Eddy current

“ Beating their way up the river flood was very different from coming down, and it was awe inspiring to the boys to press against the vast current, winding and curving to miss the onrushing chunks of drift. In eddies they could swing out into the reverse current and run with the circling waters, but at the heads of eddies they had to put on all their power and nose into the swirling sucks where the fast main flow insolently turned the eddy back into the true direction again. ”

“ Irrespective, however, of any such local causes, we must bear in mind the general tendency of air currents towards motion of a circular or spiral character. When we meet a breeze blowing in a direction contrary to that which ordinary experience leads us to expect, we must not forget the possibility that it may be a portion of the ordinary current which has formed an eddy. The main facts of meteorology are now well established, but the local deviations may give room for prolonged study. ”

“ A rod of solid metal or any electrical conductor, when subjected to an alternating magnetic field, has electromotive forces set up in it. These electromotive forces cause what are known as "eddy currents." ”

“ Experimental data, again, can alone decide upon the amount of eddy currents that may be expected in given armatures, and caution is required in applying the results of one machine to another in which any of the conditions, such as the number of poles, density in the teeth, proportions of slot depth to width, &c., are radically altered. ”

“ If a domestic flat iron is placed on the top of the poles of a properly laminated electromagnet, supplied with alternating currents, the flat iron is speedily heated up by the eddy currents that are generated internally within it. The eddy currents set up by induction in neighboring masses of metal, especially in good conducting metals such as copper, give rise to many curious phenomena. For example, a copper disk or copper ring placed over the pole of a straight electromagnet so excited is violently repelled. ”

“ They consume considerable energy and often occasion harmful rise in temperature. Armature cores, pole pieces, and field magnet cores are specially subject to these currents.
Fig. 290.—Arago's experiment illustrating eddy currents. Arago found that if a copper disc be rotated in its own plane underneath a compass needle, the needle was dragged around as by some invisible friction. The explanation of this phenomenon, known as Arago's rotations, is due to Faraday, who discovered that it was caused by induction. ”

“ We can use a strong field and slow movement of conductor, or we can use a weak field and rapid movement of the conductor. But we find also that where the conductor has large section it is liable to heat from eddy currents caused by one part of its section being in a stronger field than another at the same time. ”

“ If, however, they were to move like couples dancing in a ball-room, not only moving along but turning round, their motion would be called rotational. Examples of rotational, or vortex motion are seen whenever we empty a wash-basin by pulling up the plug. We see the water swirl round, or rotate, forming what is called an eddy, or whirlpool. Also eddies are seen near the margin of a swiftly flowing river, since the water is set in rotation by friction against objects on the banks. Eddies are likewise created when two streams of water flow over each other with different speeds. ”

“ He also, by the brightness and increased lengths of the sparks obtained, proved that the electric force in the atmosphere is very greatly increased with the approach of thunder clouds; and also that this force increases steadily as the kites reach greater altitude, and vice versa. Indeed Mr. Eddy and others who have conducted similar experiments, have found the electric force so strong at certain altitudes as to make the manipulation of the conducting wire a source of considerable danger. ”

“ The inertia of the stream of water, its tendency to keep on in the direction it is actually moving and with unchanged velocity, together with its viscosity, necessitate these whirls with which nearly all are familiar. Similarly, and for the same general reasons, horizontal eddies occur in the atmosphere, and the stronger the wind the more rapid the rotation of the eddy. ”

“ According to one theory, when we close the primary circuit the surrounding ether is thrown into a peculiar state of strain that we will call magnetic or electrical lines of force. When the ether wave strikes the second wire there is a molecular movement from a state of rest to a state of static strain. During the time that the molecules are moving from the normal to the strained position in sympathy with the ether we have the condition of a dynamic current, which lasts only a moment. ”

“ We can not define more clearly the nature of this ether strain or displacement until we know much more about the structure of the ether than we do at present. We can picture to ourselves the operation of compressing air as an approximation of the air molecules, but the difficulty of comprehending the nature of an electric wave arises from the fact that we cannot yet definitely resolve the notion of electric strain into any simpler or more familiar ideas. ”

“ Accordingly, the outflow, undifferentiated, of Life and Energy from the Eternal Substantive of Spirit, is never stopped by its own current in any of its differentiated streams; it is impossible for a current to be stopped by its own flow, whether it be a current of electricity, steam, water, or anything else. What then does stop the flow of any sort of current? It is the Resistance or inertia of the channel through which it flows; so that we come back to the formula of Ohm's Law, C = E/R as a general proposition applicable to any conceivable sort of energy. ”

“ If now we apply the ordinary electromagnetic equations of a system of bodies at rest to a system having a constant velocity of translation in addition to the velocities of its elements, the ether remaining at rest, the displacements of the electrons arising from the electric vibrations in the ether and the electric and magnetic forces are the same functions of the new system of parameters as for the case of rest, if we neglect quantities of the second order of the aberration. ”

“ I would suggest that almost the only hypothesis that can reconcile this opposition is that the length of material bodies changes, according as they are moving through the ether or across it, by an amount depending on the square of the ratio of their velocity to that of light. We know that electric forces are affected by the motion of the electrified bodies relative to the ether, and it seems a not improbable supposition that the molecular forces are affected by the motion, and that the size of a body alters consequently. ”

“ Etheric Force.—Charley Edison hung to the gas-pipe with feet above the floor, and with a knife got a spark from the pipe he was hanging on. We now took the wire from the vibrator in one hand and stood on a block of paraffin eighteen inches square and six inches thick; holding a knife in the other hand, we drew sparks from the stove-pipe. We now tried the crucial test of passing the etheric current through the sciatic nerve of a frog just killed. Previous to trying, we tested its sensibility by the current from a single Bunsen cell. ”

“ Relation of Pressure and Velocity in a Stream in Steady Motion when the Changes of Section of the Stream are Abrupt.—When a stream changes section abruptly, rotating eddies are formed which dissipate energy. The energy absorbed in producing rotation is at once abstracted from that effective in causing the flow, and sooner or later it is wasted by frictional resistances due to the rapid relative motion of the eddying parts of the fluid. In such cases the work thus expended internally in the fluid is too important to be neglected, and the energy thus lost is commonly termed energy lost in shock. ”

“ Hence, if a large number of electrons are suddenly started into motion in the same direction, the effect on the æther is something like casting a multitude of stones on the surface of still water, or the simultaneous action of a number of small explosions in the air. Anything, therefore, which, so to speak, lets the electrons go gradually, or softens the first rush, is inimical to the production of a vigorous electric wave. ”

“ Not yet do we fully realise what we are doing. Not yet have we any dynamical theory of electric currents, of static charges, and of magnetism. Not yet, indeed, have we any dynamical theory of light. In fact, the ether has not yet been brought under the domain of simple mechanics—it has not yet been reduced to motion and force: and that probably because the force aspect of it has been so singularly elusive that it is a question whether we ought to think of it as material at all. ”

“ It is the electron alone which has a grip of the ether. To create an ether wave, we have to start or stop crowds of electrons very suddenly. If in motion, their motion implies energy, but it is not only their energy which is concerned in the wave making, but the acceleration, positive or negative—i.e., the quickness with which they are started or stopped. ”

“ It has been ascertained that in most mineral veins a proper apparatus will detect the existence of electric currents. It may be regarded as certain, that the unequal heating of different parts of the surface at the same time, by the sun, causes a vast current of feeble [101] intensity to circulate around the earth once in twenty-four hours. The unequal distribution of heat below the surface may also produce currents subject to other laws. We should expect that these currents would take up the mineral substances diffused through rocks, and deposit them by themselves. ”

“ The mode of connection between the particles and the ether is not known: it is earnestly being sought: but the fact that therein a connection has been known a long time. We know it, because a particle cannot quiver, or inner, without disturbing the medium in which it is. A boat cannot oscillate on the surface of water without sending off waves; a bell cannot vibrate in air without sending out waves of sound; a particle cannot vibrate in ether without sending out waves of light.
So the second thing to learn about the ether is its property of conveying light. ”

“ Still there is every reason to believe that electric currents do run in the general direction of the circuit described, either one way or the other, according as the passage of the waters is up or down the channel. Where the lateral extent of the moving water is enormously increased, it does not seem improbable that the effect should become sensible; and the gulf stream may thus, perhaps, from electric currents moving across it, by magneto-electric induction from the earth, exert a sensible influence upon the forms of the lines of magnetic variation23. ”

“ A steady flux or drift of electrons in one direction and co-electrons in the opposite direction is a continuous electric current, whilst their mere oscillation about a mean position is an alternating current. Furthermore, the vibration of an electron, if sufficiently rapid, enables it to establish what are called electric waves in the ether, but which are really detached and self-closed lines of ether strain distributed in a periodic manner through space. ”

“ Immediately prior to this invention the highest state of the art of electrical distribution was represented by Edison's feeder system, which has already been described as a straight parallel or multiple-arc system wherein economy of copper was obtained by using separate sets of conductors—minus load—feeding current at standard potential or electrical pressure into the mains at centres of distribution. ”

“ To explain the ether waves, let us consider a vertical aerial.
Fig. 1 When the aerial is fully charged, the lines of strain leave the conductor at right angles to its surface. (Fig. 1.) Upon the discharge the upper ends of the strain lines rush down to meet the lower which move comparatively slowly as they pass along the earth. The earth offers more electrical resistance than the ether. When the upper ends of the strain lines reach the bottom of the aerial, the discharging current has reached its maximum, and as it reaches zero, it charges the aerial in the reverse direction as shown in Fig. ”

“ At any rate, once the existence of a semi-material ether was accepted, it was natural to suppose that the motion of our optical and electrical apparatus through its substance should exert a perceptible influence on the results of experiment. Just as the velocity of the wind adds itself to the velocity of sound waves propagated through the atmosphere, so was it logical to anticipate, in view of our understanding of light waves and of electrical phenomena, that an ether wind should carry the light waves and ether strains along with it. ”

“ We have endeavored in the preceding pages to state the fact clearly that in the Edison three-wire system of incandescent electric lighting the pressure upon the wires is kept constant. A constant pressure implies a constant current, to measure which the Edison meter has been invented. ”

“ In other words, Edison made the sharp fundamental distinction between high pressure alternating current for transmission and low pressure direct current for distribution; and this is exactly the practice that has been adopted in all the great cities of the country to-day. There seems no good reason for believing that it will change. It might perhaps have been altogether better for Edison, from the financial standpoint, if he had not identified himself so completely with one kind of current, but that made no difference to him, as it was a matter of conviction ”

“ When the rod is set in motion these electrical forces change. Electricity in motion constitutes an electric current. But electric currents give rise to forces of a different type from those due to electricity at rest, viz. magnetic forces. Moreover these forces arising from the motion of electric charges will naturally be of different intensity in the directions along and across the line of motion. ”