Construction of the interior galleries of the Palais du Champ de Mars

From the first in 1851, universal expositions were opportunities to experiment with new construction techniques, and the 1878 Exposition was exemplary in this respect. The Palais du Champ de Mars, specially built for the event, covered a 25-hectare quadrilateral. The glass roofs of the interior galleries were supported by metal Polonceau trusses with a 25-metre span. Four companies were selected to each construct three sections of fifty-eight trusses. These lucrative contracts were also exceptional opportunities for these builders to demonstrate their skills. Émile Baudet decided to assemble the elements on the ground then raise them using a steam-powered machine mounted on travelling scaffolding. A scale model of this apparatus was made for the Exposition and donated to the Conservatoire after the event.