PRINCIPLES OF DESIGN. 



83 



sectional area of the whole being 1*86 sq. in., the specific 

 gravity of about 4*5, and the tensile strength, at 30 tons per 

 square inch, equal to 56 tons. Sections of light and heavy 

 types of shore-end are given to actual dimensions in Fig. 39. 



The strength of sheath and approximate weight of finished 

 cable in any of the above types for any given weight of iron 

 in the sheath can be found by reference to Fig. 40, which 



60 



§ 30 



5 10 15 20 



Tons 'per naut of Iron, 



Fig. 40. 



represents the average of several types. Thus a finished shore- 

 end cable having 17 tons of iron per naut would weigh about 

 22 tons in air and 15 tons in water. 



After pickling in hot compound the sheathing wires are laid 

 on spirally, each wire making one complete turn round the cable 

 in a certain length, known as the " lay." Thus the usual lOin. 

 lay of a deep-sea cable sheath means that the sheathing wires 

 make one complete turn round the cable in a length of lOin., 

 or, in other words, that when the wires are put on the cable 



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