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 such a switch.  The contacts, C1 to C5, lie in the path of the switch lever, and are connected through binding posts T1 to T6 with one terminal of their respective cells.  The cells are coupled up in series to one another, and one terminal of the series with binding posts T0 and T6.  By moving the lever, any number of the cells can be put in circuit with T7.  The button under the head of the lever should not be wide enough to bridge the space between any two contacts.  Change the order of the cells occasionally to equalize the exhaustion.

[Illustration:  Fig. 50.—­Adjustable resistance for controlling current.]

Resistance.—­With accumulators, a “resistance” should be included in the circuit to regulate the flow of current.  The resistance shown in Fig. 50 consists of a spiral of fine German silver wire lying in the grooved circumference of a wood disc.  One of the binding posts is in connection with the regulating lever pivot, the other with one end of the coil.  By moving the lever along the coil the amount of German silver wire, which offers resistance to the current, is altered.  When starting the motor use as little current as possible, and open the resistance as it gets up speed, choking down again when the necessary speed is attained.