On page 34 Engineer Willm declares; *The principle of the float 

 and of using steel-shot as ballast were the only survivals from Piccard's 

 FNRS 2.' This is simply untrue. Engineer Willm momentarily forgets 

 that the cabin of the FNRS 2, in short the main part of the bathyscaphe, 

 was used, without any change, for the FNRS j. Moreover, a whole 

 series of features in the first bathyscaphe which were new for sub- 

 marines were taken over at Toulon: the trail-rope, which can be 

 jettisoned by electro-magnet; unballasting by breaking the current; 

 two propellers steering the bathyscaphe without a rudder ; the control 

 valve ; the lateral lighting with bulbs immersed in distilled water ; the 

 empty dive with automatic pilot (controlled by pressure gauge, clock- 

 work, bottom detector and detector for leaks in the cabin) and many 

 other details; finally, the plexiglas portholes. Do all the theoretical 

 and experimental researches that I had devoted to these windows since 

 before the war count for nothing.'^ (See page 150.) Nevertheless it is 

 to these same portholes, able to resist pressures of tens of miles, and 

 not only of 9000 metres (5-6 miles), as Commander Houot says 

 (page 212), that the French naval officers and Professor Monod, with- 

 out hesitation, trusted their lives. Were these a mere detail .^l I invite 

 Engineer Willm to refer to Beebe's book, where the difficulties en- 

 countered by engineers before the use of my plexiglas portholes are 

 described. 



Next, to belittle even more the importance of what had been taken 

 over from the FNRS 2, Engineer Willm continues (page 34): 'But 

 on the prototype most of the ballast had consisted of cast-iron blocks 

 that were cumbersome and unwieldy. Bird-shot played only a secon- 

 dary part . . . Gempp2 had been led to abandon mixed ballast. . . .' 

 Here confusion is so great that I wonder if it was really Engineer 

 Willm who wrote this passage. In fact the principle of releasable 



1 I suppose that this depth of 5*6 miles was reached as a result of a faulty 

 calculation. We obtain, in fact, this order of magnitude by neglecting the 

 radial components of forces operating at the conical surface. However, these 

 components are in no way negligible for they combine in the plexiglas with the 

 axial forces in such a way as to produce quasi-hydrostatic pressures in three 

 dimensions. But the elementary theory of the strength of materials teaches us that 

 such a uniform pressure is not prejudicial to the solidity of the piece. For the 

 rest, a glance at our diagram on page 150 shows that the pressure at breaking 

 point must be several times 5*6 miles of water. 



^ Gempp is the engineer who preceded Engineer Willm at the time of the 

 construction of the FNRS 3. (Ed.) 



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