Page 401 



EQUIPMENT AND INSTRUMENTS 



4711 



The second type of deep-sea thermometer is an ordinary thermometer mounted 

 in a special water bottle (4716), insulated to maintain the temperature constant while 

 it is being brought to the surface. 



is the pro- 

 instrument 



4711. Protected Reversing Thermometer 



The type of deep-sea thermometer in general use by the Coast and Geodetic Survey 

 tected reversing thermometer without an enclosed auxiliary thermometer. It is a delicate 

 of expert workmanship. Tlie thermometer is of special design and so constructed that 

 the column of mercury in the capillary tube is parted when the instrument is inverted. 

 This thermometer is illustrated in figure 84 in the position in which it should be lowered 

 into the water. The entire thermometer is enclosed in a heavy glass case A to protect 

 it from the pressure of the water. The glass capillary tube B is held in place at its upper 

 end by a rubber ring or metal clasp C and at its lower end by a special composition seal D 

 that also serves to incase sufficient mercury in the lower end to surround the mercury 

 reservoir E of the thermometer, providing for rapid temperature conduction from the 

 surrounding water. The special features of the thermometer are: A knife-edge in the 

 capillary tube at F which is made by an appendage in the tube; a gooseneck which may 

 take the form of a U-turn, S-turn, or a complete circle, as illustrated at G, at which point 

 the capillary tube is enlarged; and a supplementary mercury reservoir H at the upper end 

 of the tube. 



When the thermometer is inverted the extra weight of the mercury in the enlarged 

 section of the capillary tube in the gooseneck breaks the mercury column at the knife- 

 edge; the mercury flows into the supplemental reservoir, and extends into the graduated 

 stem where the temperature is read when held in an inverted position. This type of 

 thermometer contains a large volume of mercury, permitting an expanded scale of grad- 

 uations, since they are based on the expansion and contraction of the total amount of 

 mercury in the reservoir and capillary tube; but the reading of the scale is based on the 

 amount of mercury above the knife-edge after it flows into the smaller reservoir. This 

 type of thermometer is usually graduated in degrees centigrade, with a range from — 2° 

 to +35° C, each degree being subdivided into five parts, although some are only sub- 

 divided into half -degrees. 



4712. Temperature Errors 



Temperatures measured with protected reversing thermometers may 

 contain small errors from two different sources. One of these is an intrinsic 

 error of the thermometer due to slight irregularities in the capillary tube 

 and slight errors in the graduations of the temperature scale. The other error 

 is due to a change in the voliune of the mercury contamed in the capillary De°ep^sea re- 

 tube and smaller reservoir caused by the different temperature of the sur- versing ther- 

 rounding air after the thermometer has been brought to the surface. The ™°™®'''''- 

 temperature in situ may be obtained by correcting the observed temperature for 

 these errors from the report of the calibration test ijiade by the National Bureau 

 of Standards. A copy of this is furnished with every reversing thermometer. This 

 report contains the manufacturer's number, the National Bureau of Standards num- 

 ber, the thermometer scale, the value of each graduation, and in addition, the follow- 

 ing type of information in tabular form: 



465382—44—27 



