thereby formed it is then in this sense that 34 plurality 34 is used in these specifications and in the appended claims with the internal cables connected to the radial cables it will be noted that if any juncture or node between internal cable 42 and radial cable 41 is moved in a tangential direction as for example point 34 a 34 that all other junctures represented by points 34 b 34 through 34 f 34 must follow the motion of point 34 a 34 while it is contemplated that because of added weight only one series of internal cables be used per cable set i e only one internal polygonal enclosure formed per cable set under certain circumstances more internal cables may be used now referring to fig6 the attachment of restraining member 43 may be seen restraining member 43 preferably includes but a single flexible cable tautly connected between adjacent attachment sites 34 g 34 and 34 h 34 on either the compression rings as shown in fig6 or on rigid columns 30 the restraining member attaches at or adjacent to one of the junctures of the internal cables 42 with one of the radial cables 41 as at point 34 a 34 in fig6 it may now be observed that juncture 34 a 34 as well as all other respective junctures denoted by the letters 34 b 34 through 34 f 34 are fixed in a plane now referred to as the x y plane fig7 and 8 show the attachment by rigid outer columns 30 of two compression rings 20 and 20 39 each having flexible cables sets 40 and 40 39 the cable sets are also connected to one another by a plurality of rigid internal columns 60 several of.