16 THE YOYAGE OF H.M.S. CHALLENGER. 



described hereafter ; to the other a small tackle was hooked, to haul the rope close to 

 the ship's side when required. The dredge or trawl being ready to go over, the ship 

 was put before the wind, and the jib hoisted, the wind being kept a little on the quarter 

 of that side of the ship it was intended to work from, in order to drift the dredge clear 

 of the propeller. The dredge was now triced up to the block below the accumulators, 

 and the burton on the mainyard hauled out until the dredge plumbed the sea; it was then 

 lowered down a fathom or two below the surface, and the rope checked, so that from the 

 platform the tangles might be seen to trail clear of the dredge-bag. This having been 

 satisfactorily ascertained, the rope was let go and allowed to run out freely, the ship 

 forging slowly through the water, leaving the dredge' to sink astern, and thus prevent- 

 ing all chance of fouling. The rope was checked occasionally to ensure its being taut 

 from the dredge. 



When from 300 to 500 fathoms had been paid out, a toggle was lashed to the rope, 

 which was then let run until a sufficient quantity had been paid out to allow the toggle 

 to reach the bottom were the line perpendicular. The dredge and rope then occupied the 

 position A B, shown in fig. 6, and the ship was brought to the wind and kept stationary, 

 or, if there were much wind, steamed slowly towards the dredge, taking care not to over- 

 run it. A weight of Ij cwt. was now attached to the thimble through which the rope 

 was rove before it was secured to the dredge chain, as mentioned above, and the weight 

 and thimble being let go they travelled down the curve of the rope until they were 

 brought up at the toggle. The dredge and rope by means of this additional weight 

 now successively assumed the positions A C, A D, and A E, until finally the dredge 

 reached the bottom at F, the weights being in the position of G', Gr", and G'", &c. It is 

 evident that, provided there were no surface or under-current, the dredge must reach 

 the bottom with the tangles trailing fairly after it, if sufficient time had been allowed 

 for it to sink. The surface current could always be ascertained and allowed for ; when 

 the dredge, therefore, came up foul, as it occasionally did, we could only ascribe its 

 doing so to the influence of some under- current, which need not necessarily have been 

 at the bottom, — or to the rope when new twisting the dredge round and round. 



We found by experience that about three hours were required to sink the dredge in 

 this manner when the depth was about 2500 fathoms. When it had reached the bottom 

 the ship was allowed to drift broadside to the wind for a certain time, until the accumu- 

 lators pointed out, by their extension and contraction, that the dredge was being 

 dragged slowly over the ground. When the dredge fouled, the strain of the ship 

 immediately stretched the accumulators to their utmost, the line was at once let go 

 to prevent its carrying away, and the ship was brought head to wind and kept stationary, 

 the rope being hove in slowly ; if it continued foul, the ship was steamed ahead of and 

 all round the supposed position of the dredge to endeavour to clear it (as a boat's anchor 

 is cleared when jammed on a coral reef or amongst rocks) ; finally the dredge either got clear 



