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.

Electrical Connections.--The current collector, CR, should be well turned
up at the end, so as not to catch on the centre rail joints, and not press
hard enough on the rail to cause noticeable resistance. The fixed end of CR
is connected through T2 with one brush, B, and both wheel bearings with T1.

[Illustration: FIG. 48.--Reversing switch.]

Electrical Fittings.--The best source of power to use is dry cells giving
1-1/2 to 2 volts each. These can be bought at 1s. apiece in fairly large
sizes. Four or five connected in series will work quite a long line if the
contacts are in good condition.

A reversing switch is needed to alter the direction of the current flow.
The construction of one is an exceedingly simple matter. Fig. 48 gives a
plan of switch and connection, from which the principle of the apparatus
will be gathered. The two links, LL, are thin springy brass strips slightly
curved, and at the rear end pivoted on the binding posts T1 T2. Underneath
the other ends solder the heads of a couple of brass nails. The links are
held parallel to one another by a wooden yoke, from the centre of which
projects a handle. The three contacts C1 C2 C3 must be the same distance
apart as the centres of the link heads, and so situated as to lie on the
arcs of circles described by the links. The binding post T3 is connected
with the two outside contacts--which may be flat-headed brass nails driven
in almost flush with the top of the wooden base--by wires lying in grooves
under the base, and T4 with the central contact. As shown, the switch is in
the neutral position and the circuit broken.

[Illustration: Fig. 49.--Multiple battery switch.]

Multiple Battery Switch.--To control the speed of the train and economize
current a multiple battery switch is useful. Fig. 49 explains how to make
and connect up suc