FLOATING. 405 



rivers, the wood is left to itself, but if the water is shallow, 

 assistance must still be afforded from reservoirs. 



Usually the principal reservoirs of the subsidiary streams, 

 if they help one another, and flow one after the other into the 

 main stream, assist greatly in floating the principal sweep. 

 Experience shows how long a flood from a reservoir takes to 

 reach the main stream, and this period is chosen for the in- 

 terval between the opening of the sluice-gates of neighbouring 

 reservoirs. In long and weak floating-channels the reservoirs 

 of the tributaries are not sufficient to maintain high water in 

 the main stream, and in such cases reservoirs should be pro- 

 vided along the main channel. In floating a sweep great care 

 must be taken that the reservoirs on the subsidiary and main 

 channels work together well. As soon as the reservoirs of the 

 tributaries are again full, more wood is launched and floated ; 

 this continues daily until all the wood has been launched 

 and has gradually reached the booms, when it is either collected 

 in tanks, or taken out of the water, according to the nature of 

 the boom. 



Whenever a floating-channel passes through a lake the 

 wood must be stopped as it enters the lake and towed across it. 

 Everywhere for this purpose light coniferous logs are used, 

 which are bound together by iron rings, or withes; they thus 

 form a long floating girdle which may be used to surround the 

 wood in the lake and keep it together. AVith this object, the 

 chain of logs is placed in an arc before the entrance to the lake, 

 and as soon as it has enclosed as many logs as possible, its 

 ends are joined. The raft thus formed is then borne to the 

 other end of the lake, either by help of a favourable wind, by 

 beasts or manual labour; the chain is then opened and the 

 logs floated further down the stream. 



Favourable weather is necessary for this crossing to be 

 effected; storms not unfrequently break up these rafts and 

 scatter the logs over the surface of the lake, so that great 

 expense is incurred in collecting them. On the Pacific coast 

 of North America, and also in Norway and Sweden, where it 

 is quite usual to convey logs in those temporary rafts, screw 

 steam- boats of light draught are attached to them, or they are 

 dragged forwards by ropes attached to windlasses on boats 



