1058 
gas-current in question is such as not to give rise to capricious 
modifications of the temperature of the experimental space; /) the 
heat-capacity of the walls of the experimental space is sufficient to 
efface the rapidly alternating deviations from the mean value of 
the temperature of the gas-current in question, which are due to the 
changes in the heat-development in the heating-wire, the consequence 
being that the walls only follow the changes of the mean value; 
g) tbe gas in the experimental space owing to its low temperature 
has a very much higher beat-capacity than under normal circum- 
stances and finally 4) the gas-current emerging from the heat- 
exchange tube in the experimental chamber keeps the gas in continual 
motion *) along the walls and the apparatus: 
In the experiments which have been made with the cryostat so 
far, it was noticed that capricious disturbances from time to time 
interrupted the periods of constant temperature’). But when the 
measurements were continued for a long time, generally periods of 
more than half an hour or longer were repeatedly found in which 
the temperature of the experimental apparatus and thermometers 
remained constant to .01 of a degree, whereas these periods are 
preceded by even longer ones during which the temperature did 
not vary by more than .02 of a degree, so that the measuring 
apparatus during this time were able to assume the desired tempera- 
ture with very near approximation. 
Physics. — “/sothermals of mon-atomic substances and their binary 
mixtures. XVIII. A preliminary determination of the critical 
point of neon.” By H. KAMERLINGH Onnes, C. A. CROMMELIN 
and P. G. Carn. (Communication N°. 151 5 from the Physical 
Laboratory at Leiden). 
(Communicated in the meeting of June 24, 1916). 
1. Zntroduction. The chief reason why the critical data of neon 
are not known yet with any degree of accuracy — notwithstanding 
their great importance for the comparison of its thermal properties 
with those of other, especially monatomic substances — is doubtlessly 
the fact, that so far it had been inrpossible to obtain temperatures 
1) In eryostats with baths of liquefied gas strong stirring is necessary on other 
grounds. 
?) Each time after a fresh adjustment of temperature it is necessary to wait 
some time for the experimental space and the measuring apparatus to arrive at 
the new temperature. 
