VIATECTURE. 449 



the Liverpool and Manchester road, that their importance was appre- 

 ciated ; and they were found to be adapted for rapid, as well as cheap 

 transportation. 



The subject of Viatecture, is naturally divided into the study of 

 Common Roads and Bridges ; of Rail Roads ; of Canals and Water- 

 works ; and of River and Harbor Improvements. Perhaps Gas 

 Lighting belongs most closely to this branch of the arts ; to which, 

 if so, it may be regarded as an appendix. 



1. The construction of Common Roads, as well as of other via- 

 tectural works, should be based on a reconnaisance of the route or 

 location; requiring, in all important cases, a regular survey, with 

 levellings. The arts of Surveying, and Topography, belong, we 

 think, more closely to this than to any other branch of the arts ; and 

 although they depend on mathematical principles, they are rather 

 applications than essential parts of Mathematics. Roads, should, of 

 course, be as straight as the places to be connected, and difficulties 

 in the way, will allow. The rise should not be greater than 1 foot 

 in 14, or 1-14 ; unless in extreme cases. The transverse, or cross 

 section, should be convex ; and for a road 20 or 24 feet wide, at least 

 6 inches higher in the middle than on the sides. Side drains, to 

 carry off the water, and occasional cross drains, are necessary, to 

 preserve roads in good order. To prevent the action of rain and 

 frost on earthen roads, is the object of stone roads; which are 

 covered with a crust of finely broken stone, called metal, from 8 to 

 12 inches deep, ultimately becoming so compact as to resist the, im- 

 pression of carriage wheels. 



Bridges, are variously constructed, of wood, stone, or iron : and 

 they may be classed either as elevation, or suspension bridges ; the 

 latter hanging on chains, firmly fixed at the extremities. Bridges 

 should always rest on firmly founded piers. The simplest piers, 

 used for wooden bridges, are formed by driving piles, or sharpened 

 posts, in rows, crosswise of the bridge ; and these rows framed 

 together with cross timbers, are sometimes called trestles. Stone 

 piers are sometimes founded by means of a coffer dam, or strong 

 enclosure ; from which the water is pumped out, leaving the bottom 

 temporarily dry. Sometimes they are built in a close caisson, or 

 water tight box, made to sink in its place, as it is filled with the 

 masonry : and sometimes they are built by means of an open caisson, 

 made of piles and pile planks driven down, and filled with beton, or 

 a mixture of small stones and hydraulic mortar. The ends of piers, 

 called starlings, have usually a rounded or pointed form, to break 

 the ice, and divide the water in its passage. The abutments, or 

 extreme piers, when they are to resist the pressure of an arch on one 

 side only, have need of great thickness and strength. 



2. The construction of Kail Roads, like that of the best common 

 roads, requires a careful preliminary survey, and great judgment in 

 the location. The track, or line of parallel rails, must have no angu- 

 lar points, but change its direction by means of curves ; which, unless 

 in extreme cases, should have a radius of not less than 400 feet. 

 Neither should the slope, or inclination of the road, exceed 30 feet in 

 a mile, or in extreme cases 50 feet ; if intended for locomotives with 

 57 2 P2 



