Return to Physics of the Ether

40. The Phenomena of "Attraction" and "Repulsion" — In returning to the consideration of the phenomena of "attraction" and "repulsion," we may first give some quotations from some papers contained in the 'Philosophical Magazine' (November, 1870; June, 1871), descriptive of experiments with masses of matter vibrating in air (tuning-forks, &c), these experimental results being illustrative of the power of vibrating masses to disturb the equilibrium of pressure of the intervening medium, attended by the effects of attraction and repulsion.

These phenomena appear to have been experimentally investigated at about the same time, and independently, by Guthrie, Gruyot, and Schellbach. In these papers numerous interesting experiments are detailed relative to the attraction and repulsion of various freely suspended substances, by tuning-forks and other vibrating bodies, and we may give the following quotations, as showing the striking and distinct character of the results obtained. We give, first, some quotations illustrative of the experimental results obtained by Mr. F. Guthrie.

41. Experiment 7. — "To one end of a splinter of wood 0.5 metre long, a card .08 metre square was fastened in such a way that the plane of the card was vertical, and contained in the line

• Phil. Mag.,' Nov., 1870.

29

of the splinter. The whole was hung from a fibre of unspun silk, and counterpoised. The tuning-fork was set in vibration, and was brought towards the card in three relative positions. In all three cases the card moved towards the fork. The rate at which the card moved was greatest when the fork was sounding loudest. In all three cases it was possible to draw the card from a distance of • 05 metre at least.

To test the reciprocity of the motive tendency the following experiment was tried: Experiment 8. — "The tuning-fork was fastened to the end of a rod 1 metre long; the end of the rod was counterpoised, and the whole was hung from a silk tape." The description adds, that when a card was held near the vibrating suspended fork, the fork moved towards the card; this being evidently the exact converse of the previous experiment. The following quotation illustrates this point further : Experiment 9. — " Further, instead of a card, a second fork B was set in vibration and brought into the neighbourhood of the vibrating suspended fork A. In every case the suspended fork approached the stationary one." " Hence, to whatever cause the approach is due, the action is mutual." The following few quotations serve to show the distinct character of results obtained by M. Schellbach.* When a sounding box was used, the description adds, " The above-mentioned sounding box distinctly attracted and brought into contact with itself easily movable metallic sheets and balls, even such as weighed 120 grammes, and were at a distance of 8 centimetres/' Another experiment was as follows : " A ball, weighing three kilogrammes, hanging from a silk thread 2 metres in length, could be set in visible vibration when the fork was stroked isochronously with the pendulum vibration."

The following account of an experiment is of interest, as pointing to the analogy between the vibrating tuning-fork put in resonance by waves of sound (air waves), and the vibrating molecule put in " resonance/' so to speak, by waves of heat (ether waves) : " These and the previously mentioned phenomena (i. e. phenomena of attraction) were also produced, although to a less degree, when a tuning-fork was set in vibration by means of a second fork in unison with it. Actions were still visible when the distance between the forks was one metre."

42. These striking experimental facts carry their practical deductions with them, and in their application to molecules vibrating in the ether, there are only two conditions, important in a mechanical point of view, which require to be satisfied, viz. first, the existence of an ether pressure of a value commensurate with the high static value of the effects observed in the case of vibrating molecules; and, secondly, the vibrations of molecules must take place with an energy commensurate with the energy of the effects. The first of these two conditions has been already con-

• « Phil. Mag./ June, 1871.

30

sidered and disposed of; for it is not only possible to show that an adequate ether pressure commensurate with the effects is practicable, but the observed speed of a wave of light, as pointing to the high normal speed of the ether particles, renders the existence of a forcible pressure a necessity, although every allowance be made for the low density of the ether. The existence of this forcible pressure is evidently a necessary mechanical condition to the effects, for the pressure of the agent must, at least, reach the highest static value of the force with which the vibrating masses or molecules are urged together. Thus, in the case of the air, for example, the attraction of vibrating masses, such as for instance the mutual attraction of two vibrating tuning-forks, however great the vibrating energy, could never exceed or indeed reach the static value of 15 lb. per square inch of surface acted against, this being the limit of the normal air pressure, the approach of the forks being due to the excess of the normal air pressure above the reduced air pressure between the forks, due to the vibrations. In the case 01 the ether, therefore, where the observed effects in the case of vibrating molecules attain a static value far surpassing that possible in air, the existence of a forcible ether pressure is, therefore, an absolutely essential physical condition.

The second of the two physical conditions requiring to be satisfied, viz. the existence of a degree of vibrating energy in the case of molecules, commensurate with the observed energy of the phenomena of attraction and repulsion, we shall now proceed to consider more particularly.

48. Absolute Mechanical Value of the Molecular Vibrations. — In regard to the normal " temperature " (normal degree of molecular motion) possessed by the various materials on the earth's surface, one is perhaps liable to overlook, or at least not to appreciate fully, the fact that the absolute mechanical value of this molecular motion is extremely high. A general equilibrium of temperature tends to be maintained, and only changes of temperature (which are extremely small compared with the absolute temperature) can affect the senses, so that the absolute energy of the molecular vibrations (the absolute u temperature ") might possess any value, however high, and yet the senses would be wholly unable to detect the fact of the existence of this energy, and only would the intensity of the molecular energy actually existing become apparent in the most striking manner if in any one instance this motion were to cease. From the fact, however, that a general equilibrium of molecular motion is maintained on all sides, its existence neces- sarily eludes notice, and there is therefore a tendency for the absolute mechanical value of these molecular motions and their practical teaching to escape a due appreciation.

44. In order to form a just estimate of the energy of the effects of attraction and repulsion capable of being produced by vibrating molecules, it is necessary to form an adequate realization of the

31

absolute mechanical value of these vibrations, and the mechanical value of the vibrations of molecules must then be compared with the mechanical value of the vibrations of masses, such as the tuning-forks, &c, by which the observed effects of attraction, already described, were produced.

It may be safely assumed that the mechanical value of the vibrations of the tuning-forks, in the experiments referred to, was not greater than that which would be produced by a blow upon the prong, due to a fall of the fork through 10 to 20 feet, and thereby striking its prong against a hard surface. This is merely intended to give a rough idea of the small mechanical value of the vibrations of the forks (merely stroked with a violin bow) which produced the distinct effects of attraction described; the actual mechanical value of the vibrations being probably less than the above estimate.

We will now endeavour to investigate, approximately, the actual mechanical value of the vibrations of the small component parts of the fork, which are termed " molecules," to the vibrations of which (by the waves generated in the ether) the mutual "cohesion" of the molecules is to be referred. We will suppose the fork to be at the normal temperature of 60° Fahr., this representing an absolute temperature of 519 of Fahrenheit's degrees, reckoned from the absolute zero. The addition of 1° Fahr. to the temperature of a mass of water represents, as is known, an addition to the energy of the motion of its molecules, which would be competent to project the mass of water (i. e. each molecule) to a height of 772 feet, or is equivalent, in mechanical value, to the energy developed at the impact of the mass after a fall from the above height. The specific heat of iron or steel being one tenth that of water, the addition, therefore, of 1° Fahr. to the temperature of a mass of steel represents an addition of energy equal to that developed at the collision of the mass after a fall of 77*2 feet.

The actual value of the vibrating energy possessed by the molecules of the steel fork at normal temperature is, therefore, equal to the energy developed at the collision after a fall of the fork through 519 x 77*2 feet, about 7£ miles, this corresponding to a velocity of 1600 feet per second. If, therefore, we imagine the molecules of the fork tp be without vibratory motion (i. e. without " heat," or at the " absolute zero ") at the commencement of the fall through the above height, and that the work of the collision were entirely expended in developing vibratory motion in the molecules of the fork (raising the " temperature " of the fork),, then the fork would be at 60° Fahr. after the collision. The vibratory motion of the molecules of the fork at normal temperature (60 Fahr.) therefore takes place with such an energy, that the vibratory motion if entirely utilized would be competent to project the molecules to a height of about seven miles, or to

32

project the molecules of the fork apart at a speed in excess of that of a bullet

45. If, therefore, the molecular vibrations take place with this intense energy, then surely the forcible effects of attraction observed in the case of molecules are only consistent with the high intensity of the vibrating energy possessed by them. If the feeble vibrations of a tuning-fork be competent to produce dis- tinct effects of attraction, then if only due weight be given to the incomparably more intense vibrating energy of molecules which derive their energies from the powerful dynamic agency of the sun, then the power of the molecular attractions reconciles itself with ordinary mechanical principles, as powerful effects are the inevitable result of powerful causes. It may also be noted that the separating distances of the molecules of substances being extremely small, the energy of the wave motion set up in the ether is but little reduced by distance, also on account of the great subdivision characterizing the molecular state, the extent of surface exposed to the action of these waves must be exceedingly large.

46. These considerations have a general application, and the remarkable fact of the extreme variety of violating period ob- served in the case of molecules, the observation of which has formed a special study with the spectroscope, has a definite object, viz. that of fixing the " affinity," or special " combining power," of the molecule, for it is clear that if the movements of molecules comprised under the phenomena of " attraction and repulsion," be dependent on the molecular vibrations as a physical cause, then so important a change as a change of wave period, and indeed any change whatever affecting these vibrations, must have its influence on the effects of these vibrations, i. e. on the movements and deportment of molecules; an influence on the physical cause being necessarily attended by an influence on the physical effect, the vibrations supporting each other or interfering more or less as the wave period changes.

The vast variety of wave period observed points all the more convincingly to the fitness of the molecular vibrations as the regulator of the complex and varied effects exhibited in the movements of molecules in " chemical action," or those diverse molecular movements which belong to the science of chemistry, the remarkable diversity in the character of the physical cause producing naturally a remarkable diversity in the effects.

The term s "attraction" and "repulsion" serve as convenient terms to denote the direction of the motion or tendency to motion exhibited by masses or molecules due to a disturbance of the equilibrium of the dynamic action of the particles of the surrounding medium. The term "repulsion" gives some idea of the mode of action. Possibly a term less vague than "attraction" might be used with advantage : "attraction" and " repulsion "

33

being simply impulsion in opposite directions of the mass or molecule under the dynamic action of the particles of the medium.

47. In viewing the phenomena of the movements and mutual actions of molecules as a physical problem, it really is not conceivable that anything could be more admirably adapted to produce the effects than the vibrations of the molecules, which also by variation of wave period are capable of building up the almost endless variety of chemical compounds. In fact, if the question be fairly examined into, there exists no other conceivable process by which one mass or molecule of matter could move or act upon another mass or molecule placed at a distance than by means of vibration. For in the first place, in order for a mass of matter to be capable of moving, or physically affecting a second mass placed at a distance without approaching it, the mass must have a motion of some kind so as to be capable of disturbing the surrounding medium, which forms the only physical connection between the masses. Secondly, since the mass or molecule in acting upon the second molecule maintains a fixed position, it follows that the motion of the molecule must take place in such a way that the molecule can maintain a fixed position, and nevertheless can disturb the surrounding medium. Now, a vibratory motion of the molecule constitutes the only conceivable means of satisfying these conditions, as by this form of motion the molecule can retain a fixed position by oscillating about a fixed point, and yet can disturb the surrounding medium by its motion. Hence, in a mechanical point of view, nothing can be more obvious or to the purpose than the vibratory motion of matter so constantly presenting itself in physical phenomena.

48. A molecule of matter surrounded by the ether cannot possibly be in motion without disturbing the ether, and thereby giving up or dissipating continually its motion in the surrounding ether. This disturbance of the ether by the motion of molecules is illustrated by the waves emitted by the molecules of substances, and the attendant loss or dissipation of the motion of the molecules is exemplified by the cooling (loss of molecular motion) of heated substances when suspended in the free ether. It follows, therefore, from this that the motion of molecules which is being continually dissipated in the ether must be sustained by some external source of motion, or otherwise the motion of molecules would soon cease. This is illustrated by the known fact that the motion of molecules is sustained by the sun, it being an important fact to observe that the character of the sustaining motion is a vibratory or wave motion traversing the ether.

The fact of the special character of the motion of molecules being a vibratory motion is therefore only an illustration of the simple mechanical principle that the motion of molecules must necessarily be that form of motion which admits of being sustained by the action of a vibratory motion traversing the surrounding ether.

34

49. Thus the vibrations or "resonance" of masses by the sustaining action of air waves (such as waves of sound) and the vibrations, "resonance" — so to speak — of the smaller masses ("molecules") by the sustaining action of ether waves (the waves of heat) are in perfect analogy with each other: and in the same way a resonant mass and a " resonant " molecule (as proved by the spectroscope) is sustained by ("absorbs") a motion pf the same character (same wave period) as it emits.

All physical effects being effects of motion, and since vibratory motion constitutes one of the fundamental forms of motion, it would be a thing to be expected beforehand that the general phenomena of vibratory motion, including the production of stationary vibrations in the intervening medium by the reflection of the waves from masses and molecules, would have a most important bearing on all branches of physical science, and have a most influential part to play in physical phenomena.

50. The Static and dynamic Effects of the Ether. — It would appear a priori natural and even necessary that certain "static" effects, or effects of pressure, should exist in the case of that influential agent the ether, just as static effects of pressure are apparent in the case of the air. The phenomena of "cohesion" or the general phenomena of the aggregation of molecules, including the physical conditions governing the equilibrium of molecules, would come under the "static" effects of the ether; while the phenomena of the motions of molecules, such as the phenomena of chemical action, would come under the dynamic effects of the ether.