up in the cabin for longer than the apparatus is capable of maintaining 

 life, for example, if serious damage prevented the emptying of the en- 

 trance-shaft. In such a case the bathyscaphe would have to be towed to 

 the port, the petrol would have to be emptied out, and the submarine 

 lifted out on to the quay by a powerful crane. And all this before the 

 occupants could be freed. That could last several days. The imprison- 

 ment would doubtless be very painful, but disaster would be avoided 

 if the cabin could be ventilated by communication with the outside 

 air. With this in view, we furnished the cabin with two schnorkel 

 tubes by which we could ourselves, by using the electric ventilator, 

 set up a good ventilation of the cabin. The passing of the schnorkels 

 through the wall of the cabin and their closing during dives presented 

 quite a pretty problem for solution. (See Appendix.) 



On the other hand it was important to be able to control the con- 

 dition of our atmosphere. From the point of view of humidity, it was 

 very simple : a hair hygrometer was a sufficient indicator. The amount 

 of carbon dioxide was indicated by a Siemens electric apparatus which 

 did not employ any reagent. It was based upon the variations in the 

 thermal conductivity of the air as a function of its carbon dioxide 

 content ; a small needle galvanometer indicated the percentage of this 

 gas. 



As for controlling the oxygen, this is in general rather a complicated 

 affair. In order to avoid the use of corrosive liquids^ of white phos- 

 phorous or copper filings heated red-hot, I invented a very simple 

 apparatus. It was based upon the following reasoning: since we can 

 neither produce nor absorb nitrogen, the quantity of this gas contained 

 in the cabin is constant. Since the relation of oxygen to nitrogen should 

 not vary, the quantity of oxygen contained in the cabin must also be 

 constant. If we, for the moment, leave aside the carbon dioxide, we 

 must require that the total weight of air enclosed in the cabin should 

 remain constant. As the temperature is variable, a barometer measuring 

 the pressure would not suffice, and to it must be added a thermometer 

 and a slide rule. Here is the apparatus which replaces these three 

 instruments (Fig. ii): a U-shaped glass tube placed halfway up the 

 cabin contains in its base a certain quantity of mercury ; one branch 

 is always open, the other is provided with a cock which is closed at 

 the same time as the cabin door. Thus enclosed between the cock and 

 the mercury is a constant quantity of air of which the temperature is 

 pretty much that of the average temperature of the air in the cabin. 



[94] 



