perhaps also in a light alloy of aluminium magnesium. This would be 

 easy to calculate. But it would be very much better to build it entirely in 

 transparent plexiglas. This material is less strong than steel, and we 

 should thus have to give a greater thickness to the walls. But plexiglas 

 is lighter than steel: its specific gravity is only 1-19. 100 cu. in. of 

 plexiglas in sea water weighs only -607 lb., while that amount of steel 

 weighs 24-59 It). 



Such a cabin, built to go down to 1 100 fathoms, would have greater 

 static lift than a steel cabin of the same strength and the same internal 

 diameter. It would be able to carry a more powerful engine and battery 

 of accumulators than the metallic cabin. 



But — and this is the most important thing — being as transparent as 

 the best glass, it would present a wonderful panoramic view to the 

 observers. The observer would no longer be obliged to fix his eye to a 

 little porthole from which he can see only a small part of his environ- 

 ment. He would live in the middle of the sea, and be able to let his 

 glance rove in all directions like the free diver, the frogman. The mere 

 thought of such a dive stimulates the imagination. What will the realiz- 

 ation be like ^ 



Here a few technical questions arise. Would not our vision be dis- 

 torted by the refraction of the water and the plexiglas ? The answer is 

 simple : the water would become like a concave lens, and the eye applied 

 to the wall of the cabin would become slightly long-sighted. An eye- 

 glass of a dioptric third would be enough to make the necessary correc- 

 tion. If one moved away from the wall, certain distortions» of vision 

 would be produced. But these would not be disagreeable. In the ante- 

 chamber of the Trieste we looked out (at shallow depths) through the 

 large round window in plexiglas, the curvature of this window 

 being double that of the cabin. Objects naturally appeared shrunken 

 in the horizontal direction, but this deformation was practically 

 unnoticeable. 



To calculate the strength of a plexiglas cabin is not easy, as this 

 material safely sustains slight deformations beyond its elastic limit 

 (which is, moreover, a great advantage in our case). It would be 

 necessary, before having the real cabin built, to proceed to numerous 

 tests with models subjected to high pressures. It is only after these 

 laboratory researches that we should be able definitely to settle the 

 depth possible to be reached and the thickness required for the walls 

 of the cabin. 



[ M4 ] 



