The chief demand for an interrupter has come from the scores of experimenters who are working with wireless telegraphy. In 1894 Mr. Marconi began communicating through space without wires, and it may be said that wireless telegraphy has ever since been the world's imminent invention. Who has not read with profound interest the news of Mr. Marconi's success, the gradual increases of his distances? Who has not sympathised with his effort to perfect his devices, to produce a tuning apparatus by means of which messages flying through space could be kept secret? And here at last has come the invention which science most needed to complete and vitalise Marconi's work. By means of Mr. Hewitt's interrupter, the simplicity of which is as astonishing as its efficiency, the whole problem has been suddenly and easily solved. Mr. Hewitt's new interrupter may, indeed, be called the enacting clause of wireless telegraphy. By its use the transmission of powerful and persistent electrical waves is reduced to scientific accuracy. The apparatus is not only cheap, light, and simple, but it is also a great saver of electrical power. The interrupter, also, is a simple device. As I have already shown, the mercury vapour opposes a high resistance to the passage of electricity until the current reaches a certain high potential, when it gives way suddenly, allowing a current of low potential to pass through. This property can be applied in breaking a high potential current, such as is used in wireless telegraphy, so that the waves set up are exactly the proper lengths, always accurate, always the same, for sending messages through space. By the present method an ordinary arc or spark gap--that is, a spark passing between two brass balls--is employed in sending messages across the Atlantic. Marconi uses a spark as large as a man's wrist, and the noise of its passage is so deafening that the operators are compelled to wear cotton in their ears, and often they must shield their eyes from the blinding brilliancy of the discharges. Moreover, this open-air arc is subject to variations, to great losses of current, the brass balls become eroded, and the accuracy of the transmission is much impaired. All this is obviated by the cheap, simple, noiseless, sparkless mercury bulb. "What I have done," said Mr. Hewitt, "is to perfect a device by means of which messages can be sent rapidly and without the loss of current occasioned by the spark gap. In wireless telegraphy the trouble has been that it was difficult to keep the sending and the receiving instruments attuned. By the use of my interrupter this can be accomplished."