344 DR. J. A. HAEKER ON THE HIGH-TEMPERATURE STANDARDS 



I. Introduction. 



IN a paper " On the Comparison of Gas and Platinum Thermometers," read before the 

 Eoyal Society in 1900,* Dr. P. CHAPPUIS and the author described a series of 

 experiments in which several platinum-resistance thermometers, constructed of wire 

 of specially high purity, were compared with the gas thermometer at a number of 

 steady temperatures from below zero to above the boiling-point of sulphur, and in one 

 set of measurements to just short of 600 C. 



The results were such as to substantially confirm the conclusion of CALLENDAR and 

 GRIFFITHS that the indications of platinum thermometers may be reduced to the 

 normal scale by the employment of CALLENDAR'S well-known difference formula 



where d = the difference between T, the temperature on the normal scale, and 

 pt = the " platinum " temperature. The constant 8 for pure platinum wires is 

 approximately 1'5, the three temperatures chosen for its determination being 0, 100 

 and the boiling-point of sulphur. 



The paper concludes with the sentence, " until further investigations have been 

 made as to the relations of the various gas scales at high temperatures and as to the 

 influence of the initial pressure and the effect of impurities and traces of water vapour 

 in the gases employed, and until exact determinations have been made up to high 

 temperatures of the coefficient of expansion of the material used as thermometric 

 reservoir, we think that for the purposes of high-range thermometry a scale deduced 

 by the parabolic formula from that of the platinum thermometer will suffice. In the 

 present state of our knowledge any attempt to improve on such a thermometric scale 

 would be attended with such uncertainties as would probably render it futile." 



Since that time, however, a substantial advance has been made in our knowledge, 

 direct determinations of the expansion of porcelain up to high temperatures having 

 been made by different observers, namely, Mr. BEDFORD, t at Cambridge, and Messrs. 

 HOLBORN and DAY at the Reichsanstalt.J A discussion by Dr. CHAPPUIS of the 

 results obtained by these observers and their influence on high-range thermometry is 

 found in the 'Philosophical Magazine,' (5), October, 1900, and February, 1902. 



An examination of the difference formula for the platinum thermometer shows that 

 it can only represent a physical reality over a limited range, the value of pt for a wire 

 having a 8 of 1*5 reaching a maximum about 1700 pt, a value numerically not far 

 exceeding such as may safely be attained. It woiild not therefore be surprising if the 

 formula which actually holds remarkably closely at low ranges should be found to 



* 'Phil. Trans.,' A, vol. 194, pp. 37-134. 



t BEDFORD, 'Proc. Phys. Soc.,' XVII., Part III., p. 148, and 'Phil. Mag.' 



\ HOLBORN and DAY, ' Ann. Phys.,' vol. 6, 1901, p. 136. 



