(36) 
The piézometer tube which has been exhausted by means of the 
mercury pump, hand has been sealed off at the cock-piece fastened 
to the sealing capillary and filled in a sloping position by breaking 
off that point under mercury, is carefully centred and placed verti- 
cally in a reversed position in the water jacket (comp. Communica- 
tion N°. 67. 8 1). The positions of the meniscus with regard to 
the divisions are read by a cathetometer. The marks are made on 
Mark. | le | u | Difference. 
2 57.666 57.662 — 0.004 
8 57.270 57.271 +0.C01 
9 53.599 53.601 —J-G.002 
0 41.582 41.585 0.003 
2 35.369 35.370 —J-0.001 
7 34.868 | 34.868 0.000 
1 25.550 25.550 0.000 
4 25.253 25.255 +0.002 
6 20.106 
1 19.729 12.728 —0.001 
3 12.534 12.533 — 0.001 
8 6.130 6.131 +0.001 
3 | 5.628 5.630 | +0 .002 | 
3 2.665 2.665 0.000 | 
the side so that the middle of the groove can be read in the same 
way as in the experiments (comp. Communication N°. 67, § 2). The 
distances between the marks are measured outside the bath. For the cali- 
bration we chose those marks at which (according to preliminary 
measurements) the adjustments would be made during the obser- 
vations. 
The principal point is the accuracy with which the distances 
between the marks can be determined. The preceding table gives 
two independent series of readings for the tube / A (corrected for 
the temperature!) and for the reading of the level). 
In order to read the mercury menisci very accurately a black 
1) The lengths and all following measures have been given for 20° C. 
