= MINING. 127 
Machines for injecting or exhausting air are also employed extensively. 
Pl. 24, fig. 35, represents an exhausting engine driven by steam, erected at 
the mine of Bois de St. Ghislain. The exhausting cylinders have ten feet 
diameter; they are made of oak staves hooped with iron hoops, their 
bottoms as well as the pistons are of cast-iron, and have each ten valves 
which are counterpoised. At each stroke of the engine one of the cylinders 
exhausts air from the mine while the other is descending freely. 
The centrifugal ventilator is also frequently employed for ventilating 
mines. 1. 26, jigs. 6 and 7, represent half sections of this apparatus: six 
curved rings or guides, @, a, are attached to a disk at the upper end of the 
vertical axis; on the lower side of the guides is attached the annular disk, 
cc, which lies in the plane of the head of the cylinder, pp, which covers the 
opening of the shaft. To ce is attached a sheet iron cylinder, ee, dipping 
into water contained in a circular trough, 7, in order to prevent leakage; 
the difference in the height of water on both sides of the cylinder, ee, is 
due to the difference of pressure between the exterior air and the interior, 
which is set in motion by the rotation of the ventilator. /%gs.8 and 9 repre- 
sent a similar apparatus, which revolves on a horizontal axis. /7%g. 10 is a 
ventilating screw, which will act either as an exhauster or a blower, accord- 
ing to the direction in which it is turned. 
The manner in which the circulation of air to the furthest extent of a 
mine is insured by regulating its course by means of doors, is shown in pl. 
24, jig. 33. The air comes in at the shaft a, circulates through all the work- 
ing levels by following the course indicated by the arrows, and escapes 
again through the shaft B; the dark portions of the figure are exhausted 
workings which are separated by air-tight partitions. At a, a, a, is shown 
how the current is guided into the foreheads of the mine. /%g. 34 represents 
another system of working and ventilation, which is in general use in coal- 
mines. The current descends through the shaft a, and is divided into two 
parts, which remain separate throughout the whole mine until they unite 
again near the shaft B, through which the air rushes out; pis a furnace 
which keeps up the ventilation. 
In most mines there are persons whose sole duty it is to examine con- 
stantly the state of ventilation. An anemometer, which is frequently used 
for the purpose of ascertaining the velocity of the air-current, is represented 
on pl. 26, figs. 13, 14, and 15, in two side-views and a top-view. To the 
axis, A, are attached four wings of gold-foil, making an angle of 80° with a 
plane perpendicular to the axis: an endless screw, v, drives a wheel, r, of 
100 cogs, which by a small lever, c, moves the wheel x’, having fifty teeth, 
by one tooth for every revolution of x. Thus for 5,000 revolutions of the 
fans the wheel, r', makes one ; when the axis of the instrument is presented 
to the draught, the number of revolutions of the fan counted by the indica- 
tors, 2, 2’, will show the relative velocity of the current. 
3. Ixnumination or Mines. The pit-bottoms only and the straight gallerie: 
of transport are lighted by stationary lamps (pl. 23, jig. 36, the bottom of 
the engine pit of a Newcastle coal mine). The miners either carry smal} 
tallow candles, which when at work are fixed in front of their hats, or oil 
707 
