8J: Mr. Alexander B. Binnie [Marcli 6, 



a lenfyth of 2579*6 feet. In other words, tlie inclined approaches 

 will not be so steep as parts of St. James's Street and Eegent Street, 

 and very mncb less so than the east side of Trafalgar Square opposite 

 Morley's Hotel ; they will, however, be about equal to that of the 

 Haymarket. The work may be divided into three portions : open 

 approaches with side walls ; cut and cover arched over with brickwork ; 

 and tunnel proper composed of cast-iron rings lined with concrete 

 and faced with white glazed tiles, all the other parts of the work 

 being faced with white glazed bricks. 



The lengths of the various portions, including the shafts, are as 

 follows : — 



Feet. 



Open approach .. 1735 



Cut and cover ]382 



Cast-iron tunnel 3083 



6200 

 or a total of a little over 1 mile. 



To facilitate the work, so as to permit of altering its direction, 

 which it would be difficult to do by means of a long curve in a tunnel 

 of this description lined with cast iron, and to secure ventilation, 

 there are four shafts varying in depth from 75 to 98 feet, and having 

 an internal diameter of 48 feet. 



The tunnel proper is circular in cross section, 27 feet outside 

 diameter, or 6 feet larger than that of St. Clair (the largest hitherto 

 constructed), built up of fourteen cast-iron segments and a key-piece ; 

 each complete ring of segments is 2 feet 6 inches in width. The 

 thickness of the cast iron is 2 inches, the flanges are 12 inches in 

 depth, measured from the outside, and each segment weighs about 

 one ton. The joints are brought to a true and even surface by 

 machine planing, and all are bolted to each other and to the adjacent 

 cast-iron rings by wrought-iron bolts and nuts. To ensure that the 

 cast-iron plates have a firm abutment upon and against the surround- 

 ing earth, there is a hole near the centre of each fitted with a screw 

 plug through which grout is forced as wdll be presently described. 

 Tiie internal edges of the flanges of the plates are recessed for a 

 depth of 2 inches, and after they are fixed in position and bolted 

 together this recess is filled and caulked with rust joint cement com- 

 posed of iron borings and sal-ammoniac. The space between the flanges 

 and for a distance of 4^ inches beyond in front is filled up solid 

 with Portland cement concrete faced with white glazed tiles, so that 

 the effective diameter of the tunnel is 24 feet 3 inches. Within this 

 the road of 16 feet, with two foot-paths each 3 feet IJ inches in width 

 is formed, resting on an arched subway 12 feet in width and 5 feet 

 6 inches in height for the reception of water pipes. There are also 

 proper drains for the road, and channels for smaller pipes for road 

 cleansing, &c. This road of 16 feet will be of the same Avidth as parts 

 of Little Queen Street, Holborn, and King Street, Westminster, and 

 of a greater width than parts of Drury Lane, Fetter lane. Upper and 



