NAVIGATION. 115 



when the ship is going at a speed of twelve 

 knots, involves so much labour and requires so 

 many men to haul in the rope that it would not 

 be practicable to take casts more frequently than 

 once ever>' hour. The method of navigation with 

 the lead, described in the preceding paragraph, was 

 only used in very exceptional circumstances. But 

 with the wire sounding machine (already referred 

 to > 37 above : see on this subject, articles " On 

 Deep-Sea Sounding," &c, in present volume), 

 this laborious operation is no longer necessary 

 The wire offers so very little resistance when 

 going through the water that two men can easily 

 take a cast in any depth up to 100 fathoms with 

 the ship going at any speed up to sixteen knots. 

 The whole operation does not take more than 

 from two to six minutes, according to the depth, 

 so that a sounding can be regularly taken every 

 ten minutes.] 



In moderate weather, with her engines in work- 

 ing order, and coal enough on board to keep up 

 steam, no steamer making land from the ocean, 

 in a well explored sea, need ever, however thick 



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