3. EQUIPMENT AND INSTRUMENTS 



97 



capillary tube and the small reservoir caused 

 by the different temperature of the surround- 

 ing air after the thermometer is brought to 

 the surface. The amount of this correction 

 is computed from the auxiliary thermometer 

 reading on precise thermometers. A detailed 

 discussion of methods for computing these 

 corrections is contained in H.O. Pub. No. 614, 

 Processing Oceanographic Data. 



3-121 Nansen bottles. — The Nansen bot- 

 tle (Fig. 35), is a cylindrical metal reversing 

 sampler with a capacity of 1.25 liters (2.25 

 pints). Each end of the tube is fitted with 

 slit valves which operate synchronously by 

 means of a connecting rod. The rod joins 

 the clamping and releasing mechanisms. Nan- 

 sen bottles are used with the oceanographic 

 winch to obtain water samples and tempera- 

 tures at any depth. They may be used in 

 more limited numbers and in comparatively 

 shoal depths with the BT winch. 



Each Nansen bottle is fitted with a frame 

 to hold two reversing thermometers. Brass 

 tubes in the frame are slotted to permit easy 

 reading of the thermometer scale. One end 

 of the tube is perforated to permit circula- 

 tion of the water around the thermometer. 

 The large reservoir end of the thermometer 

 is placed at this end of the tube. Rubber 

 pads backed by helical springs are fitted in 

 each end of the tube to hold the thermometer 

 in place and to guard against shock. 



Nansen bottles should be carefully checked 

 before they are used to see that all moving 

 parts are properly greased and move freely. 

 Close the air vent and draincock, secure the 

 bottle to the wire with the clamp and ful- 

 crum assembly at the bottom. A messenger 

 must be attached to all but the lowest bot- 

 tle on the cast. Before lowering the bottle, 

 check to see that the mercury in each ther- 

 mometer has drained down to the main 

 reservoir. 



Not more than 12 Nansen bottles should 

 be used on one cast with %.^-inch wire, and 

 not more than 5 should be used with the BT 

 cable. As the bottles are lowered a flushing 

 action takes place, but they will carry some 

 water down with them. After the bottles are 

 lowered to the desired depths they should be 



Figure 35. — Nansen bottle. 



