1 70 J- N. Carruthers 



wire-angle gauge designed for use on the hydrographical wire which carries the water 

 bottles used for the routine collection of water samples and temperature data. The 

 gauge is messenger-operated and is usable intermediately with the bottles. From it one 

 learns the actual slope of the wire both in magnitude and direction so long as the wire 

 is sufficiently weighted (<200 lbs) to preclude the heavy pendulous gauges from 

 introducing local deformations into the wire because of their own weight. 



We shall describe a simple method of checking the showings of such gauges— a 

 method which could be extended to determine the underwater course of a deep-sea 

 trawling cable leading all the way down into the greatest ocean depths. Then, it 

 would be possible to learn the amount and direction of slope at discrete intervals all 

 the way down such a cable as was used by Bruun from the Galathea when bottom- 

 dredging in the Philippines Trench, in keeping with Kullenberg's calculations. 



It should be remarked that when describing the earliest versions of the current- 

 measuring cone above referred to, a description was added of how both direction and 

 slope could be determined from a compass poised in hot gelatine only — without 

 need to use the kerosene as well (Carruthers, 1954 a, p. 185). 



We are particularly interested to detail simple ways of determining the underwater 

 course of lines, wires, ropes or warps let down from stopped vessels occupied with the 

 activities of routine oceanographical stations, or towed behind ships engaged in trawl- 

 ing or analogous operations. Clearly, if jelly bottles of the kind described were 

 suitably affixed to such lines, their simple round shape would be a great boon because 

 it would not matter how they were disposed on the wire (above, below, or laterally) so 

 long as parallelism were maintained. 



It is not overlooked that a jelly bottle whose gelatine will remain uncongealed long 

 enough to permit slope determinations to be made of hydro wires, may have too short a 

 liquid life to be usable for investigating the underwater course (slope and direction) 

 of the warps on which a pelagic trawl is towed, but it will be an easy-enough matter 

 to achieve longer timings by using greater bulks of hot jelly in bigger bottles, or by 

 encasing the jelly bottles in suitable covers to be filled with hot water before immersion 

 in the sea. Whatever be the form of slope indicator decided upon, neutral buoyancy 

 will be approximated to guard against the production of local deformations in the line. 



This is a matter of importance because of the great interest which attaches to deciding 

 the fishing depth of an off-bottom trawl. 



It is believed that the simple devices here being considered could be profitably 

 used to find at what depth a pelagic trawl had fished, at what height above bottom its 

 foot-rope had ridden, what had been the distribution of its vertical gape and of its 

 horizontal gape. 



We have here no concern at all with the very ingenious instruments which use 

 electronics and acoustics to telemeter net depth back to the towing ship whilst the 

 tow is in progress, but fully appreciate the value to a fishing skipper of always knowing 

 at what depth his pelagic net is fishing, so that he can alter his speed or warp length 

 to keep it at the depth where his echo sounder tells him the fish are. 



Because it seems quite unlikely that ordinary fishing craft will ever carry the tele- 

 metering net-depth indicators now being tested, it has seemed well worth while to line 

 up with opinion that a necessary pre-requisite to achieving anything simpler which 

 can be relied upon, is to determine the exact underwater course of the towing warps 

 all the way from ship to net. 



