The miners agree that the direction of a draught in a
mine remains permanent for years, but if a fire in a
mine changes the draught, it never changes back. A
" down-cast " has thus been changed in an hour to
an "up-cast." The general tendency of air currents
in the Comstock is in the same direction as the slope
of the ore chimneys — that is, southward. Each new
connection makes changes in the air currents in all
the mines.
There is machinery in the mines, and often a great
deal of it. Steam makes too much heat, but com-
pressed air, hydraulic power, and electricity are now
used Avith entire success. Small engines run the
"blowers" to force fresh air through pipes to every
part of the mine, but particularly to the heads of the
news cuts, drifts, and upraises; others hoist and lower
rock and other materials in the various winzes, and still
others drive the drills. All this makes a network of



226 THE STOKY OP THE MINE.
pipes, mostly for compressed air, extending through-
out the mine.
