[Illustration: Figure 22.--BROADSIDE PUBLISHED AFTER COMMENCEMENT OF WORK on the Thames Tunnel, 1827. (MHT collections.) OPEN TO THE PUBLIC EVERY DAY (_Sundays excepted_) _from Seven in the Morning, until Eight in the Evening_, THE THAMES TUNNEL. Fig. 1 shows a transverse section of the Thames, and beneath it a longitudinal section of the Tunnel, as it will be when completed; with the ascents in the inclinations in which they will be finished. Fig. 2 shows the two arched entrances of the Tunnel from the shaft. Fig. 3 is a representation of the iron shield, and shows a workman in each of the compartments. The Entrance to the Tunnel is near to Rotherhithe Church, and nearly opposite to the London-Docks. The nearest landing place from the river is Church Stairs. The Greenwich and Deptford coaches which go the lower road, start hourly from Charing-cross, and Gracechurch-street, and pass close by the works at Rotherhithe. Books relative to the Tunnel may be had at the works. The Public may view the Tunnel every day (Sundays excepted) from Seven in the morning until Eight in the Evening, upon payment of One Shilling each Person. The extreme northern end of the Tunnel is for the present secured by a strong wall; but visitors will find a dry, warm, and gravelled promenade, as far as to almost the centre of the river, and brilliantly lighted with oil gas. The entrance is from Rotherhithe Street, and by a safe, commodious, and easy stair case. H. Teape & Son, Printers, Tower-hill, London.] [Illustration: Figure 23.--VERTICAL SECTION THROUGH BRUNEL'S SHIELD. The long lever, x, supported the wood centering for turning the masonry arches of the lining. (LAW, _A Memoir of the Thames Tunnel._)] [Illustration: Figure 24.--THAMES TUNNEL. SECTION THROUGH riverbed and tunnel following one of the break-throughs of the river. Inspection of the damage with a diving bell. (BEAMISH, _A Memoir of the Life of Sir Marc Isambard Brunel_.)] The Tower Subway at first operated with cylindrical cars that nearly filled the 7-foot bore; the cars were drawn by cables powered by small steam engines in the shafts. This mode of power had previously been used in passenger service only on the Greenwich Street elevated railway in New York. Later the cars were abandoned as unprofitable and the tunnel turned into a footway (fig. 32). This small tunnel, the successful driving due entirely to Greathead's skill, was the forerunner of the modern subaqueous tunnel. In it, two of the three elements essential to such work thereafter were first applied: the one-piece movable shield of circular section, and the segmental cast-iron lining.