1057 
60 ce. of gas measured under normal conditions is made to flow 
through the experimental chamber only '/,"" of which is accounted 
for by the supply of hydrogen at ordinary temperature through 5,, 
the remainder being supplied by the evaporation of the liquid 
hydrogen. 
When the adjusting-thermometer (resistance of the tin wire) indi- 
cates that the temperature has been reduced to a value slightly below 
the desired one, the heating current is put in action '). According to the 
reading of the two checking thermometers in the experimental space, the 
adjustment of the automatic regulating-thermometer is then modified, 
until the desired temperature in the experimental space has been 
attained. A rise of .1 mm of the float corresponds to about .003 degree. 
The micrometer-screw « thus affords a high sensitiveness of adjust- 
ment of the temperature. 
The high degree of uniformity and constancy of the temperature 
of the measuring apparatus in the experimental space which is 
obtained with the apparatus and the method of working above 
described may be considered to be due to the following circum- 
stances: a) the access of heat by radiation and conduction to the 
copper enclosure of the experimental space has been reduced 
to an extremely small amount’); 6) the interchange of heat 
between the gas supplied from the heating space and the walls of 
the experimental chamber is much promoted by tbe long winding 
path followed by the gas in the side-walls, the exchange taking 
place over a large surface of highly conducting material which is 
moreover distributed as uniformly as possible; c) the difference of - 
temperature between the gas in the experimental space and the 
walls has been reduced to a very small value; d) the speed of the 
gas supplied from the heating space is sufficient to prevent quantities 
of heat which are supplied having an influence on the temperature 
of the experimental space; ¢) the constancy of the velocity of the 
1) In the adjustment to 29°.5 K the heating current was 0.06 amp., when the 
float was not making coniact, and 0.14 amp. when it did. At. 55° K. these 
currents were 0.114 amp. and 0.264 respectively. 
2) Comp. section 1 note 4 page 1050. In using the’cryostat for experiments, care 
has to be taken that galvanic generation of heat and supply of heat by conduction 
along experimental wires are reduced to a minimum; in the experiments to which 
the figures refer the conducting wires were taken very long and were wound in 
the cryostat in a manner which excluded heat-conduction to the experimental 
chamber. In experiments on condensation and expansion it is necessary to waita 
long time before it may be assumed that temperature equilibrium has been 
reestablished. 
