L. T. KNIGHT

The transmitting instruments of a wireless station comprises the induction coil, interrupter and primary battery, a key for sending, the Leyden jar battery, adjustable spark gap and a variable self-inductance. In general appearance the induction coil is similar to the X-ray and experimental coil, and right here at the start arises a difference of opinion as to whether the secondary shall be wound for extremely high potential or simply a normal one. There seems a preference in the German systems for coils of much less potential than the commercial X-ray coils, because a high charging power is required to charge the Leyden battery, which is continually discharging across a small spark gap. Any ordinary Rulm-korff coil will suffice for such experiments as the reader will probably care to make while following these articles; in many instances the amateur will find it to his advantage, financially, to construct the coil himself.

Referring to the last chapter, we note that the electrical "blows" were to be struck in even time. So with the interrupter of the spark coil, the interruptions must be steady, even and without variance. Vibrators that vary in frequency because of unreliable contacts at the make and break points, will not give the satisfaction of the higher grade vibrators, or the chemical or mercury break. It is, therefore, essential in selecting an interrupter, to choose one that is permanent and true in action.

The variable inductance consists of bare wire turns about an insulated cylinder or open frame work, arranged in such shape that connections may be made with pegs, clamps or otherwise, on any part or turn of the coil as required. The

Leyden jars are connected in multiple.

In the elementary diagram here given is shown the transmitting circuit. The lower end of the inductance coil is connected to a secondary spark gap and also to the outer terminal of the Leyden jars. Two variable points or clamps affixed to flexible conducting cords are also provided. Their location is plainly shown in the diagram, and it is patent that with these two cords any portion or all of the inductance coil may be cut out, thus varying the capacity and inductance and determining the length of wave whieh the station will transmit.

The proper adjustment of the spark gaps having been once acquired, few changes in their position will have to be made. Generally speaking, the farther it is desired to transmit the longer the spark gap, and the stronger the current required in the primary of the induction coil. The spark, however, must be kept white and snappy, and frequent usage will make one familiar with that particular spark length and primary current which gives the most satisfactory results.

In such a transmitting circuit as is here described, the secondary charges the Leyden jar battery until the potential is high enough to jump across the spark gap. Then oscillations are set up through the Leyden jars, the induction and spark gap. As a thorough description of this part of the circuit will be necessary in explaining the receiving circuit and the adjustment of the receiver and transmitter to meet the proper communicating conditions, further comment will be postponed until the receiving station has been dealt with in the next chapter.