Fig. 128 gives a larger vertical section of the lower wheel with the guides, shaft, and connecting members. The guide passages, and the wheel passages, are triple as shown so that the latter may be filled not only at full gate, but also when it is one-third or two-thirds open, thus avoiding the loss of energy due to sudden enlargement of the flowing stream. The two horizontal partitions in the wheel are also advantageous in strengthening it. The inner radius of the wheel is 31-1/2 inches and the outer radius is 37-1/2 inches, while the depth is about 12 inches. In this figure the gate is represented closed and to open, it moves downward uncovering the guide passages as shown in Fig. 126, the position it occupies loaded. In Fig. 127 is shown a half-plan of one of the wheels, in a part of which are seen the _guides and vanes_, there being 36 of the former and 32 of the latter. Although the water on leaving the wheel is discharged into the air, the very small annular space between the guides and vanes, together with the decreasing area between the vanes from the entrance to the exit orifices, _ensures that the wheels move like reaction turbines_ for the three positions of the gates correspond to the three horizontal stages or openings through the guides as shown in Fig. 128, _i. e._, three stages of gate. NOTE.—A test of one of these wheels, made in 1895, developed 5,498 electrical horse-power, generated by an expenditure of 447·2 cubic feet of water per second under a head of 135·1 feet. The efficiency of the dynamo being 97 per cent., the efficiency of the wheel and approaches was 82-1/2 per cent. [Illustration: FIG. 127.] The average discharge through one of these twin turbines is about 430 cubic feet per second, and _the theoretic power_ due to this discharge is 6,645 horse-power. Hence if 5,000 horse-power be utilized _the efficiency_ is 75.2 per cent. Under this discharge the mean velocity of water in the penstock is nearly 10 feet per second, but the loss of head due to friction in the penstock will be but a small fraction of a foot. The pressure-head in the wheel case is then practically that due to the actual static head, or closely 141-1/2 feet upon the lower and 130 feet upon the upper wheel. The absolute velocity of the water when entering the wheel is about 66 feet per second, so that the pressure-head in the guide passages of the upper wheel is nearly 66 feet. The mean absolute velocity of the water when leaving the wheels is about 19 feet per second, so that the loss due to this is only about 4 per cent. of the total head.