THE RELIABILITY OF DEEP-SEA REVERSING 



THERMOMETERS 



By H. F. P. Herdman 



(National Institute of Oceanography) 



and L. H. Pemberton 



(National Physical Laboratory) 



(Figs. 1-7) 



INTRODUCTION 



A^riTH the advance of our knowledge of oceanography Uttle remains to be written about the 

 W construction and methods of using deep-sea reversing thermometers; they have, in fact, 

 become standard equipment and, in general, the performance of any individual thermometer over a 

 period of years appears to be taken very much for granted. This uncritical attitude is no doubt associ- 

 ated with the more universal use of this instrument. Until fairly recent times the use of deep-sea 

 reversing thermometers was confined largely to the few major oceanic expeditions where, on the 

 return of the ship, the bulk of the equipment was generally sold, or stored away in some unlikely 

 place, and forgotten. Even when sold the only information usually available to the new owners was 

 the original certificate of calibration. Periodic checks on the zero point of all the 'Meteor' deep-sea 

 thermometers were, however, made by Bohnecke and Wiist (Wiist, 1932) during the Expedition of 

 1925-7, and a critical survey of the accuracy of the reversing thermometers used in the ' Carnegie ' in 

 1928-9 was pubUshed fifteen years later (Sverdrup, Fleming, Soule and Ennis, 1944). Wust's check 

 was made to determine any change in zero point during the period of the Expedition whereas the 

 examination of the ' Carnegie ' temperature readings was made to assess the reliability of the deep-sea 

 thermometers, especially with regard to minor differences in the temperatures recorded by each pair 

 of thermometers.* So far as we have been able to find out, no other pubhshed data exist— except for 

 a very brief reference in the ' Carnegie ' report— concerning any possible change in the characteristics, 

 or in the behaviour generally, after their use, or storage, over a number of years. Nor has there been 

 any comparison between thermometers by different makers. Akhough not specifically referring to the 

 behaviour of deep-sea thermometers with regard to their continued use, a recent note by Whitney 

 (1955) should perhaps be mentioned. Doubts have been expressed at the Woods Hole Oceanographic 

 Institution about certain aspects of the behaviour of unprotected reversing thermometers, mainly in 

 respect of the determination of the mean pressure coefficient (m.p.c. or ' Q '), and in his paper Whitney 

 describes the re-examination, after a period of three years, of a group of such thermometers. Results 

 of the tests were largely negative but, nevertheless, are extremely valuable in that they emphasize the 

 individuality of these instruments and so the difficulty of attempting to codify their characteristics. 



At the last check (1953-4) by the National Physical Laboratory (N.P.L.) of nearly all the deep-sea 

 thermometers now held by the National Institute of Oceanography (N.I.O.), some eighty of these 

 instruments were examined. Of these, thirty-six protected and two unprotected deep-sea reversmg 

 thermometers had been the property of the Discovery Committee, and had been in use or, when not 

 * Mostly two protected thermometers were used by the 'Carnegie' at each depth-a practice adopted for all depths by 

 the Discovery Committee and, in turn, by the National Institute of Oceanography. 



