is closed. It contains a resistance formed by a regular helical coil of 

 thin constantan wire, one end of which is short-circuited by dipping in 

 the mercury. This coil does not extend up to the top of the tube, but it 

 is prolonged by a straight wire, of which the resistance must be 

 insignificant. Let R be the additional resistance that the spiral would 

 have if it were prolonged up to the top of the tube. Let us now close 

 our electric circuit by a resistance Y, a milliammeter A with shunt Z 

 and a small dry battery E, so that all the external resistance is precisely 

 equal to R. Then, as long as the mercury does not go beyond the top 

 of the coil, the total resistance of the circuit will be proportional to the 

 volume of air enclosed above the mercury. But this volume of air is 

 (if we ignore the effects of temperature) inversely proportional to 

 the pressure: and since the current is inversely proportional to the 

 resistance, it follows that the current is proportional to the pressure. 

 The adjustable resistances Y and Z allow us to adjust the external 

 resistances to the desired value and to regulate the sensitivity of the 

 milliammeter in such a way that its scale gives the depths directly in 

 metres, for example, but always increased by the constant of 33 ft. 

 representing the pressure prevailing at the surface of the water. As 

 soon as the resistance in the spiral is entirely short-circuited by the 

 mercury, the current no longer increases and the ammeter does not 

 risk being overloaded. 



One could naturally leave out all the electric parts and place the 

 pressure gauge near the porthole in such a way as to permit direct 

 observation of the position of the mercury. But reading it would not 

 be easy and I think it would be preferable to read the depths on the 

 instrument panel inside the cabin. 



AN ATTEMPT AT A RESTATEMENT 



When the French edition of this work was already in the printer^ s hands, 

 I became acquainted with the book which Commander Georges Houot and 

 Naval Engineer Pierre Willm have just published under the title: Le 

 Bathyscaphe à 4,050 mètres au fond de l'océan^ and in which the authors 

 give a fine description of the bathyscaphe and its performances and a great 

 deal of most interesting information. 



However, certain of their statements call for comment. I venture to 

 analyse some of these statements. 



1 Published in England as 'Two Thousand Fadioms Down' (Hamish Hamil- 

 ton and Rupert Hart-Davis, 1955). 



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