious defect 

 for military use. A few bullets could destroy the effect of the 



