396 HYDROGRAPHICAL SURVEYING [chap. xviu. 



wire, the sinker remains suspended ; but on striking the bottom, 

 the wire slackens, and the weight of the sinker drags the slipping 

 lever down till the stud K bears against the upper part of the 

 slot H. By this action the point M of the slipping lever is 

 brought to bear against the upper end of the standard E F, 

 being thereby forced outwards sufficiently to ensure that the 

 weight acting at the point G will tilt the slipping lever right 

 over, and thus disengage the sling. The tube being then drawn 

 up, the sinkers are left behind. In descending, the valves at 

 top and bottom, opening upwards, allow the water to pass 

 through freely ; but on drawing up they are closed, thus retain- 

 ing the plug of sand or mud with which the tube is filled. 



For water under 2,000 fathoms, two conical weights are 

 sufficient. In deeper water, a third cylindrical weight should 

 be put between them. 

 Splicing It is important to have a piece of hemp line, some 10 

 Hemp^^*° fathoms long, interposed between the end of the wire and the 

 lead or rod. This is for the purpose of preventing the wire 

 from kinking when the lead strikes. A piece of sheet lead 

 about 1 pound in weight A\Tapped round the hemp just below 

 the junction keeps the wire taut, vvliile the hemp slacks. 

 To splice the hemp to the wire, lay the wire in the lay 

 of the hemp for about 6 feet, putting on a good racking 

 seizing of well-waxed twine at about every foot. Test this 

 splice well. 



Before splicing, the wire must be led from the reel of the 

 machine, between the jaws of the guiding lever, tlirough the 

 hollow spindle of the swivelling frame, and over the register- 

 ing wheel. 

 Winding The whce must be carefully transferred from the drum on 

 the Wire, ^yhich it is supplied to the reel of the machine by mounting 

 the former on a temporary spindle, and fitting a brake, by 

 which the wire can be kept taut. Winding must be even, the 

 wire passing tlirough a piece of greased canvas in a man's 

 hand. 

 Wire Small brass screw stoppers are provided for holding the 



toppers. y^.^j.Q^ j£ necessary, during a sounding. These should be 

 fitted A\dth a hempen tail to make fast to a cleat or other 

 fixture. 



For the greater depths it is usual to sound from forward, 



