Fig. 78. {upper) Perhaps most important is the adjustment of the oxygen valves, which 

 must be perfectly clean and must give out two litres of oxygen every minute — no more, no 

 less. Fig. 79. {lower) A photograph taken through the window and the bathysphere, made 

 just as we are about to climb inside, all the apparatus having been installed. The remark- 

 able clarity of the fused quartz windows is evident. 



