TEST A: EXPLOSION IN AIR 



the fireball had lost itself in the rapidly rising mush- 

 room cloud. 



The fireball's real punch occurred within the first 

 half second. In this brief interval an appreciable frac- 

 tion of the total energy released by the bomb sped out- 

 ward at the velocity of 186,000 miles per second. It was 

 in this interval that fiash burns were produced on 

 target equipment and animals. 



The initial output of optical radiation was hundreds 

 of trillions of watts, greater than the aggregate power 

 output of all the electric light bulbs ever manufactured 

 by man. 



In the first few tenths of a second the fireball grew 

 very rapidly. As it grew, each square inch of its sur- 

 face became less brilliant, but there were, of course, 

 more square inches in its surface. Accordingly, the 

 total output of light decreased according to a somewhat 

 complicated formula. Aerial photographs, analyzed 

 with the help of densitometers, were particularly valu- 

 able in following the detailed course of this split-second 

 life-history. 



Photometrists found that the greatest surface tem- 

 perature of the fireball was well above 100,000 degrees 

 Fahrenheit. Interior temperatures were far higher. 

 To observers 10 miles away, the illumination pro- 

 duced per square inch of fireball area was several times 

 that of the sun at noon. The fireball produced a bluer 

 light than the sun, which again indicates the fireball's 

 greater intensity. 



17 



