1884.] on London (heloio bridge) North and South Communication. 495 



bridge, should be interrupted at unknown times, to admit of the 

 passage of vessels ? and if the duplex bridge were resorted to, matters 

 would be but little improved. It is of the very essence of the success 

 of a means of important communication, that there should be perfect 

 certainty of passing at all times. 



Two other modes of crossing from side to side deserve notice, as 

 instances of ingenious contrivance : one, the dredging of a channel 

 across the river, the bed of which channel is to be perfectly hori- 

 zontal, and is to support several lines of rails. On these rails a 

 subaqueous carriage is to be placed, having a framework tall enough 

 to carry a platform at the height of the level of the shore. A steam 

 engine on the platform, by appropriate connection makes the wheels 

 revolve, and thus the carriage travels from side to side of the river ; 

 such a contrivance is in use at St. Malo, and a di'awing of one is 

 upon the wall. It need hardly be said, however, that, having regard 

 to the danger to the rails from ships' anchors, and from the chances 

 of vessels grounding on them, this cannot be looked upon as a feasible 

 plan to be employed in the Thames. The next scheme is the 

 converse of the St. Malo plan, viz. a platform at the shore level 

 suspended by a framing from an overhead girder placed at such 

 height as to be clear of the tallest masts. It will be seen that both 

 these plans result in a platform moving like the deck of a steamer 

 across the river, but, unlike the deck of a steamer, not affected by 

 changes in the water-level. 



We now come to the question. What plans are really open for 

 consideration, bearing in mind that the object to be attained is the 

 maximum of accommodation, coupled wdth the minimum of interference 

 with other interests, and (most closely allied to this second con- 

 sideration) the minimum of cost ? In arriving at the cost, there has 

 to be borne in mind, the acquisition of property, the expenses of 

 the work, and the annual charges for maintenance or for working, as 

 the case may be. In my view the possible plans resolve themselves 

 into three : high-level bridge — a tunnel — ferries. 



Leaving ferries on one side for the moment, as being rather very 

 valuable supplementary means, than principal means, the choice really 

 lies between a high-level bridge and a tunnel. 



I have stated the objections that were successfully urged by 

 wharfingers and shipowners, against the Metropolitan Board high- 

 level bridge proposed in 1879. It is clear that nothing short of 

 raising the bridge so high that no masts, not even the topgallant 

 masts, need be struck, would put an end to the ojjposition. The ques- 

 tion may be asked. Why not make the bridge of this height ? and this 

 brings into consideration the difficulties of the work. I do not mean 

 to say that, in the present state of engineering knowledge, a bridge at 

 a level high enough for the Monument to stand under, could not be 

 built with the most absolute certainty as regards safety, and success 

 as a structure, if money enough were spent upon it. Let me instance 

 the magnificent work of the Forth Bridge, with its 1700 feet spans 



