But, on the other hand, if two passengers are to be shut up for a long 

 time in this submarine cabin, it is important that they should have 

 some comfort relatively. The bathysphere of Professor Beebe had an 

 internal diameter of 4y ft. Beebe and Barton have shown that two men 

 can live for long hours in such a space : but they themselves found that 

 it was very uncomfortable. I spent a few minutes in it myself, in 

 Beebe's laboratory of course, not in the open sea. Although I was 

 alone in the sphere and my height is not much greater than that of 

 Beebe, I found the situation rather painful. 



After some trials made with mock-ups we settled for an internal 

 diameter of 6j ft. (2 m.). 



When the Trieste was being built I adopted the same dimensions 

 for the new cabin — a proof that I have not regretted my initial 

 decision. 



Let us note in passing that if I had held to the diameter of 6-9 ft., 

 the weight of a cabin with the same safety would have increased in the 

 proportion of 100 to 116, that is to say, in our case, by 3520 lb., which 

 would have resulted in a considerable increase in the dimensions of the 

 float. 



In what material should we make the cabin and what should be the 

 thickness of the walls ^ 



To calculate precisely the stresses to which the wall of a sphere 

 will be subjected, if the thickness is the same throughout and the 

 pressures which it bears are uniform, presents no difficulty. But it was 

 otherwise in our case. Several openings were cut in the cabin : portholes, 

 hatch, passages for electric cables and some tubes ; this decreases its 

 solidity. It is clear that the thickness of the wall must be increased 

 around these holes, and it is here, particularly when we pass from simple 

 thickness to reinforced thickness, that calculation falls short. We were 

 forced to make tests with models which alone could give us the 

 necessary data. Scale models rigorously conforming to plan and, of 

 course, constructed in the same material as the real thing, were placed 

 in the laboratory in a steel tank filled with oil in which the pressure 

 was increased progressively by means of a pump until a violent 

 explosion announced that the little sphere had been crushed. The 

 pressure at which this took place was that at which the full-size cabin 

 would also probably be crushed. 



The pressure to which it could be subjected in safety would 

 naturally be less. What is called the factor of safety is the relation 



[41 ] 



