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      While most mines are now lighted entirely by electric safety lamps, the Davy lamp is still used to test for the presence of fire-damp. Though flames cannot pass through the wire gauze, gas can pass in. If fire-damp is present, the color of the flame in the Davy lamp changes to blue. That change in color says, "Take care! Danger!"
    There is a railroad in this underground city. A car stands near. Our guide tells us to get in. After a ride of about a mile, we come to a room where miners are at work. There are not using hand picks and shovels, as all miners once did. In a great modern mine like this one machines run by electricity do almost everything. The miners merely guide the machines.

An undercutting machine at work
An undercutting machine at work

    An undercutting machine is cutting a long, deep gash in the wall of coal just above the floor. Farther on is a miner drilling holes with an electric drill in a wall of coal already undercut.