CHAPTER I. 



SURVEYING THE ROUTE. 



The selection of a safe route for laying a cable has a most 

 important bearing on its life and on the cost of its mainten- 

 ance. The main point to avoid is sudden change in depth, 

 for if a cable hangs festooned between two submarine banks, or 

 falls suddenly into deep water over a submarine cliff, it will chafe 

 and wear through very quickly. Near coasts under-currents 

 from river mouths are to be avoided, and generally a sand or 

 ooze bottom is to be preferred to rock. For so important a 

 matter it is now generally recognised that the cost of sub- 

 marine survey over such parts of a proposed route as may be 

 unknown is well justified. Information may be available from 

 Admiralty surveys or prevous cable expeditions, in which case 

 no special expedition is necessary, but in any case the apparatus 

 is carried by cable-laying steamers for use in any unexplored 

 portions of the route. Observations are taken on depth, tem- 

 perature of water and nature of bottom, the ship crossing and 

 recrossing the proposed route in a zig-zag course. The ship's 

 position for every observation is ascertained by bearings if 

 near land or by dead reckoning if out at sea, and is marked on 

 the chart. 



Deep-sea sounding is now almost universally carried out by 

 means of pianoforte steel wire of No. 22 B.W.G., with a sinker 



