503 



Even — gives this tempera! me with sufficient accuracy. Tlie zero- 



pressure foi- the hydrogen thermometer was //p=z1J91 in.m. '), for 

 the helium thermometer //„ = 1J24 m.m. Circumstances unnecessary 

 to be mentioned here, had pi-eveuted tiiese pressures from being made 

 more equal. A new set of determinations in ^vhich this will be 

 attended to is planned. The pressure coefficient of hydrogen at the 

 above mentioned pressure was taken at 0.0036628 ; for helium at 

 0.0036614. the vahie derived bj Kamerllngh Onnes ') from tlie 

 isotliermals at 0° C. and 100° C. If we calculate with the pressure 

 coefficient 0.0036617 deduced from the isotliermals of 20° C. and I00°C. 

 we find, after the introduction of the necessary corrections, almost 

 the same temperature on the absolute scale. 



§ 4. Arrangement for the resistance measurement. In order to 

 measure and to compare resistance thermometers two identical differ- 

 ential galvanometer circuits were fitted up according to Komlkausch's 

 method. Both galvanometers can be read from one place, so that 

 nearly simultaneous measurements can be made. This removes all 

 irregularity in the temperature of the bath in the com[)arison of 

 resistance thermometers. Two moving coil differeiUial galvanometers 

 from Hartmann and Braln were used. Witii an additional resistance 

 of =b 1000 i2 in each of the coils these are practically aperiodic in 

 the measurement of resistances less than 130 <2, as with all our 



other thermometers. The sensitivity is sufticient to measure il 



100000 



with a current of dt 5 milliainpères, while the condition of propor- 

 tionality between deflection and current-strength is very well fulfilled. 

 Test-measurements have shown, that with this arrangement resist- 

 ances of about 100 ii, such as our thermometers have at ordinary 



1 



temperature, can be compared to without any difficultv. Our 



^ 10000 ' J ^ ^ 



1) At these pressures even at the meltiiig puiiil of hydrogen no altenlon need 

 be paid to the thermo-molecular pressure according to Knudskn (Gonip. Suppl. 

 N". 34 § 7 and a Gonnn. by H. Kamerlingh Onnes and S. VVebkk which is 

 shortly to be expected, on Die determination of the lempei'alures which can be 

 obtained with liquid helium). 



~) H. Kamkrlingh Onnes. Comm. No. 1U2^. The value is here increased by U.OOODÜÜl, 

 in consideration of Ihe value 273.09 since assmned for 7'<)» C. Gomp. H. K.\meklingh 

 Onnes und W. H. Keesom. Die Zustandsgleichung. Math. Enz. V 10, Suppl. No. 23 

 Einheilen c, and § 826. 



