BOMBS AT BIKINI 



In the fourth place, the gages must be able to bide 

 their time. Even if the explosion were to be post- 

 poned slightly, the instruments must be ready at the 

 new H-Hour. Batteries must not run down; record- 

 ers must be ready. In many cases the problem was 

 solved by installing special starter-clocks; in other 

 cases ''black box" remote-controlled starting devices 

 were used. (These are discussed in Chapter 7.) In a 

 few instances, the instruments were started by the flash 

 of light emitted by the exploding bomb itself. 



A difficulty peculiar to the measurement of the 

 pressure wave was designing instruments which would 

 operate fast enough to catch the pressure wave at 

 its instantaneous peak. For at any given point (say 

 on a target vessel only a few hundred yards from the 

 Zeropoint) the pressure would, of course, increase ex- 

 tremely suddenly — so much so that the pressure ex- 

 perts, when drawing sketches of the wave, usually pic- 

 tured the wave as having what they called a ''square 

 front." After its extremely rapid rise, the pressure 

 would, of course, decrease again nearly as rapidly; 

 then for a moment the pressure would actually fall to 

 less than normal, in what is called the suction phase. 

 Obviously a slow-acting gage would become confused 

 by the many sudden changes in pressure, and would 

 present only a sort of average value. Unfortunately, 

 average values would be of little use ; every effort was 

 made, therefore, to design fast-acting "mas!-let^.s" 

 gages. 



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