452 BULLETIN OF THE 



open and tliu.wn back in the figure, so as to show the net. The Eng- 

 lish Deep-Sea Dredging Expedition used a double bag, the outer being 

 a close net of sounding-line, the inner a piece of " bread-bag," a some- 

 what open canvas. To prevent the bag from being turned inside out 

 in going down, a stout brass wire, bent in a semicircle and put inside 

 the ba" with the ends fastened to the frame, will be found very con- 

 venient. 



The dredge used by the Swedish expeditions is a little different, the 

 ba^ being simple and made of canvas with several square holes closed 

 with wire-gauze. Light objects would seem liable to be washed out 

 of this bag when hauling up, still it appears to have worked satisfac- 

 torily. 



Mr. Bowerbank used a bag formed of two pieces of raw hide con- 

 nected at the ends and bottom by a net made of cod-line. 



The dimensions of a dredge vary according to the depth or bottom on 

 which it is to be used. From two feet by six inches up to four feet by 

 ei^ht inches will be found the most useful dimensions. For deep-sea 

 dredging, the dredge ought to be heavy, so as to sink rapidly, and be 

 kept on the bottom by its own weight. A heavy lead was attached to it 

 with advantage in the United States Coast Survey Expedition. The 

 English dredgers consider it an impediment, and prefer to have the 

 weight in the metal of the dredge. The rope used by the United States 

 Coast Survey in deep-sea dredging was from one and a half to one and 

 three fourths inches in circumference, made of best Italian hemp by 

 Messrs. Sewall, Day, & Co., of Boston, and gave entire satisfaction. 

 The Porcupine Expedition used hemp rope two and two and a half 

 inches in circumference. 



In dredging over rocky ground, the rope is fastened to the ring of 

 one of the°af"ms only, whilst the other is tied to it with spun-yarn. 

 Should the dredge get foul of a rock, the stop will break and the 

 dredge come up endwise, the whole pull acting then on one arm. 



As a rule the length of line should be about twice the depth. On 

 very soft bottom it is somewhat shortened, to keep the dredge from 

 getting filled too soon. In very great depths it was found by the 

 English Porcupine Expedition that the line could be kept much shorter 

 by attaching to it weights of one hundred or two hundred pounds at 

 about one fourth the depth from the dredge. The dredging is then 

 carried on, as it were, from the weight, and not from the vessel. In 



