[5] A NEW SYSTEM OF FISH WAY-BUILDING. 47 



aged, with the conviction that an efficient shad-way was a thing of the 

 future. 



4. The principles of the new fishway, and the details of 



its arrangement. 



The conditions to be satisfied in a successful fishway construction are 

 as follows: (1) The water should be delivered down a straight unob- 

 structed channel. (2) In sufficient volume to invite the entrance of fish. 

 (3) With such moderate velocity as to permit their ready ascent. (4) 

 With a view to economy in construction, it is important that the incli- 

 nation or slope of the way should be much more considerable than in 

 the ordinary inclined-plane fishway. 



How to construct so as to fulfill these conditions was the problem to 

 be solved. Two methods suggested themselves. It was possible to make 

 the water do work in its descent, and thus control velocity. A fishway 

 could be constructed on this principle by an evident modification of the 

 ordinary turbine wheel. And such a fishway could be made to serve 

 both as a j^assage-way for fish and as a motive power for machinery. 

 This idei\, however, was soon abandoned, for the double reason of its 

 comiilexity and the limitations to its application that would necessarily 

 exist. The second fruitful idea was that if each molecule of water could 

 be compelled to traverse a constrained path, its final direction in any 

 one circuit being against gravity, it could be brought to rest at a lower 

 level — the friction developed in movement having neutralized in part 

 the force of acceleration. The molecule falling from its second position 

 of rest through a similar circuit, and in succession through any number 

 of circuits, would finally reach any defined lower level with no greater 

 velocity than that attained in the first circuit described. Were it prac- 

 ticable to subject every molecule of water passing through a fishway to 

 the constrained movement above indicated, the result would be a de- 

 scending current, the average velocity of which would not exceed the 

 average velocity of a molecule in passing to consecutive positions of rest 

 under the conditions above stated. 



How this idea has been realized in practical constructions will be 

 understood by reference to the following figures and descrii^tions. 



[f we take a hemispherical bowl (Fig. 1), and holding a marble at A, 

 upon the edge of the bowl, we release it, it will fall, under the influence 

 of gravity, through A' to A", coming to rest at A", some distance be- 

 low the edge of the bowl. The vertical distance between the positions 

 A and A" measures the force of acceleration that has been counteracted 

 by friction by traveling the constrained path A A' A". If now we 

 take a number of similar bowls and cut them off to the line A A", and 

 arrange them as in Fig. 3, and start a marble at D', it will pass from 

 D' to C, reaching C with no greater velocity than that acquired in 

 passing from A to A'. If, however, the marble were allowed to roll 

 unobstructed from A to A", down the incline plane D (Fig. 2) it will 



