252 



THE DEPTHS OF TILE SEA. 



[cii.Ar. vi. 



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

 largest we ever used, was 225 lbs.; it AA'as 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 50 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, 1809, 

 has already been described in detail. 

 When 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 (Fig. 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 when the 

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

 descent of the dredge, rendered oblique by the ten- 

 sion of the rope. AVhile the dredge is going down 

 the vessel drifts gradually to leeward ; and when 

 the whole (say) :>.<>(0 fathoms of rope are out, c, w, 



Pig. 19.— The End «( the 

 Dredge-frame, showing 

 tin' mode "I attachment 



of the JI:i;.'. 



