WOOD IN CONTACT WITH WATER. 12 '5 



wooden bridges and works used in connection with them for 

 strengthening the hanks of watercourses, sluices, weirs, booms 

 and other timber-catching apparatus on streams used for floating, 

 require pieces of many different shapes. Although iron bridges 

 are now becoming usual even across narrow streams, and roads 

 are replacing water-carriage for timber to a large extent, yet the 

 importance of canals for cheap traffic of heavy goods is being 

 more and more felt, so that very large quantities of timber are 

 required in hydraulic engineering. 



Timber thus used is greatly exposed to decay, so that oakwood 

 and resinous wood of larch and Scotch pine are generally 

 employed for these purposes. 



In the case of works for floating timber, it would be highly 

 advantageous were the best wood used, but owing to its abund- 

 ance in mountainous districts, and to the great cost of oak and 

 larch, sprucewood is usually employed, although its durability 

 is small. 



Water-wheels for flour and sawmills and other purposes 

 should also be made of oakwood, but are usually made of the 

 wood of Scotch pine, larch or even spruce. 



Bridges are usually boarded with beech, which gives a 

 smoother surface and is less liable to splinter than oak or 

 coniferous wood, but the considerable amount of warping and 

 shrinking of beechwood must be allowed for. 



The axle of a water-wheel must be thoroughly sound and free 

 from flaws, it is seldom more than 18 feet long, and is usually 

 made of the wood of oak, larch, Scotch pine, spruce or even beech. 



The diameter of the axle does not depend entirely on the size 

 of the wheel, and the amount of the work to be done, but also 

 according as the spokes of the wheels are dovetailed into the 

 axle, or fastened to it tangentially. 



Iron wheel- axles rest on beech or hornbeam bearings, which 

 are supported by a strong framework of oak, &c. 



2. Fascines. 

 Fascines are often used to support banks, a fascine being a 

 bundle of young stool-shoots of diflereut species and dimen- 

 sions. Their usual length is 10-12 feet, the height to which 

 the coppice grows, and they should measure 12 inches in 



