PROPERTIES AND USES OF TIMBER. 371 



It is sometimes imagined that wood kept below 

 water must be very subject to decay, and must soon 

 be destroyed by rottenness ; an opinion which ap- 

 pears to have arisen from the well known fact, of 

 moisture being productive of decay in vegetable 

 substances exposed to the weather. It is only 

 when wood is exposed to the action of the atmo- 

 sphere, however, that water or dampness produces 

 rottenness. If kept always completely below water, 

 timber of almost any kind will last longer than 

 when kept entirely free from moisture. Kotten- 

 ness, or natural decay, is most speedily produced in 

 all vegetable substances, by alternations of mois- 

 ture and drought, or being kept between wind and 

 water. Some species of wood resist the evil conse- 

 quences of such changes better than others ; but, in 

 general, an exposure to them is the most trying si- 

 tuation in which timber , can be placed^. Paint, 

 pitch, turpentine, and resinous substances in gene- 

 ral, are well known preventives of rottenness, and 

 are commonly employed, frequently with much suc- 

 cess, for that purpose, when wood is used in circum- 

 stances peculiarly exposed. 



* I do not here speak of dry-rot^ which is not attributable to 

 natural decay, but to particular diseases, or rather to the at^ 

 tacks of fungous vegetables, and of insects. 



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