FLOATING. 393 



level ; their height varies, therefore, with the depth of the water 

 in which they are placed. Planks are then placed from gabion 

 to gabion, forming a footway, and stout poles {a a a) are bound 

 to the gabions by means of withes. The grating-rails (h h) are 

 then bound to (c) outside the water, and let down into it from the 

 footway, till each rail rests on the bottom of the river. The 

 several rails are then bound by withes to {a a a), and along the 

 grating floating logs are placed. 



These gabions have the advantage of costing little, of being 

 erected in a short time by the floating-gang and of being easily 

 repaired. At the same time, they are not durable, and are often 

 overthrown by heavy floods, to which they offer a great resisting 

 surface. They are speciall}- adapted for small temporary sweeps 

 of floating timber, especially on unimproved mountain-torrents. 



Finally, floating booms must be mentioned. They consist for 

 the most part of spruce-logs which are united at their ends by 

 iron rings and fastened together in sufficiently long chains. 

 These chains of logs are fastened at one or both ends, and float on 

 the surface of slowly flowing streams, on which floating is done 

 only occasionally. In order to give them a greater power of resist- 

 ance, some of the logs are anchored to the bottom of the river. 

 In spite of this, however, they cannot resist a sudden flood, as 

 has been often experienced, in the breaking of such booms, 

 especially if the stream is fairly strong (the river Inn). 



[In the river Jumna, at Daghpathar, a boom is placed at a 

 point where the river is 120 yards broad. It consists of two 

 portions, a raft 35-1 feet long, constructed of railway-sleepers as 

 shown in fig. 235. It is fixed at one end to a rock on the right- 

 hand side of the river, and kept obliquely inclined towards the 

 current by Avire ropes anchored to the other bank. This portion 

 of the boom is placed in the full current of the powerful stream. 

 From its other end extends a line of logs fastened end to end by 

 a wire rope, and 910 feet long. The floating sleepers are stopped 

 by the raft-bojm, and then float along the line of logs into slack 

 water, when they are easily caught by men swimming on inflated 

 buffalo-skins, and landed. 



The construction of the raft-boom is as follows : — 



Two broad-gauge sleepers are placed 6| feet apart and with 

 their broad face vertically downwards ; transversely to these and 



