272 



LOADING UP 



about 15 minutes altogether. As a result of this haste to get into 

 " free air," constructional engineers are afraid to put their men 

 under more than +3-5 atmospheres. Bullion has been salved 

 from ships lying 171 feet below the surface. The divers in this case 

 stayed below for only 20 minutes at a time and took 20 minutes 

 to ascend. Even then some of them were stricken with paralysis. 

 Greenwood endured compression to 7 atmospheres (=210 fret ! 

 sea water), but took over 2 hours to decompress. These long 



(00 



90 



BO 



7O 



60 



(30) 



(60) 



(90) 



MINUTES 

 (l20) (ISO) 



.0 



O I 23^-5 



MULTIPLES OF THE TIME REQUIRED TO PRODUCE HALF-SATURATION 



FIG. 57. Curve showing the progress of saturation of any part of the body 

 with nitrogen after any given sudden rise of air pressure (after Haldane). 



periods of decompression which seem necessary for safety, put 

 the men in charge in an awkward dilemma when, on account of 

 some mishap, it is necessary to bring men at once to the surface. 

 From table XL VIII. it will be seen that the diver is brought to 

 the surface from the bottom in stages. These stages are three 

 metres apart and the time spent at each one depends on the 

 duration of his stay on the bottom. This method of decom- 

 pression by stages depends on the empirical fact that no 

 untoward results arise from even a rapid decompression of one 

 atmosphere or less. 



