Appendix 12 



Low-pressure Gauge 



We have seen that the Trieste is provided with four Haenni pressure 

 gauges which measure pressures up to 600 atmospheres, corresponding 

 approximately to depths of 3 J miles. As these pressure gauges cannot 



have a high sensitivity, it 

 would have been interesting to 

 have at one's disposal a pres- 

 sure gauge with range, for 

 example, corresponding to o to 

 55 fathoms of depth only. 



Nothing is simpler than to 

 utilize a normal pressure gauge 

 constructed for these pres- 

 sures. But such an instrument 

 naturally would not bear high 

 pressures. It would be neces- 

 sary therefore to provide it 

 with a cock that the pilot 

 would have to close as soon 

 as the pressure approached the 

 maximum for which the in- 

 strument was designed. This 



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outside 



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the 



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Fig. 28. 



Pressure gauge for use in 

 the shallows 



solution, however, is not suit- 

 able in practice, for if the pilot, 

 who has many things to think 

 about, forgets this detail, the 

 gauge explodes. Naturally the 

 use of an automatic cock could have been envisaged, but it would 

 be better to find a pressure gauge which, while still being fairly 

 sensitive to low pressures, could without danger bear the highest 

 also. Although it has not yet been designed in detail, I should 

 here like to describe an idea for an instrument which seems to 

 me rather interesting. Fig. 28 gives the principle of it. It is a com- 

 pressed-air gauge intended to be placed in the antechamber, therefore 

 subjected to sea pressure. It is formed by a U-shaped tube in thin glass, 

 of which the base contains mercury (Hg). One arm is open. The other 



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