292 PROCEEDINGS OF SECTION D. 



back the surface film of leaf-dust, leaves, grass, &c. Such au arrange- 

 ment as this, however, could not get over the difficulty presented by 

 the absence of free circulation of the comparatively deep water of the 

 ponds — particularly the smaller ones. 



The efiect of the outflow-boxes to be now described has been — 

 (1) to keep up as even a circulation as is practically possible under the 

 circumstances, (2) to increase enormously the straining area for the 

 water as it passes from pond to pond, and (3) to reduce screen-clogging 

 to an almost negligible quantity. 



The outflow-boxes are constructed and arranged as follow : — 

 Out of 1-in. pine timber four-sided sections of fluming are made in the 

 shape of an " T " (see Figure 1). These are made of varying widths 

 to suit the size of the outflow and the quantity of water to be passed ofi. 

 One of these is placed at the end of each pond, the upper arm of the 

 " r " projecting into the overflow gutter or channel, and the vertical 

 part being laid against the end wall of the pond (as shown in Figure 2). 

 I consider it is preferable to have the upper part of the " T " uncovered, 

 80 as to facilitate cleaning or asphalting at any time. Owing to the 

 width of the boxes in use at Prospect, I thought it desirable to fasten 

 a stout cleat of wood around at a short distance from each end of the 

 vertical section of the fluming, as shown in the diagram, to prevent 

 "buckling." On the inner side — that which lies against the wall of 

 the pond when the outflow-box is in position — the cleats haA^e the 

 additional iise of keeping the whole contrivance just clear of the wall, thus 

 giving the water all roimd free access to the " straining basket." On 

 the sides of the projecting arms at the top, are one or two small fillets 

 of wood to facilitate the fixing of the outflow-boxes. In the case of 

 those in use at Prospect, I had these so placed as to enable them to slide 

 down in the grooves already there for the old surface screens. 



Over the lower end of the fluming is slipped a " basket " of (vari- 

 ously) brass or galvanized wire. The latter is arranged to fit the 

 outside of the fluming or " box " exactly, and is made of mesh suitable 

 to the size of trout in the pond in which it is placed. The only object 

 of the basket, of course, is to prevent the free passage of the trout 

 from pond to pond ; consequently, in the case of fry, the mesh need be 

 no smaller than will be just sufficient to keep the fishes from working 

 through. I endeavour to have the mesh as large as possible in each 

 case so as to promote the best circulation possible. Because of 

 the large straining surface that is possible, and the consequent absence 

 of water pressure at the screen, under the conditions offered by the use 

 of the outflow-box it is practicable to use a considerably larger mesh 

 than if the straining screen were at the surface of the water. The 

 basket-shaped strainers in use at Prospect run in mesh from one- 

 sixteenth of an inch up to half-an-inch. The half -inch mesh is used 

 for the ponds containing larger trout of two, three, or four years. A 

 much greater mesh might be used, of course, but there would be nothing 

 gained by this. 



