196 Prof. H. L. Callendar on Platinum Thermometry. 



case of platinum. But, that the formula did not represent 

 singularities due to change of state or structure, such as those 

 occurring in the case of iron at the critical temperature, or in 

 the case of tin at the point of fusion. 



This paper attracted very little attention until the results 

 were confirmed by the independent observations of Griffiths**, 

 who in 1890 applied the platinum thermometer to the deter- 

 mination of certain boiling- and freezing-points, and to the 

 testing of mercury thermometers of limited scale. The 

 results of this work appeared at first to disagree materially 

 with the difference-formula already quoted, the discrepancy 

 amounting to between 6° and 7° at 440° C. After his work 

 had been communicated to the Royal Society a direct com- 

 parison was made with one of my thermometers in his appa- 

 ratus ; and the discrepancy was traced to the assumption by 

 Griffiths of RegnaiuYs value 448°'38 C. for the boiling-point 

 of sulphur. We therefore undertook a joint redetermination 

 of this point with great care, employing for the purpose one 

 of my original air-thermometers which had been used in the 

 experiments of 1886. The results of this determination were 

 communicated to the Royal Society in December 1890, and 

 brought the observations of Griffiths into complete harmony 

 with my own and with the most accurate work of previous 

 observers on the other boiling- and freezing-points in question. 

 The agreement between his thermometers when reduced by 

 the difference-formula (2), employing for each instrument the 

 appropriate value for the difference-coefficient d, was in fact 

 closer than I had previously obtained with platinum wires 

 from different sources. But the agreement served only to 

 confirm the convenience of the method of reduction by 

 means of the Sulphur Boiling-Point (S.B.P.) which we 

 proposed in that paper -"-. 



Proposed Standard Notation and Nomenclature. 



It will be convenient at this stage, before proceeding to 

 discuss the results of later work, to explain in detail the 

 notation and phraseology which I have found to be useful in 

 connexion with platinum thermometry. This notation has 

 already in part been adopted by the majority of workers 

 in the platinum scale, and it would be a great saving in time 

 and space if some standard system of the kind could be gene- 

 rally recognized. In devising the notation special attention 

 has been paid to the limitations of the commercial typewriter, 

 as the majority of communications to scientific societies at 



* Phil. Trans, clxxxii. (1891), A, pp. 4S-72. 

 f Ibid. t.c. pp. 119-157. 



