We turn, in the next place, to the consideration of those devices for putting more power into the aerial than can be achieved when the aerial itself is simply employed as the reservoir of energy. Professor Braun, of Strassburg, in 1899, described a method for doing this by inducing oscillations in the aerial by means of an oscillation transformer, these oscillations being set up by the discharges from a Leyden jar or battery of Leyden jars, which formed the reservoir of energy. The induction coil is employed to produce a rapidly intermittent series of electrical oscillations in the primary coil of an oscillation transformer by the discharge through it of a Leyden jar. Mr. Marconi immensely improved this arrangement, as described by him in a lecture given before the Society of Arts on May 17, 1901, by syntonising the two circuits and making the circuit, consisting of the capacity of the aerial and the inductance of the secondary circuit of the oscillation transformer, have the same time-period as the circuit consisting of the Leyden jars, or energy-storing condenser, and the primary circuit of the oscillation transformer, and by so doing immensely added to the power and range of the apparatus. Starting from these inventions of Braun and Marconi, the author devised a double transmission system in which the oscillations are twice transformed before being generated in the aerial, each time with a multiplication of electromotive force and a multiplication of the number of groups of oscillations per second. This arrangement can best be understood from the diagram (see Fig. 15). In this case a transformer, T, or transformers receive alternating low-frequency current from an alternator, _a_, being regulated by passing through two variable choking coils, H_{1} and H_{2}, so as to control it. This alternating current is transformed up from a potential of two thousand to twenty, forty or a hundred thousand, and is employed to charge a large condenser, C_{1}, which discharges across a primary spark-gap, S_{1}, through the primary coil of an oscillation transformer, T_{1}. The secondary circuit of the oscillation transformer is connected to a second pair of spark balls, S_{2}, which in turn are connected by a secondary condenser, C_{2}, and the primary circuit of a third transformer, T_{2} and the secondary circuit of this last transformer are inserted between a Marconi aerial, A, and the earth E. When all these circuits are tuned to resonance by Mr. Marconi's methods, we have an enormously powerful arrangement for creating electric waves, or rather trains of electric waves, sent out from the aerial, and the oscillations are controlled and the signals made by short-circuiting one of the choking coils.