ALLMAIST. — USE OF THE TOWING NET. 



53 



on or near the surface of the sea in the way of the net as it is thus 

 towed behind the vessel, will necessarily pass into it ; and after 

 it has been allowed to remain out for a period varying with the 

 abundance of surface life in the sea at the time, it is to be hauled 

 in and examined. 



Though the richest results are usually obtained by using the 

 towing net close to the surface of the sea, it will frequently be 

 found important to employ it at various depths^ in order to obtain 

 information regarding the organisms which either habitually or 

 temporarily inhabit zones other than the most superficial one. 



For this purpose the net is to be weighted ; the weight attached 

 to it depending on the depth to which it is desired to sink it, and 

 on the velocity of the ship. Care should be taken that while the 

 net is out the motion of the vessel be not interrupted, and that 

 sufficient way be given to keep the net constantly distended iq its 

 passage through the water. 



It will generally be advisable to employ two nets at the same 

 time, one working close to the surface, and the other sunk to 

 some determined depth below it.* 



In the directions now given, the towing net is supposed to be 

 towed behind the vessel in open water ; but the Arctic explorer 

 should be reminded that some of his richest fields will be found 

 in places where the ice is for short distances discontinuous, and 

 where small portions of unfrozen water will be thus exposed. 

 Here oceanic forms will congregate in rich profusion attracted by 

 the light and air. In the smaller spaces so exposed we may use 

 with most advantage a towing net similar to that here described, 

 but, instead of being provided with a towing line, it should be 

 fixed to the end of a pole, and worked with the hand. 



Another mode of using the towing net, 

 wliich is often attended with the best re- 

 sults, consists in leaving it suspended 

 from the ship while at rest in the tideway 

 or in the course of currents. It may be so 

 left for several hours, and then hauled in 

 for examination. A net used in this way, 

 however, will be found most effective if it 

 be constructed somewhat differently from 

 the ordinary one. A piece of the same 

 material as that of which the rest of the 

 net is composed should be sewed within 

 its mouth so as to form a sort of diaphragm 

 in the shape of an inverted cone with an 

 open apex, as shown in the annexed 

 figure. This serves to retain whatever 

 has once made its way into the net. The 

 fundus of the bag is closed by simply 

 tying a cord round it, and its contents are 

 to be examined from the bottom by un- 

 tying the cord and washing out the bag 

 in the way to be presently described. 



* I am informed by Captain Nares that this 

 during the voyage of If. M.S. " Challenger." 



plan Avas commonly adopted 



