48 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [6} 



have acquired a velocitj^ equal to 8 VdB ai)i)roxiinately. ^^'e see, tbeu^ 

 iu tliis case, lio^v it is possible to deliver a molecule from a giveu posl- 

 tiou to a definite lower positiou without the increase of velocity that 

 would arise if the molecule fell freely under the action of gravity or 

 rolled down a smooth incline, it it be possible to compel every mole- 

 cule of water descending through a fishway to submit to the conditions 

 above indicated, then the problem how to control the velocity of a de- 

 scending current would be solved. Xow, to apply this to liquids, we 

 arrange a series of bent tubes, shown in Fig. 4. By suitable arrange- 

 ments we keep the longer branch of the higher tube of the series full 

 of water. The water escaping from each tube will rise against gravity 

 until it comes to rest, then fall into the longer branch of the adjacent 

 tube iu the series, and, after passing through the entire series, be finally 

 discharged from the shorter branch of the lowest bent tube with no 

 greater velocity than it acquired iu passing through the first member of 

 the series. 



Construct a series of these tubes with branches brought close together, 

 cut away obliquely the upper end of the longer branch of each member 

 of the series, so as to permit access of water, pack them side by side in 

 oblique position iu an inclined sluice, as shown in Fig. 5, and we have 

 the solution of the problem with which we started. For if we suppose 

 a current of water to be running through the inclined trough or sluice- 

 way, the first effect will be to fill the tubes with water and establish a 

 flow through them; the water entering the longer branch of each tube 

 will escape from the shorter branch with a velocity due to the head or 

 vertical distance between the two ends of the tube. This final direction 

 being obliquely up the sloi)e, each particle of water will describe a path^ 

 as is indicated by the curved arrows shown in Fig. 5. The effect will 

 be that we will have an ascending current iu the sluice on that side of 

 the sluice where the shorter branches of the tubes are situated. The 

 velocity of this ascending current will become less and less as we pass 

 toward the middle of the sluice, w^here there will be a line or section of 

 practically eddy water, and beyond a descending current, becoming 

 more rapid as we pass to the further side of the sluice, where we find a 

 current descending with uniform velocity, the maximum limit of which 

 will be the velocity of the water escaping from the shorter branches, 

 provided the supply of water and the capacity of the tubes are i^roperl y 

 proi)ortioned. 



The illustrations here given present briefly and graphically the prin- 

 ciples aijplied in the McDonald system of fishway building. 



5. Adaptability of the system. 



The flexibility of the system adapts it to the widest range of condi- 

 tions occurring in practice. An effective passage may be provided 

 for fish over obstructions, with the supply of water that will flow 

 through a cross section six inches square, or the fishway may be ex- 



