Physics. — '■'Till' .specific heat at low temperatures. IV. Mea.sure- 

 ments of the specific heat of liquid hi/drogen. Preliiiiinary 

 results Oil the specific heat of solid hydroifen and on the heat 

 of fusion of /u/drogen." By W. H. Kkesom and H. Kamkiujngh 

 Onnks. CommuiHcation N". lo'Sa from tlie Physical Laboratory 

 at Leiden, ((.^oininunicaled by H. Kamkklingh Onnks). 



(Communicated in the meeting of June 24, 1916). 



^\ L After the nieasnrenients of the specilic heat of solid and 

 liquid nitrogen (Comm. N". 149^/ Jan. 19J6) others were undertaken 

 concerning licpiid and solid hydrogen. The apparatus used were those 

 described in Conini. N". 149«. 



In order to obtain a temperature as nearly as possible uniform 

 in the experiments '\n which the calorimeter was surrounded by 

 solid hydrogen, the calorimeter-vessel in the last three series of 

 measurements was surrounded by a cylinder of copper which was 

 closed at the top by tin-foil ^). As the cryostat did not provide 

 suflicient room for both the copper cylinder and the stirrer, the lattei 

 was removed in this case. 



In the measurements of Oct. 23 (table 11) and of Nov. 3 (table I), 

 as it appeared afterwards, an error has crept in the measurement 

 of the tension of the heating current at the terminals of the con- 

 stantin wire of the central heating-core ^). For these measurenjents, 

 therefore, the number of Joules supplied was calculated from the 

 current and the resistance of the heating-wire. This resistance which 

 inclndes that of the platinum supply-wires which reach outside the 

 calorimeter- vessel is a little different according to the vacuum in 



1) Cf. p. 1004 note 1. 



2) For the purpose of accurate measurements of the specific heat of metals and 

 alloys (e.g. of nickel and copper in connection with the magnetic properties of 

 these alloys, comp. Suppl. No. 36 c, May 1914, p. 110 note 1) a new heating- 

 core has been constructed in which the thermometer wire is suspended freely in 

 a gas filled space in order to get rid of the changes to which the thermometer- 

 wire is subject when it Ues enclosed in enamel-paint. 



