266 TUB BOTTOM OF THE SEA. 



may remain in their normal state, and he may pre- 

 serve his presence of mind, to a depth of 130 feet ; 

 but when he exceeds this depth by 10 or 20 feet, 

 the external pressure causes physiological effects on 

 his organs independent of his will. One hundred 

 and thirty feet is therefore the depth which experi- 

 ment shows to be the greatest at which any hope 

 can be entertained of performing any prolonged 

 submarine work. . . . Within this limit, security to 

 life is perfectly compatible with the conditions in- 

 volved in an attempt to recover any ship or sunken 

 treasure which will pay the necessary expenses. 



(Signed) '* Carvallo." 



6. Extreme difficulty of working below Water — Submarine founda- 

 tions — Stone worked when in position. 



It appears from what we have stated above, that, 

 notwithstanding all the efforts of genius, we cannot 

 penetrate the oceanic abysses. Nearly all that we 

 can do must be done on the borders of the vast ex- 

 panse. Nevertheless, our visits to the sea, though 

 limited, have a great theoretical and practical im- 

 portance, of which we have already cited numerous 

 examples. 



The art of diving is almost indispensable in build- 

 ing submarine constructions. What great work can 



