well known, the earliest deep-sea reversing ther- 

 mometer also had this same pressure protection. 

 It is not so surprising, therefore, to discover 

 that useful, and apparently original, piezometer 

 was constructed during the cruise by removing the 

 protective shell of one thermometer. The purpose 

 obviously was to determine actual depth indepen- 

 dent of length of cable paid out. This was 

 especially important when a cable of hemp was 

 used because of larger drag caused by water move- 

 ment. 



Unprotected Thermometer 



The traditional depth gauge of oceanography, 

 the unprotected reversing thermometer, grew out 

 of these experiments at sea that were so well 

 reported. Professor Tait of the University of 

 Edinburgh made extensive investigations into the 

 behavior of thermometers under pressure immedi- 

 ately following the cruise. As a matter of fact, 

 there is a laboratory piezometer named after him 

 that is essentially an unprotected thermometer. 



Final Developments 



The later models of reversing thermometers 

 and Nansen's later modification of the stop-cock 

 bottle, together with use of steel cable and 

 sliding messengers, provided a compact and widely 

 applicable measuring system. There never has 

 been and never will be any such thing as a truly 

 "universal" measuring instrument but this under- 

 sea combination has come as close to "universal" 

 application as can probably ever be hoped for. 

 Work has been carried out with it over all the 

 seas, from pole to pole, and from top to bottom. 

 For roughly three-quarters of a century it has 

 been seen on large ships and small as the back- 

 bone of the world's ocean measurement capability. 



THE METEOR EXPEDITION 



The high point of perfection of this system 

 was realized during the METEOR expedition? of 

 1925-27 when thermometer measurements, even at 

 sea, were read out to 0.001°C (at least before 

 sensible round-off) . These were made by dedi- 

 cated physical oceanographers , people so much 

 interested in their work that they designed 

 special thermometer scales, selected special 

 instruments and then repeatedly made calibrations 

 with great care whether ashore or at sea. 



Still more significant, they became well 

 acquainted with the manufacturers and shared 

 their enthusiasm with them. This, together with 

 training and discipline at sea, produced results 

 perhaps never to be equalled. The Richter family 

 of Berlin is now represented by the third genera- 

 tion associated with this specialized instrument. 

 They cherish old letters indicating how often 

 Wansen, Petersen and other oceanographers have 

 visited their shop to bring the instrument into 



a form more useful at sea. There have been times 

 when hardly more than pride in this association 

 kept this little firm going. 



STATUS OF REVERSING THERMOMETER 



The classical hydrographic bottle and its 

 accessories are now taken for granted; to many 

 they may constitute physical oceanography in its 

 entirety. Truly, it is a perfect example of the 

 very natural law that Darwin proposed, the one 

 which sent the CHALLENGER out to sea. This 

 mechanical transducer definitely has been a suc- 

 cess and has survived in face of competition 

 because it was at home in its environment and 

 compatible with other measurement things . Few 

 instruments have been so successful. Few have 

 become so standardized for so long. The impres- 

 sion should not be left that the reversing ther- 

 mometer persisted entirely because of good 

 fortune. It is truly a remarkable instrument. 

 It is hard to accept the historical evidence that 

 most of this "selection" was carried out within 

 a few years after the CHALLENGER returned and was 

 likely due to her findings and definitive 

 reporting thereon. 



We all know the limitations of this classical 

 thermometer. Many new ways for doing the same 

 job better have been proposed. Significantly, 

 one-third of the papers to be presented here in 

 this Symposium concern long -needed systems and 

 devices for measuring temperature, pressure, 

 salinity and density; functions that the classical 

 tool has so long performed. 



Good Features 



What other reasonably portable temperature 

 recording instrument, old or new, can perform so 

 reliably with so little attention? I know of few 

 other transducers of any kind that can be cali- 

 brated (and I mean in an absolute sense) to 

 ±0.03$ and then continue to function with this 

 precision over months and years. Yet, it is 

 routine to calibrate to 1 part in 3>000; that is, 

 to +0.01°C over a 30°C range and to find satis- 

 factory replication at a much later date. What 

 other simple pressure transducer spans such a 

 wide range and still can reproduce hydrostatic 

 pressure measurements (also on an absolute basis) 

 to the order of 10.1$. The reversing instruments 

 in fact have carried out temperature and pressure 

 measurements at sea with these precisions and 

 absolute accuracies that are not too commonly seen 

 with elaborate equipment in shore laboratories. 



Most of the credit can be claimed by the basic 

 mercury-in-glass structure. Some people have 

 forgotten that this is a simple, relatively noise- 

 free transducer, amplifier and "readout." Many 

 years ago, at a time when it was of interest to 

 standardize temperatures by means of liquid-in- 

 glass thermometers, special glasses were 

 developed to reduce hysteresis. All glass has 



