Electromagnetism

“ If it should be found that the velocity of propagation of electromagnetic disturbances is the same as the velocity of light, and this not only in air, but in other transparent media, we shall have strong reasons for believing that light is an electromagnetic phenomenon, and the combination of the optical with the electrical evidence will produce a conviction of the reality of the medium similar to that which we obtain, in the case of other kinds of matter, from the combined evidence of the senses. ”

“ I will not explain those sparks to you to-day, because I wish to talk to you about electromagnetic effects of electricity and how they are utilized. The first is the production of magnetism. I have here an electro-magnet, which is simply a bar of iron enveloped by an insulated copper wire, and a poker. A poker can be utilized for a great many purposes, but my present purpose is to place it on the large electro-magnet before you. ”

“ To take the induction method first. Whenever a current is sent through a wire magnetism is set up in the ether surrounding the wire, which becomes the core of a “magnetic field.” The magnetic waves extend for an indefinite distance on all sides, and on meeting a wire parallel to the electrified wire induce in it a dynamical current similar to that which caused them. Wherever electricity is present there is magnetism also, and vice versâ. Electricity—produces magnetism—produces electricity. The invention of the Bell telephone enabled telegraphers to take advantage of this law. ”

“ The same reasoning as above applied to electric attraction and repulsion may also be applied to forces produced by magnetism, but if we attempt an experimental verification of the general law of forces acting through space we encounter some difficulty. When dealing with electricity it is quite easy to isolate a positive from a negative charge each on its own conductor, or, as we may also term it, it is possible to accumulate free electricity of one sign on a conductor. It is not possible to accumulate only north magnetic matter, or only south magnetic matter on one piece of steel. ”

“ One ampere of current passing through an ordinary incandescent lamp will produce a light equal to ten candles, and I have shown that by simply moving this small flat spiral a current is induced in it from the earth's magnetic field equal to 0.0007 ampere. With these facts before us, surely it would not be boldness to predict that a time may arrive when the energy of the wind or tide will be employed to produce from the magnetic lines of force given out by the earth's magnetism electrical currents far surpassing anything we have yet seen or of which we have heard. ”

“ These magnetic storms are attended by brilliant displays of the aurora, and this fact strengthens [Pg 37] the theory that the earth is a great electromagnet; for the stronger the electrical current the more powerful we should expect the magnetism to be, and this is shown by the action of the magnetic needle at such times. The stronger the magnet the more intense will be the lines of force, and naturally the more intense the light, if indeed these lines of force are the cause of the light. ”

“ In light waves periodic changes in the ether are taking place at the rate of some five hundred billions per second; the most rapid electro-magnetic changes we have yet produced are some few millions per second. The laws of these vibrations, when they are completely known, will give us the secret of the ether, and will enable some disciple of Clerk Maxwell to take that step which the master himself in his ‘Electricity and Magnetism’ confessed himself unable to take, and to explain the mechanism at one time of light, electricity, and magnetism. ”

“ We must next bear in mind that rarefied air is a good conductor of electricity; indeed, according to recent experiments, an extremely good conductor. The return-trades that pass above from the hotter equatorial regions to the poles of cold, consisting of moist rarefied air, are therefore to be regarded in the light of good conductors crossing lines of magnetic force; we may therefore expect them to be the vehicle of electric currents. Such electric currents will of course react on the magnetism of the earth. ”

“ It appears therefore that certain phenomena in electricity and magnetism lead to the same conclusion as those of optics, namely, that there is an ethereal medium pervading all bodies, and modified only in degree by their presence; that the parts of this medium are capable of being set in motion by electric currents and magnets; that this motion is communicated from one part of the medium to another by forces arising from the connections of those parts; that under the action of these forces there is a certain yielding depending on the elasticity of these connections ”

“ And thus he was enabled, at the end of his second series of ‘Researches’ (December 1831) , to give, in general terms, the law of nature to which may be referred the extraordinary number of new and curious experiments which he has stated (Arts. 256–264) , namely, that if a wire move so as to cut a magnetic curve, a power is called into action which tends to urge a magnetic current through the wire; and that if a mass move so that its parts do not move in the same direction across the magnetic curves, and with the same angular velocity, electrical currents are called into play in the mass. ”

“ But when I opened the switch and cut off the electric current, one boy with one finger in the ring lifted the bar with perfect ease.
"Electro-magnets are now made with a magnetic intensity 90,700 times that of the earth's magnetism. Electro-magnets are used for hoisting iron castings weighing many tons. Here is a picture of an electro-magnet lifting a whole wagon load of kegs of nails from the wagon to the hold of a ship.
"Electro-magnets are our only means of utilizing electricity for power. It is the pull of electro-magnets that moves the electric car. ”

“ If other electrons follow the first within a wire, their passage along the wire will be what is called an electric current.
When the electron is subjected to an acceleration, a transverse wave is produced, and an electromagnetic radiation is generated, of which the character may naturally change with the manner in which the speed varies. If the electron has a sufficiently rapid periodical movement, this wave is a light wave; while if the electron stops suddenly, a kind of pulsation is transmitted through the ether, and thus we obtain Röntgen rays. ”

“ From all these cases we can come to but one conclusion, that both electricity and magnetism are but forms of motion; electricity being a form of motion in ordinary matter, for it cannot be made to pass through a vacuum, while magnetism must be a form of motion induced in the ether, for it is as effective in a vacuum as out of it; electricity always needing some material conductor, magnetism needing no more than do radiant heat and light. ”

“ This, then, is a force acting on a body caused by its motion through the electromagnetic field, or by changes occurring in that field itself; and the effect of the force is either to produce a current and heat the body, or to decompose the body, or, when it can do neither, to put the body in a state of electric polarization, - a state of constraint in which opposite extremities are oppositely electrified, and from which the body tends to relieve itself as soon as the disturbing force is removed. ”

“ Can a current of electricity in a conductor induce a current in another conductor not in any way connected with the first? Can current electricity produce effects through space? Is there an electromagnetic induction?
It has been seen that a current-carrying wire has a magnetic field, and that magnetic fields can act through space. It is evident, then, that a conductor will be surrounded and cut by lines of force when it is placed in a magnetic field, or near a wire or coil through which a current passes. ”

“ When it is under the influence of a magnetic field passing through the magnetic axis—an electrical current through the electrical axis—and a beam of light through the optical axis its mass increases according to some exponential function of the energy levels of the radiation that is passing through it. ”

“ This result cannot be reconciled with the electromagnetic theory of light, unless we suppose that there is less loss of energy when the electromotive forces are reversed with the rapidity of the vibrations of light than when they act for sensible times, as in our experiments.
Absolute Values of the Electromotive and Magnetic Forces called into play in the Propagation of Light.
(108) If the equation of propagation of light is
the electromotive force will be
and the energy per unit of volume will be
where P represents the greatest value of the electromotive force. ”

“ The cases in which any distinctively magnetic action is involved in the phenomena of light are so exceptional, that it is difficult to see any sufficient reason why the general theory should be called electromagnetic unless we are to call all phenomena electromagnetic which depend on the motions of electricity. ”

“ Bodies are attracted to electrics in a right line toward the centre of electricity: a loadstone approaches another loadstone on a line perpendicular to the circumference only at the poles, elsewhere obliquely and transversely, and adheres at the same angles. The electric motion is the motion of conservation of matter; the magnetic is that of arrangement and order. The matter of the earth’s globe is brought together and held together by itself electrically. The earth’s globe is directed and revolves magnetically ”

“ It would lead us into matters beyond the scope of elementary lectures if we were to attempt to summarize all the evidence which exists tending to show that the phenomena of electricity and magnetism must depend upon actions taking place in some medium called the electro-magnetic medium. ”

“ Lines of Electric Strain between a Positive and Negative Electron at Rest. these charges move towards each other and disappear by uniting, the lines of electric strain then collapse, and as they shrink in give rise to circular lines of magnetic flux embracing the rods. This external distribution of magnetism constitutes an electric current in the rods produced by the movement of the two opposite electric charges. At this stage it may be explained that the electrons or atoms of electricity can in some cases make their way freely between the atoms of ponderable matter. ”

“ When, however, we come to deal with electro-magnetic phenomena, which are the results and effects produced by electricity and magnetism, we find certain phenomena similar to those that we find in relation to light and heat. Thus, when light is emitted by a luminous body, a certain amount of energy is given out by that body, and if such light is absorbed by another body, the latter becomes heated, a clear proof that it has received energy or motion from some outside source. ”

“ Once we assume the existence of this physical though imponderable, that is, weightless substance, we may regard it as instrumental not only in the transmission of gravitational forces, but also of electric and magnetic forces and as the carrier of light and heat rays. There is, indeed, very strong experimental evidence that light, electricity, magnetism and all other manifestations of energy are propagated by ether vibrations. ”

“ Part of the work done by an electromotive force acting on a conducting circuit is spent in overcoming the resistance of the circuit, and this part of the work is thereby converted into heat. Another part of the work is spent in producing the electromagnetic phenomena observed by Ampere, in which conductors are made to move by electromagnetic forces. The rest of the work is spent in increasing the kinetic energy of the current, and the effects of this part of the action are shewn in the phenomena of the induction of currents observed by Faraday. ”

“ Starting with a nucleus of permanent magnetism, the magneto-electric currents are used, in the first instance, to form a powerful electro-magnet much stronger than the first, and this powerful electro-magnet is again made use of in the same way as the first, in order to give, by means of magneto-electricity, an induced current of very great strength. ”

“ From the mathematical standpoint the paper is a comprehensive statement, without a suggestion of theory, describing the known facts of Electro-magnetism in terms of a system of vectors supposed to exist at all points of the field. Precision is here given to Faraday’s idea of lines of [Pg 35] force, whether electric or magnetic, by means of the analogy of the motion of an incompressible fluid. The new vector here introduced into Electro-magnetism is that of momentum, and its rate of change is shewn by a dynamical, argument to be responsible for electro-magnetic induction. ”

“ Professor Fitzgerald’s lecture on electro-magnetic radiation shows that scientific men are beginning to realize, and that fairly, the truths appertaining to the new philosophy. The professor admits that electricity and magnetism are of differential character, and he is right. The progressive subdivision, induced on molecules by different orders of sympathetic vibration, and the resultant conditions evolved on the inter-molecule and inter-atom, by introductory etheric dispersion, prove that the magnetic flow of itself is a triple one, as is also the electric. ”

“ On the electro-magnetic theory of light, now universally accepted, the energy streaming to the earth travels through the ether in electric waves; thus practically the whole of the energy at our disposal has at one time or another been electrical energy. The ether must, then, be the seat of electrical and magnetic forces. ”