(36) 
cleaning the inner surface we therefore do not meet with the difficulty, 
which generally is occasioned by the bottom part. At their lower 
ends the compression cylinders are closed by nuts 4, similar to 
those at the upper ends; through these they are coupled to steel 
tubes 1,,/5,/3,/, bent rectangularly, terminating in the stopcocks 
ity, kg, ky. ky) which serve to couple each manometer (sometimes two) 
to the pressure-conduit or to disconnect them according as to 
whether or no the pressure to be measured is within the range of 
the manometer. 
These stopcocks are below the upper rim of the compression cylin- 
ders so as to allow us to fill without difficulty the compression- 
cylinder and the tube entirely with mercury; as they are provided 
with cork stuffing the mercury cannot become dirty by streaming 
along, in or out. 
The pressure is transferred on to the mercury in the compression- 
cylinders by means of mercury in the tubes sj. The stopcocks of the 
different compression tubes are mounted on a board, screwed on to 
the stand V (see Pl. I fig. 1 and 2) together with a system of 
supply-tubes. These supply-tubes filled entirely with mercury con- 
nect the compression-cylinders with: 
10. a mercury-reservoir Zj, serving to supply mercury and to gua- 
rantee that, when the apparatus is not watched there still remains in case 
of change of temperature and atmospheric pressure a sufficient excess of 
pressure in the apparatus even if the stopcocks were open. ‘This reservoir 
is always closed by the iron stopcock 4; when determinations of 
pressure are being made. 
29, the principal tube s; through which the pressure is trans- 
ferred on to the mercury in the tubes, and which may be closed 
by an iron stopcock 4 *). 
The tubes s, are entirely filled with mercury by exhausting them 
and then admitting mercury from 2; the stopcocks, like the other 
ones are provided with cork stuffing. 
Through the supply-tube #5, immersed in the mercury down to the 
bottom of the reservoir Bg we supply from the mercury in 2, as 
much as is required to compress the gas in the manometer tubes. 
The pressure to be measured is transferred on to the mercury in 
the reservoir by means of compressed gas. In order to apply the 
1) The construction of steelwork of this kind is described in Comm. N°. 27 and 44, 
2) These stopcocks did not require the same great care as bestowed on the steel 
stopcocks of the single manometers (which must be perfectly reliable) as not all mano- 
meter-tubes may be exposed to the highest pressure. 
