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 being of course essential that the traffic at the Central Station should not be interfered with.  During these hours, night after night, trenches were cut at intervals of 10 feet across the roadway connecting the arrival platforms at the station, and into these were placed strong balks of timber, across which planks were laid as a temporary roadway.  Beneath these planks, which were taken up and put down as required, the rock was excavated to a depth of 9 feet, and the balks supported upon stout props.  Then from the driftway or rough boring beneath well holes were bored to the upper excavation, and through them the strong upright iron pillars designed to support the roof of the new tunnel station were passed, bedded and securely fixed in position.  No sooner were they in situ than the most troublesome part of the task was entered upon, for the balks had then to be removed in order to allow to be placed in position the girders running the length of the new station, and resting on the tops of the upright pillars.  From these longitudinal girders cross girders of great strength were placed, and between these were built brick arches, packed above with concrete.  This formed the roof of the new station.  One portion of it passed under the rails in the station above, and had to be