,000 men working three
shifts of eight hours each, but were greatly accelerated by the use of
Colonel Beaumont's boring machine, on which disks of chilled iron are
set in a strong iron bar made to revolve by means of compressed air.
This machine scooped out a tunnel 7 feet in diameter; and by
successive improvements Colonel Beaumont attained a speed of 150 feet
per week, leaving the old method of blasting far behind. As the
machine moved forward the rock behind was broken out to the size of
the main tunnel and bricked in in short lengths. One remarkable
circumstance in connection with the work is that the boring from the
Birkenhead side and the boring from Liverpool were found, when they
were completed and joined, to be out of line by only 1 inch.

This excellent result was attained by careful calculations and
experiments with perpendicular wires kept in position by weights,
which, to avoid oscillation, were suspended in buckets of water. From
shaft to shaft the tunnel is 1,770 yards in length and 26 feet in
diameter; but for a length of 400 feet at the James Street and
Hamilton Square stations the arch is enlarged to 501/2 feet. The tunnel
is lined with from six to eight rings of solid brickwork embedded in
cement, the two inner rings being blue Staffordshire or Burnley
bricks. For the purpose of ventilation a smaller tunnel, 7 feet in
diameter, was bored parallel with the main tunnel, with which it is
connected in eight places by cross cuts, provided with suitable doors.
Both at Liverpool and at Birkenhead there are two guibal fans, one 40
feet and the other 30 feet in diameter. The smaller, which throw each
180,000 cubic feet of air per minute, ventilate the continuations of
the tunnel under Liverpool and Birkenhead respectively, and the larger
tunnel under the river. The fans remove together 600,000 cubic feet of
air per minute, and by this combined operation the entire air in the
tunnel is changed once in every seven minutes. By the use of
regulating shutters the air passes in a continuous current and the
fans are noiseless. The telegraph and telephone wires pass through the
tunnel, thus avoiding the long detour by Runcorn. Probably, as a feat
of engineering, the construction of the new station at Bold Street is
not inferior to any part of the scheme advanced. Under very singular
and perplexing difficulties it could only be proceeded with in its
first stages from midnight until six o'clock the following morning, it