on the Principle of Cementitious Architecture. 193 



son of Christ's Hospital, in 1754, as to this point, still retains 

 all its force: " Whatever obstacles (he says) are laid in the way 

 of the tide, across any channel, the utmost rise or high-water 

 mark at different times will be respectively the same; because 

 the water will continue to rise till the fixed quantity of tide is 

 disposed of and no longer, and in like manner the low-water 

 mark will not be affected by such obstacles." 



If the present London Bridge were away, the tide of flood 

 would be disposed of, and attain its greatest height sooner 

 than it now does ; and below Bridge the water would not rise 

 quite so high. The ebb-tide would in like manner be disposed 

 of sooner; so that the general effect would not vary materially 

 from what it now is. By regulating sluices applied to a new 

 bridge, both the rise and the fall might be so modified as to 

 produce the most salutary results. 



With regard to the proposed designs for the new bridge, 

 it seems quite impossible to speak with adequate precision, 

 independently of an inspection of the plans, elevations, &c. 



Thus much, however, may be remarked ; viz. that whether 

 the "cementitious," or the "bonding" principle be adopted, 

 it will not be safe in arches of so large a span as from 120 to 

 160 feet, to disregard the consideration of the gravitating ten- 

 dency of the superincumbent masses and the resulting theory 

 of equilibration. In arches of small or moderate spans, con- 

 siderable deviations from the relative dimensions prescribed 

 by the theory of equilibration are admissible; because the in- 

 equalities of pressure thereby introduced are always far within 

 the measure of the modulus of fracture. But in very wide 

 arches, I should entertain considerable apprehensions of risk in 

 any case where the curve of equilibration due to the structure 

 did not actually fall within the materials of the arch. 



The cementitious principle is doubtless susceptible of a 

 more extensive application than it has met with in modern 

 times. Have any experiments been instituted with a view to 

 determine after two or more masses of stone have been thus 

 united (say for a month or six weeks), what weight will tear 

 the particles of cement asunder by hanging; or what will de-. 

 stroy the useful cohesion by pressing downwards upon the 

 substance united? 



On the whole, 1 should, for so capacious an arch, be disposed 

 to jirefer that upon the principle of bonding, provided the 

 materials of the structure can be so arranged (which is a prac- 

 tical question) that no one or more of the separate stones shall 

 be allowed to act with a mechanical disadvantage upon others 

 wljether near or remote. 



N.S. Vol. 11. No. 63. March 1832. 2 C If 



