CHAP. VI. | DEEP-SEA DREDGING. 24] 
open to allow the water to pass freely through, with 
the openings so distributed as to leave a part of the 
bag close enough to bring up the finest mud. 
The late Dr. Robert Ball of Dublin devised the 
modification which has since been used almost uni- 
versally by naturalists in this country and abroad 
under the name of ‘ Ball’s Dredge’ (Fig. 45). The 
“ee on this ae used_ in Britain for ten 
1838, were usually oT and rather heavy — not 
more than from twelve to fifteen inches in length 
by four or four and a half inches in width at the 
mouth. There were two scrapers the length of the 
dredge-frame, and an inch and a half or two inches 
wide, set at an angle of about 110° to the plane 
of the dredge’s mouth, so that when the dredge 
was gently hauled along it took hold of the ground 
and secured anything loose on its surface. I have 
seen Dr. Ball scatter pence on the drawing-room 
floor and pick them up quite dexterously with 
the dredge drawn along in-the ordinary dredging 
position. 
Latterly we have used Ball’s dredges of consider- 
ably larger size. Perhaps the most convenient form 
and size for dredging from a row-boat or a yawl at 
depths under a hundred fathoms is that represented 
by Fig. 45. The frame is eighteen inches long, and 
its width is five inches. The scrapers are three 
inches wide, and they are so set that the distance 
across between their scraping edges is seven inches 
and a half. The ends of the frame connecting the 
scrapers are round bars of iron five-eighths of an 
inch in diameter, and from these two curved arms of 
R 
