makes it impossible to use the
ordinary model rolling stock. To its credit one may place the fact that
only two rails are needed.

3. The third and, we think, best system, which has an insulated third rail
as one half of the circuit, and both wheel rails as the return, the motor
being kept in connection with the third rail by means of a collector
projecting from the frame and pressing against the top of the third rail.
The last, for reasons of convenience, is placed between the wheel rails. We
will assume that this system is to be employed.

[Illustration: FIG. 42.--Details of rails for electric track.]

Gauge.--For indoor and short tracks generally it is advisable to keep the
gauge narrow, so that sharp curves may be employed without causing undue
friction between rails and wheels. In the present instance we specify a
2-inch gauge, for which, as also for 1-1/2 and 1-1/4 inch, standard
rolling stock is supplied by the manufacturers.

Track Construction.--It is essential that the centre rail and at least
one of the wheel rails shall have all joints bonded together to give a
clear course to the electric current, and the centre rail must be insulated
to prevent leakage and short-circuiting. Where a track is laid down more or
less permanently, the bonding is most positively effected by means of
little fish-plates, screwed into the sides of the abutting rails; but in
the case of a track which must be capable of quick coupling-up and
uncoupling, some such arrangement as that shown in Fig. 42 is to be
recommended.

Fig. 42 (a) is a cross vertical section of the track; Fig. 42 (c) a
longitudinal view; while Fig. 42 (b) shows in plan a point of junction of
two lengths of rail.

The wheel rails are made of carefully straightened brass strip 3/8 inch
wide and 1/16 inch thick, sunk rather more than 1/8 inch into wooden
sleepers (Fig. 42, a), 3-1/2 inches long and 3/4 inch wide (except at
junctions). The sleepers are prepared most quickly by cutting out a strip
of wood 3-1/2 inches wide in the direction of the grain, and long enough to
make half a dozen sleepers. Two saw cuts are sunk into the top, 2 inches
apart, reckoning from the inside edges, to the proper depth, and the wood
is then subdivided along the grain. The saw used should make a cut slightly
narrower than the strip, to give the wood a good hold. If the cut is
unavoidably too large, packings of tin strip must be forced in with the
rail on the outside. To secure th