^yman.] 130 [February 6, 



the water will flow only over the lower portion ; the opposite half of 

 the next tank is cut out in the same manner, and the range of steps 

 thus forms an alternating cascade, having advantages similar to those 

 of the bulkhead arrangement in the pass. Where it is desirable to 

 make the stair short, it may, so to speak, be doubled on itself; that 

 is, two lines of tanks may be joined side by side : the water from tank 

 No. 1 would foil to the right into No. 2 ; then forward into No. 3 ; 

 then to the left into No. 4 ; and so on, each tank lower than its pre- 

 decessor. The channel, or the particular current of the river, that 

 leads to the foot of the pass, must be deep enough, and not too vio- 

 lent or too much obstructed. The regulation of the water at the up- 

 per end is very important ; otherwise, in a freshet, the fish-way would 

 be so flooded that the fish could not easily get up, and the structure 

 itself might be carried away. The regulation may be made by a 

 simple contrit'ance of movable bulkheads, or cross-boards. The head 

 of the pass may be protected from floating ice by its position, and, if 

 need be, by a boom. The tanks of a stair should be built with slant- 

 ing sides, so that they may not be burst by ice. It has been shown 

 that polluted water, discharged into a river, loses, almost immediately, 

 its chief deleterious elements. This suggests an easy and cheap 

 method of preventing the poisoning of the main body of a large 

 river by the discharge from race-ways. Let there be erected in the 

 river, opposite each race Avay, and far enough from it to avoid back- 

 water against the wheels, a close plank screen, running parallel to the 

 river bank, and at right angles to the race way. This screen should 

 be of a height proportionate to the depth of the water ; and it should 

 start just above the race-way, and extend down stream forty or fifty 

 feet. When the foul water rushes from the mill, it will come in con- 

 tact with the screen, and will be deflected in a direction parallel with 

 the river bank, and nearly coincident with the river current. Pre- 

 vented, in this way, from flowing into the middle of the river, it will, 

 atter a run of a few hundred feet, probably, become pure enough to 

 mingle with the rest of the water. 



Finally, there comes the last essential of a fish-way, namely, that it 

 should be open for the fish, both coming and returning. From about 

 the 25th of April till the loth of July, shad are either running up the 

 two rivers to spawn, or are returning after the performance of that 

 function ; while, in the first part of this period, salmon also would be 

 making their way to the head-waters, and smolts would be passing 

 down to the sea. From about the 20th of August to September 15th, 

 the young shad are going down to the sea, and the grilse would be 

 coming up. From that time to the middle of October, on the Con- 

 necticut; or from October loth to November 15th, on the Merrimack, 

 the old salmon would be going down to the ocean. Therefore, if 



