gles, 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.

[Illustration: A switchboard and its connections: _G._ Dynamo; _A._
Shunt field coils; _B._ Series coils; _DD._ Fuses; _FF._ Main switch;
_F._ Field switch; _C._ Ammeter; _V._ Voltmeter; _E._ Lamp; _R._
Rheostat. Dotted lines show connections on back of board]

_Items of Cost_

This water wheel would cost $250 new. There is a duplicate in the
neighborhood bought at second-hand, for $125. The dynamo cost $90,
and was picked up second-hand in New York City. New it would cost
$150. The voltmeter cost $7, and the ammeter $10; and the switches and
fuses could be had for $5. A wheel one-half the size, using one-half
the amount of water at full gate, would do the work required, and the
cost would be correspondingly less.

_Capacity_

This plant supplies two farms with electric light. One farm (that of
the owner of the wheel) has 30 lamps, of 16 candlepower each, and two
barn-yard lamps of 92 candlepower each. His wife has an electric iron
and an electric water heater. Needless to say, all these lamps, and
the iron and water heater are not in use at one time.

[Illustration: Carbon Lamps Gem Type (1/4 scale)]

The partner who owns the electric part of the plant has 30 lamps in
his house and barn, many of them being 25 watt tungsten, which give
more light for less power, but cost more to buy. They are not all in
use at one time, though (since the current costs nothing) the
inclination is to turn them on at night and let them burn. In his
kitchen he has an electric range, and a water heater for the 40 gallon
boiler. In addition to this he h