296 THE UTILISATION OF WOODLAND PBODUCE. 



(20 to 40 per cent). With too low a gradient such wooden 

 slides are useless ; and with too high a gradient the velocity of 

 the logs may cause them to spring out of the shoot. Hence, 

 wherever a dangerous velocity is likely to be acquired, a brake 

 can be formed by fixing two stout poles of equal length and 

 girth firmly at their thinner upper ends well above the slide 



Fig. 82. 



A Brake or Check on a Wooden Timber-Slide. 



and letting their thicker lower ends hang loosely on the base 

 of the slide (Fig. 82), and as a log raises them, and passes 

 through between them, the strong friction reduces the speed. 

 Such wooden shoots cost far more to make and maintain than 

 roadway timber-slides, and do not last so long, their average 

 life being about 7 years ; and even then the logs used in making 

 them get so battered as only to be fit for fuel. 



Flumes or Water-shoots (Fig. 83) are broad V-shaped water- 



