Chapter 22 Chapter 20 Faraday, Maxwell, and Hertz

The nineteenth century saw many revolutionary advances in physics, although none of these—whether in their scientific or intellectual content—had the worldwide impact of Darwin's revolution. The achievements of physics in the 19th century, including the new energy theory and the law of conservation of energy, the wave theory of light, gaseous kinetic theory and statistical mechanics, the law of electric current, the theory of magnetism and electromagnetism, the principle of motors and generators, the new spectrum (spectroscopic) theory, the discovery of radiation and the absorption of heat, the extension of radiation to infrared and ultraviolet radiation, and many other such advances, etc.But most physicists, as well as a new generation of historians of modern physics, agree that one of the most profound revolutions—if not the only one—is that famous for Maxwell's theory—that people This revolution is sometimes attributed to Maxwell and Michael Faraday, and sometimes it is more justly attributed to Faraday, Maxwell and Heinrich Hertz.The importance of Maxwell's revolution lies in that it not only made fundamental revisions to the theories of electricity, electromagnetism and light, but also made the first large-scale revision of Newton's natural science ideology.

While certain features of this revolution can be understood by all readers, the core, or essence, of Maxwell's thought is elusive even to many historians trained in physics.A major problem here is to see the connection between Michael Faraday's ideas and the theory developed by Maxwell.There is no doubt that Faraday's contributions are extremely important, including his important concept that the magnetic field is composed of lines of force and the extraordinary insight that the conduction of electromagnetic induction is not instantaneous but takes time.However, Faraday's fundamentally non-quantitative and non-mathematical formulation did not yield a value for what he called the transit time.In his essay "On Faraday's Lines of Force," Maxwell extolled Faraday's implicit thought, and went on to say, "Although the basic forms of space, time, and electric (magnetic) forces are perfectly clear, yet, perhaps, In the interest of science, Faraday did not become a professional mathematician".Faraday expressed his ideas "in a natural, non-technical language" and, - says Maxwell - "I have written this paper with the main expectation of making these ideas the basis of a mathematical method".All those who have studied the history of the discipline warn us that Maxwell's "contribution would be grossly undervalued if it were regarded as merely that of interpretation" (Tricker, 1966, 102).As M.As Planck once eloquently pointed out, "Maxwell had a rich imagination and mathematical insights. He was far beyond Faraday, whose views he had generalized, generalized, and made more accurate."Maxwell "has thus created a theory which not only rivals the accepted correct theories of electricity and magnetism, but ultimately surpasses them altogether" (1931, 57).

Historians, as well as historically minded scientists, agree that Faraday's papers might never have sparked a revolution if Maxwell had not profoundly reworked Faraday's ideas in the process of creating a mathematical theory—and so we Maxwell's mathematical theory can be called Faraday.Maxwell's theory.Maxwell not only transformed Faraday's ideas into ideas with mathematical form, but also developed a way of expressing quantities that related the fundamental principles of electrostatics and electromagnetism to the speed of light—an achievement that made the theory of electromagnetism even more plausible. unambiguous, and opens up the possibility of experimental detection through the actual generation of electromagnetic waves.Acknowledging Faraday's role in the formation and development of Maxwell's thought emphasizes the creative transformation process that produced Maxwell's theory, but in no way diminishes or trivializes Maxwell's important contribution to the Maxwell revolution.This is even truer in the case of William Thomson's contribution to this revolution (see below), since, "Thomson's extraordinary talent produced persuasive unsystematic insights rather than complete Theory" (Everett 1974, 205).By using Thomson's method of visualizing electrical phenomena and Thomson's results of "applying the principles of energy to electricity," Maxwell was able to appreciate their importance.

Maxwell developed his ideas in a series of papers published in 1855-1856, 1861-1862, 1863, 1864, and 1865, and they were largely finalized in his 1873 essay "On Electricity and Magnetism".But this revolutionary new theory remained a revolution in theory for years to come, and it became a revolution in science only when the work of Heinrich Hertz confirmed electromagnetic waves.For this reason, the revolution is sometimes called the Faraday-Maxwell-Hertz revolution; even those who discuss Maxwell's revolutionary work point out that it was not Maxwell's revolution alone.For example, Albert Einstein discussed "the great revolution that will forever be associated with the names of Faraday, Maxwell, and Hertz" (1953, 161; 1954, 268).But, he added immediately, "Maxwell made the greatest and most important contribution to this revolution."On another occasion he inadvertently ignores Hertz and refers only to "the revolution in electrodynamics and optics wrought by Faraday and Maxwell"; A great and important advance" (1953, 154-155; 1954, 257).In his autobiography, however, Einstein spoke only of "Maxwell's theory" and said that it appeared "revolutionary" when he was a student (Shilp, 1949).

Maxwell's Transformation of Faraday's Thought This transformation process can be seen in Maxwell's famous paper "On Lines of Force in Physics".In discussing Faraday's idea that there must be some kind of stress in a space where lines of magnetic force exist, Maxwell actually begins by asking what kind of stress distribution is required for a space to exhibit the actual distribution of stress required by Faraday's hypothesis? What about a conductor? C． W． F．Everett traces Maxwell's use of Scottish engineer W. J． M．Rankin's ideas and William Thomson's (Lord Kelvin's) conclusions to create his own theory of lines of force in physics.Here we can see elements of the process of an authoritative transformation of scientific thought that produced a radically new idea that electricity could be "traveled through space" and not necessarily merely "a fluid confined to conduits." In the conclusion of his paper Maxwell spoke of what was called a "surprising discovery"—that the vibrations of this newly proposed conductor would not only demonstrate magnetic field lines, but would also have the same properties as light".Maxwell expresses the distinctive features of his results in italics.He writes (1890, 1:500) that we are "almost impossible to evade the inference that light is a transverse wave in a medium which is also the cause of electromagnetic phenomena.

But even here the germs of Maxwell's thought can be found in Faraday's noteworthy paper—"Some Thoughts on the Vibration of Light" in the Philosophical Journal, May 1846. Papers - found in.In this treatise, Faraday proposed that the bold notion that "radiation is an advanced form of vibration in lines of force" is "a speculative shadow".Perhaps what interests us most in this paper is—as Sylvinas, P.Thompson in 1900 (p. 193)—it has received little attention, not even from earlier biographers of Faraday.Because these men wrote their biographies before the general acceptance of Maxwell's electromagnetic theory of light, they had not yet realized in them the importance that was later ascribed to it.John Tyndall (1868) dismissed Faraday's musings as merely "one of the most remarkable musings ever undertaken by a scientist".Henry Bens Jones only mentioned it in passing in half a line in 1870.John Hall Gladstone didn't even mention it in 1872.However, Maxwell later said, "The view that the propagation of transverse magnetic disturbances repels the normal magnetic field was apparently proposed by Professor Faraday in his reflections on light-vibration (1890, 1:535)".In Maxwell's view, "the electromagnetic theory of light which he [Faraday] presented was essentially the same theory which I had begun to develop in this paper, except that in 1846 there were no data to measure the speed of propagation".I agree with CWF Everett that take Maxwell's comments on Faraday's "Some Thoughts on the Vibration of Light" with a grain of salt, since, "any immediate influence" of that paper was on the development of Maxwell's thought can be clearly seen. "These comments were made some years after the fact, and are an example of Maxwell Don Quixote's generosity. His comments in letters with Faraday and Thomson at the time did not suggest any such influence".

In a review of Maxwell's contributions to physics (1896, 204205), R. T．Glazebrook draws attention to five fundamental features of Maxwell's theories and "acknowledges that, in Maxwell's day, there is little direct evidence for them".One of the boldest assumptions made by Maxwell was that the same medium that sustains light waves must be able to be the medium in the electromagnetic field.He asserted that electromagnetic waves must exist in space.Moreover, Maxwell, a pioneer in spatial analysis, pointed out that the factor that unites the two systems of units of electricity, electrostatic and electromagnetic, is a velocity, which in fact has a value very close to the speed of light, which This means that light itself is an electromagnetic phenomenon, a series of electromagnetic waves.Maxwell wanted to say in 1864 that the numerical results seemed to "reveal that light and magnetism are operations of the same substance, and that, moreover, light is an electromagnetic disturbance propagating through fields according to the laws of electromagnetism."

Max Planck (1931, 57) saw in this insight the most practicable illustration and illustration of "criteria for evaluating a theory". "It really explains phenomena other than those on which it is based".It did not occur to Planck that neither Faraday nor Maxwell "was initially considered the study of optics in connection with their investigations of the fundamental laws of electromagnetism", but that "the entire field of optics which for more than a hundred years has provoked attacks from mechanics But it was proved and convinced by Maxwell's "Dynamic Theory of Electromagnetic Field", so, "Since then, every optical phenomenon can be directly regarded as a problem of electromagnetism".For Planck, "at any time this will be one of the greatest triumphs of human intellectual endeavor".

Contributions of Heinrich Hertz So here's a test -- not just to see if electromagnetic waves can be produced, but to see if they have the speed of light.In this way we can appreciate the importance of the series of experiments carried out by Heinrich Hertz in the years leading up to 1888; these experiments by him finally confirmed the predictions of Maxwell's theory.Hertz not only produced electromagnetic waves, but also discovered (by measuring the wavelength of standing waves of known frequency) the speed of electromagnetic waves; he showed by experiments that these electromagnetic waves are similar to light in characteristics such as reflection, refraction, and polarization, and that they can be focused.Hertz himself saw this theory as "a theory that Maxwell developed on the basis of Faraday's views and which we call the Faraday-Maxwell theory" (1893, 19).

Hertz's contribution was not merely to plan and carry out an astute experiment, although the achievement of this experiment was enormous.He also showed how important his experiment was as "the first demonstration of the finite spread of a putative long-distance activity." (Mccormack, 1972, 345).Therefore, the role of his experiment is to make physicists realize the point of view of electromagnetism from "long-distance instantaneous activity" to "Maxwell's theory that the electromagnetic process occurs in the dielectric body, and an electromagnetic ether contains A fundamental shift in the older view of the function of the luminous ether" (ibid.).But to complete this revolution, Hertz also had to articulate clearly "what theory physicists are advocating for when they call themselves followers of Maxwell". (See McCormack's excellent overview on p. 346 on this point, especially his discussion of Hertz's account of Maxwell's "vector potential".) Finally, he removes some of the "unnecessary" aspects of the theory. "necessarily complicating formalism" is characteristic of physics (1893, 21), and (in the introduction to his "Electrical Waves") asserted that "Maxwell's theory" was nothing but "Maxwell's system of equations".Since the acceptance of Maxwell's theory, especially in continental Europe, has been along the lines proposed by Hertz, we can understand why Einstein and others used Hertz's Daimyo are also included.

Maxwell's theory is difficult to accept and understand for many reasons.First, it was conceptually innovative, with some radical concepts such as "displacement currents."Second, Maxka not only regards this theory as a mathematical refinement or elaboration of new principles, but also puts it forward in terms of physical patterns.First, these new principles are embodied in mechanical devices such as cogs and pulleys; his sincere admirer Glazebrook could not help introducing a "somewhat vulgar idea" to these devices (1896, 166), Although he does stress that these installations are only "a model" to their creators.Maxwell never completely abandoned the spinning tube and the vortex of the ether.In his "Electricity and Magnetism" (2: &831; 1881, 2:428), he wrote that "the magnetic force is the action of the centrifugal force of the vortex" and that the "electromotive force" is "acted upon stress" results.The French mathematician Henri Poincaré had a strong stance on Maxwell's theories (see below).He couldn't help introducing a book, Lectures on Maxwell's Theory and the Electromagnetic Theory of Light (1890, V), in order to show that when "a French reader first opened Maxwell's book", a sense of unease and even How feelings of wonder often intertwine with his praise.In another work (1899; English translation 1904, 2), Poincaré admitted that the "complex structure" Maxwell ascribed to the ether "made his system eccentric and dull".In fact, according to Poincaré, one "seems to be reading descriptions of workshops with transmissions, tie rods with transmitted motion and bending under exerted forces, with wheels, belts and governors".Moreover, Poincaré argues, it reflects "the British preference for such concepts; these concepts arose precisely to suit the British mind".But, he also notes, Maxwell himself "was the first to abandon his own bizarre theory" and, moreover, "it does not appear in his complete writings."The "complete work" mentioned here may refer to Maxwell's series of papers.Poincaré immediately adds that we must not be upset that "Maxwell's wisdom has pursued this by-pass, because it has thus led to the most important discoveries", and Poincaré insists (p. 12) that "the eternal The "element" consists in the fact that "it is independent of any particular interpretation". Experiments carried out by Hertz at the suggestion of the great German physicist Helmholtz confirmed Maxwell's prediction.On the Continent, and especially in Germany, (Gauss, Weber et al.) tended - as Planck explained (Planck, 1931, 58-59) - "according to potential theory - this is the Gaussian Deduced for the electrostatic magnetic field from Newton's law of action at a distance, and from which a very high mathematical achievement has been made" - specifically seeking "achievements of electrodynamics".Faraday-Maxwell's insight that there is no such "direct action at a distance" and that force fields have "an independent physical reality" was so incredible and so incomprehensible that, in Planck's view, this new The theory "couldn't find any foothold in Germany, and the month ... hardly even attracted attention".Helmholtz developed a theory of his own in which he tried to preserve the formula of instantaneous action and still contain Maxwell's equations.He encouraged Hertz to conduct experiments, not only to find out whether electromagnetic waves exist or can be produced (since both are needed for his theory and Maxwell's), but also to choose between two different views , because both views lead to very difficult predictions about the physical properties of electromagnetic waves. (For a concise account of the theoretical differences between Helmholtz and Maxwell, see Turner 1972, 251-252.) In a popular—that is, non-mathematical—work on "Maxwell's Theory and Hertz's Oscillations" (1899; English translation, 19O4, chap. 7), Poincaré explained Hertz's experiments How posed an "experimental conundrum" between Maxwell's theory and its opponents.While both theories agree on many proven predictions (for example, electrical disturbances travel along a wire at the same speed as light, and electromagnetic disturbances travel through space), they disagree on the timing of the propagation of these effects through space.If there were no Maxwell's "displacement current", then propagation should be instantaneous.But, according to Maxwell's theory, the speed of propagation in air or a vacuum should be the same as the speed of propagation along a wire—that is, it should be the same as the speed of light.therefore.Poincaré raised such a problem: "Therefore, here is an experimental problem: we must determine at what speed electromagnetic disturbances propagate through the air by induction. If this speed is infinite, then we must follow the old theory; if It is equal to the speed of light, and then we have to accept Maxwell's theory." Hertz's original experiments did not provide an easy answer.The results of the experiment "seem to undeniably refute the old electrodynamic theory", however, "seem to condemn Maxwell's theory".Writing in 1899, Poincaré said that "this failure still cannot be explained satisfactorily".He speculated that Hertz used a mirror "too small for the wavelength" so that "the refraction disturbed the observed phenomena".In any case, later experiments (first by Saracen and Delarife) proved irrefutably that Maxwell's theory was correct.This marked the end of theories based on long-distance transient actions, and indicated the beginning of general acceptance of the theory of the Maxwellian field, with a finite speed of propagation equal to the speed of light.Thus, the revolution in Faraday-Maxwell theory turned into a revolution in Faraday-Maxwell-Hertz science. Proof of the Revolution In 1888, Hertz notified Helmholtz of the final results of his experiments on radio waves.In a lecture given that year, Helmholtz (1907, 3) spoke of a "complete revolution" in theoretical physics ("Theoretical Physics of the Ether") caused by "the ideas of Faraday-Maxwell". Revolution" (eine vollstandige Umwalzung).Helmholtz (p.4) then discusses, in Kuhn-like language, the "crisis" that electrical theory is likely to experience first ("eine Krisis, die erst durchgemacht werden muss").But the difference between Helmholtz's "crisis" and "revolution" and Kuhn's "crisis" and "revolution" is that Helmholtz seems to have seen that emerging from the "revolution" "Crisis", and the conditions are different from before. A more cautious formulation of "revolution" can be found in the 1894 textbook "Introduction to Maxwell's Theory of Electricity" by August Faupple.It was from this textbook that Einstein learned Maxwell's theories when he was a student in Zurich. (Holton's 1973 book (205-212) discusses the important role of Fupper in the development of Einstein's thought.) In the preface to the textbook, Fupper emphasizes how Hertz not only proved the nature of electromagnetic waves existence (and velocity), and theoretically established a "turning point" that powerfully moved physicists away from the old theory (of Weber and others) based on distant actions.Hertz's discovery produced a "turn in public opinion" ("Umschwungder Meinungen"), leading to a "reversal of public opinion" [i.e. inversion; and possibly a revolutionary change] (iii, iv). Soon, the French philosopher and scientist Pierre Duhem made a similar point.Duhem's discussion is more interesting, because he is not only a famous scientist and outstanding philosopher, but also a well-known historian of science.He claimed that his work was a "historical and critical study" of Maxwell's theory of electricity.When describing the influence of Maxwell's works, Duhem (1902, 5) used two terms in succession: bouleverser (to turmoil, shock) and revolution (revolution) - this is exactly what we later wrote in Engels' "Anti-Dühring". The same two words are translated from the German Umwalzung (revolution) in the French edition.Duhem stated bluntly that "this revolution was the result of the efforts of a Scottish physicist, James Clerk Maxwell" (1902, 5).In a digression on history, Duhem notes, "Maxwell overturned the natural order from which theoretical physics developed; but he did not live long enough to see Hertz's discovery transform his bold assumptions." Be a prophet of prophecy" (p.8).In a discussion of Maxwell's first paper, Duhem compared electrical phenomena with the motion of a fluid in a resistive medium.At the same time, he found that Maxwell's language seemed to indicate that "revolutionizing the discipline of physics" was not "his intention" at all (p. 55).Duhem also highly praised the writings of Ludwig Boltzmann published in 1891 and 1893.In these works (papers), Boltzmann attempted "to construct a system in which Maxwell's equations could be logically linked together, using completely new concepts", and Duhem believed that this system was excluded from Maxwell himself. The approach to a major problem in the process of coming up with his different equations.Duhem found that in Maxwell's series of equations, full of "contradictions and fallacies" (pp. 223-224). A year after Duhem discussed Maxwell and the Revolution, Johann Theodor Merz published volume 2 (1903) of his History of European Thought in the Nineteenth Century.In this volume, he regards Maxwell's papers on the theory of electromagnetism as a "revolutionary series" and states that "Maxwell's ideas had an important impact on the development of scientific - not only that, but even public - thought." Considerable influence" (pp. 77-78, 88). I have already mentioned that Einstein continued to talk about Maxwell in revolutionary terms.In a talk in 1920 (Moskovsky 1921, 60), Einstein summarized Maxwell's revolution as follows: Classical mechanics ascribes all electrical and mechanical phenomena to the direct interaction of particles with each other, regardless of their distance from each other.Newton's expression of this simplest law is this: "Gravity is equal to the product of mass divided by the square of the distance" (gravitation is directly proportional to the product of the masses of two matter particles, and inversely proportional to the square of the distance between them).In contrast, Faraday and Maxwell introduced an entirely new kind of physical reality, the force field.The introduction of these new realities has helped us so much that the notion of action at a distance, which is contrary to our everyday experience, is first of all unnecessary, since fields attach themselves from point to point to Throughout the space, there are no breaks or gaps.Second, the laws of fields, especially as far as electricity is concerned, assume a much simpler form than if no fields were assumed to exist, and only mass and motion are considered real. In his "Autobiographical Notes" (Hill 1949, 32-33), Einstein elaborates on this theme: Some half a century after Hertz's experimental confirmation of electromagnetic wave predictions, Einstein's perceptive assessment of a Maxwellian revolution was re-articulated in Karl Popper's lucid and striking overview of the scientific revolution (1975, 89).He said that "the revolution of Faraday and Maxwell, from a scientific point of view, is as great as the revolution of Copernicus" because "it overthrew Newton's main dogma - the dogma of centripetal force". Many commentators have pointed out that Maxwell's theories enjoyed more general support in Great Britain than in continental Europe.However, there are still differences of opinion.Lord Kelvin is one of them.In his "Baltimore Lectures" given at Johns Hopkins University in 1884, he stated bluntly: "If I know what the electromagnetic theory of light is, then I may be able to relate the basic principles of the wave theory of light to to think about it".Furthermore, "I might say that, in my opinion, the only thing about it that seems comprehensible is exactly what I think is unacceptable".In his analysis of the situation in England between 1875 and 1908, Sir Arthur Schuster said that in England no experiments were carried out to confirm Maxwell's predictions because "we may be too confident in the inherent truth and simplicity of Maxwell's views".Since we "consider that an extensive experimental study is not worthwhile in view of the circumstantial evidence supporting the electromagnetic theory", why should such an experimental study be carried out which "will certainly occupy and consume a great deal of time and labor"?Actually, there doesn't seem to be much point in conducting such an experiment, since it seems obvious that the "result" of the experiment will be "a conclusion".But, says Schuster, the young people at the Cavendish Laboratory were "wrong" because they "forgot that abroad, and to some extent in this country, the vast majority of scientific thought was not of interest Even reluctant to abandon a flexible, solid, and very useful ether for a medium whose properties do not resemble those of any known body". Maxwell's revolutions were somewhat different from those we have been discussing; those revolutions could be related more easily to the scientific thought of a single individual like Lavoisier or Darwin.This revolution, which has been going on for more than half a century, requires three significant contributions, namely, the contributions of Faraday, Keswell and Hertz.There are different views on the important role of these three great physicists.The title Maxwell's Revolution probably stems from the fact that the theory of electromagnetism is epitomized in Maxwell's equations, which may be why Einstein believed that Maxwell "played the biggest role" in this revolution.But Einstein respected Faraday just as much, and described both vividly in his studies.The revolution looked like the one that was attributed to Copernicus.In the Copernican revolution, Kepler transformed Copernican concepts, and Newton then developed them.However, there is still a fundamental difference between the two, because Kepler basically abandoned Copernican's principle, while Maxwell put Faraday in a very important position in his theory, giving Faraday's concept a new life. The precision and importance of the science, and developed Faraday's ideas in the sense that Newton built on Kepler's ideas. Maxwell's contribution to a new kind of physics was not limited to his theory of electromagnetism.They also cover many other topics, among them molecular physics, thermodynamics, and kinetic theory of gases.He made scientists aware of the importance of dimensional analysis and spread the concept of modes in physical theory, which has become an important feature of physics in our time.We have seen that Maxwell's electromagnetic theory has successfully passed the test of three revolutions: the testimony of eyewitnesses, the judgment of historians, and the opinions of scientists.The fourth test—the record of physical thought—shows that Maxwell's revolution (or Faraday, Maxwell Hertz's revolution) was from the classical physics of the eighteenth and nineteenth centuries to the new relativistic physics and An important factor in the transformation process of quantum theory.Like the Newtonian Revolution and other revolutions in science that adopted and extended new ways of understanding phenomena in the external world, it was also a great revolution in human thought.