:i; Messrs. H. L. Callendar and E. H. Griffiths. [De<-. I*. 



December 18, 1890. 

 Lieut -General STRACHEY, R.E., Vice-President, in the Chair. 



The Presents received were laid on the table, and thanks ordeml 

 for them. 



The following Papers were read : 



I. " On a Determination of the Boiling Point of Sulphur, and 

 on a Method of Standardising Platinum Resistance Thermo- 

 meters by reference to it." By HUGH L. CALLENDAR, M.A.. 

 FelJow of Trinity College, Cambridge, and E. H. GRIFFITHS. 

 M.A., of Sidney Sussex College, Cambridge. Communi- 

 cated by J. J. THOMSON, F.R.S., Cavendish Professor of 

 Physics. Received November 29, 1890. 



(Abstract.) 



Experiments by different observers have shown that electrical 

 resistance thermometers afford the most convenient and accurate 

 method of measuring temperature through a very wide range. By 

 selecting a particular thermometer as the standard, and directly com- 

 paring others with it, it has been found possible to attain a degree of 

 accuracy of the order of 0'001 in the relative measurements between 

 and 100 C., and of the order of 0'01 at 450 C. 



In a previous communication* it has been shown that, if t be the 

 temperature by air thermometer, and if pt be the temperature by 

 platinum resistance thermometer, the difference between them is 

 very closely represented from to 700 C. by the formula 



d = t-pt - 6 {*/100| 2 -</100} (<*) 



The value of the constant c for a particular wire was found to be 

 1-570. 



The object of the present paper is to describe a method of finding 

 the value of this constant for any such thermometer, by means of a 

 single observation at some known fixed point other than or 100 C. 



The boiling point of sulphur happens to be the most convenient 



for this purpose. We have therefore made a careful determination 



of this point by reference to the standard air thermometer, and have 



given a full description of the method and apparatus which we have 



* Callendar, 'Phil. Trans.,' A, 1887, p. 161. 



