HOW THE SEA-DEPTHS ARE EXPLORED. 



265 



five feet long by a foot or so in width at the mouth, with a scraper like 

 a narrow hoe on one side, and a suspending apparatus attached to the 

 rope on the other. From the frame is suspended a bag, about two feet 

 in depth, of wide netting or hempen cord. The naturalists' dredge has 

 a scraper on each side, the bag is deeper, and the meshes so fine as to 

 allow only the water to pass through. 



Fig. 6. 



Dredge with Hempen Tangles. 



Fig. 5 represents the dredge devised by Dr. Ball, of Dublin, and 

 which scraped the surface so perfectly that, when drawn along a 

 drawing-room floor, it would pick up the pence that had been scattered 

 before it. Dr. Thomson states that the most convenient size for 



