CHAPTER XII
THE MOST STRIKING INVENTION OF RECENT TIMES
Probably no invention has made such a sensation during recent years as wireless telegraphy. And since it is the direct outcome of the most abstruse, purely scientific investigations, there could be no more appropriate subject for a place in this book.
For many years there has been a belief in the existence of a mysterious something to which has been given the name of "The Ether." Totally different, it should be noted, from the chemical of the same name, it is entirely a creature of the intellect. None of our senses give us the slightest direct indication of its existence. No one has either seen, felt, heard, smelt or tasted it. Yet we feel that it must exist, for the simple reason that some things which our senses do tell us of are utterly inexplicable without it.
It was originally thought of in connection with light. Standing at night upon the top of a hill, we see the lights of a town a mile away. How is it that those distant gas or electric lamps affect our eyes? They are a mile away; and the idea that one object can affect another at a distance is one which the human mind refuses to accept. We feel compelled to believe that there is something in contact with the source of light which is affected first, and through which the disturbance, whatever it may be, is conveyed to our eyes, with which it must also be in contact. We feel that there must be a something stretching from our eyes to the distant objects, by which the light is carried. Of course the air fills the space referred to, but that cannot be the carrier of light, for if we look through a glass vessel from which the air has been exhausted we see distant objects undimmed. We also have good reason to believe that the air belongs specially to our globe, and does not extend upwards for more than a few miles. Consequently it cannot be air which brings sunlight and starlight. We are forced to fall back, therefore, upon the belief in something, of which we have no other knowledge, which must fill all the vacant spaces in the whole universe, passing, even, between the particles of which ordinary matter is composed, reaching as far as the remotest star, able to penetrate everything, and consequently not excludable from the most perfect vacuum. It is something so different from anything of which we have any direct knowledge that one is tempted sometimes to doubt whether there must not be some other explanation of light. In order to transmit light at the speed at which we find that it does in fact travel, the ether must be more rigid than the hardest substance we know of. Many, many thousand times more rigid, indeed. Yet it seems to offer no resistance to the passage of the planets through it. Still, there is no other alternative, so far as men can conceive, and we are compelled, therefore, to believe in the existence of the ether.
The first things discovered by the telescope were the larger satellites of Jupiter. With that precision for which astronomers are noted, they soon drew up time-tables, showing not only the past movements of these bodies, but also their future ones. They were soon puzzled, however, by the obvious fact that the moons of Jupiter were not working according to schedule, to use a railway expression. They got later and later for a time, and then gradually quickened up until they got too fast. Then they slowed down again. This repeated itself, and is going on still, with this difference, however, that the cause has been discovered and the schedules amended accordingly. The solution of the puzzle was that when the earth and the great planet are on the same side of the sun they are some 186 millions of miles nearer together than when they are on opposite sides of the sun. The evolutions of the satellites are quite regular, according to the astronomers' calculations, but they seemed to the earthly astronomers to vary, because of the time which light took to traverse that 186 millions of miles. When the two bodies were nearest together the occurrences seemed to happen about 1000 seconds (16 minutes) earlier than when they were farthest apart. Consequently it became evident that light took 1000 seconds to travel 186 million miles, or that, in other words, it moved at the prodigious speed of 186 thousand miles per second. That discovery was, of course, many years ago, but experiments since have proved the figure mentioned to be about right.
It put beyond question the fact that the action of a distant light upon the eye was not an "action at a distance," for such action, were it possible, would take effect at once. Seeing that light passed from the distant satellites at a definite velocity, and took a certain time to reach us, it was evident that it was, during that time, passing through a medium of some sort, and that medium must be the ether, for no alternative explanation will suffice.
So it became recognised that light really consists of waves or undulations of some sort in the ether; that a distant, luminous body set these waves going; that they travelled with a definite velocity, and then, striking our eyes, produced the sensation known as light. Many things were found out about light in the years which followed the discovery of its velocity. The lengths of the waves were ascertained—that is to say, the distance from the crest of one to the crest of the next. The different lengths were sorted out and found to give rise to different colours, while longer waves, which produced no sensation of light, were found to carry heat, thereby explaining how the heat reaches us from a distant fire, or from the sun.
Of the actual nature of the waves, however, little was known, although there was a vague idea that they were connected in some way with electricity, at which point in the story there comes in the famous name of James Clerk Maxwell, a professor of Cambridge University, who in 1864 produced before the Royal Society the explanation of the nature of the waves and their connection with electricity and magnetism. That in itself was a wonderful achievement, but far more wonderful still is the fact that he truly predicted the existence of longer waves than any then known, which no one knew how to cause, or how to detect if caused. That prediction has since been fulfilled. The long waves have been found; we know how to make them and how to perceive their presence. They are the messengers which carry our wireless messages.
The discovery of these, at that time unknown waves, on paper, by simply calculating and reasoning about them, is more marvellous even than the feat of Adams and Le Verrier in discovering a planet on paper before anyone had seen it. It established Maxwell among the heroes of science for all time.