The general arrangements required for the proper erection of turbines are well understood by competent millwrights and do not in ordinary cases present any serious difficulties. It may be of interest to many, and to the advantage of some who may consider the use of water power, if a few general remarks on this subject are added. In practice there is almost always a little loss of head due to the velocity with which the water passes through the channels leading to and away from the wheel, and it should be the aim in constructing flumes to bring the loss to a minimum. When the size of the wheel and the quantity of water to be used have been determined, 1, the size of the conduit for carrying the water to the wheel, 2, the width and depth of the wheel-pit and tail-race, and 3, the dimensions and location of the flume for the wheel are to be considered and properly arranged. All of these should be of such dimensions as to insure the flow of water through them at a moderate velocity, and with as little change of direction as may be practicable. The larger the pipe or canal the better, but there must be a limit in practice, and it may be laid down as a general rule that a velocity of _three feet per second_ is good practice in short tubes of uniform section of not more than fifty feet in length; but _the velocity should be reduced as the distance increases_, until in a length of 200 feet, it should not exceed two feet per second. The same rule applies to the tail-race, except that the velocity should be somewhat lower in ditches cut through rock or earth and having the naturally resulting roughness of sides and bottom. The width and depth of the pit below the wheel may, for a given wheel, vary somewhat as the water discharged into it is greater or less; therefore, the dimensions should increase with a greater head for the same wheel. The following is an approximate rule for the dimensions of the pit, say for a head of twenty feet: width of pit equal to four times the diameter of wheel, depth below the level of tail-water one and a half times the diameter of wheel. The flume for the wheel should be about three times the diameter of the wheel in its width or diameter, and if it is decked over at the top it should be high enough inside to clear the coupling on the wheel shaft. _The Watertight Turbine_ is a special machine designed to keep the case tight by the pressure of the water against the gates at the sides, no matter how much these gates wear. Fig. 125 shows the plan of chutes, gate-seats, gates, and buckets of the wheel. Part of the gates are shown open, and others are closed. The gates make a quarter of a turn in opening, and the same in shutting, and to open all the gates, the gate wheel makes half a revolution. The upper half of case shows the gate-wheel and pinion for operating its parts. [Illustration: FIG. 125.] [Illustration]