260 THE DEPTHS OF THE SEA. [CHAP. VI. 
there ought to be one or two tubs about two feet 
in diameter and twenty inches deep, and each tub 
should be provided with a set of sieves so. arranged 
that the lowest sieve fits freely within the bottom 
of the tub, and the three succeeding sieves fit freely 
within one another (Fig. 52). Hach sieve is pro- 
vided with a pair of iron handles through which 
the hand can pass easily, and the handles of the 
largest sieve are made long, so that the whole nest 
ean be lifted without stooping and putting the arms 
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Fic. 52.—Set of Dredging Sieves. 
into the water. The upper smallest sieve is usually 
deeper than the others ; it is made of a strong open 
net of brass wire, the meshes a half inch to a side. 
The second sieve is a good deal finer, the meshes 
a quarter inch to a side. The third is finer still, 
and the fourth so close as only to allow the passage 
of mud or fine sand. The sieves are put into the 
tub, and the tub filled up to the middle of the top 
sieve with sea-water. The top sieve is then half 
filled with the contents of the dredge, and the set 
of sieves are gently moved up and down in the 
