301 
tables prepared beforehand, for changes occurring during the measure- 
ment in the quantities determining the corrections (such as change 
in the temperatures of the volumenometer, the piezometer, the dead- 
space, change in the capillary depression, etc). 
In this way the actual change in the difference between the pres- 
sure and the equilibrium pressure was known at all stages of the 
measurement. During the measurements a curve was drawn with 
this pressure difference as ordinate and time as abscissa, and the 
observation was regarded as at an end as soon as the plotted points 
began to fluctuate about a line drawn parallel to the abscissa axis. 
The accompanying diagram (unit ordinate representing 0.1 mm. 
mercury) is taken from the above investigation and refers to the 
adjustment of the pressure equilibrium on July 18, 1911, an occasion 
on which circumstances were particularly unfavourable. The observed 
pressure differences, increased by a certain fixed quantity, are re- 
presented by circles. At the end of $ 3 we shall return to this diagram. 
20 
2m 3h 4h GN kn of 
Fies i: 
§ 2. Calculation of the pressure change from the experimental data. 
The curve giving the change in the pressure difference between 
the two communicating vessels as a function of the time was now 
calculated from the dimensions of the apparatus and from data 
determining the temperature distribution along the glass capillary. 
As will be seen from the end of § 3, calculation is in complete 
agreement with observation, and is therefore suitable for checking 
the smallest pressure difference experimentally determined by the 
above method in the case discussed in §3. The reduction of the 
theoretical calculation to formulae has the result that it not only 
covers this particular case, but it can also be applied to gauge the 
degree of pressure equilibrium in similar cases in which capillary 
connections occur in experiments at low temperatures, 
