:
 
 TT-'iO-T 
 
 THE TOWER BRIDGE. 
 
 A LECTURE. 
 
 BY 
 
 JOHN WOLFE BARRY, 
 
 M.INST.C.E. 
 
 XonDon : 
 
 BOOT, SON AND CARPENTER, 
 24, OLD BAILEY, B.C. 
 
 1894.
 
 ERRATA. 
 
 Page 43, line 11, for 12 inches" read " 27 inches; 
 Page 45, line 3, for "their" read "these;" 
 Page 51, line 16, for "down" read "into."
 
 PREFACE. 
 
 Lecture was composed in 1893 for an audience 
 consisting in part of persons well acquainted with 
 engineering matters, but more largely of those who took an 
 interest in the Tower Bridge as members of the general 
 public. It is not to be regarded as being such a professional 
 description of the Bridge as would be suitable to a body of 
 experts ; but it may be of interest to a considerable number 
 of persons who have seen the Bridge in its various stages of 
 progress, or who wish to form a general conception of its 
 design and of the various considerations which led up to 
 its inception and determined its mode of execution. 
 
 J. W. B.
 
 THE TOWER BRIDGE. 
 
 A LECTURE. 
 
 BY 
 
 JOHN WOLFE BARRY, M.lNST.C.E. 
 
 Introductory. 
 
 T)EFORE entering upon a description of the structure of 
 the Tower Bridge, it may be interesting if I touch 
 first upon the history of the principal bridges of London, and 
 then upon the necessity of means being afforded for crossing 
 the river below London Bridge, with a glance at the various 
 suggestions which have been made to meet the want. 
 
 A bridge appears to have existed on the site, or a few 
 yards lower down the river than the site, of the present 
 London Bridge, from remote antiquity. We read of Canute 
 attacking and being repulsed from London Bridge, and some 
 writers have held that a bridge at this spot dates from the 
 Roman occupation of London, which was then known to the 
 world as the town Augusta, and must have been of con- 
 siderable importance. Stow says that in the year 994 the 
 Danes were repulsed in an attack which they made on 
 London, because they took no heed of the bridge ; but 
 probably there is some misconception here, for it is recorded 
 that only in the previous year Anlaf, the Dane, sailed up
 
 2 A LECTURE ON 
 
 the Thames as far as Staines with ninety-three ships and 
 ravaged the country. Discarding the tradition of a Roman 
 bridge, it seems clear that the first London Bridge of which 
 any record exists was erected between the years 993 and 
 1016, when Canute attacked London a second time, and made 
 a canal on the south side of the river so as to bring his ships 
 past the bridge. The first bridge was probably of wood, and 
 
 FIG 1. OLD PUTNEY BRIDGE. 
 
 somewhat of the form which many of us remember in the 
 cases of old Putney and old Battersea bridges, the piers being 
 formed of piles driven into the bed of the river, and the 
 openings spanned by timber beams. (The view (Fig. 1) is 
 taken from a photograph of old Putney Bridge, and iUustrates 
 that mode of construction.) This wooden bridge had great 
 vicissitudes. It was washed away in a flood in 1 091, was rebuilt 
 m 1097, and burnt in 1136. It was again rebuilt, but was
 
 THE TOWER BRIDGE. 3 
 
 in so bad a state in 1163 that a new bridge was resolved on, 
 and this time in more durable materials. 
 
 A certain monk, Peter Curate of St. Mary, Colechurch 
 being known for his skill in bridge building, was employed to 
 erect the new bridge, which was begun in 1176 and finished in 
 1209. Peter of Colechurch did not live to see the completion 
 of his great work, but died in 1202. 
 
 The bridge though of stone, gave cause for anxiety early 
 in its history, for the structure was in bad condition in 1280, 
 and five of its arches were borne down by the ice and floods 
 after the great frost of 1282. When the design of the 
 bridge, with its 20 small arches and thick piers, is considered, 
 it will be seen what an obstruction it must have caused 
 to the flow of the water, and how serious the wash must 
 have been through it. In fact, we know that there was, 
 even without any exceptional flood, a fall of five feet on the 
 surface of the water through even the widest of the arches. 
 Apart from the danger to the structure from such a rush of 
 water, the impediment to river traffic must have been very 
 great, and shooting London Bridge in a boat must have been a 
 hazardous enterprise at most times of the tide. 
 
 The piers were built on a forest of piles, the tops of which 
 were about 9 feet above the bed of the river ; and either 
 originally, or as the necessity for protection to the piles was 
 recognised, starlings or projections all round the piers were 
 added. The starlings consisted of pilework, carried 3 feet above 
 the tops of the main piles of the bridge, the intervening 
 space being filled in with stone or chalk.
 
 4 A LECTURE ON 
 
 The bridge at first was like modern bridges in being 
 unencumbered with houses, except that St. Thomas's Chapel 
 was built on its east side on the ninth pier from the north end. 
 The chap-dl was 65 feet long, 20 feet wide, and 14 feet high, and 
 it must have projected beyond the roadway on to the pier. 
 
 There was a drawbridge near the southern end, partly for 
 defence, but probably also for the passage of ships. To this 
 extent, it was prophetical of the Tower Bridge. 
 
 FIG. 2. OLD LONDON BRIDGE. 
 
 In 1426 a tower was built on the north side of the draw- 
 bridge to resist an enemy, and in 1471 a commencement was 
 made in building houses on the bridge. These were added to 
 from time to time, and amongst them was a famous structure 
 called Nonsuch House, which was a very beautiful building in 
 the architecture of its period, and was greatly admired. I 
 suppose that the houses were chiefly of wood ; for it is recorded
 
 THE TOWER BRIDGE. 5 
 
 that, in 1632, forty-two houses were burnt, which were subse- 
 quently rebuilt ; and, again, in the fire of London in 1666, almost 
 all the houses were burnt, great lamentations being made over 
 their destruction. One would have thought that the bridge wa,s 
 rather improved by the catastrophe : but Londoners did not 
 think so in those days, for it appears to have been an important 
 business street, and the sites were let out to tenants at large 
 rents. In ten years' time the houses were all rebuilt, and the 
 bridge appeared as in the view (Fig. 2) which dates from 1725. 
 
 At that time the bridge was described as 9 1 5 feet and 1 inch 
 long. Observe the nicety of one inch in such a measurement. 
 Its height above the water was 43 feet 7 inches. The whole width 
 was 73 feet, of which only 20 feet was devoted to the roadway, 
 and 53 feet to the buildings on both sides of it. The approaches 
 to the bridge must have been very steep and inconvenient. 
 
 Such was old London Bridge, and so it existed till 1758. 
 It might, I think, be described as inconvenient for road traffic, 
 dangerous for river traffic, and more like an indifferent weir 
 than a bridge over a navigable river. Indeed, its functions 
 as a weir were utilised in 1582 ; for water wheels were erected 
 in several of the arches at the north end, by which water was 
 pumped for the supply of London. 
 
 Whatever we may think now of the ancient bridge, 
 people in the 18th century were proud enough of it, and 
 occasionally burst into poetry about it. Here is a translation, 
 made in 1725, of a Latin ode of the same date in its honour : 
 
 " When Neptune from his billows London spyed, 
 Brought proudly thither by a high Spring-tide,
 
 (5 A LECTURE ON 
 
 As through a floating wood he steered along, 
 And dancing castles clustered in a throng ; 
 When he beheld a mighty bridge give law 
 Unto his surges and their fury awe ; 
 When such a shelf of cataracts did roar, 
 As if the Thames with Nile had changed her shore ; 
 When he such massy walls, such towers, did eye, 
 Such posts, such irons, upon his back to lye ; 
 When such vast arches he observed, that might 
 Nineteen Rialtos make for depth and height : 
 When the Cerulean God these things surveyed, 
 He shook his trident, and astonished said 
 Let the whole earth now all the wonders count, 
 This bridge of wonders is the paramount ! " 
 
 There is a little poetical license in more ways than one in 
 the ode ; for the Rial to has a span of 90 feet as compared with 
 the narrow openings of old London Bridge, varying from 10 to 
 30 feet in width and obstructed by the starlings round the 
 piers. You will also see that the local poet was even proud of 
 the cataracts, which endangered the lives of travellers in boats 
 when they shot the bridge with the current, and made it impos- 
 sible for any one to pass the bridge against the stream. 
 
 The houses on London Bridge or sufficient of them to 
 aiford a wide roadway and two good 'footpaths were ordered 
 to be finally pulled down in 1746. 
 
 Various designs were made from time to time for improving 
 London Bridge, and especially in respect of the waterway. 
 The views (Fig. 3) show two proposals, the upper one by 
 Labeleye, the other by Sir Christopher Wren. Neither design 
 was executed ; but that of Wren is a good example of
 
 THE TOWER BRIDGE. 
 
 the grasp by that distinguished architect of the problem to be 
 dealt with, and would, if it had been carried out, have been an 
 immense improvement of the navigation. 
 
 In 1758-9 an arch 70 feet wide was made (by removing the 
 centre pier of the bridge) for the accommodation of the river 
 traffic : but before long it was felt that the old bridge had 
 outlived its day, and it was replaced by the present beautiful 
 
 FIG 3. LABELEYE'S & WREN'S DESIGNS FOR IMPROVING OLD LONDON BRIDGE. 
 
 bridge, by Rennie, which was begun in 1824 and opened in 
 1831, at a cost, including the approaches, of about 1,500,000. 
 The gradients leading to Rennie's bridge from the south are 
 unfortunately steep, being 1 in 27 from the Borough and 1 in 
 21 from Tooley Street, and are very distressing to the horses 
 of heavily laden wagons and omnibuses. 
 
 It is remarkable how long London existed and flourished 
 with only one bridge across the Thames ; for it was not till 1729 
 that any other bridge was built. This was Putney Bridge,
 
 A LECTURE ON 
 
 already alluded to, which could, indeed, from its distance from 
 the town, scarcely be called a bridge to serve the needs of 
 London. Such, however, was the jealousy of the Corporation 
 of London that they espied in the project of building a bridge 
 at Putney an attack on the interests of London, petitioned 
 Parliament urgently against it, and prophesied that, if it were 
 authorised, the trade of London would wane and decay. 
 
 Putney Bridge cost the modest sum of 23,750, and lasted 
 till 1885, when the handsome stone bridge now existing was 
 built out of the rates, costing, with its approaches, about 
 600,000. For some years before the bridge was pulled down 
 it had a central opening, which did not exist in the original 
 structure, but was made by removing some of the old piers and 
 spanning the opening by iron girders, supported on iron cylinders. 
 
 ;. 4. OLD WESTMINSTER BRIDGE. 
 
 Old Westminster Bridge (Fig. 4) followed soon after Putney
 
 THE TOWER BRIDGE. 9 
 
 Bridge in order of date, an Act of Parliament having been 
 granted for it in 1735, and the bridge having been opened in 
 1750. It was 44 feet wide and 1,223 feet long. The centre arch 
 was 76 feet wide, and the whole structure was greatly admired. 
 The cost of it appears to have been about 390,000, which 
 sum perhaps includes the cost of the approaches. The engineer 
 was Charles Labeleye. It fell into decay from failure of the 
 foundations, which rested on timber caissons, and was replaced 
 by the present bridge about 1861. The view is taken from an 
 old print, and gives some idea of the old bridge in its palmy 
 days, before settlements and decay had set in. 
 
 Old Blackfriars Bridge (Fig. 5) was authorised in 1750, and 
 opened in 1769. It was not unlike Westminster Bridge and was 
 
 FIG. 5. OLD BLACKFRIARS BRIDGE. 
 
 built by Robert Mylne. As in the case of Westminster Bridge, 
 its foundation failed, and from the same causes. It was replaced
 
 10 A LECTURE ON 
 
 in 1869 by the present fine bridge, constructed of iron and 
 stone, from the designs of Joseph Cubitt. 
 
 It is usual to hear, in these days of iron and steel 
 construction, that the old stone bridges had an element of 
 permanence in them greater than can be hoped for in the case of 
 those constructed of iron or steel. But it is a curious com- 
 mentary on this view that within our memory Westminster 
 and Blackfriars bridges had to be pulled down within 100 
 years of their construction, that the piers of Waterloo Bridge 
 have required to be strengthened, and that some of the founda- 
 tions of new London Bridge have given rise to anxiety. 
 
 The main reason of these failures or partial failures is, no 
 doubt, to be found in the increased scour of the river, due to 
 the removal of old London Bridge, which, as has been said, 
 acted very much as a weir, and prevented the free flow of the 
 tide. But it is doubtful whether this was the only cause. 
 Apart from the question of scour, there can be no doubt 
 that stone bridges bring a heavy weight on the foundations, 
 which therefore require great care. They also involve an 
 arched form of construction. The Eastern proverb says truly 
 that the arch never sleeps, and thus defective foundations in 
 an arched bridge involve serious results. 
 
 Another bridge of the 18th century was old Battersea 
 Bridge, which was similar to old Putney Bridge. 
 
 Vauxhall Bridge was opened in 1816, at a cost of 300,000. 
 It is a poor example of bridge building, and is unworthy of the 
 age which produced Southwark Bridge. It is already found 
 inadequate, and is to be replaced by a better structure.
 
 THE TOWER BRIDGE. 
 
 1 1 
 
 Waterloo Bridge was designed by Rennie, and was opened 
 in 1817 at a cost of 800,000. It is a very fine work, but 
 is narrower than foresight should have predicted. 
 
 Southwark Bridge (Fig. 6), designed by the same engineer 
 as New London and Waterloo Bridges, was, at the time of 
 its erection, and still remains, an excellent example of iron 
 and stone construction. It was opened in 1819 at a cost of 
 
 FIG. 6. SOUTHWARK BRIDGE 
 
 800,000, but it also is narrow and the approaches are unduly 
 steep. In the view of Southwark Bridge old London Bridge 
 appears with the central arch as widened in 1759. 
 
 Proposals for Crossing the Thames beloiv London Bridge. 
 
 We see, from the above imperfect history of bridge building 
 in London during this period, that, though London Bridge alone
 
 12 A LECTURE ON 
 
 served our forefathers for upwards of seven centuries, no less 
 than eight bridges were built in a single century, from 1730 to 
 1830. To this number five more bridges, exclusive of railway 
 bridges, were added in the next half century. 
 
 All this activity must have resulted from a great develop- 
 ment of South London, and no doubt aided immensely in that 
 development. But London Bridge still remained the bridge 
 lowest down the river, and but little was heard of any other 
 means of crossing the river below this spot till 1824, when Sir 
 Marc Isambard Brunei conceived the project of the Thames 
 Tunnel between Wapping and Rotherhithe. 
 
 The difficulties of that work are known to everybody. 
 There were frequent irruptions of water into the works, and it 
 was not till 1843 that the Tunnel was opened for foot traffic 
 only, the original idea of accommodating vehicular traffic having 
 been abandoned, owing to the expense which had already been 
 incurred, and which had amounted to about 468,000. The 
 Thames Tunnel was purchased about twenty-five years ago by 
 the East London Railway Company, whose trains now run 
 through it. 
 
 South London, probably, did not begin to extend much 
 below London Bridge till after Lambeth and Southwark had 
 first been developed. I came upon an old print lately (repro- 
 duced in Fig. 7) which indicates what Bermondsey was like only 
 90 years ago. It shows the ruins of the old and famous Abbey 
 of Bermondsey, which stood near the present Tooley Street, and 
 you will see that fields and hedges at that time extended in all 
 directions where now an enormous population lives and labours.
 
 THE TOWER BRIDGE. 13 
 
 This is merely an instance of what is true of all South 
 London for miles down the river. 
 
 It has been stated, I believe correctly, that 39 per cent, of 
 the population of London now live east of London Bridge, and, 
 indeed, a town as large as Manchester and Birmingham put 
 together has rapidly grown up south of the Thames below 
 London Bridge, as is evidenced by any map of London of the 
 present day, which compares strikingly with the print of the 
 
 7. BERMOXDSEY ABDEY. 
 
 ruins of Bermondsey Abbey. The question of further com- 
 munication thus became more and more the subject of discussion, 
 and various attempts (apart from the Thames Tunnel already 
 referred to) were made to deal with the subject, commencing 
 with the Tower Subway. 
 
 The Tower Subway, which consists of an iron tube about
 
 14 A LECTURE ON 
 
 7 feet in diameter, extending from Great Tower Hill (on the west 
 side of the Tower of London) to near Pickle Herring Stairs 
 on the Surrey side of the river, was constructed by a joint- 
 stock company, and was opened in 1871, Mr. Peter Barlow 
 being the engineer. It was originally intended to work the 
 traffic through the subway by means of a car drawn by 
 ropes, but, this plan having been found inconvenient, the 
 subway has been since used merely as a footway. In spite of 
 its small size and the inconvenience of its being approached by 
 long nights of stairs, nearly a million foot passengers have 
 passed through it per annum, at a charge of ^d. each. 
 
 FIG. 8. METROPOLITAN BOARD OF WORKS PROPOSED TOWEK BRIDGE. 
 
 In 1879 the Metropolitan Board of Works applied to 
 Parliament for powers to construct a high level, or rather medium 
 level bridge, on the site of the present Tower Bridge. This 
 bridge, designed by the late Sir Joseph Bazalgette, was 
 proposed to consist of a single arch of 850 feet span, supporting 
 a horizontal roadway at a height of 65 feet above high water, 
 and is shown in Fig. 8. It was intended to be approached on 
 the north side by a straight raised approach, rising from 
 opposite the Mint, and on the south side by a long spiral 
 approach, each with a gradient of 1 in 40.
 
 THE TOWER BRIDGE. 15 
 
 The estimated cost of the bridge was 600,000 for works, 
 800,000 for property, total 1,400,000, and this expenditure 
 was to have been met out of the rates. 
 
 The proposed bridge was strongly opposed by shipowners 
 and wharfingers as being too low, and the long gradients (no 
 less than 5,700 feet in length of 1 in 40) being also thought very 
 objectionable, the scheme was rejected after a long enquiry. 
 
 In the Session of 1883 a proposal was made by a private 
 company for a large subway for vehicular traffic, from Great Tower 
 Hill to the Surrey side of the river. Access to this subway would 
 have been afforded exclusively by large and numerous hydraulic 
 lifts. The Bill was opposed by the Metropolitan Board of 
 Works, and was rejected. The subway would not have been 
 toll free. 
 
 In 1884 the Metropolitan Board of Works promoted their 
 Thames Crossings Bill, by which they sought to construct a 
 subway for vehicular and foot traffic under the Thames at 
 Nightingale Lane, about a mile east of the Tower. This subway 
 would have been approached by gradients 5,800 feet long of 1 in 
 40, or somewhat steeper. In the same Session an independent 
 company promoted a " Duplex " bridge at the Tower, on the 
 site of the present Tower Bridge. This bridge, as its name 
 implies, was a double one at the central portion, and its action 
 resembled that of a lock. The down river bridge being opened 
 would allow a vessel to pass up into the space between the two 
 bridges, and when this was done the down river bridge would be 
 closed and the up river bridge opened to allow the vessel to 
 proceed. Of course for vessels descending the river the operation
 
 16 A LECTURE ON 
 
 would be reversed. The " Duplex" bridge would have been a 
 great obstruction in the river, and it would have been difficult 
 to manage vessels passing through it with a tide running as 
 it does in the Thames. 
 
 The two Bills were referred to a hybrid committee of the 
 House of Commons, who reported that neither Bill ought to be 
 proceeded with, and that a low level opening bridge at the east 
 side of the Tower was the best way of meeting the various 
 opposing views, and they invited the Corporation of London to 
 undertake the work. 
 
 Prior to 1884, there had been several proposals for low 
 level bridges at or near the site of the present Tower Bridge 
 one for example by Colonel Hay wood for a fixed bridge without 
 an opening span, others by Sir Douglas Galton and Sir John 
 Hawkshaw for an opening bridge of the ordinary type, with 
 horizontal girders revolving on a central pier. There were also 
 proposals by Sir G. Bruce for a bridge which would roll 
 transversely across the river on isolated piers, and various 
 modifications of Sir Joseph Bazalgette's proposal. Early among 
 these various suggestions was a proposal made by Sir Horace 
 Jones (the City Architect) for a bascule bridge. 
 
 I may mention, in passing, that the French word " bascule " 
 means a see-saw, and, as applied to a bridge, means a balanced 
 bridge, which can move up and down. The view (Fig. 9) shows 
 one of the old bascule bridges across a Dutch canal. It will 
 be seen that there are two beams balanced on two upright 
 posts, the inner ends of the beams being attached by chains 
 to a hinged platform across the canal, and the outer ends having
 
 THE TOWER BRIDGE. 17 
 
 counter-balance weights on them. As the outer or landward 
 ends of the beams are lowered, the inner ends are raised and 
 pull up the hinged platform and thus open the bridge for the 
 passage of craft. Numerous examples of similar bridges exist 
 in this and other countries. 
 
 The Bridge House Estates Committee of the Corporation 
 of London, who, as representing that body, had given for many 
 
 Fie. 9. BASCULE BRIDGE ACROSS A DCTCH CANAL. 
 
 years much attention to the subject, appointed in 1884 
 a deputation to visit the Continent, Newcastle-upon-Tyne, 
 and other places where there were opening bridges of various 
 descriptions, and finally they came to the conclusion to recommend 
 the Corporation to accept the invitation of the hybrid committee 
 of 1884 and promote a Bill for the erection at the Tower site 
 of a " bascule " bridge as the best means of meeting the case.
 
 18 
 
 A LECTURE 
 
 After the original sketches made by Sir Horace Jones, 
 ^hich are reproduced in the two views (Figs. 10 and 11), 
 
 FIG. 10. SIR H. JONES'S DESIGN* OF A B.\scn,E BKIDGK (.shut against i- 
 
 FIG. 11. SIR H. JONES'S DESIGN OF A BASCULE BRIDGE (open for ships.) 
 
 it was seen that any arched form of construction across 
 the central opening would be very objectionable; as the 
 masts of ships would be in danger of striking the arch 
 unless they were kept exactly in the centre of the span.
 
 THE TOWER BRIDGE. 19 
 
 Accordingly, various other sketches were made, and this was 
 the condition of affairs when in 1884 I became connected 
 with the undertaking as engineer, Sir Horace Jones being 
 at the same time appointed architect to the work, and we 
 decided that any girders over the central span, when open 
 for the passage of ships, must be horizontal and not arched. 
 The result of these considerations was an amended sketch 
 
 FIG. 12. DESIGN SUBMITTED TO PARLIAMENT. 
 
 shown in Fig. 12. In 1885 the Corporation, in accordance 
 with these ideas, promoted the Act of Parliament, of which the 
 present structure, though greatly altered from the original 
 sketch, is the result. 
 
 The problem to be solved is one of no small difficulty, for it 
 is necessary to reconcile the requirements of the land traffic with 
 the very important interests of the trade of the Upper Pool. 
 This part of the river is always crowded with craft of various 
 kinds, and this fact made the "bascule" system unusually 
 desirable. Any opening bridge revolving horizontally would 
 have occupied so large an area of the river as to be 
 undesirable from many important points of view, whereas 
 
 a bridge revolving in a vertical plane, not only occupies the 
 
 c
 
 20 A LECTURE ON 
 
 minimum of space in the river, but also at an early stage of the 
 process of opening affords a clear passage for ships in the central 
 part of the waterway, increasing in width rapidly as the operation 
 of opening is continued. 
 
 The mode in which the traffic of the Pool is conducted pre- 
 scribed the general arrangement of the spans of the bridge. 
 Sea-going vessels of all kinds are moored head and stern in two 
 parallel lines in the Upper Pool, on each side of the centre line 
 of the river, leaving a central channel from 200 to 250 feet wide 
 free for the passage of vessels up and down the river, and this 
 space is frequently contracted, by barges and small craft lying 
 alongside the larger vessels, to a width of from 160 to 180 feet. 
 The spaces in the river occupied by the large vessels on 
 each side of the free central channel are called tiers, and as 
 vessels lie in the tiers two or sometimes three abreast, with 
 barges alongside them, it will be seen that if the piers of a 
 bridge were made alignable with the tiers there would be no 
 obstruction to navigation and little to the flow of water by two 
 piers of a width not greater than that of the tiers. On each 
 landward side of the tiers channels are preserved for the passage 
 of vessels to and from the wharves, and it was of course necessary 
 that these side channels should not be obstructed by any pier of 
 the bridge. Thus the mode, in which the river traffic has for 
 many years adjusted itself, made it evident that a bridge with a 
 clear central opening of from 160 to 200 feet, and two side 
 openings of about 280 or 300 feet, would meet all requirements, 
 and that there could be no objection to piers wide enough to 
 accommodate a counter-balance, seeing that the width of two
 
 THE TOWER BRIDGE. 21 
 
 vessels lying in the tiers would be more than the width necessary 
 for such an extension of the moving girders into the piers, as 
 would provide for a sufficient counterpoise. 
 
 The proposals of the Corporation, however, encountered 
 a strong opposition in Parliament from the wharfingers, who 
 carried on business with sea-going vessels above the site of the 
 bridge, and the Bill was also opposed by the Board of the 
 Thames Conservancy. The Bill was referred to strong Com- 
 mittees of both Houses of Parliament, and eventually was 
 passed very much in the condition in which it was brought in, 
 but with several stringent clauses for the protection of the 
 interests of the river traffic. 
 
 With these few words on the principles that governed the 
 main features of the Tower Bridge, we will proceed to consider 
 the details of the structure generally. 
 
 General Description of the Bridge. 
 
 The Act of Parliament defined the leading dimensions of 
 the Tower Bridge to be as follows : 
 
 (1) A central opening span of 200 feet clear width, 
 with a height of 135 feet above Trinity high water when 
 open, and a height of 29 feet when closed against vessels 
 with high masts. (It may be mentioned in passing that 
 the height of the centre arch of London Bridge is 29| 
 feet above Trinity high water.) 
 
 (2) The size of the piers to be 185 feet in length 
 and 70 feet in width.
 
 22 A LECTURE ON 
 
 (3) The length of each of the two side spans to be 
 
 270 feet in the clear. 
 
 The Act also defined the utmost permissible size of the 
 temporary stagings in the river. 
 
 The Conservators of the Thames, who very properly con- 
 sidered chiefly the importance of the river traffic, procured the 
 
 The doffed //nes she**" 
 re/sresonr oufs'de ///7 o 
 above toed of fttver . 
 
 (first fty' of Works) 
 
 .. ,__ t-le*- Hf*t*r_W*j[_ 
 (Second stag* of Works) 
 
 #?/, 2. 3 . S.6.78 /J J4. /S /6. /9. Sf. 
 
 22 $ 23 *re Square Cussons 
 f/.' 9, /O. // /2, /7. IS. 2O. j Z4- JLT* 
 
 Tr/asiffuJa-r 
 
 FIG. 13. PLAN TO SHOW LIMIT OF TEMPORARY WORKS. 
 
 insertion in the Act of Parliament of a clause obliging the 
 Corporation to maintain at all times during the construction of the 
 bridge, a clear waterway of 160 feet in width, and this necessity 
 occasioned much delay in the construction of the permanent piers,
 
 THE TOWEtl BfclDGE. 23 
 
 as the opening defined was too wide to permit of both piers being 
 constructed simultaneously. The plan (Fig. 13) shows the limits 
 of the temporary works as defined by Parliament. The outer lines 
 round each pier are the limits of the necessary stagings, and it 
 will be seen that, in order to give a navigable width at all times 
 of 160 feet, there could be only one staging at a time of the 
 full width required for building the piers. 
 
 The formal ceremony of commencing the works of the 
 Tower Bridge was performed by the Prince of Wales on 21st 
 June, 1886. 
 
 The Government authorities gave every facility for the 
 execution of the works, and, to enable the north approach to the 
 bridge to be made without interfering with very important 
 wharf property, allowed a small part of the Tower Ditch to be 
 occupied by a portion of the works. If this concession had not 
 been made, the cost of the land for the undertaking would have 
 been almost prohibitory. It was stipulated in return that the 
 design of the bridge should be made to accord with the archi- 
 tecture of the Tower, and at one time it was intended that the 
 new works should be made suitable for the mounting of guns and 
 for military occupation. The latter idea was afterwards to a 
 great extent discarded. 
 
 The piers of the Tower Bridge are essentially different from 
 the piers of an ordinary bridge, inasmuch as they have to contain 
 the counterpoise and machinery of the opening span, as well as 
 to support the towers which carry the suspension chains of the 
 fixed spans and the overhead girders above the opening span. 
 They are thus very complex structures, as will be seen by the
 
 24 
 
 A LECTUBE 
 
 illustrations (Figs. 14, 15 and 16.) Theirfonn in plan (Fig. 15) 
 may be described as a square of 70 feet elongated by cutwaters 
 
 __ _. _ 
 
 LONGITUDINAL SECTION OF PIER. 
 
 FIG. 14. 
 
 QUARTER PLAN AT A. 8.
 
 THE TOWER BRIDGE. 
 
 25 
 
 at each end, bringing the total length to 185 feet 4 inches. 
 Their total depth from the roadway level to the London clay, on 
 which they rest, is 102 feet. 
 
 TRANSVKRSK SECTION Of PIER 
 
 x- 
 FHJ. 10. 
 
 We will first consider the form of the piers up to the level 
 of the roadway, which is 32 feet above Trinity high water. 
 Each contains (l) a large cavity to receive the landward end and 
 counterbalance weight of one leaf of the opening span ; (2) two 
 large chambers for the hydraulic accumulators ; (3) two chambers 
 for the machinery which actuates the opening span ; and (4) 
 two long tunnels, one for receiving the main pivot shaft on 
 which the leaf of the opening span revolves, and the other for 
 the pinion shaft by which power is transmitted to the opening 
 span from the machinery. 
 
 A diagram (Fig. 28, page 39,) will explain the method of
 
 26 A LECTURE ON 
 
 actuating the opening span. The old bascule bridges of Holland 
 (Fig. 9) had their counterbalance above the roadway level, 
 mounted on posts at the abutments, and attached to the bridge 
 by chains or ropes. The dimensions of the Tower Bridge forbade 
 such an arrangement of an overhead counterweight, and the 
 counterbalance is there applied, as shown in Fig. 28, directly to 
 a prolongation of the girders of the opening span. These girders 
 turn on the main pivot, behind which a space, or cavity, 
 has been provided, to permit of the movement up and down of 
 the landward ends of the girders and the counterweight. 
 This space, which is called the bascule chamber or opening, is 
 in the form of a quadrant, and its dimensions are 50 feet from 
 north to south, 44 feet from east to west ; it is 50 feet in height 
 next the central or opening span, diminishing to nothing next 
 the landward or fixed span of the bridge. The two machinery 
 chambers are each 35 feet by 30 feet, and 10 feet high, and the 
 two chambers for accommodating the accumulators are each 30 
 feet by 20 feet 4 inches, and are 50 feet in height, extending 
 from below the floor of the machinery chamber to within 
 26 feet of the bottom of the foundations. 
 
 Before describing the mode in which the substructure of 
 the pier was constructed, it will be best shortly to describe 
 the general arrangement of the remainder of the fixed portion 
 of the bridge. 
 
 The mode adopted for spanning the landward openings is 
 by suspension chains, which in this case are stiffened. The 
 chains are anchored in the ground at each end of the bridge, 
 and united by horizontal ties across the central opening at a
 
 THK TOWER BRIDGE. 27 
 
 high level (Fig. 30, page 49). These ties are carried by two 
 narrow bridges 10 feet in width, which are available as foot 
 bridges when the bascule span is open for the passage of vessels. 
 The foot bridges are 140 feet above Trinity high water, and, as 
 their supports stand back 1 5 feet from the face of the piers, their 
 clear span is 230 feet. Access is given to them by hydraulic 
 lifts and by commodious staircases in the towers. 
 
 Above the landings, at the tops of the stairs and on which 
 the foot passengers land from the lifts, come the roofs of the 
 towers, the tops of which are 162 feet above the roadway level, 
 or 264 feet from the bottom of the foundations. 
 
 Having now given the leading dimensions of the structure, 
 I will proceed to describe (l) the mode in which the piers were 
 constructed up to the roadway level ; (2) the details of the 
 opening span and machinery ; (3) the details of the fixed super- 
 structure, namely, the towers, the suspension chains, and the 
 overhead footways ; (4) the mode of erection of the super- 
 structure. 
 
 Tlie Mode of Constructing the Substructure of the Piers. 
 
 Iron caissons strutted with strong timbers were used in 
 excavating the bed of the river and building the foundations 
 of the piers. During these operations the external pressure of 
 the water and earth surrounding the caissons was very great, 
 as there is a depth of 32 feet of water at high tide at this part 
 of the river, and the caissons had to be carried about 21 feet into 
 the bed of the river to secure a good foundation. The caissons 
 employed were boxes of wrought iron, without either top or
 
 28 
 
 A LECTUHE ON 
 
 bottom, and with the bottom edges made sharp and strong (Fig. 
 18,) so as to easily penetrate the ground. 
 
 There are twelve caissons for each pier, as will be
 
 THE TOWER BRIDGE. 
 
 understood from Fig. 13. Those about the central parts 
 of the pier are 28 feet square in plan, and those near the 
 cutwaters are triangular in plan, the dimensions being 35 
 feet by 33 feet 8 inches. Fig. 17 shows a square caisson and a 
 triangular caisson in plan, with their timbering and other details. 
 I will describe the mode of sinking one 
 caisson, and the description will apply more 
 or less to all, though, of course, the circum- 
 stances attending the different caissons 
 required some differences of treatment. 
 
 The temporary staging for the pier 
 having been made with piles, the next 
 operation was to erect the caissons upon 
 the staging. 
 
 ROLLED STEEL CUTTING FOGE. 
 Fio. 18. 
 
 HALF CROSS SECTION OP PIER. ' HALF CROSS SECTION OF PIER, 
 
 SHOWING CAISSON BEFORl LOWERING SHOWING CAISSON WHEN SUNK 
 
 TO THE BED OF THE RIVER. 6 BEING FILLED WITH CONCRETE. 
 
 FIG. 19. 
 
 The bottom part of the caisson, having to be sunk deep into 
 the bed of the river, could not be removed on the completion of 
 the pier, and was thus named the permanent caisson. The 
 purpose of the upper part of the caisson was merely to exclude
 
 30 A LECTURE ON 
 
 the water during the process of building the pier, and it could 
 be removed when the brickwork and masonry were finished. 
 This part was thus called the temporary caisson. 
 
 The permanent caisson was 19 
 feet in height, divided horizontally 
 into two portions. It was erected 
 on timber supports, which were 
 slightly above low water mark (Fig. 
 19), where it was rivetted together 
 and firmly strutted inside with strong 
 timbers, 14 inches square. It was then 
 lifted slightly by four powerful screws 
 attached to four rods, from which was 
 slung the weight of the caisson and the 
 timbering in it. The timber supports 
 were removed, and the caisson was lowered by the screws on to 
 the bed of the river, which had previously been levelled by divers. 
 
 After the permanent caisson reached the ground various 
 lengths of temporary caisson were added to it till the top of the 
 temporary caisson came above the level of high water. The 
 junction between the permanent and temporary caissons was 
 made with india rubber, as shown in Fig 20. 
 
 Divers working inside the caisson, excavated first the 
 gravel and then the upper part of the clay forming the bed of 
 the river, and as they dug away the soil, which was hauled up 
 by a crane and taken away in barges, the caisson gradually sank, 
 until at length its bottom edge penetrated some 5 to 10 feet into 
 the solid London clay. 
 
 PETAI L OF 
 INDIA-RUBBER JOINT. 
 
 FlG. 20.
 
 THE TOWER BRIDGE. 31 
 
 London clay is a firm, water-tight stratification, and, when 
 the above-mentioned depth was reached, it was safe to pump out 
 the water, which up to this time remained in the caisson, rising 
 and falling with the tide through sluices in the sides. The 
 water having been pumped out, navvies proceeded to the bottom 
 of the caisson and dug out the clay in the dry. 
 
 Additional lengths of temporary caisson were added as the 
 caisson sank, so that at last each caisson was a box of iron, 57 
 feet high and of the dimensions above stated, in which the 
 preparation of the foundations could be commenced. A detailed 
 view of one of the completed caissons is given in Fig. 21. 
 
 I may mention in passing how important it is, in order to 
 ensure success in sinking caissons or cylinders, that they should 
 be controlled from above and be prevented from sinking unevenly. 
 It is very easy to prevent a caisson from going wrong (like many 
 animate subjects as well as inanimate) by timely control, but it 
 is a very different thing to put the matter right when a wrong 
 course has been pronouncedly taken. 
 
 London clay being peculiarly hard and uniform in texture, 
 advantage was taken of this circumstance to increase the area of 
 the foundations by digging out sideways or undercutting 
 below the edge of the caisson, as shown at the bottom of Fig. 21. 
 The caisson having been controlled from the first by the 
 suspending rods to which allusion has been made, its descent 
 any further than was desired was easily arrested by the rods, 
 when the bottom of the caisson was 20 feet below the bed of 
 the river. The clay was then excavated 7 feet deeper than the 
 bottom of the caisson, and outwards beyond the cutting edge
 
 32 
 
 A LECTURE ON 
 
 28 FEET CAISSONS . 
 HALF INSIDE ELEVATION. HALF OUTSIDE ELEVATION. 
 
 1 1 
 
 FIG. 21. COMPLETE CAISSON WITH TIMBERING AND SUSPENSION RODS.
 
 THE TOWER BRIDGE. 
 
 33 
 
 for a distance of 5 feet on three of the four sides of the caisson. 
 
 In this way not only was the area of the foundations of the pier 
 
 enlarged, but as the sideways excavations adjoined similar 
 excavations from the next caissons 
 (Fig. 22), the whole foundation was 
 made continuous. The whole of the 
 permanent caissons with the spaces 
 between them were then completely 
 filled with concrete, upon which the 
 
 BETWEEN W TWO ADjo", C N U G TT cA ( lssoNi. brickwork And masonry were com- 
 
 FIG. 22. , . . , 
 
 menced in the temporary caisson, and 
 
 carried up to 4 feet above Trinity high water, as shown 
 in Fig. 23. 
 
 Fiu. 23. CROSS SECTION OF PIER, SHOWING OUTSIDE WALL COMPLETED. 
 
 It was not desirable to build isolated portions of the brick- 
 work and masonry, even if they were joined together afterwards. 
 Accordingly the temporary caissons were so designed as to admit 
 of their sides being removed (Fig. 15) and of the whole area 
 enclosed by their front and back plates being thrown together to
 
 34 
 
 A LECTURE OX 
 
 permit of continuous building. For this purpose the corners of 
 the caissons were united by timber piles, which were driven 
 in a groove on each caisson (Fig. 24), and when these 
 had been driven and made water-tight (as to which no difficulty 
 
 Xolca Cor- 1 " 
 ZK-ct afxirV 
 ' uu/ IftujtJiJt cf Gtlascfn'. 
 
 LI.3-X 3fi 
 
 DETAIL OF VERTICAL dOlNTS 
 AND PILE GROOVES 
 
 FIG. 24. ENLARGED PLAN OF THE ANGLE OF A CAISSON. 
 
 occurred), the sides of the temporary caissons were removed. 
 In this way the outside portions of the piers were built, and 
 eventually formed a continuous ring of a strong masonry wall,
 
 THE TOWER BRIDGE. 
 
 35 
 
 water-tight and able to resist the external pressure of the 
 water. (Fig. 25). The foundations of the central portion of 
 the pier, enclosed by the outside walls, were then excavated 
 arid the pier completed. 
 
 N CAISSONS BEFORE DRIVING THE P.LES,^ 
 BETWHN THC CAISSONS / 
 
 FIG. 25. HALF PLAN OK PIER AT DIFFERENT PERIODS OF CONSTRUCTION. 
 
 The abutments of the bridge were built within ordinary 
 coffer dams, and, though formidable in size and depth, presented 
 no new features of construction such as have been explained 
 with regard to the piers. 
 
 When the piers and abutments had reached a height of 
 4 feet above high water, the first contract was finished, and new 
 contracts for the superstructure were let.
 
 36 A LECTURE ON 
 
 The work of the foundations was troublesome and tedious, 
 owing to the isolation of the piers, and still more to the 
 great amount of river traffic, rendering the berthing of barges 
 difficult. The substructure thus occupied a considerably longer 
 time than was anticipated. 
 
 FIG. 26. VIEW OF THE FOUNDATIONS IN PROGRESS. 
 
 The view Fig. 2G gives an idea of the appearance of the 
 works during the construction of the piers. 
 
 The Opening Span. 
 
 The stipulated dimensions of the opening span have been 
 already given, as providing, when the bridge is open for ships, a 
 clear waterway of 200 feet in width, with a clear height 
 throughout the 200 feet of 135 feet (which has been increased in
 
 THE TOWER BRIDGE. 37 
 
 construction to 140 feet) from Trinity high water mark. I may 
 mention in passing that I think these dimensions constitute the 
 largest opening span in the world. The next largest opening 
 is, I believe, at the Newcastle bridge, where there are two 
 separate spans of 100 feet each. 
 
 The opening span of the Tower Bridge consists, as already 
 explained, of two leaves, each turning on a horizontal pivot of 
 solid forged steel. This pivot, which rests on live rollers, is 
 1 foot 9 inches in diameter, and weighs 25 tons. Each leaf is 
 formed with four main longitudinal girders, 13 feet 6 inches apart 
 from centre to centre, which together provide for a clear width of 
 bridge between the parapets of 50 feet. This width will be 
 divided into 32 feet for a roadway (which is sufficient for four 
 lines of road traffic) and for two footpaths each 9 feet wide. The 
 spaces between the longitudinal girders are filled with cross 
 girders and roadway plates, on which will be laid the wood 
 pavement of the roadway and footpaths. 
 
 The total length of the moving girders resting on each pier is 
 162 feet 3 inches (Fig. 27). They turn on the main pivot, the 
 position of which is 12 feet 9 inches back from the face of the 
 pier. Thus from the centre of the main pivot riverwards to the 
 end of the girder is 112 feet 9 inches, and to the end of the 
 girders landwards is 49 feet 6 inches. The centre of gravity of 
 the part over the river is 48 feet from the centre of the main 
 pivot, and the estimated weight of this portion of the semi -span 
 is 424 tons. A counterbalance box is attached to the landward 
 end of the girders, and is intended to be filled with 422 tons of 
 iron and lead. The centre of gravity of this portion of the
 
 gg A LECTURE ON 
 
 girders and the counterbalance weights will be 32 feet 9 inches 
 from the centre of the main pivot, and the total weight land- 
 ward of the main pivot will be 621 tons. Thus the total 
 weight of each leaf of the opening span, resting on the main 
 pivot when the bridge is being moved, 'or on the blocks 
 when the movement is completed, will be the sum of the two 
 weights given above, or 1,045 tons. The pier has, therefore, 
 to carry on its riverward face a heavy load, which is distributed 
 on the masonry by a longitudinal and several cross girders.* 
 >. 
 
 i - 
 r---fe-49 6 *-- - ur H2-9 
 
 LUX* 
 
 FIG. 27. DIAGRAM OF WEIGHTS OF BASCULE. 
 
 The two outside girders carry at their counterbalanced ends 
 a quadrant (Fig. 28), on which are fixed teeth, and these teeth 
 engage with similar teeth on revolving pinions, which are 
 actuated by the hydraulic machinery. It will be seen that, when 
 the pinions are turned round, the whole of each leaf of the 
 
 * The various weights above given are matters of estimate. They may be slightly 
 modified in execution.
 
 THE TOWER BRIDGE. 
 
 39 
 
 opening span is made to rise or fall at will. It may be 
 mentioned that there are two distinct pinions to each quadrant, 
 making four pinions to each leaf, and that any one of the four 
 pinions is strong enough to actuate and control the whole leaf. 
 
 |_ 100.0 
 
 FIG. 28. DIAGRAM OF BASCULE TO SHOW QUADRANT OR SECTOR. 
 
 It will be observed that the landward ends of the 
 main girders are bent downwards, and extend backwards into 
 the bascule chamber in the pier, so as to carry the counterbalance
 
 40 A LECTURE ON 
 
 box ; but it is, of course, necessary that the road and footpaths 
 should extend continuously up to the opening span. This is 
 effected by eight fixed longitudinal roadway girders, which carry 
 the roadway over the bascule chamber, and between which the 
 longitudinal moving girders can rise and fall. Where the 
 moving roadway over the central span adjoins the fixed roadway 
 over the bascule chamber, there must be, of course, a cross 
 slit or joint. This space is covered by a hinged flap, which 
 rises and falls with the movement of the moving girders. 
 
 Such are the main features of the opening span, and 
 before leaving the subject, I will give a short account of the 
 actuating machinery in its main features. It will be, of course, 
 impossible to describe it within the time now available in any 
 minute detail. 
 
 Some of my hearers may not be acquainted with the 
 leading principles of hydraulic machinery in general, and so I 
 may be excused if to others my remarks appear somewhat 
 elementary. The principle of the application of water to 
 hydraulic engines is shortly as follows. First of all, a pump is 
 required, which is powerful enough to pump water under great 
 pressure in the present instance under a pressure of about 
 850lbs. on every square inch. This pressure is nothing unusual, 
 but its magnitude will be appreciated when we remember that in 
 the boiler of a locomotive engine the steam pressure is usually 
 not more than about one-fifth of the above amount. 
 
 The water pressure, being so high per square inch, enables 
 the pistons and pipes of hydraulic machinery to be comparatively 
 small, and, as the water can be conveyed anywhere in pipes of
 
 THE TOWER BRIDGE. 41 
 
 suitable strength, the power produced by the pump can be 
 applied at any desired place. In the present case the pumps 
 are on the Surrey side of the bridge, and are actuated by two 
 steam pumping engines of 360 horse power. The high-pressure 
 water is brought thence by pipes along the Surrey fixed span, 
 up the Surrey tower, across the high level foot bridge, and down 
 the Middlesex tower. Return pipes convey the water when it 
 has exerted its pressure at the hydraulic engines, which are 
 fixed below the footway on each pier back again to the pumps 
 at the steam engines, where it is again subjected to pressure 
 and made ready for work again. 
 
 There is, however, one important feature of hydraulic 
 machinery to be explained, and that is the accumulator. The 
 object of the accumulator is, as its name suggests, to accumu- 
 late power, which is effected as follows. We have seen 
 that the origin of the power is the steam engine actuating 
 a pump or pumps, and, if the machinery were always working 
 and always requiring the same amount of power, an accumulator 
 would be of comparatively little use ; for the pumps could pump 
 the water direct to the hydraulic engines, to be used there in a 
 continuous effort. But such is not the requirement. The 
 hydraulic machinery at the Tower Bridge, and in almost every 
 other application of hydraulic power, is not called upon for a 
 continuous effort, but, as it were, for spasmodic efforts lasting 
 over a certain number of minutes, and the accumulators are 
 employed to store up the power provided by the pump, in order to 
 give it out at a greater speed than the pump, though working 
 continuously, would provide.
 
 42 
 
 A LECTURE ON 
 
 In accordance with these principles, the accumulator (Fig. 
 29) is a large cylinder, in which fits a long plunger, on the top 
 of which are placed weights, which bring a pressure of 850lbs. 
 on every square inch of the area of the cylinder. The steam 
 pumps pump water into the accumulator, with that pressure, and 
 
 STEAM EJVG/fJS 
 
 Fio. 29. DIAGRAM OF APPLICATION OF ^HYDRAULIC POWER. 
 
 as it is a principle of hydraulics that any pressure applied to 
 water in a closed vessel is communicated to the whole of the 
 water in that vessel, the pumps, though much smaller than the 
 large plunger of the accumulator, raise it with its superincum- 
 bent weight, but proportionately slowly. 
 
 The pipes to work the hydraulic engines are in communi- 
 cation with the cylinder of the accumulator, and this, being of 
 great internal capacity, can supply high pressure water with 
 great rapidity to work the hydraulic engines for what I have 
 called their spasmodic efforts. In the meantime, the pumps are 
 working away to re-supply the accumulator. 
 
 At the Tower Bridge there are six accumulators, viz., two 
 near the pumps on the Surrey side of the river and two on each
 
 THE TOWER BRIDGE. 43 
 
 pier. Their capacity is ample for the most liberal demands of 
 the hydraulic engines. 
 
 It will not be possible to describe the hydraulic engines 
 themselves in any detail. It will be sufficient to say that there 
 are two sets of engines on each pier, and that their leading 
 principle is that of reciprocating cylinder engines. Rams in 
 cylinders are worked to and fro by the high pressure water, and 
 by cranks communicate rotatory motion, through a series of geared 
 wheels, to the toothed pinions, to which allusion has already been 
 made, and which actuate the quadrants of the openmg span. 
 Each engine has three rams with a stroke of tt inches ; 
 those on the smaller engines are 7^ inches in diameter, and 
 those on the larger engines 8|- inches in diameter. 
 
 When the Tower Bridge was being discussed in Parliament, 
 the disaster to the Tay Bridge was fresh in the minds of many, 
 and some alarm was expressed lest the machinery might not be 
 strong enough to control the opening span in heavy winds. 
 The Board of Trade had reported with regard to the Tay 
 Bridge, that provisions should be made in all future structures 
 for a wind pressure of 56lbs. per square foot, and, though this is, 
 I think, an excessive estimate, even for the wind in such an 
 exposed place as the Firth of Tay, and is much more excessive 
 in the comparatively protected position of the Tower Bridge, it 
 was considered right not only to provide for the extreme 
 pressure of 56lbs. per square foot, but also to provide the 
 machinery of this strength in duplicate on each pier. Thus we 
 have machinery equal to twice the requirements of the Board of 
 Trade, An ordinarily strong wind, however, will riot give a
 
 44 A LECTURE ON 
 
 pressure exceeding about 17lbs. per square foot, and therefore 
 the hydraulic engines are arranged in pairs, one engine of each 
 pair exerting a power equal to a 17lbs. wind, and the other 
 equal to a 39lbs. wind, the two together being equal to the 
 extravagant pressure of a wind of 56lbs. On each pier the 
 duplicate pair of engines follow up the work of the first pair 
 and provide against breakdowns. 
 
 I should mention that when the two leaves of the opening 
 span are brought together, there will be long wedge-shaped 
 bolts, actuated by hydraulic machinery, fixed on one leaf and 
 shooting into the other leaf, to complete the union of the two. 
 
 All the machinery of the opening span will be worked from 
 cabins on the piers, in which there will be levers like those in a 
 railway signal box, so interlocked one with the other that all 
 the proper movements must follow in the arranged order. 
 
 The time required for the actual movement of the opening 
 span from a position of rest horizontally to a position of rest 
 vertically is estimated at about 1% minutes. To this must be 
 added the time necessary for stopping the road traffic and clearing 
 the bridge, and withdrawing the bolts. This may take, perhaps, 
 some 1 J minutes more, and we then have to add the time for 
 the passage of a ship and the lowering of the bridge. The time 
 of Ij- minutes for opening or shutting the bridge gives a 
 mean circumferential speed at the extremity of each leaf of 2 feet 
 per second, which is a moderate speed for an opening bridge. 
 
 Signals will be provided by semaphores by day and signal 
 lamps by night, to show ships whether the bridge is open or 
 shut. By night when the bridge is open for ships, four green
 
 THE TOWER BRIDGE. 45 
 
 lights will be shown in both directions, and when it is shut 
 against ships four red lights will be similarly exhibited, and 
 then- lights will be interlocked with the machinery, so that 
 wrong signals cannot be shown. By day similar intimation will 
 be afforded by semaphore arms on the same posts as those which 
 carry the signal lamps. During foggy weather, a gong will be 
 used in specified ways. 
 
 One other part of the machinery remains to be mentioned. 
 This is that of the passenger lifts between the roadway level and 
 the high level foot bridge. 
 
 There are two lifts in each tower, consisting of a cage, 13 
 feet by 6 feet, and 9 feet high, raised and lowered by an ordinary 
 hydraulic ram with chain gearing, and capable of lifting 20 to 25 
 passengers in about lj minutes, including the delays of opening 
 and shutting the doors. As the lift will have to descend carrying 
 a cargo of passengers before it can take a second load of ascend- 
 ing passengers, we may assume three minutes from one start to 
 the next ; or, as there are two lifts on each tower, 1^ minutes. 
 
 In addition to the lifts, there are ample flights of stairs 
 in the towers. 
 
 The Fixed Superstructure. 
 
 The fixed parts of the superstructure of the Tower Bridge 
 consist, as has been said, of two shore spans, each of 270 feet, 
 and of a central high level span of 230 feet. The fixed bridge 
 is of the suspension form of construction, and the chains are 
 carried on lofty towers on each pier and on lower towers on 
 each abutment. 
 
 I will first describe the towers. When an opening bridge
 
 46 A LECTURE ON 
 
 was first proposed there was some outcry by aesthetical 
 people on the score of its ruining the picturesqueness of the 
 Tower of London by hideous girder erections, and it seemed to 
 be the universal wish that this bridge should be in harmony 
 architecturally with the Tower. 
 
 You will have seen the various architectural ideas evolved 
 out of these considerations, and observed that it was originally 
 intended that the towers should be of brickwork in a feudal 
 style of architecture, and the bridge somewhat like the draw- 
 bridge of a Crusader's castle. Subsequently, Sir Horace Jones 
 suggested a combination of brick and stone, and towers of a 
 form similar to that of the view Fig. 12 on page 19. 
 
 The ideas were in this condition when I was appointed 
 engineer to the scheme, with Sir Horace Jones as architect, and 
 the Corporation went to Parliament for powers to make the 
 bridge. Sir Horace Jones unfortunately died in 1887, when 
 the foundations had not made much progress, and up to 
 that time none of the architectural designs had proceeded further 
 than such sketches and studies as were barely sufficient to 
 enable an approximate estimate to be made of the cost. Since 
 the death of my coadjutor I have preserved the general 
 architectural features of the Parliamentary sketch designs, 
 but it will be seen that the structure as erected differs 
 largely therefrom, both in treatment and material. 
 
 The width, and consequently the weight, of the bridge was 
 increased by the requirements of Parliament, and the span of 
 the central opening was enlarged from 160 feet, as originally 
 intended, to 200 feet. At the same time, the provision of
 
 THE TOWER BRIDGE. 47 
 
 lifts and stairs, to accommodate foot passengers when the 
 bridge was open, was felt to be a necessity. 
 
 In this way it became apparent that it would not be 
 possible to support the weight of the bridge on towers wholly 
 of masonry, as in the first designs, unless they were made of 
 great size and unnecessary weight. It was, consequently, 
 necessary that the main supports should be of iron or steel, 
 which could, however, be surrounded by masonry, so as to 
 retain the architectural character of the whole structure. 
 
 It was clear that in any event a large part of the steelwork 
 of the towers must be enclosed in some material, for the 
 moving quadrants project upwards some 40 feet from the 
 level of the roadway, while the stairs and lifts also required 
 protection from the weather. It thus became a question of 
 surrounding the towers either with cast iron panelling or with 
 stone, and eventually a granite facing with Portland stone 
 dressings was adopted. 
 
 ^Esthetically speaking, stone seems better than cast iron, 
 which would equally hide the constructive features, and 
 practically speaking I think it also better, for I know of no mode 
 so satisfactory for preserving iron or steel from corrosion as 
 embedding it in brickwork, concrete or masonry. Careful pro- 
 vision has been made in all parts for expansion and contraction 
 of the two materials, and, though we have had great extremes 
 of heat and cold since the masonry has been built, no effects 
 resulting from any difference of temperature have been observed. 
 
 The Fig. 30, which is a half elevation of the steelwork of 
 the bridge, shows the general arrangement of the towers,
 
 48 A LECTURE ON 
 
 which have been since enclosed with masonry and brickwork, 
 and may be described as being steel skeletons clothed with 
 stone. 
 
 I am afraid some purists will say that the lamp of truth 
 has been sadly neglected in all this, and that the old architects 
 would not have sanctioned such an arrangement as a complex 
 structure of steel surrounded by stone. 
 
 One reason may be that the old architects did not know 
 much about iron or steel. Perhaps, if they had been acquainted 
 with their capabilities, they would have been as ready to 
 employ them as they were to back up stone-faced walls with 
 brick, and to hide the constructive features of their buildings as 
 Sir Christopher Wren did when he used a brick cone to support 
 the internal and external domes of St. Paul's. 
 
 However all this may be, " needs must when Parliament 
 drives," and, if the appearance of the Tower Bridge is approved, 
 I hope that we may forget that the towers have skeletons as much 
 concealed as that of the human body, of which we do not think 
 when we contemplate examples of manly or feminine beauty. 
 
 I return, however, to the details of construction. The 
 skeleton of each tower consists of four wrought steel pillars, 
 octagonal in plan, built up of rivetted plates. The pillars 
 start from wide spreading bases, and extend upwards to the 
 suspension chains, which they support. They are united by 
 horizontal girders and many diagonal bracings, to which it is not 
 necessary here to refer in detail. The chains are carried on the 
 abutments by similar but lower pillars. All these and other 
 particulars appear in Fig. 30.
 
 THE TOWER BRIDGE. 
 
 49
 
 50 A LECTURE ON 
 
 Between the pillars are spaces for the public stairs and the 
 passenger lifts, and for the quadrants of the opening span when 
 in their upward position. When all these necessary things are 
 accommodated, it will be seen that there is very little room left 
 in the towers for the first 40 feet of their height, that is to say, 
 up to the level of the archway over the road. The horizontal 
 girders in the towers above the archway carry various floors to 
 provide for landings from the public stairs and possibly for 
 rooms for the police and staff. 
 
 On the tops of the octagonal pillars rest a series of rollers, 
 which will allow the chains so to move as to accommodate 
 themselves to changes of temperature and to unequal distribu- 
 tion of the road traffic. 
 
 The arrangements of the rollers are peculiar. The amount 
 of space available for their reception on the tops of the steel 
 octagonal pillars is limited, while the weight which they have 
 to support is very large, being estimated when the bridge was 
 fully loaded at 1,000 tons. It was thus necessary that the 
 weight should be equally distributed over the whole series of 
 rollers, and that there should be no possibility of a concentration 
 of weight on any one or two rollers. This is effected by an 
 arrangement by which the weight brought on the top of the 
 system is first carried by two blocks, thus ensuring equal division 
 between them, then the weight so divided is sub-divided 
 between two plates, and the weight on each plate is again sub- 
 divided between two rollers. 
 
 The main chains, which are 60 feet 6 inches apart from 
 centre to centre, extend from the rollers on the piers to other
 
 THE TOWER BRIDGE. 51 
 
 rollers on each abutment, and support the platform of the bridge 
 by suspension rods, extending from the bottom of the chains to 
 the cross girders of the platform. These arrangements appear 
 in the view, and do not call for any further detailed description. 
 
 It may be asked why are these structures, which look like 
 girders, called chains? They are, in fact, chains, stiffened to 
 prevent deflection, and the object of the form is to distribute the 
 local loads due to passing traffic, which, in the case of an ordinary 
 suspension chain, distort the chain, continually depressing each 
 part as the load passes, and consequently distorting the 
 platform of the bridge. By making the chain, as it were, double, 
 and bracing it with iron triangulations, these local deflections of 
 the chain are avoided. 
 
 The ends of the chains on the abutments and on the towers 
 are united by large pins to the ties. The ties on the abutments 
 are carried (4S5S? the ground below the approaches, and are there 
 united to anchorage girders, which rest against very heavy 
 blocks of concrete, and are abundantly adequate to resist the pull 
 of the chains. The ties between the towers are for the purpose 
 of uniting the ends of the two chains, and by their means the 
 stress on the chains is conveyed from anchorage to anchorage. 
 
 The platform of the bridge is formed of cross girders, 
 which extend transversely from side to side, their ends being 
 immediately under the chains, to which they are suspended by 
 solid steel rods. Between the cross girders are short longitudinal 
 girders, and on these rest corrugated steel plates, which carry 
 the paving and footways. The total width between the parapets 
 on the fixed spans of the bridge and on the approaches is 60 feet,
 
 52 
 
 A LECTUBE ON 
 
 Fu:. 31. PROGRESS OF TOWER ON PIER ix RIVER.
 
 THE TOWER BRIDGE. 53 
 
 which is divided into 36 feet for the vehicular traffic and into 
 two pathways each 1 2 feet wide. I may mention in passing that 
 London Bridge is 54 feet wide between the parapets. 
 
 The total weight of steel and iron in the Tower Bridge will 
 amount to nearly 12,000 tons. 
 
 The Erection of the Superstructure. 
 
 The erection of the superstructure of the bridge has been 
 effected without any considerable difficulty. Temporary stagings 
 of pile work were erected in the river forming piers, upon which 
 wrought iron horizontal girders were erected which supported 
 timber beams and planking thus forming continuous tem- 
 porary bridges communicating from the shores to each pier. 
 Less difficulty .was experienced than was expected in 
 driving the pile work either round the permanent piers or to 
 form the supports of the temporary bridge, and but little 
 damage was ever caused to it during the time of the erection 
 of the bridge by collisions with it of river craft, which from 
 time to time occurred. Access being thus given from the 
 shores, the next thing to be done was to erect the pillars, 
 girders and bracing, forming the steel framework of the 
 abutment and river towers. All the steel work had been put 
 together at the works of Messrs. Sir W. Arrol & Co., at 
 Glasgow, and was brought thence by sea in small pieces to be 
 rivetted together at the bridge. The view (Fig 31) shows this 
 work in progress at one of the river towers. 
 
 The next work taken in hand was the erection of the high
 
 54 
 
 A LECTURE ON* 
 
 level footway bridges between the towers. These bridges when 
 finished are cantilevers for a distance from eacli tower of 55 feet, 
 and are girders for the remaining space of 120 feet between the 
 ends of the cantilevers. They were erected, however, by 
 
 FIG. 32. PROGRESS OF HIGH LEVEL_BRIDGES. 
 
 temporary expedients, as cantilevers, piece by piece from the tops 
 of the towers and without scaffolding from below, for the whole of 
 the semi-span of 1 1 5 feet till they met over the centre of the river. 
 The progress of the girders from week to week as they advanced 
 towards each other, was watched with much interest by the 
 public from London Bridge. A view (Fig. 32) shows the girders 
 a short time before they met.
 
 THE TOWER BRIDGE. 55 
 
 The chains were erected in their position by means of 
 scaffolds and trestles resting on the temporary bridge. The 
 succeeding views (Figs. 33, 34 and 35) show this work in 
 progress. Cranes on stages, travelling along the temporary 
 
 FIG. 33. PROGRESS OF ERECTION OF MAIN CHAINS. SHORT SEGMENT.] 
 
 wooden bridge, served to place the various parts of the chain on 
 the trestles, where they were rivetted together in their 
 permanent positions. In the meantime the land ties from the 
 anchorages had been brought up to the tops of the abutment 
 towers, and the long horizontal ties, which are carried by the high 
 level bridges, had been erected and rivetted in their places. The 
 holes for the connecting pins at the ends of the ties and at the
 
 56 
 
 A LECTURE ON 
 
 junctions of the short and long chains were then bored finally 
 and the pins inserted, thus forming a through connection from the 
 
 i'lo. 34. FEOGRESS OF J^KECTION 01- MAIN LUA 
 
 anchorage on the north side of the river to the corresponding 
 anchorage on the southern side.
 
 THE TOWER BRIDGE. 57 
 
 Another part of the work was the erection of the fixed 
 roadway girders and the moving girders on the river towers. 
 The fixed girders were first erected on the temporary bridge, 
 and moved from thence into their position over the bascule 
 chamber. The portions of the moving girders which would 
 eventually be landward of the main pivot and extend about 10 feet 
 riverwards therefrom were similarly erected on the temporary 
 
 FIG. 35. PROGRESS OF ERECTION OF MAIX CHAINS. GENERAL VIEW. 
 
 bridge, launched forward, and placed in a vertical position. The 
 main pivot could now be threaded through the moving girders 
 and the bearings on it adjusted. A sufficient length of the moving 
 girders to reach about 40 feet over the central span of the 
 bridge was then erected vertically, with the accompanying cross 
 girders and bracing, after which the quadrants to carry the
 
 58 
 
 A LECTURE ON 
 
 teeth by which the moving span was to be actuated, were erected 
 in their places. The teeth of the quadrants were bolted on 
 to them, and, to ensure an accurate fit, with the pinions, which 
 engage with the teeth on the quadrants, the moving girders 
 were revolved by temporary means, so that the teeth on the 
 quadrants could be fitted carefully to those of the pinions. The 
 view (Fig. 36) shows this work in progress. The regulations of the 
 
 FIG. 36. MOVING GIRDERS IN PROGRESS. 
 
 Act of Parliament rendered it necessary to confine operations in 
 the first instance to a length of 40 feet of the moving girders, so 
 as not to reduce the free passage for vessels through the central 
 opening during the process of adjustment to less than 160 feet. 
 When the adjustment was completed the erection of the 
 remaining portions of the moving girders was taken in hand 
 and the work completed to a height of about 100 feet above the
 
 THE TOWER BRIDGE. 
 
 59 
 
 roadway where the ends of the girders are when in their 
 vertical position. 
 
 The succeeding view (Fig. 37) shows the general appaarance 
 which the bridge will present when opened for the passage of 
 sea-going vessels. It will be observed that the tops of the 
 towers and the ends of the moving girders are incomplete, and 
 
 FIG. 37. VIEW OF THE BRIDGE IN THE AUTCMX OF 1893. 
 
 that part of the temporary staging in the river, on which the 
 steelwork of the side spans was erected, is still standing.* 
 
 I am glad to say that the loss of human life during the 
 construction of the bridge has, considering the magnitude and 
 nature of the works, been small. In all, six men have met with 
 fatal accidents, and at least one of these was the result of 
 sudden illness, or of a fit. 
 
 A more recent view of the Bridge, taken early in 1894, i? given as a frontispiece.
 
 GO A LECTURE ON 
 
 The Approaches. 
 
 The northern approach to the bridge is constructed partly 
 
 on a viaduct of brick piers and arches, faced with stone, and 
 
 partly by means of retaining walls, and extends from the northern 
 
 abutment to Tower Hill, opposite the Royal Mint, a distance of 
 
 330 yards. The ground on which these works stand was 
 
 acquired from Government, and was the glacis and part of the 
 
 eastern ditch of the Tower. An entrance to the Tower property 
 
 from the east is afforded by a wide archway beneath the 
 
 approach at its southern end. Some of the arches of the viaduct 
 
 adjoining this entrance are used for a guard room, and others 
 
 for stores for the fortress and for the bridge. Most of the 
 
 northern approach is level, and there is a gradient of 1 in 60 
 
 on the remainder, extending across the north shore span to the 
 
 northern pier of the bridge. The southern approach stands 
 
 wholly on property acquired from private owners, and extends 
 
 from the southern abutment to Tooley Street, a distance of 280 
 
 yards. It is partly constructed on a viaduct near the bridge, and 
 
 under the arches of the viaduct are placed the engine and 
 
 boiler houses with the coal stores for the hydraulic pumping 
 
 engines. The rest of the southern approach is upheld by 
 
 retaining walls, built go as to form cellarage for houses to be 
 
 built on each side of the approach. The gradient of the 
 
 southern approach is, throughout its length, 1 in 40, arid this 
 
 gradient extends across the south shore span to the southern 
 
 pier of the bridge. From the piers the inclines are continued to 
 
 the centre of the river by gradients of 1 in 75, on both leaves of 
 
 the opening span.
 
 THE TOWER BRIDGE. 61 
 
 Communication betiveen existing thoroughfares and the 
 Tower Bridge. 
 
 The approach to the bridge on the north side of the river 
 connects directly with the southern end of the Minories, 
 where that important street, which runs north and south, joins 
 wide thoroughfares extending eastward and westward, but the 
 access from the southern bank of the river is not at present so 
 satisfactory. The approach constructed by the Corporation 
 extends from the bridge to Tooley Street, which is an important 
 street running east and west, but there is no good thoroughfare 
 in a southerly direction from Tooley Street. The London 
 County Council undertook to make a wide southern approach, 
 extending from Tooley Street to the Old Kent Road and 
 Bricklayers' Arms Station ; but up to the present time nothing- 
 has been done, except to bring into Parliament bills which have 
 been abortive, from the fact that the Council had included 
 in them the principle of what is called betterment. It is much 
 to be hoped that this greatly needed southern approach will be 
 made expeditiously, as it cannot be doubted that, though the 
 heavy traffic of Tooley Street will be served by the present 
 arrangement, much of the utility of the Tower Bridge will 
 remain unrealised, until a direct north and south thoroughfare 
 for traffic is opened up. The Corporation have performed their 
 part of the enterprise, and it is to be regretted that the London 
 County Council are wholly in arrear with their share of the 
 undertaking.
 
 62 .A LECTURE ON 
 
 Conclusion. 
 
 The accommodation of the interests of the road and river 
 traffic at the site of the Tower Bridge has presented many 
 difficulties, hut I venture to hope that the bridge which is now 
 being erected to a great extent solves the problem. Being a low 
 level bridge the total rise of the road traffic is not great, and the 
 gradients of the approaches are short and easy. The river traffic 
 has ample width and height for passing through the bridge, 
 and the machinery for opening the bridge for the passage of 
 ships will be rapid in its action. Lastly, there are arrangements 
 for the continual accommodation of foot traffic. 
 
 The seagoing ships which pass the site of the Tower Bridge, 
 and for which the central span would have to be opened, number 
 on the average, about 17 daily. They pass by chiefly at or near 
 the time of high water, and it may well be arranged that several 
 may pass one behind the other. The number of seagoing ships 
 proceeding above the site of the bridge does not show any 
 tendency to growth, but, on the contrary, the volume of such 
 traffic will rather, I think, gravitate to the docks down stream 
 as time goes on. 
 
 I am afraid that some disappointment will occasionally be felt 
 when vehicular traffic is stopped by the opening of the bridge, 
 but it may be hoped that no serious delays will occur either to 
 seagoing ships or to vehicular traffic, as the periods during 
 which the opening span will be raised, though sufficient for the 
 accommodation of the river traffic, will not be of frequent 
 occurrence or of long duration. The Tower Bridge will,
 
 THE TOWER BRIDGE. 63 
 
 it is thought, fairly meet all the difficulties of the case, but if 
 the road traffic becomes of greater importance, and the 
 sea-going river traffic grows less, I suppose the fate of the bridge 
 will be to become a fixed bridge. How soon this may happen no 
 one can tell. It is able to fulfil its duties either as an opening 
 or as a fixed bridge. 
 
 The cost of the bridge, with its approaches and including the 
 cost of the property purchased, will be about a million sterling, 
 and the whole of the expense will be defrayed out of the funds 
 carefully husbanded and administered by the Bridge House 
 Estates Committee. Londoners will thus be presented, without 
 the charge of one penny on the rates, with a free bridge. The 
 expense of working the bridge, which will be very considerable 
 from the quantity of machinery comprised within it, will also 
 be paid by the Corporation. 
 
 As this is the first public authorised notice of the Tower 
 Bridge, I am very glad to take the opportunity of saying how 
 much the works generally, and myself in particular, are indebted 
 to many gentlemen who have assisted in the undertaking. First 
 and most important of all, my acknowledgments are due to my 
 partner, Mr. H. M. Brunei, who has supervised the whole of the 
 complicated calculations and details of the structure, and has 
 taken a very active share in the carrying out of the work from 
 first to last. Afterwards follow the resident engineer, Mr. 
 Cruttwell, who has been in control of the works from their 
 commencement ; Mr. Fyson, who has had the duty of the prepa- 
 ration of most of the detailed working drawings and calculations 
 of engineering matters, and Mr. Stevenson, who has acted as my
 
 64 THE TOWER BRIDGE. 
 
 architectural assistant. In connection with this subject, I 
 cannot but express my great regret that the work was so soon 
 after its commencement deprived of the architectural knowledge 
 and experience of Sir Horace Jones, and that he has not lived 
 to see the mode in which his conception of a large bascule 
 bridge across the Thames has been realised. In another branch of 
 duty I have to express my thanks to the various contractors 
 who have been employed to Mr. Jackson and Mr. Webster, 
 who made the foundations and approaches ; to Sir William 
 Arrol to whom the erection of the steelwork of the super- 
 structure is entrusted ; to Messrs. Perry, who are carrying out 
 the masonry ; lastly, and in a very important degree, to the 
 firm of Sir W. G. Armstrong, Mitchell and Co., to whom is 
 entrusted the hydraulic machinery, which, I believe, is without 
 rival in size and power. 
 
 The time of construction, some 7 years to the present time, 
 has seemed long, but it may be some comfort to those who are 
 impatient, to remember that old London Bridge was 33 years 
 in building, old Westminster Bridge llf years, and new London 
 Bridge 7J years, and I think my hearers will have seen that 
 the Tower Bridge is no ordinary bridge, and in no ordinary 
 position. The structure and its machinery are full of the most 
 elaborate and complicated work of all kinds. 
 
 In drawing this description of the works to a conclusion, I 
 may be allowed to express a hope that the Tower Bridge, when 
 finished, will be considered to be not unworthy of the 
 Corporation of the greatest city of ancient or modern times. 
 
 BOOT, SON AND CARPENTER, PRINTERS, 24, OLD BAILEY, E.C,
 
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