Another transmitting arrangement, which involves a slightly different principle, and employs no oscillation transformer, is one due also to Professor Braun. In this case, a condenser and inductance are connected in series to the spark balls of an induction coil, and oscillations are set up in this circuit. Accordingly, there are rapid fluctuations of potential at one terminal of the condenser. If to this we connect a long aerial, the length of which has been adjusted to be one quarter of the length of wave corresponding to the frequency, in other words, to make it a quarter-wave resonator, then powerful oscillations will be accumulated in this rod. The relation between the height (H) of the aerial and the frequency is given by the equation 3 × 10^{10} = 4_n_H, where _n_ is the frequency of the oscillations and H the height of the aerial in centimetres. The frequency of the oscillations is determined by the capacity (C) and inductance (L) of the condenser circuit, and can be calculated from the formula n = (5,000,000) / ([\sq]{C (in mfds.) × L (in cms.)}). That is, the frequency is obtained by dividing into the number 5,000,000, the square root of the product of the capacity in microfarads, and inductance in centimetres, of the condenser circuit. It will be found, on applying these rules, that it is impossible to unite together any aerial of a length obtainable in practice with a condenser circuit of more than a very moderate capacity. It has been shown that for an aerial two hundred feet in height the corresponding resonating frequency is about one and a quarter million.[22] As we are limited in the amount to which we can reduce the inductance of a discharge circuit, probably to something like a thousand centimetres, a simple calculation shows that the largest capacity we can employ is about a sixtieth of a microfarad. This capacity, even if charged at 60,000 volts, would only contain thirty joules of energy, or about 22·5 foot-pounds, which is a small storage compared to that which can be achieved when we are employing the above-described methods, which involve the use of an oscillation transformer. In such a case, however, it is an advantage to employ a spark-gap in compressed air, because we can then raise the voltage to a much higher value than in air of ordinary pressure without lengthening the spark so much as to render it non-oscillatory. When employing methods involving the use of an oscillation transformer, it is possible to use multiple aerials having large capacity, and hence to store up a very large amount of energy in the aerial, which is liberated at each discharge. The most effective arrangement is one in which the radiator draws off gradually a large supply of energy from a non-radiating circuit, and so sends out a true train of waves, and not mere impulses, into the ether, and as we shall see later on, it is only when the radiation takes place in the form of true wave trains that anything like syntony can be obtained.