The ordinary incandescent light, if worked direct from the dynamo , requires two conducting wires to convey the current, and as illumination is specially required in the working places, it seems improbable that the direct system of lighting as is employed on the surface will ever be used underground.
— Many collieries are now pro vided with the electric light underground, but the system extends only a short distance from the shaft.  The ordinary incandescent light, if worked direct from the dynamo , requires two conducting wires to convey the current, and as illumination is specially required in the working places, it seems improbable that the direct system of lighting as is employed on the surface will ever be used underground.  The working places are naturally moving day by day, falls of roof are common, and as the space is confined, con ducting wires would be quite out of place there.