OCEANOGRAPHY ISELIN 257 



on nearing the surface. This destructive release in pressure, which 

 at first destroyed nearly all specimens of deep-sea fish by causing 

 gas bubbles to form in the tissue, can now be fairly well prevented 

 by using much the same methods as employed in raising a diver. 

 Recently on the Atlantis it has been found possible to make as 

 many as five simultaneous tows with closing nets and know the exact 

 depth of each catch. In this method the wire is so heavilj^ weighted 

 that it remains practically vertical during the tow and the nets are 

 fastened to it one below the other at known intervals. A system of 

 messengers sent down the wire operate the opening and closing 

 devices of the nets. Not only are the opening and closing devices 

 extremely satisfactory but also a further refinement has resulted. 

 Since the frames of the nets are fastened to the wire rigidly, there 

 is no bridle in front of the opening to scare away the animals in the 

 net's path. With large deep-sea nets designed for catching more 

 active animals such refinements are not yet in practice. In fact, even 

 though the net used may be of the closing type, the depth at which 

 the catch is made usually becomes somewhat problematical if the 

 towing wire is at any considerable angle from the vertical. There 

 has been some experiment with pressure instruments which should 

 record the depth of the net at all times during the tow, but there are 

 still many difficulties which must be met. The technique of deep- 

 sea tow-net work is further complicated by the fact that the nets used 

 to-day do not stand much hard usage and soon develop holes and 

 tears which always try the patience of the oceanographer. It is a 

 matter of time and money before biological work at sea can be 

 conducted with satisfactory accuracy. 



The study of bottom samples taken from the floor of the ocean 

 has always been productive and has aroused considerable interest 

 among geologists as well as oceanographers. The recent develop- 

 ments in this field have also much improved the accuracy and use of 

 the observations. The old-fashioned piano-wire sounding machine 

 can now be replaced by the accurate and almost automatic sonic 

 method, so that the exact depth of the water can be found at all 

 tim.es. Formerly it took several hours to make each sounding and 

 by the time the wire was hauled back aboard, the vessel could have 

 drifted into water having a different depth. For all bottom sample 

 work, the operation is made much easier by knowing the depth in 

 advance. Otherwise several hundred fathoms extra wire may be 

 run out before the observer is sure his sampling device has reached 

 bottom. With any sampler more complicated than the ordinary 

 sounding tube this may be a great disadvantage. The extra cable 

 coiled on the bottom may kink and the instrument will probably be 

 lost when strain is again put on the wire. 



