Now electrical circuits in which currents oscillate have a natural frequency of their own. That frequency depends upon the two electrical properties of the circuit: capacity and inductance. And if you want to set up an electrical oscillation in any circuit you can best do it by giving it impulses at intervals which agree with its natural frequency. Sir Oliver Lodge seems to have been the first to appreciate fully the effects of resonance in wireless telegraphy. It is strange that in England the work of this eminent man in "wireless" matters is not more fully recognised. When wireless telegraphy reached the point at which the public became interested, Marconi was just coming to the front and so, for ever, will his name be foremost in the public estimation. Indeed more than foremost, for in the minds of many he monopolises the credit for this invention. Many people are under the impression that he is the one and only, or at any rate the original, inventor of wireless telegraphy. Now Marconi has done exceedingly valuable work in this field. Moreover, he has been the means of placing the affair on a good commercial footing. But all the same he is by no means the original or only inventor. While admitting that he is a remarkable man, who has done wonders, it is only common justice to refer to the others whose contributions to the solution of the problem are possibly of equal value. And, of these, few can compare with Sir Oliver Lodge. But to return to the question of resonance. At first the distances over which messages could be sent were but small. Now a marconigram can be flung across a hemisphere. At first little could be done by day, work had to be done mainly at night. Now communication passes by day and night alike. Yet in principle, and in many details, the instruments are unaltered from what they were several years ago. The main source of all this improvement is the use of resonance. To enumerate broadly the apparatus used for the dispatch and receipt of messages the following list will be useful:-- _Transmitting End_ (1) An Antenna, consisting of a number of wires raised to a considerable height above the ground. (2) A Spark-gap, consisting of a series of metal balls with gaps between them, the outer ones being connected to the antenna and to the induction coil. (3) A powerful Induction Coil with batteries or other source of current to work it. (4) A Telegraph Key, by which the induction coil can be started and stopped at will. _Receiving End_ (1) An Antenna precisely similar to the other. (2) A Coherer or other "oscillation detector." (3) A Receiving Instrument which may be a writing telegraph instrument, a telephone, any of a number of ordinary telegraph instruments, or a galvanometer. Transmitting and sending instruments are, of course, installed at both ends and either of them can be connected to the antenna at will by the simple movement of a switch.