252 



THE DEPTHS OF THE SEA. 



[chap. VI. 



out. The weight of the frame of this dredge, the 

 largest we ever used, was 225 lbs. ; it was forged by 

 Messrs. Harland and Wolff of Belfast of the best 

 Lowmoor iron. The dredge-bag was double — the 

 outer of strong twine netting, the inner of bread- 

 bag. Three sinkers — one of 1 cwt., 

 the other two of 66 lbs. each — were 

 attached to the dredge-rope at 500 

 fathoms from the dredge. . 



The operation of sounding at a 

 depth of 2,435 fathoms in the Bay 

 of Biscay on the 22nd of July, 1869, 

 has already been described in detail. 

 Wlien the depth had been accurately 

 ascertained, about 4.45 p.m. the 



dredge was let 



go, 



the vessel drift- 



ing slowly before a moderate breeze 

 (force=4) from the N.W. The 3,000 

 fathoms of rope were all out at 5.50 

 P.M. The diagram (I'ig. 50) will 

 give an idea of the various relative 

 positions of the dredge and the vessel 

 according to the plan of dredging 

 adopted by Captain Calver, which 

 worked admirably, and which ap- 

 pears, in fact, to be the only mode 

 which would answer for great depths. 

 A represents the position of the vessel Avhen the 

 dredge is let go, and the dotted line A B the line of 

 descent of the dredge, rendered oblique by the ten- 

 sion of the rope. While the dredge is going down 

 the vessel drifts gradually to leeward ; and when 

 the whole (say) 3,000 fathoms of rope are out, c, w, 



Fig. 49.— The End of the 

 Dredge-frame, showing 

 the luoiie of attaelimont 

 of tlie Bag. 



