BRIDGES. 587 



through the middle of the breadth ; the second a transverse one, 

 or across it, and through the summit of an arch ; and the third 

 also across, but taken upon a pier. The elevation is an orthogra- 

 phic projection of one side or face of the bridge, or its appear- 

 ance as viewed at :i distance, shewing the exterior aspect of the 

 materials, witli tbe manner in which they are disposed, &c. 



In the construction of stone bridges many difficulties must be 

 encountered, particularly those of laying foundations and walling 

 under wattr ; these are best overcome by means of the coffer-dam. 

 A due regard must be paid to the size and shape of the arch, and 

 the magnitude of the pier. Much information on these subjects 

 may be obtained from the works of Albert!. Gautier, Blonde Rio, 

 Palladio, Labelye, Perronet, and the ingenious and useful trea- 

 tises of Dr. Ilutton and M.Bassuet. 



The chief foreign bridges are, the bridge of Trajan, over the 

 Danube, the bridge of Avignon, the Pont de Garde, in France, 

 the bridge at Munster, in Bothnia, the aqueduct bridge of Alcan- 

 tara, ntar Lisbon, and the Rialto of Venice. There are nearly 

 500 bridges of different sizes over the canals at Venice. The 

 Rialio, the principal of these, is esteemed a master-piece of art : 

 it consists of one flat and bold arch, nearly 100 feet span, and 

 only 23 feet high above the water, and was built in 1588, 1591, 

 after a design by Michael Angelo. The breadth of the bridge, 

 which is 43 feet, is divided by two rows of shops, into three nar- 

 row streets, that in the middle being the widest ; and there is in 

 the centre an open archway, by which the three streets communi- 

 cate with one another. At each end of the Rialto, is an ascent 

 of 56 steps : the view from its summit is very lively and magnifi. 

 cent. The whole exterior of the shops and of the bridge is of 

 marble. The foundation extends 90 feet, and rests upon 12,000 

 elm piles. This structure cost the republic 250,000 ducats. 



W* hive many bridges of considerable note in our own coun. 

 try : such is the bridge at York, whose master arch in the middle, 

 is Si feet and a half in the clear wide, and 27 feet high. Roches, 

 ter bridge is built in the same style with that of London ; it is 550 

 feet long, and consists of 1 1 arches, the biggest of which is more 

 than 50 fn-t. The two middle arches of this fine old bridge have- 

 been recently thrown into one by that skilful and scientific archi. 

 tect Mr. Daniel Alexander. The bridge of Blenheim consists of 

 three arches, the chiti of which spans 101{ feet. There is a bridge 

 p?er the river Don, near Old Aberdeen, very much celebrated, in 



