Prof. H. L. Callendar on Platinum Thermometry. 193 



Benoit (Comptes JRendus, 1873, p. 342). Though apparently 

 little known and seldom quoted, his results represent a great 

 advance on previous work in point of range and accuracy. 



Fio-. 1. 





























/ 































/ 















Em pi 



rtca 

 A 

 /A 



'ON 



rmut 



ae - 









f 

















/ 

















^ 



^ 



\& 











/ 















^ 

 £? 







\ 





%< 



¥i 









^ 



- 









.°5 









\ 



v 



V 



W 

 &/ 



{ f 





«*£ 







"" 









Jf 









k 



/ 



/ 





^ 















1 







i 



^ 



> 



> 



P^ 

















4 





J 



?, 



^ 



^ 





















104 



^ 



^ 



^ 







%. 

















ti>?& 



) 





Temp. 



Cent. 









<!2*4J 



^52 



2G£5V 



Wjl 



1 



—300° — 2JG° -100 100° 200° 300° 400 J 500° 600° 700° 300° 900° 000° 



The wires on which he experimented were wound on clay 

 cylinders and heated in vapour-baths of steam (100°), mercury 

 (360°), sulphur (440°), and cadmium (860°), and in a liquid 

 bath of mercury for temperatures below 360°. The resistances 

 were measured by means of a Becquerel differential galvano- 

 meter and a rheostat consisting of two platinum wires with a 

 sliding mercury-contact. It is evident that the values which 

 he assumed for the higher boiling-points are somewhat rough. 

 The boiling-point attributed to cadmium, following Deville 

 and Troost, is about 50° too high according to later experi- 

 ments by the same authorities, or about 90° too high according 

 to Carnelley and Williams. It would appear also that no 

 special precautions were taken to eliminate errors due to 

 thermoelectric effects, to changes in the resistance of the 

 leading wires, and to defective insulation, &c. In spite of 

 these obvious defects it is surprising to find how closely the 

 results as a whole agree with the observations of subsequent 

 investigators. The resistance-variation of all the more common 



