al, operated by points.]

Preservation of Track.--All the wooden parts of an outdoor track should
be well creosoted before use.

The Electric Locomotive.

An elevation and a plan of this are given in Fig. 47. The two pairs of
wheels are set close together, so that they may pass easily round curves.

[Illustration: Fig. 47.--Plan and elevation of electric locomotive.]

The Motor.--A motor of ordinary type, with electro field magnets, is
unsuitable for traction, as it cannot be reversed by changing the direction
of the current, unless a special and rather expensive type of automatic
switch be used. While a motor of this kind is, in conjunction with such a
switch, the most efficient, the motor with permanent field magnets is
preferable as regards cost and ease of fixing. It can be reversed through
the rails. The armature or revolving part must be tripolar to be
self-starting in all positions.

A motor of sufficient power can be bought for half a crown or less--in any
case more cheaply than it can be made by the average amateur.

The motor used for the locomotive illustrated was taken to pieces, and the
magnet M screwed to a strip of wood 1-5/8 inches wide; and for the original
armature bearings were substituted a couple of pieces of brass strip, HH,
screwed to two wooden supports, SS, on the base, E (Fig. 47, a). It was
found necessary to push the armature along the spindle close to the
commutator piece, C, and to shorten the spindle at the armature end and
turn it down to the size of the original bearing, in order to bring the
motor within the space between the wheels.

The place of the small pulley was taken by an 8-toothed pinion wheel,
engaging with a pinion soldered to the near driving wheel, the diameter of
which it exceeded by about 3/16 inch. The pair, originally parts of an old
clock purchased for a few pence, gave a gearing-down of about 9 times.

The position of the driven wheels relatively to the armature must be found
experimentally. There is plenty of scope for adjustment, as the wheels can
be shifted in either direction longitudinally, while the distance between
wheel and armature centres may be further modified in the length of the
bearings, BE. These last are pieces of brass strip turned up at the ends,
and bored for axles, and screwed to the under side of the base. To prevent
the axles sliding sideways and the wheels rubbing the frame, solder small
collars to them in contact with the inner side