ageous from the standpoint of
the consumption of energy.

_Porous Partition._--Let us suppose that the two parts of the trough
are separated by a partition containing small channels at right angles
with its direction. It is these channels alone that must conduct the
electricity. Their conductivity (inverse of resistance) is
proportional to their total section, and inversely proportional to
their common length, whatever be their individual section. It is,
therefore, advantageous to employ partitions that contain as many
openings as possible.

The separating effect of these partitions for the gas is wholly due to
capillary phenomena. We know, in fact, that water tends to expel gas
from a narrow tube with a pressure inversely proportional to the
tube's radius. In order to traverse the tube, the gaseous mass will
have to exert a counter-pressure greater than this capillary pressure.
As long as the pressure of one part and another of the wet wall
differs to a degree less than the capillary pressure of the largest
channel, the gases disengaged in the two parts of the trough will
remain entirely separate. In order that the mixing may not take place
through the partition above the level of the liquid (dry partition),
the latter will have to be impenetrable in every part that emerges.
The study of the partitions should be directed to their separating
effect on the gases, and to their electric resistance. In order to
study the first of these properties, the porous partition, fixed by a
hermetical joint to a glass tube, is immersed in the water (Fig. 2).
An increasing pressure is exerted from the interior until the passage
of bubbles is observed. The pressure read at this moment on the
manometer indicates (transformed above the electrolytic solution) the
changes of level that the bath may undergo. The different porcelains
and earths behave, from this point of view, in a very unequal manner.
For example, an earthen vessel from the Pillivayt establishment
supports some decimeters of water, while the porcelain of Boulanger,
at Choisy-le-Roi, allows of the passage of the gas only at pressures
greater than one atmosphere, which is much more than is necessary.
Wire gauze, canvas, and asbestos cloth resist a few centimeters of
water. It might be feared, however, that the gases, violently
projected against these partitions, would not pass, owing to the
velocity acquired. Upon this point experiment is very reassuring.
After filling with