409 
ved copy of the left hand part of PL I of that Communication, to 
which we may in the first place refer. The improved diagram 
embraces the modifications which were introduced later, and which 
are described in Comm. No. 121a. Identical parts are indicated by 
the same letters in fig. 1 and in Comms. Nos. 117 and 1214, parts 
which have undergone modification are distinguished bv accents, 
while parts which are new or are now lettered for the first time 
have new letters attached to them. We may refer to W. J. pr Haas’s 
thesis for further details concerning the water circulation, IV, which, 
supplied from the-thermostat, keeps constant and uniform the tem- 
perature of the volumenometer and of the manometer. 
The volumenometer is connected to the auxiliary reservoir /” 
through the taps 4, and /,. This allows one to add gas to the 
measured quantity contained in the volumenometer, or to temporarily 
abstract a measured quantity from the volumenometer. This was 
essential in our experiments as the volume of the piezometer, in 
which the gas density was sometimes practically 20 times as great 
as that in the volumenometer, was 110 ¢.c. and that of the voluineno- 
meter was not more than 1250 ¢.c. Hence, if, for instance, the 
volume is adjusted to the smallest volume in the volumenometer 
(the neck m, in the figure) at a pressure of one atmosphere, then 
even when the volumenometer is completely filled (to the neck m, 
in the figure) the second equilibrium pressure of half an atmosphere, 
which, according to § 1, is desirable in this case, is not vet attained. 
The admission of gas from the volumenometer to /” and vice versa 
can be of use in another way, viz. in the transition to another tem- 
perature and in the adjustment of pressure equilibrium. In the course 
of our experiments, however, we have not been able to make such 
free use of the auxiliary reservoir as we should have liked. The 
volumenometer can be evacuated through the valves ,,4,,4,;; and it 
can be connected to the barometer and to the constant pressure 
reservoir, , (Comm. No. 60, Pl. VI) through &,, &,,4,,, 0, ho, han 
When the volumenometer adjustments and the value of the pressure 
permit of it, the valve /, may be closed and the pressure then deter- 
mined from the manometer J/ alone, the space above which is then 
evacuated through /,. We may refer to Comm. No. 121a by W. J. 
DE Haas for further details concerning the pressure measurement. 
To ascertain when pressure equilibrium has been attained we applied 
the method already described in Comm. No. 127a; the pressure in 
the volumenometer was under constant observation, and from the 
curve expressing the pressure as a function of the time, we deduced, 
during the observations, the time at which the pressure difference 
27 
Proceedings Royal Acad. Amsterdam. Vol. XY. 
