278
HISTORY OF ENGINEERING.
Book I.
TU U U
LJ II iJ
Fig. 287.
greatly adds to the effect of the structure. The roadway is paved throughout, and at thesides beyond the water channel is a footway, laid with a gentle inclination.
Bridye on the Serriere, near Neufchatel, constructed by M. Ceart; the foundations are ona rock, and it consists of a semicircular arch 69 feet 3 inches in span. The thickness ofthe arch is 5 feet 2 inches; that of the abutment, which does not rest against the rock, andwhich forms a pier 14 feet 1 inch high, is 16 feet 5 inches. This bridge, 26 feet 3 incheswide from one head to the other, is a good example of bridges of one arch constructedover small rivers in the departments of France : the engineers cotemporary with Ceart, andparticularly those who, like him, had studied the Roman remains in Provence , seem tohave universally adopted the semicircular form for their arches, and to have constructedtheir abutments with great solidity: the refinements which have been introduced in moderntimes have greatly economised material, the thickness of the voussoirs at the crown has alsobeen reduced. Boistard and Bcrard have pointed out how erroneous it is to consider thestrength of an arch as dependent upon the weight of its key-stone : the great depth in thepresent example is an unnecessary load, and by its adoption every other portion, down toits abutments, has been proportionablv increased, without the whole acquiring any ad-ditional strength.