S-.'yZ 



LAXD-TRANSPOIIT. 



j^a-adicnt will also lie afl'ectcd l)y the size of the piecx^s hrou^dit 

 down, so that there are slides for firewood, lof,'s, or scantling' 

 such as railway-sleepers, and in the Alps, for billets two to three 

 meters lonp: used for charcoal. 



Slides intended for hringiii^^ down lo^'s and butts must have 

 lower f,n-adients than those used for firewood, as the former 

 pieces attain a much <i:reater velocity than the lighter pieces of 

 firewood. 



In the case of dry slides, as already stated, the degree of 

 dampness of the air, and the nature of the atmospheric precipi- 

 tations affect the surface of the slide, and modify the necessary 

 gradient very considerably. 



However desirable it may be to give to each slide the most 

 suitable gradient, the nature of the ground frequently renders 

 this impossible, and the gradient is thus consequently greatly 

 modified. As a rule, by using the sides of a mountain 

 torrent, these slides run more or less directly down to the lower 

 valleys, at whatever gradient the bed of the torrent may render 

 practicable. Slight changes of gradient over a few sections of 

 the slide must however be avoided by levelling the base of the 

 slide, either by cuttings, embankments, or constructing viaducts, 

 so that the vertical section of a slide may represent a gradual 

 descent, and there should never be any decided angles between 

 two connected sections. 



It is also necessary to secure steeper gradients in the liighcr 

 portion of the slide than for the lower portion, so that the 

 latter may more and more approach the horizontal direction ; 

 the last few sections of it mav even ascend, and the 



