July 20, 1883.] 



SCIENCE. 



71 



hoisting-machine. The course taken bj- the 

 dredge-rope while in use is as follows : start- 

 ing from the reel on which it is contained, it 

 passes through a pnlK^y on the bertli-dcck to 

 the dnnn of the hoisting-engine, thence up 

 to and through an iron block at the lower end 

 of the accumulator, anil down again through a 

 sheave in the heel of the boom, from which it 



and six thousand pounds, which is less than 

 the tensile strength of the roi)e they are intended 

 to secure from bieakagc. Tiie amount of rope 

 out at all times is recorded by a registei' attached 

 to the sheave in tiie heel of tlie l)Oom, the sheave 

 measuring just half a fathom in circumference. 

 In preparing for work, the dredging-boom 

 is topped up at the requisite angle over the 



extends to the outer end of the boom, where 

 there is another large pulley-. The free end 

 of the rope is spliced into the eye of a set of 

 safety-hooks, to which the dredge or trawl is 

 fastened, and which are so arranged as to open 

 and release the apparativs. should the strain, 

 by reason of fouling on the bottom, exceed a 

 certain amount. These hooks can be adjusted 

 to detach at any point between three thousand 



starboard bow, and the loaded dredge or trawl 

 is hoisted above the deck, on which stands the 

 sieve or tubs ready to receive its contents. 

 Two methods of sifting or washing the ma- 

 terials are followed. For the trawls, which 

 generally bring up a heavy load, a lai-ge and 

 deep, square sieve, standing upon legs at a 

 convenient height for working, is used. As 

 the tail of the trawl is lifted above the deck, 



