376 POPULAR LECTURES AND ADDRESSES. 



against the action of the spiral spring depends on 

 the depth. To record the depth the marker C is 

 used. As the Recorder goes down the marker is 

 pushed along the piston. When the Recorder is 

 brought up to the surface of the water the piston 

 comes back to its original position, but the marker 

 remains at the place on the scale to which it was 

 pushed, and shows the depth to which the Recorder 

 has been. The depth is read off by the cross wire 

 of the marker. 



Between each cast the nut A should be un- 

 screwed to slacken the valve B, and the Recorder 

 should be turned upside down to empty out an)' 

 water which may- have leaked in. A little water 

 in the upper bottle will not interfere with the 

 accuracy of the indications of the Recorder. It 

 may not be found necessary to empty the bottle 

 every time. Make sure before each cast that the 

 screw A is firmly screwed up. 



Occasionally a little grease should be pushed up 

 the piston into the tube to keep the leather 

 packing of the piston in good order. 



The sinker with the Depth-Recorder, ready for a 

 cast, should always be kept bent on to the rope. 

 The rope comes out of the box through a notch 

 cut for the purpose. The sinker should be 

 made fast in a convenient position close to the 

 machine. 



