^ 2. Aijparatas. Two identical thermometers of Jena glass iöi^ï, 

 siich as had been formerly used by H. Kamkrlingh Onnks and O, 

 Braak, were connected to one manometer. The arrangement was 

 otherwise exactly tlie same as that used before. The standardmeter 

 was divided into 7^ m.m. and allowed a direct estimation of 7j„ m.m. 

 This gave a considerable saving of time, as it made the use of the 

 measuring eye-piece of the cathetometer unnecessary. The amount 

 of gas in the capillary was measured by an auxiliary capillary ot 

 much larger section, as described by Chappiis. 



Besides the two thermometer bulbs, the cryostat contained the 

 platinum resistance thermometer Pt/ and a large pump, which 

 provided for a good circulation of the licjuid. 



The hydrogen and the helium were ])uriiied by distillation, and 

 were both free from other gases. 



§ 3. Calculations. The temperature for each of the thermometers 

 forming the ditierential thermometer was calculated tVom the formula 

 given in Comm. N". 95^, but with a few alterations. The expansion 

 of the glass ƒ (0 of the bulb was not calculated from the quadratic 

 formula given there, but taken from a graphic representation in 

 which the curve was drawn through the })oints experimentally deter- 

 mined and extrapolated by means of tiie expansion for a different 

 kind of glass as determined by Cn. Lindemann. The intlueuce of the 

 ditFerent temperature function for the expansion of the glass is 

 about Vi„„° at hydrogen temperatures, at all other temperatures it 

 is negligible. Moreover the volume was divided into three parts. 

 a. The bulb at the temperature t of the bath. h. The cajiillary in 

 which the mean density of the gas was determined, l>y means of 



the auxiliarv capillarv : the mean density is proportional to — , //" 



k 



being the pressure in the auxiliary capillary at 0°, It the measured 



pressure, c. The steel capillary and the volume about the point, the 



temperature of whicli is the same as that of the room. 



If we divide all the members of the above mentioned equation 



by the volume of the bulb it becomes 



/// r '^ y.-.u. /'., V dead, „I 273 n 



= 7/.. 



/i Vraj, /'o Kleadrol 273 



The provisional temperature, which is needed for the calculation 

 of the various corrections, was calculated from the resistance of P//. 



