146 



SCIENCE. 



[Vol. IV., No. 81. 



A MERICAN APPLIANCES FOR DEEP-SEA 

 INVESTIGA TION. — THE DREDGES. 



The use of dredges for obtaining marine 

 specimens is said to have been suggested by 

 the common 03'ster-dredge, — a one-sided con- 

 trivance, well adapted for the shallow 03-ster- 



banks, on which 

 it is skilfully han- 

 dled b}^ the oys- 

 ter-fishermen of 

 both Europe and 

 America. This 

 dredge possesses 

 only a single nar- 

 row, hoe - like, 

 scraping edge, at- 

 tached to a light 

 frame above, fur- 

 nished with rigid 

 handles. The 

 net has a coarse 

 mesh of stout 

 twine, or small 

 interlacing iron 

 rings, the two 

 materials being 

 often combined. 

 This net is too 

 coarse to retain 

 the finer objects, 

 which are as im- 

 portant to the 

 naturalist as the 

 larger ; and in even moderate depths there is 



Fig. 1. — Otho Frederick Mul- 

 ler's dredge, A.D. 1750. 



{From ' The depths of the sea,' p. 239.) 



constant danger of the frame 

 descent through the water 



capsizing in its 



It was these imperfections in the oyster- 

 dredges, unsuiting them for careful work, that 

 led to the changes in the shape of the frame 

 and in the construction of the net, resulting in 

 the production of the perfect yet simple ap- 

 pliance which is now used with as much pre- 

 cision in the deepest parts of the ocean as is 

 the oyster-dredge in its few fathoms of water. 



The ordinary dredge. 



The dredges adopted by the U. S. fish-com- 

 mission in 1871, ai d still employed for all ordi- 

 nary kinds of work, are of the Ball pattern, but 

 slightly modified. The same pattern has also 

 been used to some extent b} T the U. S. coast- 

 survey. 



The fish-commission dredges are made in 

 two sizes, — the smaller, called the 'boat- 

 dredge,' being suitable for moderate depths of 

 water from small boats, where only hand-power 

 is available for the hauling-in ; and the larger, 



termed the ' deep-sea dredge,' for vessels sup- 

 plied with steam-hoisting engines. Otherwise 

 than in size, however, these two dredges do 

 not differ from one another. In the deep-sea 

 pattern (fig. 2), the mouth-frame, which is 

 constructed of the best qualhyy of wrought-iron, 

 measures two feet long by five and a half or 

 six inches wide between the hinder edges of 

 the scrapers which form the longer sides of the 

 frame. The latter are two and three-fourths 

 inches wide and a half-inch thick, being bevelled 

 to a sharp edge in front, and are joined to the 

 rounded end-pieces at an obtuse angle, which 

 causes them to flare forward, — an essential 

 feature for most kinds of dredging-work in 

 which it is required that the scrapers should 

 have a strong tendency to dig into, or ' nip,' 

 the bottom. The handles are of round iron, 

 bent double, as shown in the figure, with a 

 loop at the outer end for the attachment of 

 the drag-rope, the lower ends making a single 

 turn about the end- 

 pieces of the frame, 

 upon which the han- 

 dles move freely. 



The net is either a 

 closed bag of strong 

 twine netting, having 

 a finer mesh at the 

 bottom than at the 

 sides, or is made cyl- 

 indrical in shape, of 

 webbing having three 

 or four meshes to the 

 linear inch, the lower 

 end being tied with a 

 stout cord when in use. 

 To protect the net from 

 wear on rough bot- 

 toms, and prevent its 

 bursting open when 

 heavily loaded, it is 

 covered with a bot- 

 tomless canvas bag a 

 few inches longer than 

 the net itself. To the 

 lower end of this bag 

 and to the end of the 

 net a small round stick 

 is fastened. This is in- 

 tended to prevent the 

 fouling of the net while 

 being lowered, and al- 

 so to aid in reversing 

 and emptying it after it has been hauled back 

 upon the deck. It is purposely made of soft 

 wood, in order that it may break without tearing 

 the net if it becomes caught upon the bottom. 



Fig. 2. — The naturalists' 

 deep - sea dredge as 

 rigged by the u. s. fish- 

 commission. 



