CH. l] THE EXPLORATION OF THE SEA 5 



The recording wheel is attached to a movable arm which is 

 connected with the frame of the apparatus by two coiled steel 

 springs. When the weight of the sinker is on the wheel the arm 

 is extended stretching the springs. This releases a brake which 

 acts on the reel containing the line, so the latter runs out freely. 

 But immediately the sinker touches the sea bottom the weight is 

 taken off the arm and the springs pull the latter back while the 

 forward movement of the base of the arm tightens a brake which 

 lies close against the rim of the reel, whereupon the latter is 

 stopped. The counter is then read and the depth of the sea is 

 obtained. 



The old-fashioned sounding lead of the mariner is a lead cone 

 of about 7 to 30 pounds in weight. Remember that a very heavy 

 weight is necessary to carry the line down rapidly to the bottom 

 and prevent the latter from being thrown into coils or kinking. 

 But when we add to the weight of the sinker that of the sounding 

 line there is a very considerable strain on the latter and this is 

 enough to break any line of manageable dimensions when a deep 

 sea sounding is being taken. It is therefore necessary to devise 

 some means whereby the weight, when it has served its purpose of 

 carrying the line to the bottom, may be released and fall off, when 

 the latter can then safely be reeled up again. All sounding leads 

 are constructed with this object and all are modifications of that 

 first devised by " Passed Midshipman John M. Brooke of the 

 U. S. Navy." I describe here the latest form, the •' Sondeur 

 a Clef" of the Prince of Monaco. 



This is shewn in Fig. 2. It consists of a gun-metal tube 

 furnished with a stop-cock at its lower end. The handle of the 

 latter is a lever which, when the cock is closed, fits into a depression 

 cut in the side of the tube. When the cock is open this lever 

 stands out at right angles as is shewn in Fig. 2 on the left. The 

 opening of the stop-cock is of the same bore as the tube. At the 

 upper end of the latter is a plunger which can move up and down 

 for a short distance — the latter being regulated by a slot cut in 

 the sides of the tube in which work pins attached to the plunger. 

 The sounding line is attached to the plunger and ou the sides of 

 the latter are two notches. When this plunger falls down within 

 the tube the notches sink below the rounded upper end of the 



