KEW THERMOMETERS— A CORRECTION. 



IN an article on the ''Measurement of Temperature " in the 

 September number of "Science Progress," p. 69, I 

 wrote as follows : "I am afraid that the issuing of those Kew 

 certificates which give the second decimal figure of the 

 correction, so far from being a prevention, is a cause of 

 inaccuracy, as, unless used with a full knowledge of the 

 variations consequent on changes in the conditions, they 

 impart a false confidence to their possessors ". 



I have received from Mr. Chree information which leads 

 me to the conclusion that I was in error in assuming that 

 the department at Kew issued certificates of the nature in- 

 dicated. There have passed through my hands altogether 

 three " lists of observations " giving the results of a com- 

 parison of certain thermometers with the Kew standard to 

 within -oi , and I was under the impression that such lists 

 were regarded as certificates ; and further, that their acqui- 

 sition depended solely on the payment of an additional 

 fee. 



Mr. Chree points out: (1) that such "lists of observa- 

 tions" are not certificates ; (2) that they were only issued 

 under exceptional circumstances to scientific men of well- 

 known standing. He also states that only very rarely, and 

 also under exceptional circumstances, are certificates issued 

 giving the correction to '05° C. 



I regret if my own misapprehension in this matter 

 should have in any way influenced the judgment of others, 

 and I am glad to learn that the authorities at Kew are more 

 cautious than I had supposed. 



I cannot, however, refrain from pointing out that their 

 reservations in this matter lend additional weight to the 

 opinions I expressed (in the paper above referred to) as to 

 the difficulty of accurately measuring temperatures by 

 means of mercury thermometers. 



Finally, I consider that I have done the department a 



