OF THE NATIONAL PHYSICAL LABORATORY. 377 



XXV. Conclusions. 

 These three sets of experiments show that : 



(1.) The readings of platinum thermometers BA 2 and K 2 , which may be taken 

 as representative samples of pure platinum, when reduced to the air-scale by 

 CALLENDAR'S formula, employing his value for the boiling-point of sulphur, are in 

 reasonably close agreement with the results given by the constant-volume nitrogen 

 thermometer employing chemical nitrogen under low initial pressure and using the 

 revised values for the dilatation of porcelain. The divergence of the two scales only 

 exceeds the probable error at the higher part of the range. 



(2.) The platinum thermometers, and the thermojunctions representing the 

 temperature scale of the Reichsanstalt, based on measurements made with the gas 

 thermometer with bulb of platinum iridium, agree very closely, the thermojunction 

 giving apparently a slightly higher value throughout the range covered by the 

 experiments. 



As the result of these comparisons is to justify the application of CALLKNUAR'S 

 parabolic formula up to 1000 C., the tables previously alluded to for deducing the 

 value of T from pt over the whole range for which platinum thermometers are useful, 

 200 to + 1100, are given. From 200 to + 200 the values are given for 

 each degree,* and from 200 to 1100 for each 10. 



For the figures given in Table I, in their final form, calculated by a method 

 which renders unlikely the accumulation of errors greater than 1 unit in the last 

 figure given, I am indebted to Mr. F. J. SELBY. 



T have also to acknowledge my indebtedness to Mr. W. HUGO, who assisted during 

 the comparisons by taking the observations with the platinum thermometers, and 

 especially to the Director of the Laboratory, Dr. GLAZKBROOK, for his continued 

 interest and advice on many points. 



* In the paper as printed this table has been shortened by only giving the value of pt for intervals of 

 1 over the range - 50 to + 150. 



VOL. CCIII.- -A, 



