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Physics of the Ether - SECTION XXV

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SECTION XXV.


THE ELECTRIC PHENOMENA.

186. Before proceeding to touch upon the effects comprised as the "electric" phenomena, we will in the first place consider briefly the production of motion at a distance, or the transmission of signals as a mechanical problem. Firstly, we may note that there are two possible methods of producing motion at a distance: the one consisting in the transmission of matter across the intervening space to the object to which it is desired to communicate motion; the second method consisting in the transmission of motion (in the form of an impulse or wave) along a train of matter which exists in the intervening space between the object to which it is intended to impart motion.

The first of these methods is evidently but a clumsy mechanical device; for to maintain an entire train of matter in motion at once, or to transmit continuously a stream of matter across the intervening space in order to communicate motion to an object, would especially be ill adapted to long distances; the maintenance of the train of matter itself in motion requiring perhaps as much work as the movement of the object.

On the other hand, by the second method there is no actual transmission of matter, and therefore the resistance due to the bodily propulsion of a train of matter across the intervening space is entirely avoided; there being also other special mechanical advantages in the method of producing motion at a distance by waves, which we shall have occasion to refer to.

187. The action of the apparatus known as the "pneumatic bell" may serve as a practical illustration of this latter method. The arrangement consists essentially, as is known, of a tube containing air, along which a wave is transmitted, due to any disturbance produced at one end of the enclosed column of air, by which means the motion serving as a signal is produced at the farther end of the air column.

Regarding the mechanism of the arrangement, we have here in the form of the air column enclosed within the tube a train of matter consisting of small masses (the molecules of air), among which a rapid interchange of motion is continually going on, so that it becomes only necessary to disturb in any way the motion of these small masses at one extremity of the tube, when by a self-acting mechanism the disturbance is propagated with rapidity to the opposite extremity, the small masses simply exchanging motion and propagating the signal at their own normal velocity.

Here we have the best conceivable mechanical arrangement

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for the transmission of signals; indeed, it may be said that if one were to attempt a priori as a mechanical problem to scheme out the best or simplest conceivable device for the transmission of signals, the principle involved in this mechanism of the air column would constitute the only true solution to the problem.

188. In principle, the conditions required to satisfy the problem evidently are, first, to have a train of matter in rapid and continuous motion, so as to be disposable at any time to transmit a signal at a high speed, without the necessity for imparting to the train of matter the motion by means of which it transmits the disturbance producing the signal. Secondly, in order that this train of matter may be always at disposal, it is necessary that the motion of the parts of the train should take place in such a way that the train of matter, as a whole, preserves a fixed position, and is maintained in equilibrium. Thirdly, in order to render a high speed practicable without disturbing effects, the moving masses must be small, so that each by itself is incapable of producing disturbing effects.

These are precisely the mechanical conditions fulfilled in the simplest conceivable manner in the case of the air column by which the signal of the pneumatic bell is transmitted. In order to transmit a signal, it is only necessary to disturb, i. e. to increase or diminish, the normal velocities of the air molecules at one end of the column by an amount however small, when the disturbance is transmitted automatically, at the normal speed of the air molecules, to the farther end of the column.

If the column consisted of hydrogen gas, the normal speed of whose molecules exceeds by about four times that of the molecules of air, it would be possible to transmit a signal at about four times the speed.

It serves well to show the incomparable superiority of the method of transmitting signals by waves as contrasted with the clumsy device of transmitting a stream of matter, when it is considered that in order to produce a signal at the velocity of an air wave by the transmission of matter, it would be necessary to propel the stream of matter through the tube at the speed of a bullet. The friction and resistance in such a case may be well imagined.

189. Since the mechanism of the air column in the tube of the pneumatic bell is a type of the external air, the same considerations equally apply here, and would therefore indicate the admirable adaptability of the air as a mechanism for the transmission of motion to a distance, or as a means of intercommunication, as illustrated, for example, in the case of those waves of special periods which, by the motion transmitted to the auditory nerve, produce the sensation of sound: the same considerations also applying to the perfectly analogous mechanism of the ether as concerned in the phenomena of light.

It would surely be difficult to imagine a more admirable or sensitive mechanism than the molecules of air impinging against a musical string, ready to take up every gradation of movement of the string and transmit it to the auditory nerve, the slightest movement of the string affecting the normal velocities of the air molecules, which automatically exchanging velocities transmit the motion to a distance, the air in its physical constitution forming a mechanism of extreme delicacy and precision, and of the simplest conceivable character; and just as the molecules of air impinging against a musical string constitute the simplest and best-adapted mechanism for taking up every movement of the string, and transmitting it by interchange of motion to the auditory nerve, so the smaller scale but perfectly analogous mechanism of the ether constitutes the simplest and best-adapted mechanism for taking up every movement of the smaller scale masses (molecules), and transmitting it to the visual nerve.

The fact of the mechanism of the ether and air being the simplest conceivable, and the consequent similarity of the mechanism in both cases, therefore constitutes an illustration of the mechanical principle that to produce complex effects with precision and accuracy the mechanism concerned must be simple; the wonderful complexity of the phenomena of sound and colour rendering it equally indispensable in both cases that the mechanism producing these effects should be of the simplest character, without which precision and accuracy in the transmission of the motions would be impossible.

190. Turning now to the consideration of the electric phenomena, and taking the observed fact that a signal can be transmitted through a wire at about the speed of light, we have to inquire as to the possible physical processes by which such a result can be attained. There exist m principle but two conceivable methods: first, the propulsion of a stream of matter through the molecular interstices of the wire at the observed speed; secondly, the transmission of an impulse or wave along the wire. The first method in this case will scarcely bear a serious consideration, for even if it were conceded that a sufficiently distinct idea could be formed of the nature of so-called " fluids to warrant the hypothesis of their existence, the idea of propelling bodily a stream of fluid some thousands of miles in length, at about the speed of light, through a wire with open lateral spaces between the molecules, cannot but be regarded as unmechanical in the extreme; indeed, the idea would have some resemblance to an attempt to force water through a pipe with sides of open network. We do not imagine that the fluid hypothesis is at all seriously entertained, the term "electric fluid" being perhaps rather used as a convenience than anything else. The fact of the appreciably uniform rate of transmission of electricity, whether great or small force be employed, itself is sufficient to prove that it is not & fluid

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which is transmitted; for if anything were propelled through the wire, the rate of passage would depend on the propulsive power employed, and it would be wholly unaccountable that the rate of transmission should be always about equal to that of light, independent of the will of the operator. If, therefore, nothing be propelled through the wire, then the signal can be only transmitted by something already in the wire, in the form of an impulse or wave. It may also be noted that this appreciably uniform rate of transmission, independently of the force used, is one of the known and essential characteristics of a wave motion.

191. Regarding the structure of the wire, we have a series of molecules at certain distances apart, maintained in positions of stable equilibrium under the action of the ether which surrounds the molecules and pervades the molecular interstices of the wire, the ether within the wire forming an unbroken train of matter, since the molecular interstices necessarily communicate with each other.

There exist, therefore, two possible modes by which a wave can be transmitted along the wire, viz. either by the ether independently, or by the ether and the molecules conjointly; for since the molecules are separated by the ether, it would be impossible for the molecules themselves to transmit a wave independently, i. e. without the participation of the ether.

Now, on considering the question, it becomes tolerably apparent that the transmission of the wave by the molecules and the ether conjointly, involving as it does a continual change of motion between dense and light masses, would be far too slow for the speed of electricity. If the molecules at one end of a wire be disturbed from their positions in any way, then this movement produces a change of the ether pressure upon the adjacent molecules, which causes their movement, and thus a wave is transmitted along the wire at a certain rate dependent on the promptitude with which the disturbed molecules recover their positions of equilibrium, which varies with different substances, the velocity of this species of wave transmitted by the molecules and the ether conjointly, being given by the velocity with which the substance transmits a wave of sound. Since, however, the velocity of transmission of such waves will not bear comparison with the speed of electricity, we are bound to reject the assumption that the molecules are concerned in the transmission of the waves producing the electric effects, and we are therefore reduced to the one remaining possible solution to the problem, viz. that the wave is transmitted by the ether independently.

192. It may also be observed that the velocity of transmission of a wave propagated by the molecules of a substance would necessarily depend on the molecular structure of the substance, the velocity varying considerably with different substances; whereas this has not been observed to be the fact in the case of

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electricity; indeed, the appreciably uniform rate of transmission of electricity in materials of the greatest diversity would by itself warrant the inference that something independent of the materials themselves, but present in all, would be the agent concerned in the transmission of electricity. The ether would satisfy this condition, and it may be observed, lastly, that the ether alone (as indicated by the speed with which it transmits a wave of light) possesses in the normal motion of its particles a velocity at all adequate to propagate, by interchange of motion, a small disturbing effect to a distance with the speed of electricity.

193. As regards the mode of transmission of the waves" producing the electric effects, precisely the same considerations in principle apply as in the case of the air column of the pneumatic bell, only the particles of matter in the form of ether have a very much higher normal velocity, the train of ether in a metallic wire forming an analogous, beautiful, self-acting mechanism for the transmission of signals, it being only necessary to disturb in any way this moving train of matter at one extremity of the wire, when the disturbance is propagated in the form of a wave to the opposite extremity. The mechanism is automatic and of the simplest conceivable character, the wave being propagated simply by the re-establishment of the equilibrium of motion along the circuit.

At the same time the system of waves or impulses forms the suitable mechanical adaptation for producing by vibration that disturbance or change in the ether pressure about the apparatus employed, by which the various motions forming signals are produced.

194. Continuous motion of some kind constitutes the only possible physical means by which a disturbance or change of the ether pressure can be permanently maintained; for since the ether penetrates freely the molecular interstices of matter, it becomes impossible to maintain a permanent change of pressure by using matter as a barrier to exclude the ether, as can be done in the case of the air (by the evacuation of air); so that continuous motion alone (i.e. the motion of a mass or molecule of matter, or of a portion of the ether itself), by affecting the velocities of the ether particles, and thereby excluding the ether by rarefying it, can produce a permanent change of the ether pressure.

it will become evident, on considering the question, that a vibratory form of motion is the only form of motion mechanically adapted to this purpose; for since the disturbance or change of the ether pressure is maintained at a fixed spot, the moving mass, therefore, which produces the disturbance must have such a form of motion that it can maintain a fixed position and yet disturb the ether. For reasons already indicated, a vibratory form of motion is in principle the only form of motion adapted to satisfy these conditions; for by this form of motion the moving mass of matter

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or ether can maintain a fixed position by oscillating about it, and yet can disturb the surrounding ether and produce a change of pressure.

195. The above considerations as to the mode of transmission of electricity may serve to remove any difficulty that might have existed in appreciating how an electric signal can be transmitted at such an immense speed with the feeble means employed, the real state of the case being that the velocity of transmission is not generated at all, but exists already; it being only necessary to change (increase or diminish), by an amount however small, the normal velocities of the ether particles at any point of the circuit, when the disturbance is propagated by the simple re-establishment of equilibrium along the whole length' of the circuit, and thus by the feeble disturbance produced by a drop of acid, a signal may be sent thousands of miles with the velocity of light.

It appears a reasonable conclusion that the velocity of trans- mission of the wave might be affected to a certain, relatively small, extent by the presence of the molecules of the circuit, the wave probably undergoing inflection; also, it may be observed that tne normal velocity of the ether particles upon which the velocity of transmission directly depends, is affected to a certain, relatively small, extent by the vibrations of the molecules.

APPENDIX.

Being obliged to conclude here, for the present, we will merely give a short summary of conclusions regarding certain fundamental points, to which we have been led as the natural deductions resulting from the previous inferences regarding the part played by the ether in physical phenomena, reserving a more detailed consideration of the subject to a future opportunity.

Firstly, when an electric circuit is interrupted the waves are reflected, necessarily producing stationary waves. " Static " electricity, or the " static " electric state, therefore consists in stationary vibrations of the ether in the interior of a body when said to be " charged," these vibrations also disturbing the external ether and producing the phenomena of "attraction" and "repulsion" characteristic of vibratory motions.

Since, also, the ether within a mass of matter or " conductor " is freely movable, the plane of the waves can therefore shift itself. Thus, when a charged metallic sphere is surrounded concentrically by matter, such as by the appreciably uniform distance of the walls of a room, then the waves are also concentric, and radiate in stationary vibrations on all sides. But when a plane metallic surface is approached near the charged sphere, then the stationary vibrations are necessarily intensified by reflection between the two, the conditions of equilibrium causing the plane of the waves to swing round and become parallel to the plane surface; the lateral energy of the waves is therefore taken off, and concentrated be- tween the opposed surfaces, the sphere accordingly now only appearing "charged" on that side where the plane is situated.

The special action of points will be clear when it is considered that a mass of aeriform matter in stationary vibration tends to expand in every direction, and would therefore act with special energy along a point when a point is fixed to a charged conductor.

It is evident that friction or any molecular disturbance whatever would naturally throw the ether within a mass of matter into vibration. The stationary vibration of a mass of ether has its analogy in the stationary vibration — "resonance" — of a mass of air, produced by friction, &c. The change of "static" electricity into "dynamic" electricity, or the "static" state into the "dynamic" state, and conversely, is simply the change of stationary vibrations into progressive vibrations, the one of these being necessarily always capable of producing the other.

The " magnetic " condition consists in the disturbance or wave movement necessarily produced outside a circuit, such as a wire — due to the communication existing between the ether within the wire and the external ether — when a wave is transmitted through the wire.

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It is a known and remarkable fact that the electric energy within a circuit is the same at all points, however far from or close to the source of energy, and however diverse the materials may be of which the circuit is composed; this fact possibly having led to the idea of its being a current.

This uniformity in the energy in all parts of the circuit, and also the necessity for having a circuit, is explained by the fact that the vibrations of the ether outside the wire or circuit can only be in equilibrium among themselves, and, indeed, can only exist when the circuit is complete, and thus the oscillating masses of ether can abut against each other and be in equilibrium of pressure; just as the component stones of an arch can only be in equilibrium when there is a keystone, or when the circuit is complete. Indeed, the closed or complete circuit is one of the conditions for the existence of stationary vibrations in a medium without masses of matter for these vibrations to abut against, the vibrations abutting against them- selves in a complete circuit.

The stationary vibrations of the ether between two molecules of matter exist without a complete circuit, from the fact that these vibrations can abut against the molecules; but when matter is wanting altogether in the line of the vibrations, then these vibrations can only exist by abutting against themselves, which is only possible in a complete circuit; and the condition for equilibrium of pressure requires that the energy of the vibrations should be perfectly uniform in all parts or throughout the circuit. Indeed, this uniformity is necessarily self-adjusting.

Since, therefore, the vibrations outside the circuit or wire (the magnetic vibrations) are necessarily connected with and dependent on the vibrations inside the wire, the one reacting upon and influencing the other; accordingly, therefore, the uniformity in the vibrations outside the wire is necessarily followed by uniformity inside, whatever the nature of the different materials forming the circuit. Thus when, for example (without interrupting the circuit), an additional length of wire or resistance is brought into the circuit, the energy of the internal (electric) waves first falls at or near this point of the circuit, and thus the equilibrium of motion between the internal (electric) vibrations and the connected external (magnetic) vibrations is upset at this point of the circuit, and in the readjustment of equilibrium, therefore, motion is transferred from the stronger external vibrations to the weaker internal. The energy of the external (magnetic) vibrations, accordingly, next falls at this point of the circuit, and immediately in the self-acting readjustment of the equilibrium of motion among the external vibrations, a magnetic wave rolls round the circuit, readjusting the uniformity of wave motion out- side (i.e. the magnetic vibrations), and with it the uniformity of the connected wave motion inside (i.e. the electric vibrations). Thus the conditions for equilibrium require that the electric wave motion should be uniform throughout the circuit, and the magnetic vibrations cannot exist at all without a complete circuit.

The electric spark is due to the disturbance produced in the ether, attendant on the sudden change of stationary vibrations of the ether into progressive vibrations, by which the molecules of air are displaced and shaken into vibration, emitting light. It may be observed, that one of the characteristics of a stationary vibration of matter is that the effects are perfectly balanced, or the oscillating segments into which an aeriform medium in stationary vibration is broken up, impinge against each other

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and balance each other's effects, the nodes or points of no motion remaining stationary. But when from any disturbing cause the equilibrium of the vibratory movement of the medium is upset at any one point, and the vibrations consequently become progressive, then the effects are no longer balanced, the nodes shift their positions, and the molecules of matter immersed in the ether may be met on one side by a condensation, on the other by a rarefaction, as the wave passes, and thus the molecules may be displaced or driven out of their positions. Thus, in the powerful effects of lightning, for example, the sudden change from stationary to forcible progressive vibrations of the ether within a mass of rock may be sufficient to disintegrate it completely, or to shatter it to fragments.

When the human system is connected to the charged conductor of an electric machine, the stationary vibrations produced in the ether within the system are unfelt, but when by touching some external object (connecting to earth), the vibrations suddenly become progressive, a tremor is felt, or the molecules of the system are shaken, and with a sufficient power may be displaced with injurious effects. It would be difficult to imagine a more searching or effective means of disturbing the molecules or integral parts of a mass of matter than by disturbing the ether which pervades the mass; indeed, one might infer a priori that this would be one of the most effective means of producing powerful dynamic effects.' The remarkable character of the effects of lightning, by which the most rigid structures are overthrown and solid masonry shattered to fragments, is in perfect mechanical harmony with the special nature of the physical cause concerned; a powerful pulse down the ether which pervades a tree, for example, being sufficient to split it into fibres. Indeed, the observed effect is precisely what might be expected from the nature of the physical cause, the disturbance of the ether which pervades matter to the core, scattering the integral parts in all directions, and at the same time nothing could point more unmistakably to the existence of a powerful dynamic agent — by the disturbance of whose equilibrium these effects are produced — than the observed remarkable dynamic effects of lightning.

Regarding "conductors" and "non-conductors," a "conductor" may be defined as a body whose molecular structure is such that its molecules are least affected by the passage of the electric waves, while a "non- conductor," or bad conductor, partly takes up the motion of, and partly reflects the waves. It is obviously merely a question of degree, nut of kind; for the molecules of all substances whatever take up the vibratory movement of the waves to a certain degree, or all substances are heated by the passage of electricity, and those which are heated least, or those substances whose molecules take up the motion of the waves least, are the best "conductors," conducting power being inversely as the heat developed. A forcible wave movement of the enclosed ether may be sufficient to raise the vibratory motion of the molecules until they lose their positions of stable equilibrium, and by their vibrations break up the ether into waves of light, as illustrated, for example, by the fusion of an iron wire by the passage of powerful electric waves. The attendant disintegrating action of the' wave motion is. illustrated by the observed distortion of shape and occasional scattering of the parts of an iron wire at the point of fusion.
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