Page:Walker (1888) The Severn Tunnel.djvu/115

58 it was necessary to use it as the only means of access to the works.

It was therefore arranged by Sir John Hawkshaw that, instead of ultimately filling up this heading, it should be at once lined with brickwork, being first enlarged so as to leave a circular adit, 9 feet in diameter, inside the brickwork. This it was proposed should be used, when the tunnel was completed, as an auxiliary passage for ventilation, leading to a fan which should exhaust air from the tunnel.