Dredging in shallow water, say ten to twenty fathoms, is an easy operation enough; but the deeper the dredger goes, the heavier must be his vessel, and the stouter his tackle, while the operation of hauling up becomes more and more laborious.  Dredging in 150 fathoms is very hard work, if it has to be carried on by manual labour; but by the use of the donkey-engine to supply power,[2] and of the contrivances known as “accumulators,” to diminish the risk of snapping the dredge rope by the rolling and pitching of the vessel, the dredge has been worked deeper and deeper, until at last, on the 22nd of July, 1869, H.M.S. Porcupine being in the Bay of Biscay, Captain Calver, her commander, performed the unprecedented feat of dredging in 2,435 fathoms, or 14,610 feet, a depth nearly equal to the height of Mont Blanc.  The dredge “was rapidly hauled on deck at one o’clock in the morning of the 23rd, after an absence of 7-1/4 hours, and a journey of upwards of eight statute miles,” with a hundred weight and a half of solid contents.

[Footnote 2:  The emotional side of the scientific nature has its singularities.  Many persons will call to mind a certain philosopher’s tenderness over his watch—­“the little creature”—­which was so singularly lost and found again.  But Dr. Wyville Thomson surpasses the owner of the watch in his loving-kindness towards a donkey-engine.  “This little engine was the comfort of our lives.  Once or twice it was overstrained, and then we pitied the willing little thing, panting like an overtaxed horse.”]

The trawl is a sort of net for catching those fish which habitually live at the bottom of the sea, such as soles, plaice, turbot, and gurnett.  The mouth of the net may be thirty or forty feet wide, and one edge of its mouth is fastened to a beam of wood of the same length.  The two ends of the beam are supported by curved pieces of iron, which raise the beam and the edge of the net which is fastened to it, for a short distance, while the other edge of the mouth of the net trails upon the ground.  The closed end of the net has the form of a great pouch; and, as the beam is dragged along, the fish, roused from the bottom by the sweeping of the net, readily pass into its mouth and accumulate in the pouch at its end.  After drifting with the tide for six or seven hours the trawl is hauled up, the marketable fish are picked out, the others thrown away, and the trawl sent overboard for another operation.

More than a thousand sail of well-found trawlers are constantly engaged in sweeping the seas around our coast in this way, and it is to them that we owe a very large proportion of our supply of fish.  The difficulty of trawling, like that of dredging, rapidly increases with the depth at which the operation is performed; and, until the other day, it is probable that trawling at so great a depth as 100 fathoms was something unheard of.  But the first news from the Challenger opens up new possibilities for the trawl.