This page contains information about a host of major figures in the history of EM. More precisely, the history of electricity and magnetism, since the conjoining of these two concepts in the term "electromagnetism" was itself a part of this history. The list is, of course, not exhaustive of all important figures.
Below boxes contain: links to works by the author that are in the Lehigh Library collections; biographical links and other background resources; and comments that focus for the most part on: the odyssey of the "ether" concept and related concepts on the one hand, and the path to Maxwell's four equations on the other.
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William Gilbert of Colchester, physician of London, On the loadstone and magnetic bodies, and on the great magnet the earth. A new physiology, demonstrated with many arguments and experiments ... (Mottelay translation)
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Magnetism
Duane Roller, in the De Magnete of William Gilbert, sees "action at a distance" at work in Gilbert's theory of magnetism:
"Within half a century of the publication of the De magnete, Gilbert's distinction of 'magnetic coition' in terms of the joint action of the two objects concerned, in contrast to the unsymmetrical attraction of an object by an excited electric, has become unsatisfactory; the lack of symmetry in the electric case had been disproved, eliminating this difference between the action of electrics and magnetics.
...
Gilbert denies the presence of a material medium in the magnetic case because of the ability of magnetics to act through objects that stifled the electric virtue. He is thereby driven back to an animistic position which at best is able to say that a magnet simply possesses the property of acting at a distance upon a magnetic. The view of action at a distance is by no means one that science has always immediately rejected, although scientists have never liked it: within a little more than a century of the publication of the De magnete, the property possessed by matter of acting gravitationally at a distance is being hailed as the key to the understanding of the universe. The extent to which a theory may be unreasonable and yet acceptable depends upon the breadth of the usefulness which may be found for it. We may therefore no more ask for a further explanation of Gilbert's magnetic form than we may ask for elaboration of the Newtonian property of gravitational action at a distance". (150, 153).
Whether Newton adhered to action at a distance is a matter of dispute; see Newton section.
Electricity
Page 30 of A history of the theories of aether and electricity : from the age of Descartes to the close of the nineteenth century provides an overview of Gilbert's views about electricity.
His understanding of electricity appears not to embrace action at a distance, as opposed to his concept of magnetism, if this passage from p. 30 of the reference immediately above is accurate: : "The existence of an atmosphere of effluvia round every electrified body might indeed have been inferred, according to Gilbert's ideas, from the single fact of electric attraction. For he believed that matter cannot act where it is not; and hence if a body acts on all surrounding objects without appearing to touch them, something must have proceeded out of it unseen" (p. 30).
Duane H.D. Roller in The De Magnete of William Gilbert provides this fascinating commentary:
Gilbert's theory of electric action is therefore a mixture of the older theories, mechanistic and sympathetic. The action is clearly mechanical, but it arises from a sympathy: Gilbert is unable to shake off the older view entirely. At the same time, he firmly renounces the idea of attraction, and insists that electric phenomena are contact phenomena. Since the mechanism for establishing contact is not visible, it must be invisible-but it must be. This creed, which as we have already seen does not by an means originate with Gilbert, has been the single most enduring and effective concept in the history of electricity. Gilbert's thinking in this respect is a forerunner of what is to come in English thought. An evaluation of the extent to which Gilbert may be regarded as a precursor of seventeenth-century English mechanism cannot be made until his theory of magnetism has been examined in detail".(p. 109)
Roller may not have had in mind later English physicists such as the 19th century Maxwell, and may not have in mind the ether concept that came later. Still, we see Gilbert tangling, in the framework of an early vocabulary and conceptual structure, with the problem of transmission of electric forces--how to characterize something that is invisible, and do so mechanically.
According to one account, Newton referenced Gilbert in the Opticks.See page 31 of A history of the theories of aether and electricity : from the age of Descartes to the close of the nineteenth century. Query 22 is on page 327 Newton's Opticks.
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See description in above biography of experimentation involving vacuums.
From The Beginnings of Modern Science from 1450 to 1800. Edited and with a Pref. by Rene Taton. Trans. by A.J. Pomerans. 1964.:
"He did not believe that the earth is a magnet, but agreed with Gilbert that it moves through space because of its magnetic force. Like Huygens, and in opposition to Kepler, he distinguished between attraction as such (conservatio) and magnetic virtue, which he identified with electrical attraction....
He was the inventor of the first electrical machine, a sulphur globe 'the size of a child's head' which could be rotated on its axis and rubbed by hand until it sparked and crackled. The fifteenth chapter of Book IV of his Experimental nova is a treasure-house of experimental science--it describes experiments on electrical replusion, on the acquisition and loss of electrical properties, on point potentials, on surface charges, on the electrification of a threat, on conductivity, on discharges, and on electrical sound and light effects".(318-319)
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Some scholarly resources about Newton's views on electrical and magnetic phenomena and about "Newtoniasm"::
Some items in the debate whether Newton embraces "action at a distance", courtesy Prof. Connolly of the Philosophy Department:
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Newton is generally associated with his views on mechanical forces, not electrical or magnetic ones. See above for some resources though about his treatment of the latter two concepts.
Why didn't Newton significantly advance our understanding of electricity and magnetism in the way he did for mechanical laws? One of the replies here, though non-scholarly, seems on the mark. The point about measurement is very important generally; theoretical advances are built on a great deal of antecedent empirical work:
Arguably, however, the impact of Newtonian mechanics helped drive the impetus to discover a mechanical substrate that would serve as a medium for electromagnetism.
For some references to magnetism, see Principia, p. 397 [403 in the scrolling bar] [ 302, 308 in scrolling]. Also, text in fn. 6 and surrounding text in Robert Palter and James Hynd Early Measurements of Magnetic Force.
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Experiments and observations on electricity, made at Philadelphia in America
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In his 1951 edition of A History of the Theories of Aether and Electricity, Whittaker discusses Franklin's fluid theory of electricity.
Franklin in Whittaker's account was a transitional figure who held to then prevalent fluid theory of electricity, but with a twist (see Leyden jar mentioned below).
The fluid theory "bears a suggestive resemblance to that which nearly a century later was introduced by Faraday; both explained electrical phenomena without introducing action at a distance, by supposing that something which forms an essential part of the electrified system is present at the spot where any electric action takes place; but in the older theory this something was identified with the electric fluid itself, while in the modern view it is identified with a state of stress in the aether. In the interval between the fall of one school and the rise of the other, the theory of action at a distance was dominant" (48).
Whittaker says the fluid theory "practically ended with Franklin". (p. 48), to be replaced by an "action at a distance" theory, the latter at least implicitly present in Franklin's analysis of a Leyden jar. In a Leyden jar, glass intervenes between two charged plates; there must be an influence that acts distantly through the glass. (p. 49).
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Coulomb's First Memoir, a translation of which is immediately above, exemplifies the point made by P. M. Harman in Energy, Force, and Matter. Harman mentions the work of Coulomb, Volta, and Cavendish in using "precise measurement and quantification as criteria of theory construction". He goes on to mention that "the quantification of electrostatics, which established the law of electrostatic force, was especially important in providing the paradigm of precise experimentation, quantification, and the search for mathematical laws as the methodology and objectives that characterised nineteenth-century physics".(15)
Did Coulomb adhere to the action at a distance model? This webpage would seem to suggest that Coulomb's law involves an action at a distance view: "Coulomb's law and Newton's law are both examples of what are usually referred to as action at a distance theories.".
However, Mary Hesse, in Forces and Fields: The concept of Action at a Distance in the history of physics, claims on p. 183 that "Coulomb, in 1785, described in the terminology of the fluid theories the torsion experiments by which he showed that the attractive and repulsive forces of electricity and magnetism are both proportional to the inverse square of the distance between the centres of force".
One of Maxwell's equations entails Coulomb's law.
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See comments under Coulomb.
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1. "Ampere explained the propagation of electromagnetic action by drawing on Fresnel's concept of the luminiferous ether. [see entry about Fresnel] He argued that the ether was constituted of positive and negative electric fluids; electromagnetic phenomena arose from the disturbance of the electric fluids, whereas light was produced as a result of the vibrations of the fluid". (Harman, 31).
Harman continues that "the luminiferous and electromagnetic space-pervading ether provided a physical model for the propagation of electromagnetic action, and by the 1820s the concept of an ether propagating light and mediating electromagnetic interactions was established." (Harman, 31).
2. Brief exposition of Ampere's Law and relationship to Maxwell's equations.
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Oersted famously discovered an empirical link between electricity and magnetism. Up to that point, while there was speculative discussion about how electricity and magnetism might be related, they were "conceived as independent phenomena". (Harman, 30)
What concrete role this philosophy played in Oersted's discovery is a matter of speculation:
"During a lecture demonstration, on April 21, 1820, while setting up his apparatus, Oersted noticed that when he turned on an electric current by connecting the wire to both ends of the battery, a compass needle held nearby deflected away from magnetic north, where it normally pointed. The compass needle moved only slightly, so slightly that the audience didn’t even notice. But it was clear to Oersted that something significant was happening.Some people have suggested that this was a totally accidental discovery, but accounts differ on whether the demonstration was designed to look for a connection between electricity and magnetism, or was intended to demonstrate something else entirely. Certainly Oersted was well prepared to observe such an effect, with the compass needle and the battery (or “galvanic apparatus,” as he called it) on hand."From July 1820: Oersted and electromagnetism.
It appears that Oersted denied action at a distance. Mary Hesse in Forces and Fields: The concept of Action at a Distance in the history of physics mentions (p. 216) that "in 1820 Oersted published his discovery of the effect of a current-bearing wire on a pivoted magnet in its vicinity. It appears that many years had elapsed before he recognised this effect, although he had long been searching for some evidence of connection between the powers of electricity and magnetism, but always on the assumption that any force between them must act along the line joining pole to charge. When the effect was discovered, however, it showed that an electric current exerts a force at right angles to its own direction, causing the magnet to take up a position perpendicular to the plane of the current circuit. This was the first apparent experimental proof that forces at a distance may be other than direct attractions or repulsions, and Oersted himself was inclined to explain it by postulating vortices of electric matter surrounding the current and exerting force on the magnet."
Interestingly, Oersted held (at least at some point) to a philosophy that there is an "underlying unity of the powers of nature" (Harman, 30). There is a larger question here: does the philosophical worldview of a scientist sometimes or even often play a role in motivating their selection of experimental programs? Or inform their interpretation of experimental data?
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"The advances through the 18th century in understanding electric charges and currents, notably the work of Benjamin Franklin and Alessandro Volta culminated in the work of Charles Coulomb, whose law showed that the strength of electric force varied inversely with the square of the distance to a positively or negatively charged object. This law, and a similar one for magnets, was later generalized by the work of Poisson and Gauss in the early 19th century leading to Gauss’ Law, the physics behind the first of Maxwell’s Equations." From Maxwell's Equations.
Two of the famous four Maxwell's equations are associated with Gauss.
It has been difficult to find a detailed historical account of the details of Gauss's direct influence on Maxwell's work, though it must exist. The wikipedia article about Gauss's law has this history, which perhaps provides an initial starting point (in the manner of use of Wikipedia) for further exploration of the history of Gauss mathematical work in relation to Maxwell: "The law was first[1] formulated by Joseph-Louis Lagrange in 1773,[2] followed by Carl Friedrich Gauss in 1813,[3] both in the context of the attraction of ellipsoids. It is one of Maxwell's four equations, which form the basis of classical electrodynamics.[note 1] Gauss's law can be used to derive Coulomb's law,[4] and vice versa." FN 3: "Gauss, Carl Friedrich. Theoria attractionis corporum sphaeroidicorum ellipticorum homogeneorum methodo nova tractata (in Latin). (Gauss, Werke, vol. V, p. 1). Gauss mentions Newton's Principia proposition XCI regarding finding the force exerted by a sphere on a point anywhere along an axis passing through the sphere."
Where did Gauss stand on the issue of action at a distance? Mary Hesse in Forces and Fields suggests that:
"On finding that electromagnetic waves are propagated through free space with a velocity close to that of light, Maxwell made his momentous identification of light and electromagnetic radiation. Maxwell was not, however, the first to suggest that the propagation of electric action in a finite time is of cardinal importance for electromagnetic theory. Faraday had suspected it, although in 1852 he considered that it had not been shown experimentally. As early as 1845, Gauss had written to Weber that he regarded as the corner-stone of electrodynamics the demonstration that actions are propagated between electric particles in time, like those of light. He had not himself succeeded in demonstrating this, and expresses his 'subjective conviction that it will be necessary int he first place to form a consistent representation of how the propagation takes place'.
Gauss's Continental successors were not able to provide this consistent representation, for they still preferred to speak in terms of action at a distance, although there were attempts by Riemann, C. Neumann and Betti to develop somewhat ad hoc mathematical expressions for the propagation of potential in time, without postulating any medium. These theories were criticised on mathematical grounds by Clausius, and on methodological grounds by Maxwell, who remarks that their persistent adherence to action at a distance must be due to an a priori objection to an intervening medium:..." (pp. 220-221).
Hesse cites Maxwell: "'...the question naturally occurs:--If something is transmitted from one particle to another at a distance, what is its condition after it has left the one particle and before it has reached the other?'" (p. 221)
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Oeuvres complètes d'Augustin Fresnel
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"By 1821, as a result of careful work on the nature of optical polarisation, he realised that the vibrations constituting light were purely transverse. He proposed a model of an ether consisting of molecules bound by forces acting at a distance as the medium in which the transverse vibrations were propagated. In reply to criticisms by Poisson that transverse waves would not be satisfactorily transmitted in a fluid medium, Fresnel argued that the problem lay in the reconstruction of the theory of the ether rather than in the futile attempt to deny the wave theory of light. Fresnel realised that a fluid ether could not produce transverse vibrations; to give rise to transverse vibrations the ether would have to possess the property of rigidity. The elaboration of a mechanical model of the ether had not been his primary intention, and was undertaken only in support of his undulatory theory of light. Fresnel's conclusion that light waves were transverse vibrations posed the problem of constructing a mechanical model of the ether capable of transmitting transverse rather than longitudinal waves, a problem that became a major feature of nineteenth-century optics". (Harman, 24).
This paper claims that Fresnel definitely believed in the existence of the ether, but discusses a controversy about whether this commitment to the reality of the ether played an actual role in driving Fresnel's work. It discusses the philosophical issues for the issue of scientific realism that Fresnel's discussion of the ether poses.
Generally: should we care whether a theoretical entity such as the ether actually exists, if positing it produces results and drives research? Or should we be concerned about the actual existence of the posited entities? Scientists behave as if they are discovering the nature of reality, even if this is an ongoing endeavor. Shouldn't the existence of these entities matter to them? The same issue will appear again in stark form with respect to Maxwell's attempt to provide a mechanical representation of the ether. (See below.)
For more re. Fresnel, see section on Fizeau below.
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Die galvanische kette, mathematisch
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From biography link above: “He made a useful analogy with the flow of heat through a conductor, pointing out that an electric current flows through a conductor of varying resistance from one tension or potential to another to produce a potential difference, just as heat flows through a conductor of varying conductivity from one temperature to another to produce a temperature difference.”
This is a good example of how scientific discovery can rely on drawing analogies with seemingly unrelated areas of physics.
Regarding the action at a distance issue, an article by J J O'Connor and E F Robertson claims: "It is interesting that Ohm's presents his theory as one of contiguous action, a theory which opposed the concept of action at a distance. Ohm believed that the communication of electricity occurred between "contiguous particles" which is the term Ohm himself uses."
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Experimental researches in electricity
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1.
Oersted's discovery that an electric current creates a magnetic field precipitated efforts to discover whether the opposite could occur. In retrospect, it seems truly remarkable that it took so long to discover the opposite effect: "Ampère had shown how to make magnetism from electricity — surely it should be possible to make electricity from magnetism. For a decade, scientists tried and failed. Then, in 1831, Faraday found why the goal had been so elusive: to make a current flow in a wire you had to change the magnetic state of the space around the wire. All you needed to do was to move a magnet in the neighbourhood of an electric circuit (or vice versa) and a current would flow in the circuit." From Basil Mahon How Maxwell's equations came to light.
Faraday's Law relates the change of magnetic flux to induced electromotive force. It is expressed in one of Maxwell's equations.
2.
Harman (78-79) notes:
"Faraday had introduced two distinct representations of the field, one using mediation by the contiguous particles of an ambient medium and one asserting the primacy of lines of force. Neither theory provided an explanation of the mechanism by which forces were propagated, though Faraday did suggest that the transmission of force 'may be a function of the aether'. In responding to Fardaay's theories of the field, Thomson and Maxwell attempt to develop physical theories of the propagation of forces by means of mechanical theories of the ether, and to render Faraday's concepts physically intelligible by reformulating them in terms of the programme of mechanical explanation."
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Thierry Lahaye, Pierre Labastie, and Renaud Mathevet. Fizeau’s “aether-drag” experiment in the undergraduate laboratory. See the historical overview.
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Excerpts below are from the Lahaye et al. article above.
Francois Arago did not find a "deviation of light from a distant star by a prism" in his 1810 work. Such a deviation was supposed to follow from Newtonian theory."It seems to be the first experiment in a long series,which showed the impossibility of detecting the relative motion of light with respect to the Earth."
Arago asked his friend Fresnel to look into the matter. Fresnel's "demonstration is based n the hypothesis of an absolute aether as a support of light waves, associated to a partial drag by transparent media". "The value of Fresnel's drag coefficient 1 minus n to the negative 2 precisely gives a null result for the Arago experiment. His demonstration employed "some supposed elastic properties of the aether".
Fizeau's 1851 "aether-drag experiment" "measured an effect in agreement with Fresnel's theory to within a few percent. This unambiguously ruled out concurrent theories postulating total aether drag".
The story was not over, however. See Michelson-Morley section below.
Search in Lehigh library catalog on 'Stokes, George Gabriel, Sir, 1819-1903.'
From biography (Access Science) above:
"Stokes's investigation into fluid dynamics led him to consider the problem of the ether, the hypothetical medium that was believed to exist for the propagation of light waves. In 1848, Stokes showed that the laws of optics held if the earth pulled the ether with it in its motion through space and from this assumed the ether to be an elastic substance that flowed with the earth. The classic Michelson–Morley experiments of 1881 and 1887 did not totally negate this contention; it was shown to be untrue by Oliver Lodge in 1893 and the existence of the ether was finally disproved."
From Harman, 113:
Stokes "conceived the ether as a viscous elastic solid, concluding that there must be friction between the ether and the earth moving through it". Stokes thought "the earth and planets dragged along with them the ether that was close to their surfaces; beyond the the boundary of ether drag, the ether in space was undisturbed by the motion of the earth."
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Popular lectures on scientific subjects
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See the comment about Helmholtz's influence on his student Hertz.
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A treatise on electricity and magnetism
The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science.
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Historical Background to Maxwell's Laws:
Maxwell on the Ether
Edited by Simon Saunders and Harvey R. Brown. The Philosophy of Vacuum. Pages 163 ff.
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1. Maxwell's Laws
As mentioned elsewhere on this guide, one way to help organize our understanding of the history of EM is to look at Maxwell's laws. Maxwell had at least 20 laws. These were reduced to four laws. These are associated with the following names: Gauss, Faraday, and Ampere. See the entries for each of these for some details.
The following timeline appears in: Maxwell's Equations. Engineering and Technology History Wiki.
Some history of the term "Maxwell's equations": "It was Oliver Heaviside who extracted the four key equations and put them in the form we know today. Immediately after this, Heinrich Hertz realized that the equations would lead to the existence of radio waves. The equations then became known as the Hertz-Heaviside or Heaviside-Maxwell equations. However, in the 20th century, Albert Einstein championed the primacy of Maxwell and referred to them as “Maxwell’s equations.” Given Einstein’s influence, that was the term that stuck." From Milestones Honor Maxwell's Equations and Franklin's Observations.
2. Maxwell on the ether
Faraday's views about lines of force influenced Maxwell.
Maxwell published a mechanical model of the ether here making use of vortices; see figure 2 on p. 38. This is an elaborate attempt to make sense of the mechanical structure of the ether, in the context of attempting to model magnetic induction of currents. Maxwell's attitude toward this model was, however, tentative. "Maxwell consistently emphasised that his model of idle-wheel particles and a cellular ether was only a 'provisional and temporary' hypothesis." 92
Maxwell later dispensed with this mechanical model of the ether; he "...proposed to abandon the mechanical analogy of a cellular ether so that the physical theory of the field could be formulated independently of the supposition of any specific mechanical model".
Harman emphasizes Maxwell's continued use of mechanical concepts : "the formulation of a physical representation of the field would nevertheless be constrained by the programme of mechanical explanation, for his dynamical theory of the electromagnetic field assumed that electromagnetic phenomena were produced byt he motions of particles of matter, that action was transmitted in the field by 'a complicated mechanism capable of a vast variety of motion'. (Harman, 94). Harman also notes that "the dynamical framework appears clearly in Maxwell's emphasis on the field as a repository of energy. Arguing that energy could exist only in connection with material substances, he concluded that the ethereal medium which constituted the electromagnetic field was the respository of the energy of the field. The complicated mechanism of the ether was subject to the laws of dynamics, and the field was represented dynamically as energy transformations in the ether". Harman notes Maxwell's claim that "'in speaking of the Energy of the field, however, I wish to be understood literally' (Harman, 94). WIth respect to electromagnetic energies, Maxwell's commitment to mechanism is quite strong: "Because 'all energy is the same as mechanical energy', the energy in electromagnetic phenomena was to be referred to the kinetic energy of motion of the parts of the ether and the potential energy stored up oin the connections of the mechanical structure of the ether, and the mechanism of the ether was subject to the gernal laws of dynamics. The propagation of electromagnetic waves was conceived as energy transformations in the ether." (Harman, 94-95)
Depending on one's views in philosophy of science, the position he occupied is or is not unstable. An instrumentalist might regard the position as perfectly satisfactory, provided it have predictive power. A certain type of realist may find Maxwell's sitting on the fence about his ontological commitments somewhat disturbing.
Concerning Maxwell's vortex theory of induction,I.J.R. Aitchison (in Ch. 7, "The Vacuum and Unification", in The Philosophy of Vacuum, ed. by Simon Saunders and Harvey R. Brown) writes of "Maxwell and his contemporaries to mechanical ether models", that "lest we smile too easily at the naivety of these great physicists, I show in Fig. 4 a picture, published in 1980, not wholly dissimilar to Fig. 3 ["Maxwell's vortex ether"]. Even the title doesn't sound totally unfamiliar: A COLOR MAGNETIC VORTEX CONDENSATE IN QCD".
Compare the diagram in this paper to that of Maxwell. One is reminded of Rene Descartes's effort to use vortices in his philosophy of nature. The vortex seems to have a recurring presence in the history of physics, as does (as we shall see) the concept of the ether.
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Click here for library catalog search on works by Lorentz.
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The following passage from Harman (119) conveys the complexity and richness of Lorentz's work:
"In subsequent elaborations of his theory, Lorentz further modified the traditional mechanical foundation of physical theory. The empirical discovery of the discrete unit of electricity (the 'electron') seemed to Lorentz to provide empirical confirmation of his theory, and he developed a theory in which properties of electrons were conceived in nonmechanical, electromagnetic terms. Electromagnetism was envisaged as providing the conceptual foundations of physics. Gravitation was explained by the theory of the electromagnetic ether, and the laws of mechanics were viewed as special cases of universal electromagnetic laws. Lorentz defined inertia and mass in electromagnetic terms, and he denied the constancy of mass, a fundamental principle of Newtonian mechanics. Lorentz's theory of mass as an electromagnetic concept was a striking and influential feature of this theory.
Around 1900, Lorentz's theory exerted a profound influence the development of physical theory. Many physicists argued that electrodynamics, rather than mechanics, would provide the unifying conceptual foundations of physics. The concept of the ether, denuded of all mechanical properties, seemed to many physicists to provide the basis for all physical theory. An ontology of electrons and the electromagnetic ether, not based on a framework of mechanical principles, was being developed in place of the mechanical concepts that had dominated physical theorising in the nineteenth century. In reformulating the theory of the electromagnetic field, Lorentz introduced a major departure from the programme of mechanical explanation. Whereas Hertz continued to affirm that the electromagnetic ether should be represented in terms of the motion of hidden masses, Lorentz maintained that the postulates of field theory should be based on an electromagnetic ontology. Whereas Larmor's theory of the electromagnetic field conceived a dynamical theory of an ethereal plenum and postulated electrons as centres of rotational strain in the ether, Lorentz reject the dynamical foundations of the theory of the field and envisaged the foundation of physics on purely electromagnetic concepts".
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Hertz had been a student of Helmoholtz, who influenced Hertz's research agenda. "Hertz's famous experiments on the propagation of electromagnetic waves were coneived in response to a problem that Helmholtz had proposed when Hertz was his student, an experimental test of the relationship between polarisation and electromagnetic effects. Hertz made two fundamental contributions to the development of field theory: the direct verification of the propagation of electromagnetic waves, and a radical critique of the conceptual structure of the field equations in Maxwell's Treatise, which led to Hertz's reformulation of Maxwell's equations of electromagnetism". (Harman, 107).
Here is a sketch of Hertz's experimental work: "In a series of fundamental experiments, Hertz set himself the task of detecting electromagnetic waves and measuring their velocity. He produced electric waves with a wire connected to an induction coil, and detected them with a small loop of wire with a gap in which sparks could be detected when currents were induced. This apparatus enabled him to measure the wavelength of the electric waves, and with the calculated frequency of the oscillator he determined that the velocity of the electric waves was equal to the velocity of light. Hertz also explored explored the analogy between light and electric waves, focusing the rays with mirrors, demonstrating their reflection, refracting them through a prism of hard pitch, and demonstrating polarisation effects using metal gratings. He concluded that these experiments established the 'identify o light, radiant heat, and electromagnetic wave -motion'." (Harman, 108-109)
Harman goes on to say that "the experiments were valid independently of the assumption of any particular theory, he nevertheless made it plan that these experiments favoured Maxwell's theory of the electromagnetic ether". (Harman, 109).
See the text on p. 431 [454 on the navigation bar on the bottom] of the Treatise. What test does Maxwell in effect suggest here to establish that light is an electromagnetic wave?
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A. A. Michelson and E. W. Morley. On the relative motion of the Earth and the luminiferous ether
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This paragraph is based on Janssen and Stachel (see link above): Michelson thought his 1881 disconfirmed the Fresnel theory and confirmed "Stokes' hypothesis of a dragged-along ether" (2). But then Michelson and Morley redid Fizeau's work. "The experiment confirmed Fresnel's prediction. Michelson and Morley now concluded that Fresnel had to be right and Stokes had to be wrong. However, the famous Michelson-Morley experiment of 1887 gave the same negative result as Michelson's first attempt in 1881 with reduced experimental error. They were at a loss. Both Fresnel's and Stokes' hypotheses appeared to be untenable." (2)
Some history relating to Maxwell, with a connection to Michelson (see below), is this item from Janssen and Stachel:
"Shortly after he published the seminal paper in which he first identified light as electromagnetic waves, James Clerk Maxwell (1831–1879) designed and performed an experiment aimed at detecting the effect on refraction of the earth’s presumed motion through the ether (the inverse
motion of the ether with respect to the earth is often called the “ether drift”). He reported the negative result of the experiment in a paper he sent to Stokes in 1864 for publication in the Proceedings of the Royal Society. When Stokes informed him that Arago had long ago performed similar experiments and that Fresnel had been able to account for the negative results of such experiments through the introduction of the dragging coefficient, he withdrew the paper.Shortly before his death, Maxwell returned to the problem of the earth’s motion with respect to the ether. In an entry on “Ether” for the ninth edition of the Encyclopaedia Britannica, he argued that the only way to measure the earth’s velocity with respect to the ether in a laboratory experiment is to look for variations in the velocity of light travelling back and forth between two mirrors. A simple calculation, which we shall give below, shows that the effect due to ether dri t that one expects in such an experiment is of order v2/c2, which Maxwell thought too small to bemeasurable. However, he had thought of an astronomical determination of the solar system’s velocity with respect to the earth, in which the effect to be measured was of order v/c. The method involved precise measurement of the periods between successive eclipses of the moons of Jupiter,
which, as Römer had shown, could be used to determine the velocity of light. Maxwell’s idea was to analyze the data on such eclipses spanning a period of twelve years, the period of Jupiter’s orbit around the sun. On the assumption that the velocity with respect to the ether of the solar system
as a whole remains roughly the same over such periods of time, the velocity of light determined by using Römer’s method should vary from c – v, when the light from Jupiter to earth is moving against the ether drift through the solar system, to c + v six years later, when the light is moving
with the ether drift. Maxwell wrote to the American astronomer D. P. Todd (1855–1939) to inquire whether the existing data on Jupiter and its satellites were accurate enough for this determination of the velocity of the solar system with respect to the ether. Todd had to disappoint him. Maxwell died shortly afterwards and his letter to Todd was published in Nature. In the letter, Maxwell reiterated that the method he proposed involved a first-order effect, whereas terrestrial experiments involved second-order effects, which would not be measurable.
Maxwell’s letter caught the attention of Michelson, a young officer in the U. S. Navy, who had already earned himself a reputation for high precision measurements of the speed of light. He took up the challenge to measure the terrestrial effect that Maxwell thought could not be measured." (15)
With respect to the claim in the passage above that "Shortly before his death, Maxwell returned to the problem of the earth’s motion with respect
to the ether. In an entry on “Ether” for the ninth edition of the Encyclopaedia Britannica", see here for this article, from which:
"No theory of the constitution of the aether has yet been invented which will account for such a system of molecular vortices being maintained for an indefinite time without their energy being gradually dissipated into that irregular agitation of the medium which, in ordinary media, is called heat.
Whatever difficulties we may have in forming a consistent idea of the constitution of the aether, there can be no doubt that the interplanetary and interstellar spaces are not empty, but are occupied by a material substance or body, which is certainly the largest, and probably the most uniform body of which we have any knowledge.
Whether this vast homogeneous expanse of isotropic matter is fitted not only to be a medium of physical interaction between distant bodies, and to fulfil other physical functions of which, perhaps, we have as yet no conception, but also, as the authors of the Unseen Universe seem to suggest, to constitute the material organism of beings exercising functions of life and mind as high or higher than ours are at present, is a question far transcending the limits of physical speculation. (J. C. M.)"
Perhaps Maxwell in this passage is referencing the work here: P. M. Heimann. The Unseen Universe: Physics and the Philosophy of Nature in Victorian Britain. See also: J. Clerk Maxwell. Paradoxical Philosophy, A Sequel to the “Unseen Universe”
The article references a possible "coefficient of rigidity of ether" and a "density of aether".
WORK IN LEHIGH COLLECTION
Volume 17 of Annalen der Physik contains the famous paper by A. Einstein. Zur Elektrodynamik bewegter Korper.
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The Michelson-Morley experiment is often interpreted as disproving the existence of an ether, though see the passage in the item about Stokes.
It was not long before Einstein developed the theory of special relativity, which denied the existence of an absolute reference frame of the kind implicit in the theory of the ether.
This was not the end of the concept of the ether, however. Einstein's general relativity, on one interpretation, suggests that the geometry of space-time provides a kind of reference frame in itself. Einstein affirmed the existence of a the ether in a 1920 lecture: "But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time."
Even today, the concept of the ether sometimes reappears. See the references in A Spontaneous Physics Philosophy on the Concept of Ether Throughout the History of Science: Birth, Death and Revival.
Literature mentioned in:. A Spontaneous Physics Philosophy on the Concept of Ether Throughout the History of Science: Birth, Death and Revival. Contains some bibliographic references to contemporary invocations of the ether concept:
Other material:
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