6 Mr. Ware on the Curvature of the 



\Vhenx:^12 then y by calcnlation, =: 6 5 0, by measurement, 6 4 4, 



15 6 15 6, ... 6 15 2, 



17 7 13, ... 7 1 3, 



20 7 8 4, ... 7 8 9, 



25 7 16 1, ... 7 16 6, 



By referring to the mode of framing the centering according 

 to the drawing left by Parigi, it will be observed that the strutts 

 abut against King posts, and not against each other as they 

 should have done ; and by supposing, as happened lately in this 

 metropolis in a similar case, that the masons proceeded to lay 

 the voussoirs from the imposts towards the key, without ba- 

 lancing by weights, the other parts of the centering, the little 

 variation, (too small to be seen to the scale of the diagram. 

 Fig. 1,) elicited by comparing these results, maybe satisfactorily 

 accounted for. 



These dimensions shew that the arch has sunk at the haunches 

 between the ordinates 9 and 20, and risen at the springing and 

 crown, presuming the curve to be elliptical as deduced. It may 

 be concluded, upon a balance of evidence, notwithstanding the 

 approximation of the present curve of the middle arch to a cate- 

 nary, that the curve was intended to be an arc of an ellipse, 

 whose transverse axis is 64 braccia in length, and whose semi- 

 conjugate is 8 braccia. The properties of the ellipse, necessary 

 to the setting out an elliptical rib, during the time the vaults of 

 ecclesiastical buildings were erected, were as familiar to the 

 commonest mason, as they are to every millwright by the prac- 

 tice of his trade. Mr. Rennie has, by the adoption of the conic 

 section at "Waterloo Bridge, probably by the accident of his 

 early habits and extensive business as a millwright, made a 

 great stride beyond his contemporaries, and acquired much 

 honour for himself and his country, and availing himself of the 

 lavish means afforded, he has maintained the unities of dress 

 and form, without requiring a veil like Ammanati, or a skreen 

 like Sir C. Wren. 



The principal dimensions of this bridge are written on the 

 small drawing of it, (Fig. 2,) in Florentine braccia, taken from 

 Ferroni. It remains to be observed that the depth of the archi- 



