Chap, xxii.j DEEr-SEA DREDGING. 



5or 



the vastness of its expanse, the depth is, nevertheless, so great 

 as to be difficult of adequate realisation. The greatest depth 

 as yet ascertained by sounding occurs, as will be seen from the 

 map at the commencement of this work, in the North-West 

 Pacific Ocean ; it amounts to about five miles and a quarter. 



In order to realise such a depth, the reader should think of 

 a spot distant several miles from his actual position, and then 

 attempt to project the distant point downwards, until it lies 

 vertically beneath him. The average depth of the ocean 

 between lats. 60° N. and 60° S.* is about three miles or 2,500 

 fathoms. The great depth of five miles occurs only exception- 

 ally over very small areas. 



The vastness of the depth of the Ocean was constantly 

 brought home to us on board the " Challenger " by the tedious 

 length of time required for the operations of sounding and 

 dredging in it. When the heavy sounding weight is dropped 

 overboard, with the line attached, it takes about an hour and 

 a quarter to fall to the depth of 4,500 fathoms, and thirty-five 

 minutes to reach the bottom in the average depth of 2,500 

 fathoms. 



The winding in of the line again is a much slower process. 

 It used to take us all day to dredge or trawl in any considerable 

 depth, and the net usually was got in only at nightfall, which 

 was a serious inconvenience, since we could not then, in the 

 absence of daylight, make with success the necessary examina- 

 tions of the structure of perishable animals. 



The ship, when deep-sea operations were going on, used 

 to lie rolling about all day, drifting along with the wind, and 

 dragging the dredge over the bottom. From daybreak to night 

 the winding-in engine was heard grinding away with a painful 

 noise, as the sounding-line and thermometers were being 

 reeled in. 



At last, in the afternoon, the dredge-rope was placed on the 

 drum, and wound in for three or four hours, sometimes longer. 

 Often the rope or net, heavily weighted with mud, hung on the 

 bottom, and there was great excitement as the strain gradually 

 increased on the line. On several occasions the rope broke, 

 and the end disappeared overboard ; three or four miles of 

 rope and the dredge being thus lost. 



At first, when the dredge came up, every man and boy in 

 the ship who could possibly slip away, crowded round it, to see 

 what had been fished up. Gradually, as the novelty of the 

 thing wore off, the crowd became smaller and smaller, until at 

 last only the scientific staff, and usually Staff-Surgeon Crosbie, 



* J.J. Wild, "Thalassi,"" pp. 14, 15. London, Marcns Ward & Co., 

 1877- 



