2 Mr. Warp on the Curvature of the 



is less in depth from the intrados to the extrados, than any iron 

 bridge hitherto built, with relation to the radius of curvature at 

 the vertex * ; we shall not wonder that the inquiry should be 

 continued until a satisfactory solution be obtained. The fol- 

 lowing attempt to solve this question has been made, in the 

 hope of rendering so excellent a bridge more generally known 

 than it is at present, and to mark it as an object for imitation, 

 now that it is in contemplation to erect a new bridge in the place 

 of London Bridge. Perhaps the inquiry may cause hereafter 

 some proper applications of geometry and known formulae to 

 be made to elliptical curves, of which, judging from the arches 

 of this kind which are to be seen in very conspicuous places 

 in London, — modern builders appear to be unacquainted with. 

 The historical inquiries of antiquaries have been suspended, for 

 they cannot find in the memoranda of Parigi any account of the 

 nature of the curve, nor trace the lost manuscript work of Am- 

 manati, entitled La Cittd, beyond the possession of the Great 

 Prince Ferdinand of Tuscany. Mathematicians to the time of 

 Ferroni, contented themselves principally with conjectures de- 

 rived from the resemblance of the curves of the arches of this 

 bridge to other curves, sometimes concluding them to be com- 

 posed of arcs of circles of different radii, at other times ellipses, 

 parabolas, or catenaries. Some more industrious have measured 

 the arches by taking ordinates, or various triangles, with such 

 implements as lines and tapes. But as the absolute curve had 

 not been accurately obtained before Ferroni's time, consequently 

 the curve of Ammanati could not be satisfactorily deduced. 

 Ferroni employed in 1785, Joseph Salvetti, to measure correctly 

 the middle arch of this bridge by ordinates at each braccio, and 

 he states proper implements were provided, and that the ordi- 

 nates were measured twice over ; different measurements have 

 since been published, but not such as to cause any doubt to be 

 entertained of Salvetti's accuracy. Ferroni having thus ob- 

 tained the clew, he found the labour of unwinding it more irk- 



* In the Ency. Meth. Arch, Art., Ammanati. This bridge is thus de- 

 scribed : " Son godt, sa hardiesse, et sa Icgdrete, le font passer pour le plus 

 beau de I'architpcture moderne." 



