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.