The key lever is fastened to the frame by means of a round headed 8-32 machine screw. The screw should be tightened so that the lever cannot move from side to side. The circuit closing lever is pivoted to the back end so that it can swing. The key lever should be fitted with a regular key knob and the circuit closing lever with a small knob such as is generally used for the purpose. Both of these styles of knobs can be purchased from almost any electrical supply house. The contact points are best made of silver. Silver makes a better contact metal than almost anything else, with the exception of platinum. If silver cannot be obtained a piece of large german-silver wire may be used. [Illustration: FIG. 90.—Key and Circuit Closing Levers.] One contact is soldered to the under side of the key lever. The other contact should be mounted on the head of a screw and pass through a hole in the iron key frame and through the wooden base underneath. This lower contact should be directly underneath the upper contact and be thoroughly insulated from the base. Several thicknesses of well shellaced paper will form a first class insulating medium. The length of the contacts should be such that there is a distance of about 3-32 of an inch between them when the lever is horizontal. The circuit closing lever should make contact with a small strip of spring brass under the lower contact point so that the contact is connected to the frame of the key through the circuit closing lever when the latter is "closed". The adjustment screw on the key frame is used to regulate the upward stroke of the key lever. The adjustment screw on the key lever is used to regulate the spring tension of the lever. The lower end rests against the top of a small spiral spring made of brass wire. [Illustration: FIG. 91.—American Morse Code.] Connecting the outfit is a very simple mater. The two inside terminals of the sounder magnets should be connected together. One of the outside terminals is led to a binding post mounted on the back of the base. The other terminal is connected to the lower key contact. The frame of the key is connected to a second binding post at the back of the base. The connecting wires should pass through small holes and along the under side of the base. The Morse Telegraph Code is shown in Figure 91. A single dry cell will provide sufficient current for practising the Code. The cell should be connected to the two binding posts and the circuit closing lever should be kept open at all times or the battery will become exhausted. [Illustration: FIG. 92.—Circuit for Two Instruments.] The number of batteries required on a long line will depend upon the resistance of the line and cannot easily be pre-determined.