NARRATIVE OF THE CRUISE. 79 



Tow-Nets. — These nets were continually in use during the cruise, and a stock of over 

 a dozen was always kept ready to hand. The hoops were 10, 12, 14, and 16 inches in 

 diameter, and the bags were made of fine muslin and buntin or strong cotton. 



During the daytime they were usually towed from the ship about 50 fathoms beneath 

 the surface with a 6 lb. lead, and sometimes to 200, 400 and 800 fathoms with a 14 lb. 

 lead. The weights were placed about 10 fathoms in front of them, 

 as represented in the woodcut (see fig. 23). The finest muslin ones 

 were generally used when a boat was lowered from the ship for the 

 purpose of tow-netting, and could be pulled very slowly through 

 the water. During the last years of the voyage these nets were 

 attached to the dredge fine just below the weights, and also to the 

 sides of the dredge and beams of the trawl. 



On a good many occasions they were tied alongside a rope, as 

 represented in the woodcut (see fig. 24), and sent down two miles 

 with a lead and then hauled up again. In this operation, they, of 

 course, only worked while being hauled up. The object of using 

 them in this manner was to ascertain whether or not organisms 

 lived in the deeper layers of water. 



Fig. 23.— Ordinary method of using the Tow-Net. Fig. 24. — A method of using the 



Tow-Net in deep water. 



Current Observations. 



Current Drags. — Current observations were occasionally attempted on board the 

 Challenger. The surface current could, of course, be roughly ascertained by the 

 difference between the ship's position, as found by observation and by dead reckoning; 

 but the accuracy of this estimate, depending as it does entirely on the correct steerage 

 of the ship, and the proper allowance being made for speed through the water, cannot 

 be implicitly relied on. 



When circumstances were favourable, therefore, a boat was anchored by the dredge 

 rope, and t?he speed and direction of the surface current ascertained by heaving a log from 

 the anchored boat ; and in order to ascertain by actual observation whether currents 

 existed below the surface, an apparatus was lowered to such a depth as was thought 

 advisable. As the movements of the apparatus could only be ascertained by attaching 



