212 



HYDROGRAPHICAL SURVEYING [chap. viii. 



b}' a couple of fathoms of hemp, the ship may be started 

 ahead directly bottom is struck, even at a depth of 1,000 

 fathoms, speed being gradually increased. Soundings in great 

 depths may be successfully obtained from aft in circumstances 

 M'lien the Lucas machine on the forecastle could not be used 

 ouing to heavy seas washing over it. 



In localities where currents are prevalent and vary, when 

 Soundrngs ^^'6 are running long lines of soundings in the ship off-shore, 

 off Shore, out of sight of land, it is very important to get on the return 



Fig. 58. 



Long 

 Lines of 



line towards the shore a fix as soon as possible. The soundings 

 we are obtaining may be hereafter used, especially where fogs 

 are frequent — as, e.g., British Channel, Bay of Fundy — to 

 give vessels a notion of their position, and we must therefore 

 use every dodge to get our true position at the earliest 

 opportunity, so as to depend upon dead reckoning as little 

 as we can. 



Two theodolite stations, from which a large flag at the mast- 



