The working details of the above rather complicated system of apparatus devised by Mr. Marconi would require for its full elucidation a large amount of explanation of a technical character. The general reader may, however, form a sufficiently clear idea of its performance as follows:— When the electrical waves from the distant transmitting station reach the aerial at the receiving station, they set up in it sympathetic electrical oscillations. The most favourable conditions are when the two aerials at the distant stations are exactly similar. These electrical oscillations, or rapid electric currents, set up an electromotive force in the secondary circuit of the oscillation-transformer, and this acts, as already explained, upon the metallic filings in the coherer-tube and causes it to become an electrical conductor. The cell attached to the relay then sends a current through the conductive circuit so formed and operates the relay. This last contrivance is merely a very delicate switch or circuit-closer which is set in action by a small current sent through one of its circuits, and it then closes a second circuit and so enables another much larger battery to send a current through the _Morse printer_. The printer then prints a _dot_ upon a moving strip of paper and records a signal. One other element in this rather complicated arrangement remains to be noticed, and that is the _tapper_. Underneath the coherer-tube is a little hammer worked by an electro-magnet like an electric bell. This tapper is set vibrating by the same current which passes through the Morse printer, and hence almost as soon as the latter has begun to print, the sensitive tube receives a little tap which causes the metallic filings to become again a non-conductor, and so arrests the whole of the electric currency. If it were not for this tapper, the arrival of the electric wave would cause the printer to begin printing a line which would continue. The _dot_ is, so to speak, an arrested line. If, however, trains of electric waves continue to arrive, then dots continue to be printed in close order, and form a _dash_ on the paper strip. It will thus be seen that the whole arrangements constitute an exceedingly ingenious device of such a nature that a single touch on the hand-key at one station causing a spark or two to take place between the spark-balls makes a _dot_ appear upon a band of paper at the distant station; whilst, if the hand-key is held down so that a stream of sparks takes place at the transmitting station, a dash is recorded at the receiving station. The means by which this distant effect is produced is the train of electric waves moving over the earth’s surface setting out from one aerial and arriving at the other. [Illustration: FIG. 85.]