For the rest, as I wanted to learn something more about this bridge of a hundred vast arches over the Min at Fo-Cheu, I wrote to the Rev. O. M. Jackson, whose kind help I have already acknowledged ([p. 248]). There is a river Min in Sichuan, but no news of such a bridge has reached Mr. Jackson, though he has worked in Western China for more than twenty years, and has travelled on foot over a very wide area in the province of Sichuan. Again, Mr. Jackson does not recognise the spelling “Fo-Cheu,” but refers me to the city of Fu Chow in the coast province of Fukien. One day, perhaps, research will bring me in touch with the colossal masterpiece described by Gauthey, though at present I am baffled by the variety of geographical names that travellers have given to the bridges of China. Still, the Chinese have been great bridge-builders, and some of their stone arches have been very high and very wide. Perhaps the one described by Kircher may have been as wide as Trezzo Bridge, over the Adda, with its wonderful span of 251 feet.
My favourite bridge in the class of exceptional merit is the Ponte della Trinità over the Arno at Florence, designed in 1566 by the architect of the Pitti Palace, Bartolomeo Ammanati, a devoted admirer of Michelangelo. Both in science and in art the Ponte della Trinità is complete as an original success. Its vaulting—I ought to say his vaulting, for in this bridge the male qualities of genius are much stronger than the female—his vaulting, then, if not the most scientific in the world, is not excelled by any other work either ancient or modern. There are three arches, and their curves are cycloids; the rise from the springing level is only a trifle more than one-sixth of the span. How Ammanati managed to get his effect of perfect balance and symmetry is a question very hard to answer, for there is a considerable difference between the width of his arches, the central one being 96 ft. in span, and the others 86 ft. and 88 ft. This fact has been established by measured drawings, but do you notice it out of doors, in the magic of this beautiful bridge? The piers are simple and excellent. Their width, twenty-six feet, is not too much for the spates of a freakish river, nor too heavy for the bridge as a linear composition; on the upstream side they have stern cutwaters, good foils in a piece of architecture that blends an alert grace with a supple vigour. Another point worth noting is the gradient of a roadway that starts out from low abutments. Ammanati was bent upon being a friend to the traffic of Florence, and with the help of his cycloid arches he kept the road on a mild curve. To-day this good point attracts little attention, as most of us forget that steep bridges were in vogue till late in the eighteenth century.
A Victorian pontist, William Hosking, endeavoured to prove that Ammanati made one mistake in the Ponte della Trinità. It seemed to Hosking that the piers were too bulky, so he cut them down in a sketch and spoilt the whole bridge by altering the proportions. Architects told him so, but Hosking crowed over his little sketch and published it with pride, as you will find by turning to his “Architectural Treatise on Bridge Building”—a valuable work from other standpoints.
VI
The great work of Ammanati sets thought in movement on bridge decoration, and I wish to offer some hints on this subject, not for the purpose of finding rules, but in order that a public debate may be invited. Rules would be very useful if they could be formulated, but in bridge decoration national sentiment and personal feeling have been exceedingly active; no writer, then, can do more than offer suggestions from his own point of view.
Less than twenty years ago a debate on this subject would not have been easy, for good books on the technical history of bridges were uncommon, and photographs of fine examples were far more difficult to get than they are now. English books on bridges are still formidably dull; to read them is perhaps as troublesome as hill climbing on a foggy day; but the fear of being “ploughed” in a stiff examination helps young men to be intrepid. In France, on the other hand, the public is served very well by literary pontists. M. Charles Béranger, for instance, from his Librairie Polytechnique in Paris, is publishing a series of thorough books on bridges, as useful to us as they are to French students. Already eight volumes have been issued. They include:—
1. “Ponts en Maçonnerie.” Par E. Degrand, Inspecteur-Général des Ponts et Chaussées, et Jean Résal, Ingénieur des Ponts et Chaussées. Two volumes, illustrated; 40 francs.
2. “Ponts Métalliques.” Par M. Pascal, Ingénieur. One volume; 15 francs; illustrated.
3. “Croquis de Ponts Métalliques.” Par Jules Gaudard, Ingénieur Civil et Professeur Honoraire de l’Université de Lausanne. Profusely illustrated; 20 francs.
4. “Cours de Ponts Métalliques.” Par Jean Résal. Vol. I, 375 illustrations; 20 francs.