PRINCIPLES OF CONSTRUCTION. 



93 



The sheathing machines are arranged to cover the served core 

 with wires of iron or steel and afterwards to put on two layers 

 of canvas, tape or yarn and three coatings of compound. 



g 



f^ 



. The wire as received from the makers is galvanised and in 

 coils, and the first process is to pickle these in coppers contain- 

 ing preservative compound such as Bright & Clark's Cable 



