Page:Popular Science Monthly Volume 3.djvu/277

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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.
PSM V03 D277 Hempen dredge.jpg
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