This wheel, under a 14-foot head, takes 2,312 cubic feet of water a minute; and it develops 46.98 actual horsepower (as may be figured by using the formulas of Chapter III). The water supply is provided by a small mountain river. The dam is 10 feet high, and the race, which feeds the flume from the mill pond is 75 yards long. The race has two spillways, one near the dam, and the second at the flume itself, to maintain an even head of water at all times. _Half-Gate_ Since the water supply varies with the seasons, it has been found practical to run the wheel at half-gate--that is, with the gate only half-open. A set of bevel gears work the main shaft, which runs at approximately 200 revolutions per minute; and the dynamo is worked up to its required speed of 1,500 revolutions per minute through a countershaft. The dynamo is a modern four-pole machine, compound-wound, with a rated output of 46 amperes, at 125 volts--in other words a dynamo of 5.75 kilowatts capacity, or 7.7 electrical horsepower. At full load this dynamo would require a driving power of 10 horsepower, counting it as 75 per cent efficient; and, to conform to our rule of two water horsepower to one electrical horsepower, the wheel should be capable of developing 20 horsepower. As a matter of fact, in this particular instance, shutting down the wheel to half-gate more than halves the rated power of the wheel, and little more than 15 horsepower is available. This allowance has proved ample, under all conditions met with, in this plant. The dynamo is mounted on a firm floor foundation; and it is belted from the countershaft by an endless belt running diagonally. A horizontal belt drive is the best. Vertical drive should be avoided wherever possible. _The Switchboard_ The switchboard originally consisted of a wooden frame on which were screwed ordinary asbestos shingles, and the instruments were mounted on these. Later, a sheet of electric insulating fibre was substituted, for look's sake. The main requisite is something substantial--and fireproof. The switchboard instruments consist of a voltmeter, with a range of from 0 to 150 volts; an ammeter, with a range, 0 to 75 amperes; a field regulating rheostat (which came with the dynamo); a main switch, with cartridge fuses protecting the machine against a draft of current over 60 amperes; and two line switches for the two owners, one fuse at 20 amperes, and the other at 40 amperes. Electric fuses are either cartridges or plugs, enclosing lead wire of a size corresponding to their rating. All the current of the line they protect passes through this lead wire. If the current drawn exceeds the capacity of the lead wire, it melts from the heat, and thus opens the circuit, and cuts off the current.