BOMBS AT BIKINI 



idly, of course, in accordance with the velocity of the 

 suction wave. Thus its diameter increased initially at 

 the rate of several thousand miles per hour ; later, the 

 increase proceeded at the more modest rate of about 

 780 miles per hour, the velocity of sound. 



But this great hemisphere lasted only a few sec- 

 onds. Its interior was rapidly burnt out by the trillion- 

 watt fireball located at the center. Upward growth of 

 the cloud was limited principally by too-low humidity 

 in the upper strata of air ; lateral growth was limited 

 by the gradual dying off of the suction wave. The 

 myriad droplets were evaporating fast. Within five sec- 

 onds the cloud had become a great horizontal ring two 

 miles in diameter, resting on the water and enclosing 

 the fireball. In another five seconds the ring had dis- 

 integrated; only patches of cloud remained. 



THE FIREBALL AND OPTICAL 

 RADIATION 



The fireball, unlike the condensation cloud, was 

 no mere spectacle. It dealt serious injury to ships and 

 test animals. Beginning its existence in the very proc- 

 ess of distintegration of the bomb, it was of indescrib- 

 able brightness during the first two seconds. Then, for 

 about three seconds, it was obscured by the condensation 

 cloud. At about five to eight seconds after Mike Hour 

 it came back into view again. It grew, swept rapidly 

 upward, and by ten to twenty seconds after Mike Hour 



116 



