Waves and ripples in water, air, and æther

by Sir J. A. Fleming

Mr. Marconi has also proved that it is possible to receive on the same aerial, at the same time, two different messages on separate receiving instruments from two distant but properly tuned transmitting stations.

Since the date of these pioneer inventions many different forms of wave detector have been discovered, and wireless telegraphy has shown itself to be of the greatest utility in effecting communication between ship and ship, and ship and shore. Its value in enabling intelligence to be transmitted from lightships or lighthouses to coast stations cannot be over estimated. One very remarkable feature of the apparatus as arranged by Mr. Marconi is the small space it occupies. It is in this respect most admirably adapted for use on board ship. It only requires a long, insulated, vertical wire which can easily be suspended from a mast, and the whole receiving and transmitting apparatus can be placed on board ship in a small cabin. Employing the sensitive tube and Marconi receiving arrangements, messages can easily be sent 150 miles over the sea-surface by means of an aerial 150 feet high and a 10-inch induction coil.

It is a curious fact that better results are obtained over a water-surface than over land. Two similar stations with the same appliances can communicate at two or three times greater distance if they are separated by sea than if they are on land and have no water between. This is connected with the fact that electric waves are not able to pass through sea-water, but can diffuse through dry earth. The sea-surface acts somewhat like an optical reflector or mirror, and the electric waves glide along its surface. The rotundity of the earth within certain limits hardly makes any perceptible effect upon the ease of communication. The waves sent out by the transmitter of a long-distance wireless station are from 3000 to 20,000 feet in length, and there is, therefore, a considerable amount of bending or diffraction. It is a familiar fact, as already explained, that a wave-motion, whether on water or in air, spreads round an obstacle to a certain extent. Thus an interposing rock or wall does not form a sharply marked sound-shadow, but there is some deflection of the air waves by the edge of the obstacle. The amount of bending which takes place depends on the length of the wave.

If we take two places on the sea-surface 200 miles apart, the surface of the sea at the halfway distance is just 1¹⁄₄ miles above the straight line joining the places. In other words, the rotundity of the earth interposes a mountain of water 1¹⁄₄ miles high between the places. The electric waves used in wireless telegraphy have a wave-length of about 600 to 1000 feet, or say five or six to the mile. Hence the interposition of an object, the height of which is one-fortieth of the distance, is not sufficient to make a complete electric shadow. If we were, for instance, blowing a trumpet creating air waves 5 feet long, the interposition of a cliff between two places a mile apart, but so situated that the cliff protruded to the extent of 40 yards across the line joining them, would not cut off all sound. There would be diffraction or diffusion enough of the air waves to enable the sound to be heard round the corner. In the same manner the electric waves are, so to speak, propagated round the corner of the earth. More remarkable still, they have been detected, when sufficiently powerful, at a distance of 6000 miles from the generating station, and in this case they must have travelled a quarter of the way round the earth.

A good conception of the relative speeds of water waves, air waves, and æther waves can be gained by considering the time each of these would take to cross the Atlantic Ocean, travelling in its own medium. Suppose we could, at the same moment, create a splash in the sea near England sufficiently great to cause a wave which would travel over the surface of the Atlantic at the speed of many ocean waves, say at 30 miles an hour. To cover a distance of 3000 miles this water wave would then require 100 hours. Imagine that we could, at the same moment, make a sound loud enough to be heard across the same ocean, travelling at the rate of 1100 feet a second, or about 700 miles an hour, the sound wave would cross from England to the coast of the United States in about four hours. If, however, we were to make an æther wave it would flit across the same distance in about the sixtieth part of a second.

If you have been able to follow me in these descriptions, you will see that the progress of scientific investigation has led us from simple beginnings to a wonderful conclusion. It is that all space is filled with what we may call an ocean of æther, which can be tossed into waves and ripples just as the air we breathe is traversed in all directions by aerial vibrations, and the restless sea by waves and ripples on the water-surface. We cannot feel or handle this imponderable æther, but we have indubitable proof that we can create waves in it by suddenly applying or reversing something we call electric force, just as we are able to produce air or water waves by the very sudden application of mechanical force or pressure. These æther waves, when started, not only travel through the ocean of æther with astonishing speed, but they are the means by which enormous quantities of energy are transferred through space.

From every square yard of the sun’s surface energy is cast forth at a rate equal to that produced by the combustion of eleven tons of best Welsh coal per hour, and conveyed away into surrounding space by æther ripples, to warm and light the sun’s family of planets. Every plant that grows upon the earth’s surface is nourished into maturity by the energy delivered to it in this way. Every animal that basks in the sunlight is kept warm by the impact of these æther waves upon the earth. All the coal we possess buried in the earth’s crust, and in this age of steam forming the life-blood of the world, has been manufactured originally by æther ripples beating in their millions, in long-past ages, upon the vegetation of the primeval world.

But in another way the æther serves as a vehicle of energy—in the form of an electric current. Every electric lamp that is lighted, every electric tram-car that glides along, is drawing its supply of energy through the æther. The wire or conductor, as we call it, serves to guide and direct the path of the energy transferred; but the energy is not in but around the wire. We have lately learnt to make what we may best describe as billows in the æther, and these are the long waves we employ in wireless telegraphy. But in telegraphy, whether with wires or without, we are merely manipulating the æther as a medium of communication, just as in speech or hearing we use the air.

We therefore find our physical investigations lead us to three great final inquiries, when we ask—What is the nature of electricity, æther, and energy? Already, it seems possible, we may obtain some clue to an answer to the first question, and find it in a study of the electrons, or tiny corpuscles which build up atoms. Concerning the structure of æther, physical investigation, which has revealed its existence, may be able to analyze a little more deeply its operations. But the question, What is Energy? seems to take us to the very confines of physical inquiry, where problems concerning the structure of the material universe seem to merge into questions concerning its origin and mystery. In its ultimate essence, energy may be incomprehensible by us, except as an exhibition of the direct operation of that which we call Mind and Will. In these final inquiries into the nature of things, the wisest of us can merely speculate, and the majority but dimly apprehend.

We must not, however, travel beyond the limits of thought proper for these elementary lectures. Their chief object has been to show you that the swiftly moving ocean waves, which dash and roll unceasingly against the coast-lines of our island home, are only instances of one form of wave-motion, of which we find other varieties in other media, giving rise to all the entrancing effects of sound and light. In these expositions we have been able to do no more than touch the fringe of a great subject. Their object will have been fulfilled if they have stimulated in you a desire to know more about these interesting things. Every star and flower, every wave or bird that hovers over it, can tell us a marvellous story, if only we have eyes to see, and ears to hear. We may find in the commonest of surrounding things a limitless opportunity for intelligent study and delight. When, therefore, you next sail your boat upon a pond, or watch ducks or swans swimming, or throw stones into a pool, or visit the seaside, may I hope that some of the matters here discussed will recur to your minds, and that you will find a fresh meaning and new interest in these everyday objects. Yon may thus, perhaps, receive an impulse attracting you to the study of some chapters in the “Fairy Tale of Science,” more wonderful than any romance woven by the imaginations of men, and open to yourselves a source of elevating pleasure, which time will neither diminish nor destroy.