Part 28

Our next addition was a telegraph sounder as shown in Fig. 195. B^{1} is a single dry cell, C is the coherer, R is the relay, B^{2} is now a battery of three cells. Part of its current goes to B^{3}, the tapper for the coherer, and part of its current goes to the electro-magnet of the telegraph sounder S. Ordinarily a spring holds the iron strip d up against the metal stop a, but when the current passes through the electro-magnet it pulls down this iron strip with a click against the metal stop e. But while this is happening C is being tapped by B, and is ready to respond to each wave. It was only necessary now to have some code of signals in order to communicate by telegrams. We learned the system of dots and dashes, or short and long periods marked off by the sounder, which all telegraphers use and which is known as the Morse alphabet, and very soon Harold and I were telegraphing from one room to another messages of several sentences at a time, the Morse alphabet being told off on the spark coil and being received through the coherer and telegraph sounder. It was not long before Harold and one of the neighbours' boys were exchanging messages between their homes, each having a spark coil and the necessary receiving apparatus, and having extended their antennæ to the top of the buildings into what are called in the wireless language aerials.

The fever for wireless telegraphy spread like wild-fire among the boys. In a few months they had formed a "wireless club." They had each read anywhere from ten to thirty books and articles upon the subject, and had secured the latest improved apparatus. They made it a practice to spend hours daily at their instruments picking up and keeping on file messages which were sent to and from steamers leaving the harbour for European ports. On one occasion they showed me from these files scores of messages--fond, personal, and supposedly private farewells to friends and communications between business partners which they would never have made on land without first closing the office door. The boys had acquired a mass of technical knowledge upon the subject which far exceeded my comprehension. But their teachers in school complained that they would learn nothing else, and some of the boys had already received warning that they might fail of promotion.

How to have compelling interests without riding hobbies is the great problem for both boys and men. I have known many boys who could, or at least would, do nothing well in school or out, except some specialty like manual training or science. In later years they were so deficient in education that they could hold no worthy position in anything. My anxiety was to save my boy from such a fate. I was determined that he should have a fair share of all kinds of culture. To this end we read together much of biography, history and classical literature, ancient and modern, through the medium of the English language.

As both prevention and cure of the wireless telegraph mania I deemed it not necessary to suppress enthusiasm, nor to introduce obviously useless tasks for the sake of the training which might be in them. My method was, on the contrary, to encourage my boy to have several hobbies which he might ride with enthusiasm, but to make it a rigorous rule to exchange his "mount" occasionally.

XXIV

HALLEY'S COMET AND ELECTRICAL WAVES

It was the year 1910 and Halley's comet was approaching the sun. On May 18 its tail might be expected to reach the earth. Astronomers had requested all who might be possessed of wireless telegraph apparatus to watch on that day for any peculiar behaviour of their apparatus so that evidence might be obtained whether or not the comet sends forth such ether waves as we call electricity. Harold desired me to explain the whole matter to his group of friends, which I did on a subsequent evening, as follows:

"Although Halley's comet has come within the earth's orbit about three thousand times since its first recorded appearance, I know of no man living who can give a satisfactory account of having seen it. Any one who has seen it before must be at least seventy-five years old, for it requires seventy-five years to make one complete circuit of its own orbit. But no one who is now seventy-five could have observed it intelligently, and even one who is now eighty-five years old would have to tell what he saw when he was ten years old and has remembered for seventy-five years. Furthermore, any account of how it looked on a former return is no guide to how it may appear on this trip. You may properly think of the comet as a group of solid pieces no bigger than the stones you may throw, scattered, two or three to the mile, through a space 12,500 miles broad. This extremely thin cloud of particles does not reflect enough sunlight to be visible, even in a telescope, in any part of its journey, and hence we should be wholly unaware of its existence if it did not sometimes have the strange faculty of giving out light of its own while in that part of its own orbit nearest to the sun. At such a time there is a hazy light enveloping the mass of small bodies, and streaming away sometimes many million miles from them. The mass of small bodies is generally referred to as the nucleus, and the stream of luminous gas which the nucleus gives forth is called the tail, though it reminds me more of a search-light.

"It does not trail along behind the comet but always points away from the sun (Fig. 197). The normal thing for a comet to do is to begin to develop a faint light and a short streamer as it gets near to the sun, to have its light grow brighter and its streamer to grow longer until it reaches the point nearest the sun, and then to have its light grow dimmer and the streamer grow shorter as it recedes from the sun.

"It has many times been suggested that this strange search-light appearance may be an electrical phenomenon, some form of ether waves which the comet sends forth when under the immediate influence of the sun. But not all comets are alike in this matter, nor does the same comet always act alike on succeeding trips, so that we may not predict what Halley's comet will do on this visit. It would be natural to suppose that Halley's comet, like radium, might in time lose the power to radiate off material, in which case it might at length become wholly invisible to us, even though it continued to travel in its wonted path. Our only way of knowing of its existence then would be that on its returns some of its small pieces might be attracted to the earth and enter our atmosphere as meteors. This sort of thing is continually happening, and may be the last reminders of once brilliant comets.

"For almost a century it has been the common belief that light is merely a wave motion in the ether. Our eyes respond to ether waves of certain length only. Waves a little longer than those which affect our eyes are felt by us as heat waves. Waves still longer than those of heat are the so-called electric waves. These we use in wireless telegraphy. There are still shorter waves than those of light. These affect the sensitive plate in photography. They help to form the green material in the leaves of plants and the brilliant colours in flowers. They assist in the fading of our clothes and the tanning of our skin. These are called chemical waves. Still shorter waves in the ether than those of which we have just spoken are the X rays, and all the strange things which they may do have not yet been determined. Certain it is that they can make dreadful sores in our flesh. They can penetrate through wood and paper, but not metals. They pass readily through flesh, but not bones. All such ether waves are treated in a book by Sylvanus P. Thompson, entitled 'Light Visible and Invisible,' in which he points out that electricity, heat, light, chemical rays, etc., are all alike in being ether waves, and this was suspected by James Clerk Maxwell and others half a century ago, and has come now to be quite generally believed.

"Halley's comet, already having been seen upon this return, must be sending out those ether waves which we call light; whether it is also sending forth some of the other kinds of ether waves may yet be determined."

My audience being chiefly composed of those persons who were present at Harold's birthday party, they pressed me to tell them more about wireless telegraphy and similar matters, and so I agreed to give them at some future date some account of the history of these ideas. But my present purpose was to start an interest in astronomy as an antidote for the wireless epidemic, and so I invited all who desired to do so to come again one week from that evening, bringing with them such opera and field glasses as they might be able to secure. I promised to show them how to make a telescope such as Galileo had more than three hundred years ago. I agreed to go out with them several evenings and scan the sky with our telescopes, and to tell them of some readable books and articles upon astronomical matters.

XXV

HOW THE IDEA OF A UNIVERSAL ETHER DEVELOPED

The evening for the meeting of the Science Club had arrived. Its membership had increased tenfold within a year. At its monthly meetings, which were open to the public, an audience of two hundred, old and young, was usually present--a number about three times that of the regular membership. General science was now the study of this club. At its weekly meetings, which only members attended, the studies of specific topics by individuals, oftentimes illustrated by experiments, were reported. These meetings were held in one of my laboratories, while the open monthly meeting was always held in my lecture room, with some rather famous speakers to instruct the audience. An enthusiastic friend of science had given a fund with the stipulation that we should engage the services of those who both knew their subjects and had acquired the art of presentation. The fund was $10,000 and it yielded $500 a year. I think beyond question it was doing more for science than any other fund of ten times that amount which can be mentioned.

On the particular evening of which I am about to speak, the lecturer told the members of the Science Club frankly how, beginning at the age of thirteen, he had spent forty years of enjoyment in study, that he had always found great satisfaction in the study of ancient civilizations and literatures. He had been fortunate, he said, in having teachers early in life who could make these subjects full of meaning to him. His greatest satisfaction, however, during the last twenty-five years had been found in tracing the development of modern science, both in the evolution of its theories and in its applications to modern industries. He said he was sure that young people of high-school age would find it profitable to learn, for instance, how the modern theory of combustion had developed slowly through the centuries, even if to do so they must curtail somewhat their study of how Greece and Rome developed and declined. He said that science furnished a tremendously rich field of study for young people, which as yet had been untouched by our schools, first, because educational conservatism had made it impossible to determine the relative importance of subjects of study, and, second, because education in science had, for a brief period, found its worst enemies within its own camp. He would like especially to commend on this evening some historical studies in science, and had chosen for his subject, "How the Idea of a Universal Ether Developed."

Men seem to talk freely now about the transmission of light, heat, and electricity by means of the ether. How did this idea arise? Is it a product of wild imagination? or did the idea develop out of experiences which, if given to any person of fair intelligence, would yield the same result?

A little over thirty years ago, at the Royal Institution of Great Britain, James Clerk Maxwell (1831-1879) delivered a lecture on "Action at a Distance." It was no new subject, but rather one of the oldest and most often discussed subjects from the days of the ancient Greeks down to the present. We talk of gravitation as an attraction or pull between the various bodies of the universe, but how can they pull one another without some material bond between? This was Sir Isaac Newton's great puzzle which he never solved, though he expended upon it the greatest efforts of his great intellect.

The sun appears to repel the tail of the comet, yet how can there be a push without intervening material with which to push? When we speak of light pouring or streaming in, do we think of it as a substance? When we speak of warm bodies losing heat, or when we cover them to keep the heat in, are we thinking of heat as a substance? What are heat, light, electricity, magnetism, and gravitation?

These are no new questions. They are certainly older than history. Various ideas have prevailed at different times. It is much easier to change our ideas than to change our language. You occasionally see and hear the words calorie and caloric used in connection with heat. They stand for an idea, abandoned for three generations, that heat is a substance called caloric, which saturates warm bodies and drains out of them when they cool off. I hardly think these ideas either arise or fall without good and sufficient reason. Each theory has been the natural conclusion from our observations of nature as far as we have gone with them. To be sure, it is difficult for us to see how men acquired, from any observations of nature, the idea of light which seems to have prevailed previous to the time of Aristotle, three and a half centuries B.C. This idea was that objects were made visible by something projected from the eye itself. Still, the questions which I have indicated regarding heat, light, and electricity have impelled men for many centuries to observe nature for hints as to the answers. The doctrine of the universal ether as a medium for transmitting wave motions, and of light, heat, and electricity as being motions of different wave length, is the natural conclusion of the present time. It may give place to another theory when we have further facts to reason upon. Imagine your never having seen a harp or other musical instrument. Would it require a long time, do you think, for you to find out its use, at least to this extent, that it will produce tones whenever the strings are made to vibrate? That the short strings vibrate more rapidly than the long ones, and at the same time produce tones of a higher pitch? Imagine that having become familiar with the harp you should successively come upon scores of other musical instruments of very differing types. You would soon become adept at divining their uses. Now, a study of the microscopic structure of the eye, for one thing, would suggest that light may be in the nature of a vibration. Scores of other lines of study in a similar manner have at length brought all who pursue them to the conclusion that light is a form of vibration.

Robert Hooke in England (1631-1703) and Christian Huygens in Holland (1629-1695), back in the seventeenth century seem to have been the first to give expression to this idea, which was nothing more than an inkling in Hooke's mind, but which was the necessary result of observations on the part of Huygens. For nearly a century the idea lay dormant, largely because Sir Isaac Newton (1642-1727), the cleverest thinker of his time, opposed it. It was perhaps unfortunate for the success of the theory that Huygens, its founder, adopted the word ether, for that was an old term, and had been very badly overworked. The word ether, or æther as it was often written, had been invented in the days of ignorance, for such foolish reasons as: (a) because "nature abhors a vacuum," or (b) "for planets to swim in," or (c) "to constitute electric atmospheres and magnetic effluvia," or (d) "to convey sensations from one part of our bodies to another."

"When we remember," says Maxwell, "the mischievous influence on science which hypotheses about æthers used formerly to exercise, we can appreciate the horror of æthers which sober-minded men had during the eighteenth century."

Newton in England (1642-1727) and Laplace in France (1749-1827) stoutly opposed the undulatory theory of Huygens and championed a corpuscular or emission theory, that light-giving and heat-giving bodies emit a subtile fluid.

There is no other instance in the whole history of modern physics in which truth was so long kept down by authority. Fresnel (1788-1827) and Arago (1786-1853) in France appear to be the only persons during the eighteenth century who caught a clear vision of the truth of the undulatory theory.

But it remained for Mr. Thomas Young (1773-1829), a colleague of Sir Humphrey Davy at the Royal Institution, in his Bakerian lecture (1801) on "Theory of Light and Colour" to bring together such good evidence for the ether wave theory that it has hardly been questioned since.

Young, like Davy, was a most remarkable man in literature and in science. It was he who first deciphered the Rosetta Stone, now in the British Museum, and gave us a key to the Egyptian hieroglyphics. Probably he was the only man who was able to overthrow the influence of Newton's authority even a century after Newton did his work.

Faraday's (1791-1867) chief work as director of the laboratory of the Royal Institution, London, was a study of ether phenomena, particularly electric and magnetic. About seventy-five years ago he became impressed with the fact that although wires may give direction to an electric current the electric influence is not confined to the wires, but may permeate more or less widely the region about them.