20 



V. S. BUREAU OF FISHERIES. 



paint the best preservative, copper oleate next, then the Dutch 

 method, and finally the tars. Tensile strength, however important 

 it is, is not the only consideration — indeed, in many cases is not 

 the most important consideration. 



Flexibility is a factor of great importance in many kinds of fishing 

 textiles. In gill nets a stiff or wiry line will cause the approaching 

 fish to react on coming in contact with the net and to turn and leave, 

 whereas a soft line yields and the fish becomes gilled in his effort to 

 get through. It is also said that a school of fish when surrounded 

 by a purse seme will, upon strikmg a soft net, continue to exert 

 themselves against it, forcing it outward while the net is being 

 pursed from below. In this manner the entire school is captured; 

 but if the net is stifi^ and wiry, experienced fishermen say, the fish will 

 react and ''sound," or dive, before the seine can be pursed, and 

 thus escape. The factor of flexibility of netting has long been 

 recognized in a qualitative way; but, so far as the ^\Titers are aware. 



Fig. 7.— Equipment used for testing the flexibility of lines. 



no effort has ever been made to measure it quantitatively. The 

 writers have devised a simple method of measurmg quantitatively 

 the flexibility of lines treated with various preservatives, and by 

 that means have obtained some highly interesting figures for the 

 several materials studied. 



Method of measuring flexibility. — The method consists, essentially, 

 of measuring the energy dissipated (or converted into heat) in bend- 

 ing a sample of the line through a definite angle. For this purpose 

 advantage was taken of the well-known laws of the pendulum. The 

 apparatus consists of a pair of simple wooden jaws, h, Figure 7, 

 supported from a horizontal support rod not shown m the figure. 

 A olock, g, serves as a base, and is cut out as an arc of a circle with 

 the jaws, b, as a center, so arranged that a sample of twine gripped 

 in the jaws will just fail to reach when the plummet, c, is attached 

 and swmgs freely. The plummet, c, is made of brass and is so con- 

 structed that the twine can be gripped straight and true at the center. 



The sample of line, a, is gripped m the jaws and the plummet 

 attached at the lower end. The plummet is displaced from the 



