eN 
(31) 
data for the necessary corrections can also be determined with great 
accuracy. 
Lastly care has been taken that the mercury in the apparatus 
does not come into contact with anything but carefully cleaned glass 
or iron and cork or solidified cement. Accordingly the menisci in 
the manometer-tubes remain perfect. All this entitles us to call the 
apparatus described in the following pages when used as gasmano- 
meter, a standard manometer. 
§ 2. General arrangement. The apparatus now used in the Leiden 
Laboratory is designed for measurements with 4 piezometers ranging 
from 4 to 64 atmospheres. In the construction of the apparatus, I 
have successively been ably assisted by Dr. Lepret and especially 
by Mr. SCHaLKWIJK, both assistants and Messrs. Curvers and 
Furm, instrumentmakers, to all of whom I render thanks. It 
contains, when used for measurements of pressure, and as repre- 
sented in Plate I, four closed manometers placed in a row, on 
each of which a definite range of pressure is read, viz. 4—8, 8—16, 
16—32, 32—64 atm.; each following manometer has a small range 
of pressure in common with the preceding, through which proper 
continuity and mutual testing are obtained. The piezometer-tubes 
are placed in compression-cylinders, each of which can be connected 
separately with the apparatus in which the pressure is to be mea- 
sured, while all can be connected mutually. 
The whole apparatus is mounted usually in a definite place. The 
pressure is transferred from the apparatus, in which we want to 
measure it, to the manometer through a narrow tube filled with 
compressed gas. This method offers many advantages in a research 
laboratory like that at Leiden. 
The choice of the stages of pressure agrees with the division into 
pieces for 4 atmospheres of the standard open manometer which 
ranges as far as 60 atm., and with which the closed manometer 
is used as an auxiliary apparatus in order to attain a pressure higher 
than 60 atm., in the way described in Comm. n°. 44. 
As the closed manometer for the next stage made after the same 
principle is not yet ready (it requires a compression tube with a 
thicker wall and greater volume than those existing) we use for 
pressures above 64 atm. closed manometers of simpler construction !), 
The mutual testing of the various closed manometers will be 
described when the observations made with the apparatus are com- 
1) Comp. VeRSCHAFFELT, Thesis for the doctorate, Leiden 1899, 
