PART FOUR 



TECHNICAL APPENDICES 

 Appendix i 



Strength Tests made on Model Portholes 



OUR portholes are made of pieces of plexiglas in the form of trun- 

 cated cones, of which the apex angle is 90°, as is shown in the 

 section represented in Fig. 15. The conic surface rests in a socket of 

 the same form, machined for one of the portholes in the wall of the 

 cabin and for the other in the circular hatch of the manhole (see sketch 

 of the cabin, page 43). The pressure of the sea acts upon the large end 

 of the piece formed as a truncated cone and pushes it towards its seating. 

 The watertightness thus produced is perfect, as has been demonstrated 

 in all our tests with the model. As a measure of precaution, we have 

 also added to the portholes of the bathyscaphes rubber rings, placed 

 on the outside upon the joint, according to the principle of the auto- 

 clave. 



The mathematical analysis of the distribution of stresses of such a 

 component would perhaps be possible, if its material were perfectly 

 elastic, but I think it would still be very difficult. But it is probable that 

 the plexiglas will be loaded in places beyond its limit of elasticity; 

 a deformation not proportional to the stress, that is, the plastic 

 deformation of the material, will then play an important part in its 

 behaviour under stress. This is, in my opinion, the reason the portholes 

 in plexiglas have given much better results than glass portholes. In 

 these conditions we cannot think of approaching the problem by 

 theory. Here we are in the presence of one of those instances where 

 only laboratory experiment will be able to inform us. 



Let d be the diameter of the interior face of the porthole (therefore 

 the small face) and h the thickness of the porthole. We know that the 

 resistance of such a piece to the pressure of a liquid depends solely 



upon the proportion j, and that it is independent of the absolute size of 



the piece. We can therefore proceed to strength tests on small models, 



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