130 



THE ARCH. 



there have been faced with horizontal conrscs of masonry. 

 This is not a glaring instance, but I have selected it as 

 being near home. 



Maidenhead Bridge.— The last of the drawings (not repro- 

 duced here) shows an elevation of this bridge, which was 

 built over the Thames, for the Great Western Eailway 

 Company, by Brunei. The two river arches have each a 

 span of 128 feet, with a riso of about ono-eighth of the span 

 and a crown thickness of 6 feet. The bridge is built of 

 brickwork, and the arches in rings of brickwork. 



It is a beautiful bridge, and is chiefly remarkable for the 

 last-mentionod fact, which makes it of interest in this 

 paper. 



The drawing underneath is that of a bridge as nearly 

 similar as possible, but built with equilibrated arches. It 

 is remarkable that the curvature of the arches is the same 

 in both bridges along two-thirds of the span ; the old arches 

 only depart from the tnio curve when within 22 feet of the 

 springing, from which point they are turned downwards so 

 as to give them an elliptical appearance. The actual line 

 of thrust, however, always follows the direction of the truly 

 equilibrated curve, shown in the drawing below. 



This is probably the boldest bridge ever built in rings of 

 brickwork. Had not all the central portion of the arches 

 been in the true form of curvature, and had not the parts 

 near the springing; where the true curvature was not fol- 

 lowed, been made immensely thick and solid, so that the 

 natural line of thrust could pass out of the arch into the 

 solid mass of brickwork n,t the back, it could not have 

 stood. This, however, involved the employment of a large 

 quantity of additional brickwork, not otherwise needed, and 

 the work was, after all, not so strong as the truly-formed 

 arch would have been without this additional brickwork. 



