136 



Art. XVllI.— miscellaneous INTELLIGENCE. 



I. Mechanical Science. 



1. Economical Bridge. — A bridge of suspension, or rather 

 tension, has been constructed not long since by M. M. Seguin? 

 near Annonay, department de I'Ardeche, after the model of 

 those constructed by the indigenous inhabitants of America*. 

 The following account is taken from a description of it by M. 

 Pictet. Bib. Univ.xxi. 123. 



At the place where it is constructed, the river over which it 

 passes is confined by rocks which have furnished strong points 

 of attachment for the bridge. A band composed of eight iron 

 wires, each the ^ of an inch in diameter is attached by its 

 extremity to an iron bolt fixed in the rock ; it then crosses the 

 river at a height of 10 feet above it, and on the opposite side 

 passes round a horizontal pulley three inches in diameter, also 

 made fast to a rock. The band returns parallel to its first 

 direction, passes round one pulley to preserve the parallelism, 

 and then on to another about 16 inches distant, from which 

 it again proceeds over the river and passes round a second 

 pulley on that side, and finally returns to the side from which 

 it parted, and is made fast to a bolt in the rock. Thus it 

 crosses the river four times. Small cross pieces of wood are 

 attached at intervals to these reduplications of the band, and 

 over them are placed the planks, parallel to the wires, which 

 form the foot-way of the bridge. Two other bands of wire are 

 carried across the river at a convenient height on each side of 

 the bridge, to serve as hand-rails ; they are connected by 

 descending wires to the external bands of the bridge : and, to 

 prevent every lateral motion the bridge is made fast at the 

 middle to some large stones in the bed of the river. 



This bridge though of a structure so light as to occasion 

 fear on the first time of going on to it, is yet so steady and 

 strong that no sensible bending or vibration is perceived in 

 passing over it. It is 2 feet broad, and 55 feet long. The 

 weight of iron wire used in its construction was about 24lb., 

 and the expense of the whole of the materials amounted to 

 little more than 35 francs. The expense of labour is estimated 

 at about 15 francs, so that 50 francs according to this account 

 would pay for the whole. 



* Sec also vii. 53. 



