345 



The value of K^ is ceitain-ly accurate to Vj^^ and agrees well 

 with the measurement made b}' Bannawitz ^) on neon, which Professor 

 Kamerlingh Onnes had drawn for him from the same vessel from 

 which he had supplied me with the gas I used. 



^ 3. For the determination of the temperature-coefficient of the heat 

 conductivity for neon the same aj)paratus could not be used as for 

 the absolute measurement, and on this account I resolved to appl}'' 

 Goi-dsohmidt's '') method. This method introduces another impoitant 

 improvement into Scht^kiermacher's method. The loss of heat at the 

 ends of the wire is eliminated in a simple manner by making measure- 

 ments first with a long wire and then with a short one oftliesame 

 diameter, and heating the wire in both cases with the same electric 

 current. The difference between the amount of energy developed in 

 the short and in the long wire gives the energy which is lost 

 radially by a wire of the same section and of a length equal to the 

 difference of the two experimental wires. 



The first apparatus which was used in testing Gold- 

 schmidt's method is represented in the figure, the con- 

 stants and the dimensions being collected in table I *). 

 The figure shows that the thin platinum wires are 

 stretched along the axis of the glass tubes by means of 

 platinum springs. 



In the measurements the two wires and a normal 

 resistance of 1 ii are connected up in series. When the 

 condition has become stationary, the potential-differences 

 between the terminals of the long and the short wires 

 El and Ejt are measured, as also the difference at the 

 terminals of the normal resistance I. The potential 

 differences were measured with a compensation-apparatus 

 by Wolff which is free of thermo-effects, possible thermo- 

 forces outside the apparatus being eliminated by com- 

 mutation. 



From the resistance the mean temperatures of the platinum wires 

 ti and tk are calculated. Using these results the following expressions 



1) E. Bannawitz, Ann. d. Ph. (4), 48, ^1915), p. 577. 

 «) R. GoLDSCHMiDT. Physlk. ZS. 12 (1911), p. 418. 



3) The value given here for 2r,j was found by weighing, since it is only used 

 in the correction for the temperature-drop and not in the calibration itself, astiiis 

 was carried out witli atmospheric air (see further on). 



