The ventilation by this mode is simple, and each end of every boundary is coursed by a separate and distinct current of fresh air, which sweeps the faces of the breasts and takes the nearest and most direct way to the return air-course. The obnoxious gases are not carried into other portions of the mine. If explosive gases occur, they are swept away at once and hurried off before they can become dangerous ; nor are they carried, as in the old system, from lamp to lamp and breast to breast through the entire mine before they find an exit, but enter the return air-course from each set of breasts. This not only insures life, but health and general safety.
Two shafts are better than one to secure perfect ventilation in deep mines ; but if one is carefully divided, so as to prevent the air from passing through the casing, a large single shaft will answer the purpose. The engraving with which we illustrate this mode of mining and ventilation displays a large divided shaft. The air passes down the dip side and enters the main gangway a, along which it passes to the branch or gangway c, which part of the air enters, this being the first split. The cur rent continues up the branch gangway to the upper breast. Here it again splits, and turns into the right and left hand boundaries, as indicated by the arrows. It sweeps
down the face of the breasts or chambers in each boundary, and enters the return air course below the lower breast.
The mine may be divided into any number of boundaries desired, either small or large, to suit the character of the dips and undulations of the seam, and this principle of ventilation and mining be retained.
The only objection that could possibly be made to this system is the use of inclined planes; but when we consider that inclines are not required except in a pitching seam, and that such a seam cannot be worked without inclines, we cannot see how that objec tion will hold. In the old modes, every breast becomes an incline in pitching seams, and when the cars are taken after the miner this difficulty exists. The cars may be drawn by horses ; but it is both dangerous and difficult to convey the cars down the inclines from each breast. A single incline between each boundary answers a much better purpose, and can be operated with much more rapidity and safety.
We hope these improved systems have been practically presented, and that the plans will be clearly comprehended, since they require only to be understood properly to be appreciated.