ELECTRICITY AT A DISTANCE

Evening Star, Issue 20486, 17 May 1930, Page 9

ELECTRICITY AT A DISTANCE

SDME WHOM IMPRESSIONS MARCONI AND THE SYDNEY LIGHTS WHAT CAN BE DONE AND WHAT CANNOT. [By Professor E. N. da C. Andrade, in the ‘Observer.’] Considerable interest has _ been aroused by the Marchese Marconi’s feat of operating a switch at Sydney from a station in _ Italy, and it has been made the basis of a certain amount of more or less uncritical speculation as to the possibility that, in the near future, electrical power will be transmitted over largo distances without the use of wires. A vision of large generating stations at the pit-head or at waterfalls connected to _ factories and farms solely by space in a state of vibration has been set before us. Be the remote possibilities what they may—and a man need be bold to say that this or that will never be achieved, when so many unexpected aspects of Nature have been revealed in our generation—there is nothing in the Marchese’s performance which brings the consummation any nearer. At any time during the last five years, at a very modest estimate, switches in Sydney could have been operated by wireless from, Europe; in iact,_ with modern technique, as soon as wireless signals can be received with any distinctness, _ there is no limit to the power which can be set in motion by their agency—set in motion, not transmitted. By means of the type of instrument technically known as a relay a, very minute current is made to close a circuit which permits a current, from batteries at the receiving end, to pass, and this larger current can then, in its turn, operate a relay which clears the way for a still larger current, and the process can be carried further until switches of any magnitude desired can be operated, and all available power released. It is a pretty technical feat—carried out, I suppose, with no idea of the publicity it would _ attain—but the Feeble power transmitted by the wireless signal lights the lamp in Sydney no more and no less than the strength of the pretty girl who presses the button that pushes the great ship down the launching slipway. No one suggests that because she sets the great ship in motion the day must be near when a pretty girl seated in the engine room will provide the motive power of a ship. The ordinary wireless set furnishes an excellent illustration of what modern methods do,_ and what they do not do. The collection of valves, coils, and condensers which enables the listener to hear music from Spain is a mechanism for allowing very feeble electrical impulses to govern the supply of electrical energy which operates the loud speaker, but the energy is supplied by the batteries in the receiving set, and does not travel from Spain; the exiguous power that reaches us from afar has merely a directive, not an operative, role. The difficulties in the way of an electrical transmission of power are enormous. In the first place, all, or a large percentage of, the electrical power generated must bo thrown into the form of wireless waves. In the next place these waves must be made to follow some very definite path, and not allowed to diffuse themselves in all directions. In the third place a receiving apparatus must be constructed which will collect all the energy over the very large space which, even with the best conceivable arrangement, the path would traverse. All thesetnings are, as far as we can see, very distant, the greatest difficulty of all being the confinement of the energy in a narrow path, or beam, such as a searchlight throws, although even a searchlight beam rapidly loses its sharpness of outline. Wireless waves are, as is well known, of the same nature as light, but enormously greater in wave-length —-a “short” wireless wave is some hundreds of millions times as long as a visible light wave. To discuss the difference between the propagation of light and the propagation of wireless waves the effect of this difference of wave-length must be considered. By an arrangement of aerials something approximating to a beam of wireless waves can be sent out, but the “mirror” formed by the wires is only a comparatively few, not an immense number, of wave-lengths wide, and the wireless beam is correspondingly less sharp than a light beam. A great matter for astonishment is clearly that it should be possible to send a signal of any kind, however weak, to the Antipodes, which demands that those waves, of the nature of light waves, should travel not in straight lines, but hugging ,the surface of the earth, a very un-lightlike tiling to do. The problem first came before men of science in 1901, when Marconi successfully sent a signal across the Atlantic to America by spark wireless. Now visible light, although it appears to travel in a straight line past an _ edge, ‘ and to throw a sharp shadow, is actually bent aside slightly, or diffracted, to use the technical term, and the diffraction effects become considerable when the obstacle (or opening, _ if the light is passing through a minute orifice) is small enough to be of about the same size as the wave-length. Waves do bend round corners, and, especially if the waves are Jong, the bending can be considerable in favourable circumstances. It was at first thought that diffraction was responsible for the signals reaching America, but calculation soon showed that the bending was too great to be accounted for on this basis —if the possibility of transmission to Australia had been known the suggested explanation would have seemed even more untenable. There is, however, a much more obvious way in which ordinary light can bo made to change its direction: it may be bentArefracted—in passing through a prism or the edge of a Jens or reflected. Does there exist any agent by which wireless waves can be reflected or refracted so as to hug the earth? The eccentric genius Heaviside, whose abstruse and individual mathematical methods did so much to make long-distance telephony possible, and who was one of the first to deal with the theory of wireless waves (the first intimate account of his life has just been given to the world in Mr Rollo Appleyard’s 1 Pioneers of Electrical Communication’), suggested that a layer of electricity in the upper atmosphere would act as a spherical reflector surrounding the earth, from whose inner surface the waves would be reflected, and so able to pass from Pole to Pole. This was long before the war—one of the most interesting series of researches on wireless waves carried out since the war is that by which Professor Appleton has experimentally established the existence of the Heaviside layer, measured its height, and worked out its influence on the transmission of signals. By its reflecting action it makes the transmission or long-distance signals possible—a single signal from a given station has, in fact, been twice received by a second station, once by transmission the short

way round the earth, and the second time by transmission the long way round the earth, the interval of a small fraction of a second being exactly that required by light to travel the difference of the two paths. It is intimately concerned in the difference of signal strength which is noted, at different times of the day and night. It is responsible for certain peculiar features of directional wireless. And all its properties can be worked out by suitably modifying the laws of ordinary light waves to the scale required by the enormous difference of wavelength. The actual layer consists of a cloud of electrified particles—electrons and ions—formed in the air_ bj; the action of the ultra-violet radiations of the sun, which are absorbed in the upper layers of the atmosphere and produce, as a corollary to the absorption, the electrical effects. Depending on the sun as it does, the height of the layer is different by day and night: by reflecting wireless waves from it, as from a mirror, Professor Appleton has not only the height at different times of day—it varies from fifty miles or so by day to eighty or so by night—but has established the existence #a

second layer at about double these heights. It can’ be mathematically shown that a cloud of electrified particles, such a§ the Ijiyer must be, will act for wireless waves as a mirror, the reflecting power of which is better the shorter the wave-length, as required by the results of observation. Exceedingly short waves, however, actually penetrate the Heaviside layer, and so should be adopted for interplanetary communication when a company is v created to carry it on. A very extraordinary and hitherto unexplained, feature of sbort-wavo transmission is the echoes from other space which were first announced by Jorgen Hals, and confirmed by Professor Stormer. The interval between the sending out of the echo and the return is so large that the waves .must have travelled a million miles or so before their reception again. Professor Stormer put down the phenomenon to electrified particles shot out by the sun and deflected by the earth’s magnetic influence into a vast ring surrounding the earth. There are many difficulties in the way of this theory,but none great enough to drive us to talking of signals received from intcllw gent beings xu other planets.