98 



HYDROGRAPHIC MANUAL 



permitted to stand for a minimum of 6 min- 

 utes in order that the thermometers may 

 register correct temperatures and the flush- 

 ing of the bottles completed. A messenger is 

 then dropped to the first bottle. The wire 

 angle should be measured just before or after 

 the messenger is released. It releases the 

 mechanism at the top of the bottle allowing 

 it to fall away and reverse its position at 

 the same time closing the valves trapping a 

 water sample. The messenger on that bottle 

 is released and the action repeated succes- 

 sively to the bottom. A messenger will fall 

 at a rate of 150 to 200 meters per minute 

 depending on the angle of the wire. Do not 

 begin hauling in the cast until the bottom 

 bottle has been reversed. 



The winch should always be started slowly 

 and with due regard to the rolling of the 

 ship. A sudden jerk or undue strain may 

 part the cable and a valuable group of in- 

 struments will be lost. 



3-122 Water samples. — Each Nansen 

 bottle is detached from the cable, as it 

 reaches the surface, and placed in a rack 

 constructed for that purpose. Water sam- 

 ples are drawn into glass bottles and the 

 thermometers are read. The water samples 

 may be analyzed for such constituents as 

 salinity, dissolved oxygen content, or various 

 nutrients. Detailed instructions for drawing 

 and preserving water samples are contained 

 in H.O. Pub. 607. If salinities are desired 

 for echo sounding corrections only, the sam- 

 ple may be drawn in a hydrometer jar 

 and the specific gravity measured by a 

 hydrometer. 



If the samples are titrated to determine 

 chlorinity, the salinity may be determined 

 as follows : 



Salinity =0.03+1.805X chlorinity °/00 or 

 by reference to Table 16 in H.O. Pub. 607. 



3-123 Tanner-Sigsbee reversing frame. — 



The Tanner-Sigsbee reversing frame (Fig. 

 36) is designed for only one thermometer, 

 which is held in a slotted metal tube holder 

 by means of rubber cushions backed by a 

 helical spring at each end. The lower end 

 of the holder is hinged to the bottom of the 



^ m mm. B I c 



FicuRE 36. — A. Improved Sigsbee watercup. B. 

 Tanner-Sigsbee reversing frame and reversing 

 thermometer in position to lower. C. Tanner- 

 Sigsbee frame with thermometer reversed. 



frame, the upper end being held in place 

 by a pin. The thermometer is placed in the 

 tube with the reservoir at the hinged end. 



The pin at the top is the lower end of a 

 coarse-threaded shaft to the top of which a 

 propeller is attached. The blades of the pro- 

 peller are arranged so that downward pas- 

 sage through the water forces the pin into a 

 small hole at the top of the holder, main- 

 taining it upright, but as soon as the frame 

 is drawn upward, the propeller revolves with- 

 drawing the pin from the hole so that the 

 holder is free to capsize. The frame is se- 

 cured to a sounding line, or a short section 

 of manila line, by means of a strong spring 

 which clamps at top and bottom. It must be 

 placed in such a position that the holder, 

 when reversed, will not strike the lead or 

 another instrument below it. 



This frame should not be used when the 

 vessel is rolling or pitching as the propeller 

 acts very quickly to release the holder and 

 causes reversal before the thermometer can 

 adjust to the temperature of the water. If 

 the thermometer has been lowered below the 

 intended depth no attempt should be made 

 to adjust the depth. 



3-124 Sigsbee watercup. — The Sigsbee 



