It is advisable to lay out a set of points, together with motor and signals, on a separate board.

[Illustration:  Fig. 46.—­Double-armed signal, 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 of the bearings.

The Frame.—­Having got the motor wheels adjusted, shorten E so that it projects 2 inches beyond the centres of the axles at each end.  Two cross bars, GG, 3-1/2 inches long, are then glued to the under side of E, projecting 1/8 inch.  To these are glued two 3/8-inch strips, FF, of the same length as E. A buffer beam, K, is screwed to G. A removable cover, abedfg, is made out of cigar-box wood or tin.  The ends rest on GG; the sides on FF.  Doors and windows are cut out, and handrails, etc., added to make the locomotive suggest the real thing—­except for the proportionate size and arrangement of the wheels.