140 A. L. Dci/y and R. B. Sosman — 



different temperatures ; (1) on account of the difference in 

 contamination, and (2) on account of the fact that the inside 

 element is subject to the influence of conduction and radiation 

 from below. The weights assigned were as follows : 



Temperatures Outside Element Inside Element 

 400-1100° 3 1 



1100-1300° 2 1 



1300-1550° 1 1 



The final weighted mean of the inside and outside elements is 

 given at the head of each section of the table. 



In the last section of the table are given various points 

 which were determined to aid in interpolating between the fixed 

 points by means of the thermoelement. 



The only comment which need be made here on the data 

 in Table VIII concerns the figures given under the heading 

 "copper point." In this section of the table, the values derived 

 at the two different initial pressures (217-221 mm and 34r6-347 mm ) 

 are quoted separately in order to bring out the fact that 

 the difference between the temperatures obtained from these 

 two pressures is less than the experimental error. In the other 

 sections of the table the data obtained at the two pressures are 

 not separately arranged. Above the copper point only the 

 low pressure was used, as the high pressure would have 

 exceeded the range of the manometer. 



The significance of the comparison between the inside-and 

 outside-wound furnaces, which appears in the first half of the 

 section on the copper point, has been commented on elsewhere 

 (see p. 106). 



5. Interpolation Between the Fixed Points. 

 The preparation of formulae to represent the relation between 

 the temperature defined by the gas thermometer and the elec- 

 tromotive force of a thermoelement has always been a cause of 

 considerable dissatisfaction, both to the maker and the user. 

 The chief reason for this is perhaps the fact that the formulae 

 used have been applicable only to limited portions of the curve 

 and have therefore given no suggestion of physical signifi- 

 cance. In the Reichsanstalt publication* the data extended 

 from 300° to 1100° and included several good fixed points 

 (melting points of pure metals) between which no interpolation, 

 however rough, could go far astray. Accordingly, in so far as 

 interpolation was concerned, but little attention required to be 

 given to the formulation of this relation. It was sufficient 

 that a simple formula of the form 



E = —a + bt + ct* 



could be made to represent the observations between 300° and 

 1100° within the limits of the errors of observation. 

 * Holborn and Day, 1900, loc. cit. 



