394 HYDROGRAPHICAL SURVEYING [chap, xviii. 



The wire is liable to cut grooves in the interior of the 

 swivelling frame. A file must constantly be applied to smooth 

 them down, or they will rip the splices. A roller of hard steel, 

 underneath which the wire passes, and placed in rear of the 

 swivelling frame, obviates this to a great extent. 



The wire when new has a breaking strain of 240 pounds. 



Smaller wire of 21-gauge has also been supplied, for the 

 purpose of allowing a sufficient length to be on the reel for 

 very deep soundings, but with the larger machines now sup- 

 plied will probably be discontinued. Its breaking strain is 

 190 pounds. 

 Splices. Splices are made about 5 feet in length, one wire being laid 



round the other in a long spiral of about one turn an inch. The 

 ends are soldered, and a seizing of fine wire laid over the end and 

 for 2 or 3 inches up the splice. No end must project. Solder 

 is then applied along the whole length of the splice. A third 

 seizing can be placed in the centre. 



Splices are the weakest points of the wire. They should 

 be frequently examined, and their positions noted, so that, 

 both in running out and heaving in, they may be eased round 

 the wheels, with the guider nearly in the centre to avoid 

 tearing. 

 Sounding For depths of 1,000 fathoms and under, the lead can be re- 

 s^kers' covered, and no detaching rod is necessary. A lead of 30 to 

 40 pounds weight is suitable. 



At a little risk to the wire, when sounding from astern up 

 to that depth, the ship may go ahead directly bottom is struck, 

 increasing her speed as the wire comes in ; the great saving in 

 time thus effected will often justify the increased risk of parting 

 the wire. 



For greater depths two kinds of rods for slipping sinkers are 

 supplied, the " Baillie " and the " Driver." Both are fitted 

 witli tubes to bring up a specimen of the bottom, and the same 

 sinkers fit them both. 



The construction of the " Driver " is easier than that of the 

 *' Bailhe " rod, and with a piece of gas-piping cut to the proper 

 length the ship's blacksmith can make one in a day ; it is 

 shown in Fig. 79. 



A B C is a tube about 2 feet in length, fitted at the top with 

 a flap valve, D, working on a hinge at E. The lower part of the 



