COMPARISON OF PLATINUM AND GAS THIKMOMI.I 



41 



them for verification at temperatures outside the range to 100. With this view 

 th.-y deemed it desirable to obtain an independent investigation into tin- j.rin. ijdesand 

 methods of platinum thermometry, and they consequently procured a complete 

 <|iiijiment of the necessary apparatus, which was installed at the observatory under 

 the supervision of Mr. GRIFFITHS in a special building. As the general results of the 

 experiments made with this apparatus seemed promising, the Kew Committee 

 .ipproached the Comitd International des Poids et Mesures, with a view to securing 

 their co-operation, and ultimately it was arranged that a direct comparison, extending 

 over as wide a range as possible, should be made between some platinum thermometers 

 In-longing to Kew and the Standard instruments at the International Laboratory at 

 ihu Pavilion de Breteuil, at Sevres, near Paris. The present paper is the outcome of 

 this investigation, in which it may be understood that one of us (C.) is responsible for 

 the gas and mercury thermometry involved, while the working of the platinum 

 thermometers devolved on the other (H.). In it will also be found an account of th. 

 mrans by which the range of the gas thermometer employed was extended upwards 

 from 200, the limit of the Bureau's previous experiments, for the purpose of this 

 investigation. 



III. THE FIKST FORM OF PLATINUM THERMOMETER RESISTANCE-BRIDGE. 



As a full account of the first platinum thermometer apparatus acquired by Kew 

 Observatory has been published by GRIFFITHS ('Nature,' Nov. 14, 1895), under 

 whose supervision it was standardized, it is unnecessary here to give more than a 

 general description of its chief features. A diagrammatic representation of the 

 connections is given in fig. 1. 



Fig. 1. 



Q Resistances of bridge. 

 R and S Proportional coils. 



P Thermometer spiral. 

 VOL. rxeiv. A. 



......... i , 



" ' 



C Compensator of thermometer. 

 AB Bridge-wire. 

 G Galvanometer. 



