COMtL MINES OF

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mosjiheric current passing through occupiesthe middle region of the workings, while thefire-damp, from its specific lightness, ascendsand continues on the roof, and may be foundin almost every part of a mine, as I have my-self ascertained by holding up a lighted taperand watching the flame, which, on immersionin small quantities of the fire-damp, appearsto have a yellowish semi-circle over the top.

The carbonic acid gas occupies the floor,and is only dangerous when its quantity be-comes so great as to affect the respiration, asat the Hepburn Colliery ; and in case of ex-plosion of the fire-damp, the carbonic acidwith the common air is so much expandedas to sweep every thing before it.

The mines on the Tyne and Wear are con-sidered in a peculiar degree dangerous, fromthe quantity of gas yielded by their coal; in-deed the many accounts of devastation whichhave recently occurred in this district are un<«equivocal proofs in corroboration of the state-ment. When any quantity of gas escapes froma rent or fissure, its blast is always most power-ful on the first liberation, and gradually be-comes less until the whole is spent out:should nothing occur therefore to ignite it inthe firpt instance, it may be carried off by