402 



HYDROGRAPHICAL SURVEYING [chap, xviii. 



Time 



It not infrequently happens that the wire parts for no 

 apparent cause, but this may be due to a kink in the wire from 

 a previous sounding. 



Unless conditions of current, as above mentioned, neces- 

 sitate it, it is generally fatal to let the ship fall off broadside to 

 the wind. Should she be allowed to get round with the wind 

 aft, there is probably no remedy but to heave in again, and 

 commence afresh. 



Care is necessary in heaving in the last 50 fathoms, so as to 

 stop the deck engine in time. 



The time interval with wire, when not pitching heavily, up 

 occupied. ^Q depths of between 2,000 and 3,000 fathoms, is about one 

 minute per 100 fathoms. Reeling in may be accomplished at 

 nearly the same rate. 



A sounding of 1,000 fathoms may be obtained in 25 minutes 

 from the time the weight is lowered to the time the order is 

 given to put the ship on her course. 2,000 fathoms will 

 require 45 minutes, and 3,000 fathoms 75 minutes. Beyond 

 that depth, much greater, caution being required, the time 

 occupied is correspondingly increased, and reeling in must be 

 done very deliberately. The deepest sounding hitherto ob- 

 tained is 5,269 fathoms. Soundings at such deptlis may 

 occupy as long as five or six hours. 



Though the time of running out each hundred fathoms is 

 no longer required, as with hemp, for ascertaining when the 

 sinkers strike the bottom, it is well to take the intervals, as 

 they assist in the regulation of the brake. 



If a second wire machine is available (a boat's machine will 

 do), serial temperatures can be conveniently taken from the 

 gangway whilst the sounding is being obtained forward, thus 

 gaining time. 



A 30-pound sinker is attached to the end of the wire, and the 

 thermometers are secured to the wire by the metal clips at the 

 back of the cases, at the required distances. See that the 

 indices are down before attaching the thermometers. 



There is a certain amount of extra risk in thus working 

 from the gangway while the other wire is over, as the two 

 wires may foul deep down, when the fact of the thermometers 

 acting as toggles may make them difficult to clear. The 

 time saved, however, justifies it in fine weather, and when 



Serial 



Tempera 



tores. 



