218 



HYDROGRAPHICAL SURVEYING [chap. viii. 



Lying-to 

 near 



Vigias at 

 Night. 



Credence 

 in Re- 

 ports. 



Prelimi- 

 nary 

 Search. 



Decision 

 rests with 

 Hydro - 

 grapher. 



It is rather unpleasant to be drifting about at night with 

 reported reef in the vicinity, and by no means a bad precaution 

 is to ease a kedge anchor down to 100 fathoms or so, which may 

 bring the ship up, or, at any rate, show, by drawing ahead, that 

 bottom is reached before she strikes on the reef. Constant use 

 of the wire sounding machine is above all things necessary in 

 such circumstances. 



If the reported danger is out of the usual track of ships, 

 there is nothing improbable in its having escaped notice up to 

 that time ; but where the locality is frequently passed over 

 there is more prima facie reason for doubting the report, and in 

 many instances a cross-examination of the person making the 

 report will show how very slight is the ground for it. An 

 actual cast of the lead seems a feat impossible to make a 

 mistake about, but instances have occurred where this has been 

 proved, even with so-called " bottom " brought up. In cases, 

 however, where a sounding has been obtained we must conclude 

 the report to be true, and a rigorous search must be made before 

 the vigia can be obliterated. There are numerous instances of 

 banks having been erroneously reported by ships using the 

 Thomson machine, and failing to stop and verify the sounding 

 by an up-and-down cast. 



As a general rule, for the commencement it is best to run lines 

 east and west in or near the latitude reported, as this is more 

 likely to be near the truth than the longitude. 



When going to make an exhaustive search, the first day is 

 perhaps best spent in doing this without getting more than may 

 be one positive sounding, as we can cover more ground, and 

 if the danger exists we have a good chance of finding it by sight, 

 or by the soundings taken Avhen the ship is running, as, of 

 course, the deep-sea lead will be kept going constantly. 



In every case, of course, the surveyor transmits home a plan 

 of his track and soundings, as it is at headquarters only that 

 a decision on the matter can be arrived at. 



Under the head of " Sea Observations " will be found hints 

 as to early ascertaining of the ship's position, a most important 

 matter on each morning. 



