1400
THEORY AND PRACTICE OF ENGINEERING.
Book II.
stone employed in its construction was of the ordinary weight; this centre was found tooweak for the purpose.
The Arches of St, Edme were 95 feet 6 inches span, and rose 27 feet 8 inches: theprincipals forming the centres were five in number, and placed 7 feet apart. The tim-bers used in their construction varied from 19 to 24 feet in length, were from 15 to16 inches square, and sufficiently strong for the purpose; the thickness of the arch atthe key was 4 feet 10 inches.
The Centres of the Bridge at Mantes, contrived by Perronet, show the care and attentionhe bestowed upon this portion of his constructions, and the ability he evinced in forming
Fig. 2332.
BRIDGE AT MANTES,
the temporary bridge and scaffolding for the purpose of hoisting them was equallyadmirable. The thickness of the arch at the key was 4 feet 4 inches, and it continued