218 



On High Temperature Standards. 



[Jan. 20, 



The platinum thermometers employed were one of the three used 

 by Harker and Chappuis in their earlier work, and a new one con- 

 structed in the laboratory as one of a number belonging to the British 

 Association. The different instruments, after determination of their 

 constants, were tested together in specially constructed electric resistance 

 furnaces, heated from a special battery, in which temperatures from 

 400 — 1100° C. could be very steadily maintained for considerable 

 periods. Special winding enabled a compensation to be made for the 

 greater cooling effect at the ends of the furnaces, so that over a 

 considerable length the temperature was exceedingly uniform. 



The following table gives the results of one series of comparisons, 

 and indicates the agreement obtained : — 



Second Series of Comparisons. Compensated Furnace. 

 Gas Thermometer, Platinum Thermometer BA 2 , Thermo- junction NPL 2 . 



No. of 

 experi- 

 ment. 



r 



Gas ther- 

 mometer. 



Temperature 

 Junction. 



: " P • 

 Pt. ther- 

 mometer. 



G — 



Pt. 



a-Th. 



P-Th. 



5 



523 -1 



524 -3 



524 -39 



-1 



•3 



-1-2 



-o-i 



10 



568-5 



569 -5 



569 -35 



-0 





-1 -o 



-0-2 



8 



598 -5 



597-8 



597 -62 



+ 





+ 0-7 



-0-2 



1 



599 -4 



599 -0 



598 -80 



+ 



s 



+ 0-4 



-0-2 



3 



641 -1 



641 -1 



641 -75 



+ 





+ 0-0 



-0-6 



4 



682 -4 



683 -0 



fi82 -54 



-0 





-0-6 



-0-5 



2 



776 -7 



775 -5 



775 -13 



+ 1 





+ 1-2 



-0-4 



9 



820-0 



818 -4 



818 -31 



+ 1 



i 



+ 1 -6 



-o-i 



11 



831 -4 



832 -2 



831 -86 



-0 





-0-8 



-0-3 



12 



866 -7 



868 -4 



868 '28 



-1 



•6 



-1-7 



-0 1 



6 



875 -0 



875 -4 



875 -24 



-0 



■2 



-0-4 



-0-2 



7 



959 -8 



956 -0 



955 -47 



+ 4 



•3 



+ 3-8 



-0-5 



13 



1005 -0 



1004 *4 



1004 -37 



+ 



' 6 1 



+ 0-6 



-o-o 



Thus the investigation shows that : 



1. The readings of the platinum thermometers BA 2 and K 2 , which 

 may be taken as representative instruments, when reduced to the air 

 scale by the use of Callendar's difference formula are, up to a 

 temperature of 1000° C, in reasonably close agreement with the 

 results obtained from the constant volume nitrogen thermometer, 

 employing chemical nitrogen, and using the received value for the 

 dilatation of the Berlin porcelain, of which the bulb is made. 



2. The above platinum thermometers agree very closely with a set 

 or thermo- junctions representing the temperature scale of the Reichsan- 

 stalt, and based on measurements with a gas thermometer having a 

 bulb of platinum-iridium. 



