ON DEEP-SEA SOUNDING. 375 



APPENDIX C. 



THE DEPTH-RECORDER. 



THE Depth-Recorder is shown at 

 Fig. 47. It is attached to the cover 

 of the sinker by means of a short 

 chain, from the ring at the top. 

 When a cast is to be taken the 

 Recorder is put inside the sinker 

 and is supported by the pressure 

 of the side springs against the in- 

 side of the sinker ; the slack chain is 

 put in on the top of the Recorder. 

 The object of the side springs is to 

 prevent the shock, which the sinker 

 experiences when it strikes the bottom, 

 from affecting the reading of the 

 Depth-Recorder. When the sinker 

 strikes the bottom, the Depth-Re- 

 corder slips down the inside of the 

 sinker and is thus relieved of the 

 sudden shock. 



As the sinker descends, the in- 

 creased pressure forces the piston D 

 up into the tube while the spiral 

 spring pulls the piston back. The 

 amount that the piston is forced up 



