they do not breathe at the bottom of the water. Hence they do not 

 dissolve, under high pressures, nitrogen into their blood and are not 

 prone to the accidents arising from this gas in excess. 



Let us come back to man. There is no doubt at all that, to reach 

 great depths, he must be completely protected from external pressure, 

 that is, enclosed in a rigid apartment. Conventional submarines are 

 constructed upon this principle. 



The entire hull of the submarine is subjected to water pressure and, 

 since it contains air at ordinary atmosphere pressure, the depth it 

 can attain depends upon the strength of the hull. If the weight of the 

 hull with all it contains, in machines, fuel, accumulators, arms and men, 

 is equal to the weight of the water displaced, the submarine is in 

 equilibrium, just as Archimedes could have told us. 



Hence, the weight that the builder can give his hull and also its 

 thickness, its resistance, and the depth the submarine can reach without 

 the risk of being crushed, is limited. With our present structural 

 materials this limit is between 50 and 150 fathoms. By forgoing all 

 armament and decreasing the power of the engine, Pietro Vassena 

 has been able to increase the range of depth with his pocket submarine 

 C.3. 



If a hull is to resist the pressures of the deep sea, it has to become 

 thicker and therefore heavier than the displaced water. To sustain it, 

 an external force must come into play. What is this force to be ? There 

 are two immediate solutions ; either to suspend the cabin from a cable 

 attached to the windlass of a surface vessel, or to have recourse to 

 hydrostatic forces acting upon a bulky element, lighter than water, 

 to which the watertight compartment is attached. 



We meet the first of these solutions in the rigid diving-suits used 

 for the recovery of treasure contained in ships sunk at depths inacces- 

 sible to ordinary divers: the diver is enclosed in a steel cylinder 

 furnished with portholes and hung from a cable: by means of his 

 telephone, he directs the manœuvres of the surface vessel which, with 

 explosives, hooked tools and clamps, carries out the work: this, 

 however, is not practicable beyond about 100 fathoms in depth. 

 These rigid diving-suits can be considered as being the precursors of 

 the bathysphere worked out by Professor William Beebe and Engineer 

 Otis Barton. As for the second solution, I introduce it in the bathy- 

 scaphe. 



[23] 



