506 DIETZ [CHAP. 23 



at a depth of 35,800 ft the temperature is 0°C, then the water is compressed 

 5.3% and normal aviation gasoline is compressed 13%. The differential com- 

 pressibility is then roughly 8%. Therefore, once descending, a bathyscaph 

 will fall increasingly faster; the ascent is correspondingly accelerated. To offset 

 this increase in the weight of the bathyscaph, about one ton of ballast must be 

 jettisoned for each thousand meters. However, the temperature of the gasoline 

 is also important, especially as this undergoes compressional heating during 

 descent and expansional cooling during ascent. Hence the rate of descent is an 

 important factor for establishing the amount of deballasting needed. If the 

 gasoline temperature stays above the ambient sea- water temperature, less 

 ballast is expended. 



D. Exterior Devices and Arrangements 



A conning tower in the middle of the float protects the airlock hatch and the 

 crew while topside. Stabilizing keels are present to prevent excessive rolling 

 and are placed along the interior underlines of the gasoline compartments. This 

 is in contrast to the usual exterior position of bilge keels. These internal keels 

 are very effective since they act against the gasoline rather than against the 

 rolling seas. Searchlights present a special problem since a pressure -proof metal 

 case for a normal incandescent light would weigh several hundred pounds. This 

 lighting problem is solved by utilizing pencil-sized 500-V mercury -vapor lights. 

 The strong fused-quartz envelope of this light is directly exposed to the ambient 

 sea pressure. Although originally designed to be cooled by a water stream and 

 for operating under zero pressure, these lights provide the Trieste with excellent 

 floodlights. In addition, there are two small normal incandescent lights pro- 

 tected in steel cases — one outside the forward window and the second inside the 

 antechamber. 



Propellers, driven by electric motors of 2 h.p. each, enable the craft to move 

 sluggishly forward, backward and to turn horizontally. These motors are 

 immersed in a bath of oil which is exposed to the ambient pressure of the sea. 

 A maximum speed of about one knot can be attained for a short distance. 



On the conning tower are several important instruments for navigational 

 and scientific use. These include a tachometer, an externally sensitive vertical 

 and horizontal current-meter, and a transducer for the underwater telephone. 

 To accommodate the needs of oceanographic research, the Trieste was designed 

 with sufficient buoyancy to accommodate 2.5 tons of scientific equipment. 



E. Interior Arrangement of the Sphere 



The interior diameter of the original sphere was 6.7 ft; this is reduced to 

 6.4 ft for the Krupp sphere. About half of the space is occupied by equipment 

 so that the habitable space is severely restricted permitting a crew of only two. 

 Dive 65 to the Challenger Deep lasted 9 h but it apparently placed no severe 

 strain on the divers. The ultimate length of stay is posed only by the ability 

 of the divers to stay awake — and for safety reasons the need to complete a 



