120 AMERICAN FISH CULTURE. 



Fig. 4. — Diagram of the double Fish-stair, at Lowell, showing 

 the arrangement of the tanks and the course of the water. The 

 tanks are somewhat oyer twelve feet square and about two feet deep. 

 The fall from each tank to the next, is one foot. With 2 feet and 

 4 inches of water on the dam-crest, a floating body moved down 

 the current of this fish-stair with an average speed of less than two 

 miles an hour, c, the dam. 



Fig. .5. — Diagram, to show how the width of the sheet flowing 

 into the first tank, is regulated by flashboards (6) placed on the 

 dam (c). 



Fig. 6. — Profile of Foster's fishway, showing the trough or pass, 

 (rf) sloping from the dam (c) to the river-bed. e, the water-line, 

 below the dam. 



Fig. 7. — Plan of Foster's fishway, showing the up-stream slant 

 of the cross-bulkheads (/) and the course of the water, c, the 

 dam. g, the flood-gate. 



Fig. 8. — Flood-gate of Foster's fishway, seen from the face of 

 the dam (c) ; a a, pieces of scantling, which may be removed to 

 increase the volume of water. This fishway is particularly adapted 

 to small streams, because it uses little water. In the absence of 

 any experiment, there is some doubt whether shad will freely pass 

 through so narrow an opening as this plan shows ; but alewives and 

 salmon will. The cross-bulkheads are made as high as the sides 

 of the pass, so that the water runs deep. Figs. 6, 7, and 8, are 

 drawn on a scale of 20 feet to an inch. 



