Determination of Low Temperatures. 515 



It is obvious, however, that by taking a smaller range of 

 pressure — say from the lowest to 2000 millim., or from 4000 

 millim. to the highest pressure, and by altering the constants, 

 a very much better agreement would be obtained. Extra- 

 polation beyond the limits of pressure chosen would, how- 

 ever, introduce very large errors indeed. 



In conclusion it may, I think, be stated that in a great 

 number of cases, including pairs of widely different bodies, 

 the formula of Ramsay and Young gives better results than 

 that of M. Colot ; the latter, which is very convenient, may, 

 however, be employed, even for very wide ranges of pressure, 

 when the constant B is small, and for small ranges of pressure 

 when E is large. 



LX. Note on the Determination of Low Temperatures by 

 Platinum-Thermometers. By E. H. Griffiths, M.A., 

 Assistant Lecturer at Sidney College, and G. M. Clark, 

 B.A., Sidney College*. 



IN connexion with Profs. Dewar and Fleming's recent work 

 on the resistance of certain metals and alloys at very low 

 temperatures, and the suggestion that they have made — viz. 

 that the resistance of certain pure metals (amongst which is 

 platinum) vanishes at absolute zero, — the following facts may 

 be of interest. 



Being in the possession of the constants of several platinum- 

 thermometers, whose accuracy has been exposed to severe 

 tests, we have calculated the temperature at which R = 0, — by 

 assuming the possibility of applying Callendar and Griffith's 

 method — from the formulae 



and 



^=S xio ° 



'-p^^ml-mli' 



where R 1? R are the resistances in steam under normal 

 pressure, and melting ice, respectively, and R is the resistance 

 at temperature t ; the value of 8 for each thermometer is 

 determined by observations of the resistance in boiling sulphur 

 (f = 444°-53). 



The following table gives the constants and results : — 



' * Communicated by R. T. Glazebrook, M. A., having been read at the 

 meeting of the Cambridge Philosophical Society, October 31, 1892. 



