897 



In the further description we shall assume thai Ihe drawing of the 

 apparatus as it is given in this paper will be eonbulted as a niodid- 

 cation together with that of the Jiext paper (N". 139J). The develop- 

 ment of the apparatus there described, from onr original apparatus 

 and the modification due to Oosterhuis (Comni. N". i'S^h) will bo 

 obvious on comparison vvitli Comm. N". 'J39^^ 



In tlio cryogenic [)art, we encountered in the first place a difficulty, 

 which so far had not been provided for. Measurements had to be 

 made at the temperatures between the melting-point of oxygen and 

 the boiling-point of hydrogen, as well as at the temperatures of 

 liquid and solid hydrogen. In order to be able to do this an arrange- 

 ment was made which permitted us to work both in a bath of liquid 

 hydrogen evaporating under various pressures, and in a bath of 

 hydrogen gas, the temperature of which can be regulated. 



The arrangement consists principally in a circulation of hydrogen. 

 The hydrogen, after having been cooled to the boiling point, before 

 it comes in contact with the experimental object, passes over a 

 heating-spiral, in which Joule heat is generated, and is thereby 

 heated to the desired temperature. The whole hydrogen circulation 

 is carefully shut off from the outside air. The gas streams from a 

 supply-cylinder in which it is kept under pressure, through a copper 

 spiral AB, the glass tube CBL, which from CE is double-walled, 

 and silvered, and at E is widened, to the experimental space in the 

 cryostat. It enters this through the twice bent double- walled tube 

 FG, which forms the downward continuation of the vacuum-vessel 

 of the cryostat. On the way down the gas is cooled by liquid air 

 at A (copper spiralj, and is further cooled first by hydi-ogen vapour 

 and then by liquid hydrogen at B (glass spiral). At E the gas 

 passes along a resistance thermometer ; at F is the heating wire, at 

 G in the lower part of the experimental space a resistance thermo- 

 meter. 



By means of regulating resistances the current through the heating- 

 wires is so regulated as to obtain the desired temperature in the 

 experimental space. In the upper part of this there is a helium 

 thermometer with a steel capillary, which forms part of our cryo- 

 magnetic apparatus in its usual form (Comm. N°. 139a). The gas 

 then rises further in the vacuum-vessel, and escapes through aS into the 

 gasometer or the air-punq). The tubes K and L serve for leading 

 off hydrogen. 



Of the various auxiliary apparatns we must further mention tlie 

 thick-walled copper tube J/, which surrounds Ihe experimental tube, 

 and which serves to keep the temperature of the gas which sur- 



