(32) 
municated, together with the measurements made in order to test the 
accuracy of the standard open manometer of reduced height by divi- 
ding it into two parts, which are equilibrated with each other or 
simultaneously with one or two closed manometers. 
S 3. The piezometer- or manometertubes. These are made of Jena 
normal glass and recall in so far as the general form is concer- 
ned the type used by CAILLETET (comp. fig. 3 and 4). On to 
the upper end of the stem a wider reservoir has been blown of 
about the same volume as the divided stem in order that on each 
manometer the range of the pressures extends only so far that 
the highest pressure at which an adjustment in that tube can be 
made is twice the lowest. In this way we ensure the sensibility to 
be about the same at the different parts of the graduated scale. 
The diameters of the reading-tubes (comp. fig. 3 and 4) are for 
the four manometer-tubes 8, 6, 4 and 3 mm. respectively. The 
diameters of the upper reservoirs and the thickness of the reading 
tubes and of the upper reservoirs have been chosen so as to be in 
accordance with these (comp. fig. 6). 
A very accurate determination of the volume of the enclosed gas 
when compressed is rendered possible by fixing a very fine capillary 
tube of known volume (diameter about 0.3 mm.) on to the upper 
reservoir just as with AMAGATs’s piezometer (e, comp. fig. 6). 
After sealing off we can, by measuring the length of that part 
of the capillary tube that has remained unchanged and by estima- 
ting the volume of the conical part formed by the sealing off, com- 
pute its whole volume from a definite mark. The error thus remai- 
ning may be entirely neglected. 
A wider capillary € (fig. 7) carrying a small cock has formerly 
been welded on to the capillary tube at the place where it will be 
sealed off. By means of this cock we can connect the tube with 
the vacuum pump, suck up liquids in the manometer-tube, supply 
dry air, ete. ; moreover it is useful in calibrating. 
The tube, dried and ready to be filled is sealed off at the place 
where the wider capillary tube has been welded on to the narrow 
one. If the tube has afterwards to be cleaned again, which can 
not but imperfectly be done without opening it and sucking liquid 
through, or if the tube has to be calibrated anew, the fine point is 
filed off and at that place a new tube resembling the one sealed 
off is joined on. In this way we lose in each operation only a few mm. 
of the capillary tube e and we can use the same manometer for 
numerous sets of measurements before it is necessary to weld on a 
