Drainage by Gravitation. 23 



underneath, causing the sand or mud to be stirred up and 

 mixed with the water. The force of the head of water is 

 utilised to move the boat forward and drag along the bottom 

 a " hedgehog," so as to loosen the hard crust. The machine 

 is allowed to drift slowly down with the ebb current, and the 

 material, thus broken up and scoured out, is carried away in 

 suspension. Care has to be taken in using this machine in 

 riveis passing through sand, that the water does not find its 

 way round the sides and so scour holes in the banks. 



The machine already referred to as being in use in the 

 river Welland and the Deeping Fen di*ains, has been designed 

 and brought into practical use by Mr, Alfred Harrison, super- 

 intendent of the Deeping Fen Drainage District It consists 

 of a barge, to which, from framework projections at each 

 end, is suspended a "hedgehog" or revolving drum, on the 

 periphery of which are spearheaded spades. The barge is 

 moved along the channel by means of steel ropes, anchored 

 in the bank at one end, and the other working round drums 

 on the boats similar to those used for steam ploughing appa- 

 ratus. The drums are made to revolve by gearing attached 

 to a semi-portable engine in the boat, the one drum uncoiling 

 and the other coiling up the rope. The drums are balanced 

 by chains, passing over pulleys to counterbalance weights, so 

 as to enable them to rise over any substance too hard for the 

 spades to penetrate, undue strain on the ropes being thus 

 prevented. The barge travels at the rate of about two miles 

 an hour. The framework to which the hedgehogs are 

 attached can move laterally by means of a handle, and thus 

 acts as a steering apparatus, by means of which the boat 

 travels round very sharp bends without difficulty. The 

 spades are placed alternately, and only enter a short dis- 

 tance into the bed of the stream. By the constant travel 

 of the two hedgehogs up and down the drain, the soil is 

 broken up sufficiently small for the whole of it to float and 

 be carried away by the water. A perpetual churning motion 



