354 IDEAL HOME IIFE
your induction coil or transformer is had. If current from a lighting circuit is used a variable resistance must be connected in the primary circuit to cut down the current to the amount requiied.
The spark-gap is simply a pair of brass rods fitted with brass balls and insulated'handles which slide through a pair of brass standards fixed to a marble or other insulating base. The spark-gap is connected to the terminals, that is, the ends of the wires of the secondary coil.
The tuning coil of the sending apparatus is simply a coil of heavy brass or copper wire one-eighth or one-fourth inch in diameter,, wound in a helix around a wooden frame, and it is used to enable the operator to give the electric waves sent out by the aerial a certain length in. order to conform to the Government regulations. The tuning coil is connected in circuit with the spark-gap and the condenser, and the. aerial and. ground wires are connected to it as we« shall presently see.
The high tension condenser can be either a battery of Leyden jars or it can be made* of a number of sheets of glass covered with tinfoil. The sending condenser must be proportioned to the size o-f the tuning coil and the larger it is, within certain limits, the shorter and' thicker the spark at the gap will be and the more effective the electric waves that are sent out by the aerial.
Connecting Up the Transmitter
When you have made or bought all of these pieces of apparatus, connect them up with No. 14 copper wire-, which should be insulated, that is the primary of the induction coil, or transformer; the battery, or other source o-f current, and the key are connected in series, as it is called.
Next the spark-gap, the condenser, and the tuning coil are connected in series, and then the end of the aerial wire is connected with the top binding post of the tuning coil, while one of the clips of the tuning coil and the ground wire are connected together.
Before sending wireless telegraph messages with this or