(112) 
In the following table the normal volumes found have been com- 
bined and also the relative mean errors have been given 
Tube. te | hen ur Iv. 
Norm wet 162.215 | 126.023 132.135 158.380 
Mean) rear. - 13000 | 1 : 41000 | 1 : 12000 | 1 : 10000 
S 3. The measurements at higher pressure. After the piezometer 
tubes have been placed in the compression apparatus and this has 
been connected with the open manometer, the heights of the mer- 
cury in them were read by means of a cathetometer of the Société 
Génevoise. Both rest on the same common foundation, isolated 
from the floor, and made by bridging over the firm pillars in the 
observation room with iron rails and stone slabs. 
To insure a constant temperature, the apparatus for the regular 
current of water at constant temperature was putin motion at 10.30 
a.m., and the water bath was constantly stirred, the apparatus was 
put under pressure at 12.30 p.m. and the measurements began at 
2.30 p.m. and were continued uninterruptedly till 5 p.m. without 
anything being changed in the apparatus; we might then be rea- 
sonably certain that the temperature measured with the thermometer 
agreed with that of the hydrogen and that equilibrium of pressure 
existed between the open and the closed manometers. For these 
measurements the height of the barometer must also be known, 
this was read on an aneroid, of which the correction had been care- 
fully determined. We took into account that the aneroid had been placed 
lower than the mercury in the manometer tube A. (Comm. 44 fig. I). 
It will hardly ever be possible to avoid very small leakages in 
the connecting tubes; in the measurements taken into account they 
were so small that they could not be discovered by means of soap 
solution. Hence the corrections which must be applied for the 
motion of the mercury owing to those leakages are very small; with 
a view to these corrections however all the readings must be made 
as symmetrically as possible and the time must be always noted 
for the mean mercury height both in the open and closed mano- 
meters. I will give here one observation (comp. the table of readings 
in the Proceedings of May 25% ’01, Comm. N®. 70), of which the 
calculation will be carried out as an instance. 
