CHAP. VI.] DEEP-SEA DREDGING. 241 



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 

 dredges on this pattern used in Britain for ten 

 years after their first introduction about the year 

 1838, were usually small 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 



