s, therefore, requires the most constant vigilance on the
part of the workmen, especially in the examination of the working places
that have been standing empty during the night, in which gas may have
accumulated, to see that they are properly cleared before the new shift
commences.

The actual conveyance or coursing of the air from the intake to the
working faces is effected by splitting or dividing the current at
different points in its course, so as to carry it as directly as
possible to the places where it is required. In laying out the mine it
is customary to drive the levels or roads in pairs, communication being
made between them at intervals by cutting through the intermediate
pillar; the air then passes along one and returns by the other. As the
roads advance other pillars are driven through in the same manner, the
passages first made being closed by stoppings of broken rock, or built
up with brick and mortar walls, or both. When it is desired to preserve
a way from one road or similar class of working to another, double doors
placed at sufficient intervals apart to take in one or more trams
between them when closed are used, forming a kind of lock or sluice.
These are made to shut air-tight against their frames, so as to prevent
the air from taking a short cut back to the upcast, while preserving
free access between the different districts without following the whole
round of the air-ways. The ventilation of ends is effected by means of
brattices or temporary partitions of thin boards placed midway in the
drift, and extending to within a few feet of the face. The air passes
along one side of the brattice, courses round the free end, and returns
on the other side. In many cases a light but air-proof cloth, specially
made for the purpose, is used instead of wood for brattices, as being
more handy and more easily removed. In large mines where the air-ways
are numerous and complicated, it often happens that currents travelling
in opposite directions are brought together at one point. In these cases
it is necessary to cross them. The return air is usually made to pass
over the intake by a curved drift carried some distance above in the
solid measures, both ways being arched in brickwork, or even in some
cases lined with sheet iron so as to ensure a separation not likely to
be destroyed in case of an explosion (see figs. 5 and 8). The use of
small auxiliary blowing ventilators underground, for carrying air into
work