504 dietz [chap. 23 



by Terni in Italy in 1952. The second was forged especially for "Project Nekton" 

 by Krupp at Essen, Germany, in 1958. The Terni sphere weighs 10 metric 

 tons in air and 5 tons in water; it is 9 cm in thickness, reinforced to 15 cm 

 around the portholes. The Krupp sphere weighs 13 tons in air and 8 tons in 

 water; it is 12 cm thick, reinforced to 18 cm around the portholes. 



Watertightness against the great deep-sea pressure is effected simply by 

 the careful machining of the bearing surfaces so that they fit precisely, giving a 

 metal-to-metal seal. The low-pressure seal for the Terni sphere is effected by 

 an external band and the two hemispheres are gripped together by clamps. 

 The three pieces of the Krupp sphere were originally bonded together with 

 epoxy resin but this glue subsequently failed on surfacing from a dive to 

 18,100 ft (Dive 61). The sphere was then held together by six metal bands 

 gripping two metal rings. 



For viewing the ocean, there are portholes fore and aft. The axis of these 

 windows, and the sphere as well, is inclined 18° to enable an easy view of the 

 sea floor through the forward window. The windows are made of "Plexiglas" 

 which has the advantage of yielding without brittle fracturing as does glass or 

 fused quartz. Strength and optical considerations dictated that the plastic 

 blanks should have the form of a frustrum of a cone with an approximately 

 90° apical angle. For the Terni sphere, the window dimensions were as follows : 

 15 cm thick, 40 cm wide on the outside and 10 cm wide on the interior. The 

 window is set directly against a metal seat machined into the sphere ; a little 

 lubricant is smeared along the interface. These simple windows have never 

 leaked a drop of water nor otherwise failed. 



The aft porthole is seated in the middle of a heavy vault-like door which 

 has the shape also of the frustrum of a cone. The inside diameter of the door is 

 43 cm for the Terni sphere, permitting a man to slide easily into the sphere 

 from an antechamber. The heavy door is carefully balanced by springs to allow 

 easy opening and closing. A single small screw is sufficient to hold it in place 

 when the external pressure is slight. This door has never leaked or jammed. 



Twelve holes are drilled in the wall of the sphere around the forward port- 

 hole. Eight of these are for passage of electrical cables ; two are used for snorkels 

 for emergency ventilation on the surface in the event of the passengers being 

 unable to escape from the cabin after a dive. Two other lead-throughs are for 

 high-pressure tubing for pressure gauges and compressed air to blow out the 

 entrance chamber. The stouter Krupp sphere is very similar to the original one. 

 The following differences are noteworthy; an inside diameter of 1.94 m; a 

 weight of 13 tons ; inside window diameter of 6 cm ; inside door diameter of 40 

 cm and outside diameter of 57.3 cm. 



B. Gasoline- Filled Float 



Since the steel sphere is non-buoyant by several tons, a float filled with 

 gasoline is needed for buoyancy. This float is of thin sheet steel only thick 

 enough to withstand wave buffeting and the rigors of towing. Sea-water is 



