CHEAP FIXTURES FOR THE HATCHING OF SALMON. 953 



each part through its own set of filters, as shown by the arrows. This 

 makes the single long trough equivalent to two shorter troughs, and since 

 the shorter trough would be amply long to receive the requisite screens, 

 the filtering capacity of the trough is thus doubled. "When either the 

 volume or excessive turbidness of the water demands an extraordinary 

 capacity in the filter, the water may be introduced at several points by 

 means of an additional long distributing trough placed alongside the filter- 

 ing trough, as shown by the dotted outline in Figure 2, and each of the 

 separate currents be subdivided as already described. In this way six 

 separate sets of filters may be introduced into a single trough 12 feet long. 

 The filters to be used with the foregoing arrangement are made by stretch- 

 ing woolen flannel on wooden frames. The best device consists of two separate 

 frames, one fitting inside the 

 other, (without nails,) as in 

 Fig. 3, and holding stretch- 

 ed between them a piece of 

 flannel considerably larger 

 than the frame, to allow for 

 shrinkage and for a margin ^ ^^- ^• 



to close the interstices on either side and at the bottom between the frame 

 and the trough. This filter slides down into the trough obliquely, between two 

 pairs of cleats on op- 

 posite sides, as shown ^^ rr^rnL^ ^^^^^^^^g^Psasy 

 in Fig. 4. Strips of 

 wood half an inch 

 thick are suitable for 

 the construction of 

 these frames, giving 

 a total thickness of 

 one inch to each filter, and if it is desired to save room, the space intervenino* 

 between the frames may be as narrow as half an inch, so that it is possible to 

 get eight filters into a single foot of the length of the trough. They should 

 slide easily into place, so that they may be removed whenever necessary to 

 dean them. The cloth can be removed from the frames and washed or dried 

 and brushed. There should be a large surplus of them on hand, so that a 

 clean one for immediate use should always be ready. The filters should not 

 come quite to the top of the trough, so that if they become completely clogged 

 with dirt the water may flow over their tops to the hatching-troughs; for 

 dirty water is much better than stagnation. It is better to have flannel (or 

 baize) of several grades of fineness, and pass the water through the coarser 

 ones first. If leaves and other coarse rubbish are liable to enter the filtering- 

 trough they must be arrested by a coarse grating of wood or metal above each 

 set of filters; it is better to stop all such coarse material outside the house. 



Fig. 4. 



