The quenched gap consists of a number of disks of brass about five inches in diameter having thin mica washers set between and arranged in a pile as in the illustration. The quenched gap radiates considerably more energy than any other form of gap and also has the advantage of being

HARD RUBBER
RING

ELECTRODE

FIG. 56.-Anchor gap.

practically noiseless. The crashing discharge of an ordinary gap produces a very disagreeable penetrating noise hard to eliminate. In most commercial stations the spark is muffled to a certain extent by enclosing it in a cylinder of micanite or some other insulating substance.

THE AERIAL SWITCH is necessary for quickly connecting the aerial and ground to either the transmitting or receiving apparatus. Amateurs very often employ a small "double pole double throw" switch. The switch used in commercial stations is built in the manner shown in Fig. 55.

AN ANCHOR gap is a simple little device consisting of a hard rubber ring bearing two or three small electrodes

or sparking points. It is a necessary part of the transmitting apparatus wherever a loop aerial is used. One electrode is connected to the transmitting apparatus and the other two to the opposite sides of the aerial so that the currents divide between the two halves and equalize. THE KEY is a hand operated switch which controls the electric currents passing through the transformer or coil shutting them on or off at will and so controlling the electric oscillations in the antenna to send out short or long trains of ether waves in accordance with the dot or dash signals of the Morse alphabet.

The key used in a wireless station is necessarily much larger and heavier than those employed in ordinary Morse line work, in order to carry the heavy currents used by the transmitter. In spite of their size and weight, however, such keys when properly designed may be handled with perfect ease.

CHAPTER IV.

THE RECEIVING APPARATUS.

The receiving instruments form the most interesting and ingenious part of a wireless station. They are the ears of the wireless station. They are wondrously sensitive but yet simple and incapable of much complication. The receiving station forms an exact counterpart of the transmitter, and the train of actions taking place are the reverse of those of the latter. The purpose of the transmitter is to change ordinary electric currents into electrical oscillations and thus set up electric waves, while the receptor converts the waves into oscillations and thence into currents which are capable of manifesting themselves in a telephone receiver. The instruments necessary for receiving comprise a

Detector

Telephone Receivers

Fixed Condenser
Tuning Device

Other instruments such as a potentiometer, test buzzers, variometers, variable condensers, etc., complete the outfit and improve its selectivity and sensitiveness.

THE DETECTOR forms the most vital part of the receptor. In explaining its action it may be well to recall and enlarge upon the description already set forth on page II, where it was explained that electromagnetic or as they are more commonly called when identified with wireless telegraphy, Hertzian waves have the power of exciting oscillations in

any conductor upon which they impinge. Electrical oscillations, it will be remembered, are alternating currents of

very high frequency. They are generated in the aerial of the receiving station by the action of the waves coming