[Illustration:  Viaduct over the Retiro, Brazil.]

This viaduct was constructed in the year 1875, according to designs furnished by the author, for the purpose of passing the Dom Pedro Segundo State Railway over the valley which forms the bed of the river Retiro, a small confluent on the left bank of the river Parahybuna.  It is 265 kilometers (165 miles) from Rio de Janeiro, and about 10 kilometers (6.4 miles) from the city of Juiz de Fora, in the province of Minas Geraes, Brazil.  It has a curve of 382 meters (1,253 ft.) radius, and a gradient of 1 in 83.3.  Its total length is 109 meters (357 ft. 7 in.); width between handrails, 4 meters (13 ft.); and greatest height above the bed of the river, 20 meters (65 ft. 7 in.).

The viaduct is composed of seven semicircular arches, each end arch being built of ashlar masonry, and of 6 meters (19 ft. 8 in.) diameter; five intermediate arches, 15 meters (49 ft. 2 in.) in diameter, are of iron.  The four central piers are of iron erected on pillars of ashlar masonry.  The metallic part of this viaduct is 80 meters (262 ft. 6 in.) long, and is constructed in the following manner:  The arches, and the longitudinal girders which they support, are made of two Barlow rails riveted together, with an iron plate 1/2 inch thick placed between them.  The spandrels are formed of uprights and diagonals, the former being made of four angle-irons, and the latter of one angle-iron.  Each pair of arches, longitudinal girders and uprights, is transversely 3 meters (9 ft. 10 in.) from center to center, and is connected by cross and diagonal bracing.  On the top of the longitudinal girders are fixed cross pieces of single Barlow rails, upon which again are fastened two longitudinals of wood 12 in. square in section, and which in their turn carry the rails of the permanent way.

The gauge of the Dom Pedro Segundo Railway is 1.60 meters, or 5 ft. 3 in. nearly, between the rails.  At each end of the transverse Barlow rails is fixed the customary simple iron handrail, carried by light cast-iron standards.  The iron piers are each formed of four columns, and the columns consist of two Barlow rails, with a slotted iron plate 1/2 inch thick let in between the rails, and the whole being riveted together connects each pair of side columns.

The details show the system of cross and diagonal bracing.  The columns are each supported by four buttresses formed of plates and angle-irons.  These buttresses, fastened with bolts 8 ft. 3 in. long, let into the masonry pillars, secure the stability of the viaduct against lateral strains, due mostly to the centrifugal force caused by the passage of the trains.

The Barlow rails, which constitute the peculiarity of the structure, are from those taken up from the permanent way when the Vignoles pattern of rail was adopted on this railway.  The whole of the foundations were built without difficulty.  The principal parts of the iron work were calculated to resist the strains resulting from a weight of 4 tons 8 cwt. per lineal meter traveling over the viaduct at a velocity of 60 kilometers, or about 37 miles, per hour.