200 PROCEEDINGS OF THE AMERICAN ACADEMY. 



it appears that the data may be separated into two groups, one includ- 

 ing 0°-300° ; the other 400°-1000°, which appear to have entirely 

 distinct forms of systematic error. This division corresponds to two 

 distinct groups of data, one extending from 0° to 300°, the other 

 including the second group and extending from 350° to 1075°. The 

 latter were given in the Bulletin as the final results of the high tem- 

 perature comparisons of the irido-platinum couple with porcelain bulb 

 air thermometers. The detailed statement of the 0°— 300° comparison 

 I have not seen. Although the discrepancy between the two sets of 

 systematic deviations is not extremely large, yet it has seemed to me 

 that it was beyond the limits of concordance in the higher tempera- 

 ture work, and that it would be better for the present purpose to deal 

 solely with the 350°-1075° data. Two points regarding Barus's work 

 should be noticed : one the strikingly high degree of concordance be- 

 tween individual observations even with different thermometer bulbs 

 and different thermo-couples ; the other the remark in which Barus 

 notes a possibility of being able still further to reduce the "stem 

 error " entering into the result, which so far as I am aware has not 

 yet been done. 



The high temperature air thermometer comparisons (Bulletin, 

 Series I., II., III., IV., and V.) of Barus are so numerous (108) and 

 80 distributed that the labor of utilizing them simply for deducing con- 

 stants and testing an equation would be excessive. Also they are too 

 concordant to permit interpolation on a direct plot without a sacrifice 

 of some of their precision. For the purposes of discussion, therefore, 

 I averaged them in nine groups. The first group contained all where 

 the emf, lay between 3,000 and 4,000 microvolts ; the second group 

 between 4,000 and 5,000 mv. ; and so on by steps of 1,000 microvolts, 

 except that the seventh group covered 2,000 mv. from 9,000 to 11,000. 

 These groups were not exactly equal in number of observations, and 

 therefore in weight, nor is the arithmetical average a strictly legiti- 

 mate value where the function is not linear ; but, as easily seen by 

 inspection of the originals, the errors thus introduced are negligible. 

 In Table 11., columns one and two give the direct values of the 

 averages. Column three reduces 22oC to SJe by adding 150 micro- 

 volts the value of 2^e being elsewhere given by Barus as — 150 

 microvolts. 



