" Challenger 

 trawl. 



34 



DEPTHS OF THE OCEAN 



of dredge have, however, their advantages, according to the 

 animals it is desired to procure. 



The "Challenger" used a trawl (Fig. 1 1) constructed like 

 the ordinary beam-trawl, which was employed particularly by 



Fig. 13. — Tow-Net fixed at End of Line ("Challenger"). 



the fishermen in the shallow waters off the flat English coasts. 

 The beams were of different lengths, 17, 13, and 10 feet, 

 but the lo-feet length was found to be the best 

 for deep water. It was, however, difficult to 

 tell, when the depth was at all great, whether 

 the trawl had reached the bottom right side up, 

 and whether it was open while being towed. 

 Sigsbee solved this difficulty by having tripping 

 lines on both sides (Fig. 12) ; otherwise the size 

 of his trawl was identical with that of the 

 " Challenger," viz. 10 feet between the runners. 

 Sigsbee's appliances and methods of work- 

 ing were adopted by the " Valdivia" and other 

 recent expeditions. 



Pelagic During the cruise of the " Challenger" the 



of?he"^^^ appliances used for making pelagic captures 

 "Challenger." cousisted of Small nets resembling long night- 

 caps, of fine muslin or calico, and 10 to 16 inches 

 in diameter at the mouth. They were towed 

 at various depths, even as far down as 800 

 fathoms, with a weight attached a little in front 

 of the opening (Fig. 13), or they were some- 

 times made fast to the line (Fig. 14) and lowered 

 to a depth of about 2 miles (over 3600 metres), 

 the object being to ascertain whether or not fi 

 organisms lived in the deeper layers of water 

 different from those captured in the surface layers. 



Since the time when the "Challenger" conclusively proved 

 that life was present everywhere in the ocean, not only over 

 the bottom at the profoundest depths, but also in the inter- 

 mediate layers of water, much labour has been expended upon 



14. — Tow-Net 

 fixed on the Line 

 (" Challenger"). 



