Return to Physics of the Ether
99. The Impalpable Nature of the Ether. — An intimate connection may be shown to exist between the normal speed of the particles of an aeriform medium and the disturbance produced by the passage" of masses of matter through the medium.
By the movement of translation of a mass through an aeriform medium the resistance encountered depends (as previously treated of in connection with the vibrations of masses and molecules) on the amount of condensation of the medium produced in front and of rarefication produced in the rear of the moving mass, since this is one of the conditions upon which the amount of energy imparted to the medium by the passage of the mass depends; the resistance encountered being simply the measure of the energy imparted to the medium. If there were no condensation and no rarefaction of the medium produced by the passage of the mass, then the number of impinging particles which receive motion in front of the moving mass would be equal to the number of impinging particles in the rear, which transfer an equal amount of motion to the mass; but on account of the existence of the condensation and rarefaction the number of particles which receive motion in front is greater than the number which lose motion in the rear, the excess in the number of particles which receive an increment of velocity for which there is no corresponding decrement being represented by the difference between the condensation and the rarefaction,
this difference increasing with the velocity of translation of the mass.
Further, by the passage of a mass through an aeriform medium, there is a second physical condition by which energy is imparted to the medium. Although by the passage of the mass the impinging particles of the medium in front and rear experience equal increments and decrements of velocity, the mean value of the velocity therefore remaining unchanged; yet this, as previously referred to, is necessarily attended on the whole by an increase m the sum total of the energy of the particles; so that this forms the second physical cause of the resistance encountered by the passage of a mass through an aeriform medium, and this would constitute a cause for a certain resistance, even it' there were no condensation whatever of the medium formed in front of the moving mass.
It is of course clear that if the density of the medium were extremely small, the resistance offered under the action of both these causes might be extremely small.
100. It is now an important point to observe that the amount of condensation of the medium formed in front, and the amount of rarefaction in the rear, of the moving mass will depend on the normal speed of the component particles of the medium, for the speed with which the condensed wave is carried forward and dissipated depends directly on the speed with which an interchange of .motion can take place between the particles, i. e. on the normal speed of the particles.
The actual rate of transmission of the wave, though dependent on and proportional to the normal speed of the particles, will necessarily be to a certain extent slower than the normal speed of the particles, from the fact of the interchange of motion between the particle3 taking place also obliquely to the line transmission of the wave. In the case of the air, for example, the speed of whose component molecules may be taken at 1600 feet per second, the condensed wave of displacement due to the passage of a mass would be carried forward at a somewhat less speed than this, or at the velocity of a wave of sound. In the case of the air, therefore, on account of the very moderate speed of its molecules, the resistance encountered and disturbance produced by the passage of masses, even at moderate speed, are considerable. The speed of a cannon shot is even as great, and perhaps sometimes even greater, than the velocity of forward transmission of the condensed air wave in front of the shot, hence the great resistance offered by the air to projectiles, the air molecules in the rear having barely sufficient velocity to follow up the projectile. It is evident, therefore, that even if the air had as low a density as the ether, it would, on account of the slow normal speed of its molecules, be completely unfitted to afford passage to masses at planetary rates, or its equilibrium would be totally upset.
In the case of the ether, on the other hand, the wave of displacement is carried forward at the speed of a wave of light, so that speeds of hundreds of miles per second are actually attained by cosmical masses, without disturbing the equilibrium of the ether, the wave being carried forward and- dissipated so rapidly that there is no time for an appreciable condensation to accumulate in front of the moving mass. The motion of the ether particles is so rapid that equilibrium is almost immediately re- adjusted on the slightest disturbance, and there is not time for any disturbing effect to accumulate. The high normal speed of the particles of the ether is therefore one of the essential physical conditions to adapt this agent to afford free passage to cosmical masses (the planets, &c.) at high speeds, without disturbance of its equilibrium.
101. Hence the general conclusion may b.e drawn that the higher the normal speed of the particles of an aeriform medium, the less is the equilibrium of the medium disturbed by the passage of masses through it, or the more impalpable does the medium become. The higher, therefore, the normal speed of the particles of an aeriform medium, the more does the presence of the medium elude detection, or the more impalpable the medium becomes, and the less probability is there for its existence to be detected by endeavouring, as it were, to probe it with masses, i. e. to disturb its equilibrium by moving masses of matter through it. This deduction has its direct application in the case of the ether, the known impalpable nature of which is another physical indication of the high normal speed of the particles of this agent.
102. The Physical Qualities essential to a powerful Dynamic Agent. — It might be considered at the first thought, that because the ether is so impalpable and its density is so low it would not be an agent suited to produce forcible mechanical effects, or it might be inferred, on the first consideration of the subject, that the thin impalpable ether would not be suited to act forcibly upon the masses and molecules of matter and produce powerful dynamic effects, such as those exhibited in the case of explosives, &c. Now this, like many other first impressions, will become totally altered after a due consideration of the subject.
There is, unquestionably, a natural tendency to associate ideas of energy with large visible masses of matter in motion. This is not to be wondered at, since these forms of energy appeal directly to the senses, whereas the movements of molecules or particles of matter do not. If, therefore, misleading inferences are to be avoided, it is well that this natural tendency should be guarded against; for the motions of molecules and particles of matter might well possess an intensity of energy far surpassing that of any motions of visible masses; indeed, energy in this form might almost attain any value however high, and yet would necessarily be wholly incapable of appealing directly to the senses.
There is a certain tendency, for example, to ignore, or at least not adequately to realize, the high intensity of the concealed molecular motion which is termed u heat." Thus, far instance, the energy of a passing shot is fully realized, and yet it may be shown that the energy of the molecular motion (" heat ") possessed by the shot at normal temperature, and while at rest, represents about double the energy of the translatory motion of the shot at the instant of discharge.
The normal rate of motion (1600 feet per second) of the molecules of air is almost explosive in its energy; yet from the fact that these moving molecules are too small to affect the senses directly, there is a natural tendency to overlook the existence of this energy. The space occupied by the air molecules being very small compared with the space unoccupied; if therefore we were to imagine the component molecules of a cubic foot of air suddenly to lose their motion, a practical vacuum would be formed, and the sudden restoration of equilibrium would produce a dynamic effect resembling an explosion. The stoppage of the motion of the component particles of a cubic foot of ether would be followed by a dynamic effect, the high intensity of which could only be realized by an adequate appreciation of the energy enclosed by this agent.
103. In turning to the consideration of the physical qualities essential to a powerful dynamic agent, we may first observe that the existence of a high velocity in the particles of the agent in their normal state is an indispensable condition, for unless this be the fact, an intense development of motion or an intense dynamic effect could not be produced by the agent; in fact, unless the particles of the agent had a high velocity, they would be incapable even of following up the motions of the masses in which they develop motion. Again, this high normal velocity of the particles is the sole condition on which the motion expended by the agent in the production of a forcible dynamic effect can be replenished with speed, and the loss of motion be subdivided or spread over an extensive volume of the agent, or over a large number of the particles of the agent in a short space of time.
Secondly, minuteness in the moving particles being the necessary condition to render a high speed practicable to the particles, it follows, therefore, that minuteness in the particles, or an extremely subdivided state of the matter forming the agent, is a second essential condition to a powerful dynamic agent.
It is important to note that this condition is necessarily followed by an absolute concealment of the existence of the motion from the senses, so that for an intense store of motion or energy to exist, the concealment of its existence is a necessary condition.
Thirdly, a low density in the agent or the existence of but a small quantity of matter in the unit volume of space may be shown to be an essential condition to a powerful dynamic agent.
This will be clear when it is considered that if space were encumbered with a quantity of matter, i. e. if the agent were dense, the agent would itself obstruct the very motions it develops, or, in other words, a high velocity could not be imparted without the motion of the moving masses being greatly interfered with and obstructed by the agent; so that, in fact, for the attainment of energy, the agent must rely upon speed rather than upon mass; it being also a noteworthy feet that the energy rises as the square of the speed.
Moreover, it is an important mechanical point to observe that by the absence of mass the energy becomes more concentrated, or by a reliance upon speed rather than upon mass, a greater quantity of energy admits of being concentrated upon a given spot; whereas the attainment of the same absolute amount of energy by means of large masses and slow speeds would render it impossible for the energy to be concentrated upon a small area (such as against a molecule of matter, for example), which concentration of energy is absolutely essential for the production of intense dynamic effects.
104. The above considerations, therefore, lead to the general deduction that to constitute a powerful dynamic agent the essential physical conditions are, firstly, a high normal speed for the component particles of the agent; secondly, that the particles should be minute, or that the matter forming the agent should be in an extremely subdivided state; and thirdly, that the quantity of matter relatively to the unit volume of space should be small, or that the agent should possess a low density.
This deduction has its direct practical application in the case of the ether, where we find precisely these physical qualities developed to an extreme degree.
105. That the use of minute masses endued with a high velocity is the proper mechanical proceeding when an intense dynamic effect is required, is illustrated in practice in many ways. Thus, when for any engineering purpose a powerful mechanical effect is required, then recourse is had to gunpowder. The effect observed at the explosion of gunpowder is simply produced by the action of small masses of matter ("molecules") endued with a high speed. If, therefore, gunpowder, by means of the motion transferred to its molecules by the ether, represent in the act of explosion the true ideal of a powerful dynamic agent, how much more must this be the case with the ether itself?
106. Since, therefore, we observe that a high velocity of the component particles and a low density are the qualities essential to a powerful dynamic agent, and since this high velocity of the component particles is precisely the quality which necessarily renders the agent impalpable, it follows, therefore, that the known impalpable nature and low density of the ether, instead of indicating that this agent is unfitted to produce powerful
dynamic effects, should, when justly viewed, lead directly to the opposite conclusion.
107. To illustrate somewhat further the connection which exists between the speed of the component particles of an aeriform medium and its impalpability, we may imagine the case of a con- fined mass of air cooled down to such a degree that the translatory motion of the air molecules has almost ceased. Then, in such a case, the air would become quite palpable, or by a mere motion of a mass of matter through it, the air might be completely dis- placed, vacua formed in parts, and the density increased in other parts; indeed, the molecules of air, if almost without translatory motion, might be collected in groups. The air would, in fact, by the almost complete loss of the normal speed of its molecules, have lost its elasticity and the power of eluding the grasp, which the translatory motion of its molecules at normal temperature enables it to do.
It is important, therefore, to observe that the more palpable the mass of air becomes, the less is the store of energy enclosed, or the less would the air be qualified to produce a dynamic effect; and to apply, therefore, this principle generally, the fact of a medium being palpable would indicate that it was totally unfitted as a dynamic agent, and conversely the fact of a medium being impalpable, by which the existence of the medium eludes direct detection by the senses, would, by pointing clearly to the high normal speed of the particles of the medium, directly indicate that the medium was well qualified as a dynamic agent.
108. If we imagine conversely the confined mass of air to be heated, so as to increase the translatory motion of its molecules, then the air would become more and more impalpable, it would elude the grasp, and it would be more difficult to disturb its equilibrium by moving masses of matter through it, and therefore the presence of the air would be more difficult to detect by this mtans. At the same time it is well to note that the more impalpable the mass of air becomes (due to the increase of speed of its molecules), the more intense is the store of energy enclosed, and the greater is the pressure exerted, and the more fitted does the air become as a dynamic agent.
These considerations have their direct application in the case of the ether, the remarkable impalpability of which could not be better illustrated than by the fact that no ordinary rate of motion of masses of matter has been found capable of affecting the transmission of the waves of light by the particles of the ether; in fact, the density of this agent cannot be changed by ordinary means, the readjustment of equilibrium being so rapid, and the agent completely eludes the grasp, or its existence escapes the direct detection of the senses.
109. It is, therefore, a remarkable and noteworthy fact that the very qualities which serve to conceal the existence of the
energy and the existence of the pressure, and, indeed, the existence of the agent itself from the direct perception of the senses, are precisely the qualities which are absolutely essential to the existence of this energy and pressure, or the existence of an intense magazine of motion.
It may, in fact, be observed that the existence of an intense store of energy, and the existence of an intense pressure, are not only consistent with the fact that the ether is impalpable, but they are the necessary consequences of this fact; for the impalpable quality of an aeriform medium is dependent on the rapid motion of its component particles, and this rapid motion cannot exist without the existence of an intense store of energy, and also the rapid motion cannot exist without the exertion of an intense pressure, the pressure, moreover, rising in the high ratio of the square of the speed.
110. The existence of an extensive stater of subdivision of the matter forming the agent being the essential condition to a high normal speed of the component particles of the agent, this very condition renders the concealment of the motion complete; for by the multiplicity of particles, the mean length of path, or the limits within which the particles can move before being intercepted by other particles, is rendered so small, and the pressure thereby rendered so uniform and perfectly balanced, that the existence of this energy and pressure must necessarily elude direct detection by the senses.
The greatest length of path of an ether particle might well, under the simple condition of subdivision of the matter forming the ether, be contained many times within the limits of space that a molecule of matter would occupy, so that as far as any power of detecting the motion by the senses is concerned, the particles might as well be at rest.
..* 111. Concealed Motion. — Since the concealment of the existence of the physical agent from the senses is the necessary result of the enclosure of a store of motion of a high intensity by the agent, and since, as a fact, having a general application, the concealment of motion is the necessary condition to render possible a high intensity of motion, or the enclosure of a store of energy of a high intensity; and, moreover, since the higher the intensity of the energy the more probability is there that its existence should have an important influence on physical phenomena; the investigation of concealed motion, as a general physical problem, should, therefore, have a special interest.
As a known and instructive example of concealed motion which has a considerable intensity, and a most important bearing on physical phenomena, the concealed motion termed "heat" may be referred to.
112. As a known illustration of a physical agent enclosing a considerable store of motion, and exerting thereby a considerable
pressure, both of which elude the direct perception of the senses, the atmosphere may be cited. The normal speed of the air molecules producing the pressure of 15 lb. per square inch being 1600 feet per second, the energy enclosed, therefore, is such that if a mass of air next the earth's surface were suddenly freed from confinement, the mass of air would explode in every direction, or its molecules would fly apart with the speed of a bullet. The air, therefore, constitutes an instructive example of concealed motion, and may form, as it were, a sort of stepping-stone towards the realization of the ether. If the motion of the air molecules and the attendant pressure be concealed, how much more cause is there for the complete concealment of the existence of the store of motion and the attendant pressure in the case of the ether, the cause for concealment being greater as the moving particles are more minute, and by their multiplicity the motion is confined within narrower limits, and the pressure more evenly balanced ? In the case of the air, the moving portions of matter (molecules) are sufficiently small, or the state of subdivision of the matter forming the air is sufficiently extensive, to conceal the motion completely from the senses, and to render the pressure of the air upon masses of matter so perfectly balanced on all sides that the pressure is also necessarily concealed. It may serve to contrast the states of subdivision in the two cases to note the fact of the ether being mechanically suited to exert a uniform pressure about an air molecule (as about molecules generally), while the air can only exert a uniform pressure about a mass (collection of molecules), and would be wholly incompetent to control the equilibrium of a molecule of matter, on account of the absence of an adequate degree of subdivision.
113. When from any cause the motion of the air molecules becomes abnormal, i. e. takes place in any one direction in preference to another, and the equilibrium is thus disturbed, and masses of matter are influenced on one side, then the motion and pressure become very palpable. Such an abnormal motion of the air molecules occurs in the case of a strong wind or hurricane, for example. It may, however, be computed that the energy represented by the translatory motion of the air molecules in the normal state of the air represents an energy about 120 times greater than the energy the air would possess if moving with the speed of a hurricane (taken at 100 miles an hour), and yet the energy and pressure of the air in its normal state remain concealed on account of the perfect state of equilibrium which exists.
114. Summary of the Physical Qualities of the Ether. — We may here give a short summary of the special physical qualities of the ether, as serving to show their mutual connection.
I. Low Density. — The low density of the ether, or the small quantity of matter contained in the unit volume of space in the case of the ether, is that quality by which the ether is adapted to
afford free passage to masses (such as the planets, &c.) and molecules of matter, at high speeds, without impediment. Second, this quality renders the ether mechanically well adapted as a means for the general interchange of motion between masses and molecules of matter at a distance from each other, it being an admitted principle of mechanics that for the free interchange of motion, or for the production of any distant effect, lightness in the intervening mechanism is the essential point.
II. Extreme Minuteness of the Ether Particles. — This physical quality is absolutely necessary to enable the ether to penetrate with freedom the molecular interstices of matter. Second, this minuteness of the component particles, or extreme state of sub- division of the matter forming the ether, by multiplying the number of the particles, and thereby bringing them into close
Proximity, is the necessary quality to render the pressure exerted y the ether upon the molecules of matter steady and uniform. Third, this minuteness of the component particles, or extremely subdivided state, is the necessary condition to render a high normal speed for the particles practicable, without disturbing effects.
III. High Normal Speed of Component Particles. — This physical quality is absolutely essential to constitute a powerful dynamic agent, for without this high speed dynamic effects of a high intensity cannot be produced. Second, this high normal speed of the particles is the sole condition on which the loss of motion sustained by the ether can be replenished with that degree of speed which is essential to render a continuous dynamic effect of a high intensity possible to the ether. Third, this high speed of the component particles is the sole quality by which the loss of motion sustained by the ether in producing a given dynamic effect can be subdivided or distributed over a large volume of the ether, whereby a notable local disturbance of the equilibrium of the ether is prevented. Fourth, this quality is essential for the rapid interchange of motion between masses and molecules of matter at a distance from each other, the rapidity of intercommunication or exchange of motion being strictly limited by the normal speed of the particles of the intervening agent. Fifth, this high speed of the component particles is necessary to render possible the existence of a store of energy of a high value, without the encumbrance of a large quantity of matter in space. Sixth, the high normal velocity of the ether particles is the necessary mechanical condition to enable an intense pressure to be exerted by the ether upon the molecules of matter, without the movements of these molecules and masses being obstructed by the agent exerting the pressure. For, in the first place, by this high speed of the component particles an intense pressure is attainable (more especially as the pressure rises as the square of the speed) without the necessity for the agent being dense, by which the free passage
of masses of matter through the agent would be obstructed. In the second place, the high speed of the component particles enables masses of matter to pass through the agent with the least disturbance of its equilibrium, or with a minimum of resistance from this cause, the agent becoming almost impalpable; the exertion of an intense pressure by the agent being itself the necessary condition to render the agent adapted to control forcibly the molecules of matter in stable equilibrium, as exhibited in the general phenomena of "cohesion" or the aggregation of the molecules of matter generally.
The above may serve as a general summary of the special physical qualities of the ether; and it may be noted that if the attempt were made beforehand, as a mechanical problem or speculation, to devise or scheme out what special physical qualities an agent should possess in order to be mechanically fitted to produce the varied physical effects of the character observed, then the scheme of the ether would be found to constitute the only possible solution of which the mechanical problem admits; or the ether may be contemplated as a piece of mechanism specially adapted to its work.