quartz, usually). These waves are sent through the cabin from outside : 

 they traverse it, are reflected on the interior face and come back again. 

 The time that this double journey lasts is checked. If it is -jô.^d-ô 

 second (sound goes through metals faster than through air), every- 

 thing is in order. The transmitter and receiver are moved and in this 

 way the whole cabin is probed. If there were a fault parallel to the sur- 

 face, it would reflect the sound. Even if its thickness were only a very 

 tiny fraction of a millimetre, one would see move on the screen of the 

 cathode tube the luminous point which indicates the return of the rays : 

 if the fault were only of small extent, there would be a double image. 

 On the other hand, a small spherical air-hole, though very easily 

 revealed by the gamma rays, could pass unobserved by the ultrasonic 

 method. 



It is clear that these two methods complement each other admirably. 



It was by reason of this careful study of the cabin of the Trieste 

 that I could without the slightest fear go down to 1700 fathoms with 

 my son, and if I had had greater deeps within reach, I should have 

 even gone down to 2^ miles without having the bathyscaphe first of all 

 make a descent with the automatic pilot and 50% overload as I had 

 suggested for the cabin of the FNRS 3. 



Appendix 8 



Graph of Hinge Moments on the Door 



The hinge of the door is inclined 18° from the vertical. In a closed 

 position the door will lean with about a third of its weight upon its seat- 

 ing since sine 18° equals 0-30902. The more open the door is, the less 

 its weight tends to close the door. Open at 90°, it is in equilibrium 

 (unstable). In Fig. 21 the curve represents the couple produced by the 

 weight of the door as affected by the angle of opening. It is sinusoidal. 

 To balance this varying couple, we placed a helical spring on the axis 

 of the hinge. Its couple varies of course linearly with the angle of 

 opening, so that it appears on the graph as a straight line. The com- 

 pensation for the weight of the door cannot be perfect therefore 

 throughout the whole of its movement. But that is not necessary, 

 nor is it even desirable. One could select the characteristics of the spring 

 as indicated by the dotted line. In this case the difference between the 

 two couples would have a maximum value of 10% of the door's couple. 



[ i<57] 



