CRANE. | Ventilating Machinery. 321 
VENTILATING MACHINERY. 
There is little use for ventilating machinery in the mines 
of this district, for the reason that a natural circulation is 
usually set up in the mine by conditions usually existing, 
such as a difference in elevation between the mouths of two 
or more shafts connecting with the same workings, the drip- 
ping of the water in the hoisting or pump shaft, and by the 
use of the compressed air or steam drills which supply a 
large amount of fresh air in the mine below or heat the air 
up, which, combined with the natural tendency towards cir- 
culation, will usually produce a fairly good atmosphere. The 
mine workings are not very extensive, comparatively speak- 
ing, and, therefore, the quantity of air that it is necessary to 
supply is not very great. 
As natural ventilation is almost universally depended upon, 
ventilating machinery is seldom employed. Occasionally 
blowers are employed where the ventilation is defective and 
the natural circulation is hard to establish and maintain, in 
which case a blower is installed at the mouth of the hoisting 
shaft. It is connected with the workings below by tin and 
canvas spouts, and is generally operated by the hoisting en- 
gine. It will therefore work intermittently, forcing in fresh 
air only when the hoisting engine is at work. In most cases 
this is sufficient to maintain good air below. 
Where there is only one shaft to a mine ventilation be- 
comes more difficult, but even then it is not a difficult task. 
The two sections, 2 and 3, in figure 88, show typical 
methods of ventilating a mine with only one shaft. As seen 
at 2, a canvas tube is kept expanded by means of hoops and 
is lowered into the mine and properly supported at the sur- 
face. Above the supporting frame the canvas is not sewed 
together in the shape of a tube, but is attached to a straight 
piece of wood or is fastened to a rope along the free edge, by 
which it is supported above the mouth of the shaft. The air 
impinging against the sheet or ‘‘sail’’ is forced downward 
into the mine. The fresh air entering the mine displaces the 
