Hart produced this remarkable photograph of the east end of tunnel no. 6 by reflecting sunlight into the dark interior with a large mirror during a 15 minute exposure. The tunnels were worked in two stages. First the heading, the space directly below the tunnel’s crown, was opened. This space was made only tall enough for men to work comfortably against the face, but it was made 16 feet wide, the full width of the finished tunnel. After the face of the heading had been driven some distance ahead, the second step was to lower the floor 12 feet or so to the desired level of the finished grade. In the murky distance in this image, one can make out the ledge between the heading and the bottom portion yet to be removed.
If you have red/cyan 3D glasses, click on the stereocard above to see its anaglyph in a new window.
