50 



Messrs. Holman, Lawrence, and Barr on the 



fortunately not of known composition, nor was it possible at 

 the time to obtain any whose purity -was known. An analysis 

 of the wire used may perhaps be obtained later, and it is 

 hoped to carry out further measurements with the better 

 platinum now obtainable through the recent advances made 

 in its manufacture in Germany and England. 



The aluminium was of a very high grade, but it is thought 

 that still better may be obtained, and the peculiar occurrence 

 attending its melting-point measurements should be further 

 investigated. 



The actual effect of the small impurities cannot be numeric- 

 ally estimated, but must have been inconsiderable except for 

 platinum, where the error probably has the positive sign. 



As to the third point, there was no reasonable doubt left in 

 the minds of the observers that the observed temperatures 

 were sensibly the melting-points. Except as noted for 

 aluminium, the readings with rising and falling temperatures 

 did not exceed about one part in one thousand. Also entirely 

 independent observations on separate days, and with renewals 

 of the metals in some cases, were equally concordant. The 

 average difference was much less than the error of reading 

 the ammeter. As an example of the concordance, and at the 

 same time as showing the homogeneity of the therrao wire, 

 three calibrations in sulphur are quoted in Table III. 



Table III. 



Date. 



2e, microvolts. 



Computed 



Temperature of 



Sulphur. 



2e reduced to 

 445°. 



March ? 



5287 

 5289 



5287 



44473 

 445-18 

 444-53 



5290 



5287 

 5293 



March 22 



March 29 





Between these observations a considerable length of the 

 wires was necessarily clipped off. Reduced to a common 

 temperature of 445°, the maximum difference is but six micro- 

 volts in 5290, or 0*11 per cent., while the average deviation 

 of a single observation is but 0*02 microvolt, or 0*04 per 

 cent., and of the mean but 0'02/ V3 = 0*012 microvolt, or 

 0'024 per cent. At higher temperatures the discrepancy 

 was even smaller. 



The validity of the interpolation formulae has been already 



