Such steps should and are actually taken in conjunction with the 

 program of raising the present fabrication maximum size limits. That very 

 elementary steps have already been taken is evidenced by the successful 

 assembly of glass and ceramic spheres from hemispheres and of long cylin- 

 drical hulls from short cylindrical shell sections. While the 5-foot- long 

 hull of glass DIVEAR symbolizes the present approach to monolithic con- 

 struction technique, the 9- foot- long Benthos exemplifies the only proven 

 polylithic construction technique available today for cylindrical hulls. 

 The assembly of spheres from hemispheres, and cylinders from cylindrical 

 sections or rings is only the beginning of the polylithic construction 

 design philosophy; more advanced concepts for this design philosophy and 

 construction technique are already in the offing which promise to permit 

 the design and fabrication of ceramic and glass hulls from smaller and 

 smaller modular units. 



In the design and construction of cylindrical hulls, additional methods, 

 besides those of making the hull from cylindrical sections or rings, are 

 being sought for breaking down the basic structural module to a smaller 

 size (Figure 31). The additional methods, circumscribed by the geometry 

 of the cylinder, limit themselves to breaking down further the basic com- 

 ponent of the cylinder, the cylindrical shell section. The ultimate 

 solution to this problem is the decomposition of the cylindrical section 

 into small modules, the curved bricks. The intermediate solution, on the 

 other hand, is the assembly of cylindrical sections from 180 or less 

 trough- like cylindrical segments. Both the fundamental and the inter- 

 mediate polylithic construction techniques for cylinders have been already 

 tried and found successful. 



The assembly of monocoque and rib- stiffened cylinders from two or more 

 segments, or of spheres from several spherical polygons , ■'•-' has been experi- 

 mented with so far only with acrylic resin models and found successful 

 (Figures 32-33). Not only has it been proven that the elastic stability 

 and the compressive strength of the polylithic structures is the same as 

 of monolithic structures, but that the fabrication costs are much less 

 than if the structures were made simply of hemispheres or long cylindrical 

 sections. If such structures were to be produced in glass or ceramic in 

 larger quantities, the savings would be quite substantial, as pressing of 

 individual structural modules would be substituted for the present labori- 

 ous grinding of glass or ceramic castings. Only edges of the modules would 

 require grinding for better fit in the joints. 



14 

 Attempts also have been made to by-pass the intermediate size module 



stage for cylinders and to go directly to the ultimate modular size. The 



structures experimented with were monocoque cylinders (Figures 34-35) made 



up of 99-percent alumina ceramic segments whose length was approximately 



305 



