THE LAYING OF SUBMARINE CABLES. 



173 



an easy matter to draw fresh leads in should they be faulty. 

 Of course, joints between the cable and beach cores have to be 

 made exceedingly well and pretty quickly, as the tide does not 

 allow much time. 



From the cable house to the town office similar pipe lines are 

 laid, the scheme of which is shown in Fig. 86. The tanks at 

 the office and cable-house are fixed at a height of about 12ft. so 

 as to keep a head of water on the pipes. Draw boxes are fixed 

 about every 100 yards with water-tight covers, at which cores 

 can be drawn in or cut and tested ; screw vent plugs are also 

 fixed on the pipes at various points by means of which air can 

 be permitted to escape when refilling the pipes. 



Tank in 

 Cable House, 



Tank in 

 Town Office. 



;<• 



Pipe Line. 



Cable Box at 

 Low Water-Mark. 



Fig. 86. — Arrangement of Pipe Line. 



In some cable systems aerial landlines are in use, but these 

 are never very satisfactory, being subject to low insulation, to 

 lightning discharges, and induction from other liaes which may 

 be run near to them. 



For underground landline work, when the soil is not sandy, 

 but of a moist loam or clay which can be well rammed down, 

 ordinary light-type sheathed cable laid in trench has been found 

 to answer fairly well, but for a cable to last for years without 

 repair it should be rendered impervious to air, or deterioration 

 will set in sooner or later. Mr. Charles Bright, M.Inst. C.E., in 

 an interesting work on "Subterranean Telegraph Cables" 

 {privately published, but which can be seen at the library of 

 the Institution of Civil Engineers), points out that the effect 

 of wet and dry seasons is most destructive to gutta-percha and 

 india-rubber cores, and that the most important consideration 

 in the preservation of underground gutta-percha cables is that 



