450 ARCHITECHNICS. 



considerable loads. A greater rise than this, is sometimes overcome 

 by inclined planes; with stationary engines, or other additional 

 power. A locomotive engine, with 4 tons of its weight resting on 

 the driving wheels, will draw with a force of at least 360 Ibs. or 

 l-25th of its driving weight, without slipping on the rails: and this 

 force of traction will draw a load, on level rails, at least 200 times as 

 great, that is of 200 times 360 Ibs. ; or at least 32 tons. 



After a rail road is graded, the excavations generally supplying 

 earth for the embankments, the latter should have time to settle be- 

 fore the rails are laid down. Rails of wrought iron, are now preferred 

 to those which are cast ; as being stronger for the same weight, and 

 less liable to fracture. The train rails, formerly used, having a 

 flange to keep the wheel from running off, are now almost entirely 

 superseded by the edge rail, with is rounded on the top, and does 

 not collect the dust ; the flange being transferred to the wheel. The 

 rails sometimes rest on wooden string pieces and cross sleepers ; but 

 the best are fastened to stone sleepers, by means of iron chains, or 

 fixtures. To enable the engines to pass each other, turnouts and 

 crossings are constructed ; with a switch, or moveable rail, to direct 

 the car either to the main track or to the side one. 



3. The construction of Canals, and Water Works, is based, like 

 the preceding works, on a careful survey and location. Canals are 

 used either for irrigation, or watering ; including aqueducts, for 

 supplying water to buildings and cities ; or for desiccation, as for 

 draining marshy land ; or for navigation, which last are the more 

 numerous and important class. Ship Canals are usually 20 feet 

 deep; sloop canals, 8 or 10 feet; and boat canals, from 3 to 6 feet 

 deep ; the banks having usually a slope of about 2-3, or two in 

 height, to three of base. A canal must either be on one continuous 

 level, or divided into several levels : and if one of these be higher 

 than those on either side, it is called the summit level; being the most 

 difficult to supply with water. This supply sometimes requires the 

 construction of large and expensive reservoirs, and feeders. 



The passage from one level to another, is effected by means of 

 locks, formerly called chamber locks ; with gates at each end. By 

 shutting the lower gates, and gradually filling the lock, a boat, within 

 it, is raised to the higher level ; and the upper gates may then be 

 opened, for it to pass on its way. The locks should, if possible, be 

 so located, and the canal kept of such a height, that the contiguous 

 excavations and embankments may be equalized, as nearly as cir- 

 cumstances will allow. Canals sometimes pass over streams, on 

 aqueducts, or strong bridges ; and sometimes, as in the case of rail 

 roads, they are made to pass through mountains, by tunnels, dug for 

 the purpose. Small streams pass under canals, through culverts ; 

 and superfluous water is carried off from canals by waste wiers. 

 The supply of water required, will depend upon its loss, by leakage, 

 lockage, and evaporation. 



4. The improvement of Rivers and Harbors, depends partly on 



the removal of obstructions, and partly on the construction of hydrau- 



c works ; requiring a thorough knowledge of the theory of currents, 



waves, and tides. The navigation of rivers, is improved by removing 



