WAVES AND THEIR PROPOGATION

Nelson Evening Mail, Volume LVI, 4 October 1924, Page 7

WAVES AND THEIR PROPOGATION

CAPTAIN MONCFUEFF’S J.EOTURE

Appended is the first portion of Captain M. M. Moncrieff’s address (abridged) at the Nelson Philosophical Society’s meeting on Wednesday last on “Waves and their Propagation":

INTRODUCTION In recent, years we have witnessed great development of physical science, the results so gained have tended towards a, unity of conception and a simplification of detail. It is hoped that this paper may be of interest to those, who like myself, have had no definite scientific training, but who are interested in the more important conclusions of scientific thought.

We start- to show that the ordinary and popular view of the physical world is incorrect, and give an example that matter such ns the top of a polished table lias no continuous or impervious surface. A short account of the different kinds of waves in water, air and ether follows, and an important conclusion is reached, that it is not necessary for the substance of a thing to remain the same, in order to retain its permanence, and that individuality can persist in spite of a continuous change. To understand the conception of the wave motions of the ether, the electric theory of matter is touched on, which theory maintains that all the properties of matter are- due to motion. The. substantial concept of matter is thus shown to be mistaken.

After indulging in a little philosophical speculation, it is suggested that the universe may perhaps partake of a mental nature. By a rough simile to wave motion, tlie possibility of our personality persisting through the continual flux of matter, and at the same time preserving uur individuality in spite of the continual change in onr environment, is held bee fore us.

As the writer himself possesses the scantiest acquaintance with science and philosophy, the treatment of the subject has been effected in a very elementary fashion. Should he, however, ho the means of arousing in anyone, any dormant interest in the subject- matter of ibis essay, he hopes that it may atone in some way for its many obvious short, comings.

SURFACES OF MATTER Before we take lift the phenomenon of wave motion, it will be as well to show that our knowledge of ordinary familiar objects is extremely limited; and on r»Iteetion, the surface of a solid object like a table will yield some unexpected results.

To those who have never considered Wie subject, matter, that is tlie substance of which the ordinary objects of cur surroundings consist, has been taken to be just what- our senses have revealed to us. A sheet of metal, the top of a polished wood Table has been regarded as a solid block of matter with a continuous and impervious surface. We will ignore the numerous other qualities, as colour, temperature, texture, weight, etc. Let us consider tlie surface alone and see if there is

really a continuous boundary of -socailed solid matter, when examined under an imaginary microscope of enormous power. We all know however smooth a surface appears to the naked eye, it- reveals under a powerful magnifying glass, all kinds of irregular shapes, hills, valleys, etc., (looking something like the range of mountains across Tasman Bay from the Port Hills of Nelson.) The boundary so far appears to be continuous. Supposing we took 1-100 square inch of a plate of polished glass and magnified it a million times, would there still be a continuous boundary between the surface of the -glass and the air above?

No, there would certainly be r.o continuity, there would be far gi eater spaces between the smallest particles of glass than is shown in Figure 11. There would be still greater gaps between the electrons in the atom, which compose the molecules of glass, as w i'.t be seen later.

Could we say that at any particular point here the glass ends and there the air begins? No! There is no continu ous surface of bodies, the boundaries are only mental symbols of separation and only exists in our imagination. All the other qualities of matter can likewise be shown to be other than they seem at first sight. This may come as a surprise to some, but there is still more in store when we come to waves in the ether.

Terms, used in describing waves in general: Wave length.—One wave length in the case of water waves, is the distance between the two nearest crests, or the two nearest hollows.

Wave Velocity.—When a seagull flying above the surface of the sea just keeps above a particular wave, going exactly the same speed as the wave, the speed of the gull in miles per hour or feet per minute, would be called the speed of the wave, or its wave velocity. Wave frequency.—lf we watch a cork floating on a wave tossed sea, we notice that it bobs up and down so many times in a minute. The number of times per minute or per second that the cork moves up, then down and up again, is called the wave frequency or simply the frequencyAmplitude is the distance that each in. dividual particle of the medium moves from' its mean position, or position of rest.

In the case of sea waves, the vertical height between the crests and the hollow is called the height, of the wave, and this is twice the amplitude.

WATER WAVES Let us start our study of wave motion by considering the waves on the surface of a liquid, such as those met with on the surface of the sea, which can easily be observed owing to tlheir size and small speed or velocity. Children, and I am afraid to say, even a few ‘grown ups,’ thinks that as the wave motion moves along the surface of the water, the body of water of which the wave is composed, moves along with the wave. This is not so, it is only necessary to watch a bit of seaweed floating on the surface and notice that as the wave passes, it is not carried along by it, although it rises and falls. the wave as it moves along the surface of the water, completely changes the bodv or substance of itself, yet it retains its shape and form. Each wave, which is only “a form of motion moving,” has its own individuality and characteristics, and differs in some way from its fellow waves. And it- is also able to preserve its shape and individuality for considerable periods of time, and in spite of adverse obstacles which it may encounter. Take the case pf two waves travelling

Li opposi!« directions and observe what happens. As they approach, they commence' to combine or coalesce, each wave continually changing ils original form;, and at the -same time combining to create a totally different• shaped wave of larger size, which alters its appearance from moment- to moment. It gradually increases in size, attains its maximurfl and then diminishes, until the two opposite Waves pass through each other and finally emerge to regain their own distinct and particular form. Throughout the whole of this sequence of change the substrata or body of the two -individual waves are altering, and even while they combine to form one wave, their substrata is klentieal; vet the two waves are able so to speak- to disentangle themselves, resuming their characteristic shapes again, they can continue on their respective courses without seeming any the worse for their encounter. It is most instructive to experiment in a small pond or tank containing water. Wo can then watch tlie behaviour of different waves or rippis, namolv circular, straight, and oblique, etc.

Wo can also start them from opposite sides of tlie tank, ad sec how they manage to emerge after interfering and passing through each other, eventually regaining their original shape- A miniature whirlpool or eddy, although not exactly an example of wave movement i s formed by any swift moving stream with an uneven bottom ; it is another kind of motion, which can persist and retain its characteristic form indefinitely, although tlie substratum or the body of its water is changing continuously. Tlie eddy lias a. complicated spiral movement-, something similar to the vortex ring, whose motion we will describe ]ator. ft. has been suggested by Lord Kelvin that the vortex is a possible workable conceptual model for the ultimate creation of matter from the immaterial ether. There are many other different kinds of movements which act in a similar way. _ We wish to point out tiir#- each wave, though only a form of motion, lias ns much right to be called a distinctive thing as any familiar material object, such as one of- the stones at the bottom of the streant; it has its own particular eharaetristics distinguishing it fi’om its other fellows, which it preserves, in .spite of the fact that the matter of which it is composed is ever varying. It is not necessary that the substrata or substance of -a- thing should remain the same to involve the conception of its permanence. Therefore in short, individuality is not- dependent on sameness of substratum or substance.

In reference to sea waves, one may remark in passing, that the nroper wave motion can only be -seen in fairly deep water. In shallow water the friction of the water against the bottom retards the bottom of the wave, the top part of tlie wave consequently advances more rapidly, which causes the wave Bo become steeper on the shore iside; tlie wave eventually curls over until it falls and breaks into spray. Wavs beating on shore, against piers, and harbour-works, can do great damage. This is due to the forward motion of the. water as the wave is breaking. A cubic foot of water weighs-63$ lbs, a cubic yards of water ton. Whn this water is moving at a speed of many feet per second, the energy of motion stored up i s -tremendous. A moderate sized storm sea-way may have a- mass of mam- hundreds of tons, and its energy of motion could easily amount to that of an express train in motion.

A very curious kind of mot-Lops in water known as a vortex ring or endless vortex, con heat bo studied when made, in the air. Fill a small box .witlivihe white vapour of ammonium chloride with a circular hole at one side. Give the box a sharp blow, and from the round hole, a white smoke ring shoots out, and slides through the air. The ring is seen to continually turn itself over and over, the rotation being round the circular ring axis. (To be continued).