3. EQUIPMENT AND INSTRUMENTS 



93 



Figure 32. — Bourdon type bathythermograph. 



are not interchangeable between instruments, 

 since each grid is calibrated for a particular 

 BT. Never let the temperature of the BT 

 exceed 105° F. At this temperature the 

 stylus brings up against a stop pin ; if this 

 temperature is exceeded, permanent defor- 

 mation of the brass coil in the Bourdon will 

 occur and the calibration of the instrument 

 will be ruined. 



In addition to the manual furnished with 

 each BT, observers should study Sections 

 2-32 to 2-59, inclusive, of H.O. Pub. No. 

 607, Instruction Manual for Oceanographic 

 Observations. 



3-115 Reading BT slides in the field.— 



The lacquered BT slides and log sheets shall 

 be forwarded to the Washington Office at 

 the end of the season. When project in- 

 structions require it, the BT slides shall be 

 scanned in the field and the data recorded 

 on Form 732, Field Record of BT Data (Fig. 

 33), as follows: 



Insert the slide in the proper grid. Record 

 the slide number, date and time of observa- 

 tion, surface temperature as observed with 

 the bucket thermometer, and the distance in 

 feet that the BT trace terminates above (a) 

 or below (b) the zero depth line on the view- 

 ing grid. Record the surface temperature 

 (temperature at the top of the trace) as 

 shown by the BT. In the first column at the 

 left of the form enter, from top to bottom. 



decreasing temperature values at one-degree 

 intervals to cover the range of temperature 

 to be recorded from that slide. With the BT 

 slide firmly in place in the viewing grid, read 

 and record in the second column the depth 

 at which each degree of temperature is en- 

 countered. No corrections shall be made. At 

 the bottom of each column record the tem- 

 perature and depth of water at the lower 

 end of the trace. If a temperature inversion 

 is observed, use extra columns as may be 

 needed and as shown in the illustration. 



BT slides, BT log sheets, and Forms 732 

 shall be forwarded to the Washington Office 

 in separate mails. 



3-116 Temperature and salinity observa- 

 tions. — Nearly all hydrographic parties are 

 required to measure the temperature and 

 salinity of sea water either as part of a pro- 

 gram of oceanographic observations or to ob- 

 tain data for determining the velocity of 

 sound. In the latter case, the data are re- 

 quired to correct echo soundings when the 

 calibrated velocity of the sounder differs from 

 the actual velocity (see 5-114). The program 

 of observation involves measurements from 

 the surface to the bottom at intervals which 

 will permit drawing accurate temperature 

 and salinity curves. 



The International Association of Physical 

 Oceanography, in 1936, proposed the follow- 

 ing standard depths at which observations 



