1911] Kofokl: Self-closing Plankton Net. 333 



the springs, when set for satisfactory action in the air or surface 

 waters, may not function as desired in one hundred fathoms or 

 more. A number of variables enter into the problem of adjust- 

 ment, such as resistance of the water, temperature, pressure, the 

 mesh and tension of the net, and the depth. It is possible, how- 

 ever, with a given set of springs to- adjust each coil so that the 

 jaw which it controls will certainly function at any desired depth. 

 This capacity for adjustment renders the net adaptable to mes- 

 sengers of different weights and to operation in different depths. 

 In practice it has been found advisable in determining the proper 

 tension to set the springs for operation in the air and then to 

 slightly increase the tension little by little till the trips are 

 properly released in the desired depth. The number of turns of 

 the key for the tension demanded can then be made a matter of 

 record and the given tension may thereafter be employed when- 

 ever the net is sent down to that depth. 



The cable is then inserted in the head of the net, the cable 

 slot closed, the net hoisted on the cable, and the w^eight upon the 

 foot locked in place by the set screw so that the net is w^ell 

 balanced, the jaws are both raised in the upper position (pi. 22, 

 fig. 1) and grasped by the clutches of the trips. The net is then 

 ready for descent. 



"When it has been lowered to the desired level the first mes- 

 senger is sent down, care being taken that the cable is in a 

 vertical position. This drops the lower jaw to the lower position 

 (pi. 22. fig. 2, and pi. 23, fig. 4) against the ledge in the lower 

 arc of the frame (pi. 22, fig. 1) and opens the net. The vessel 

 is then put in motion along the desired course and the net is in 

 operation in a horizontal position at approximately the depth to 

 which it was sent down. 



I know of no satisfactory way of determining absolutely the 

 precise depth at which this or any other piece of towed deep-sea 

 apparatus functions. This depth is a resultant of a number of 

 variables such as the speed of the vessel, force and direction of 

 currents, resistance of the net and cable, the weight of the 

 apparatus, the mesh in the bag, the quantity of the catch which 

 may increase resistance by clogging, etc., etc. The determination 

 of the depth of the apparatus by use of the dredging quadrant 



