Heinrich Hertz

“ Herschel, Sir John Frederick William, son of the preceding (1792–1871) ; “Preliminary discourse on the study of natural philosophy,” 1831; “Revised instructions ...” for Royal Society, 1842, 76, 99, 101, 102, 140, 141, 158, 212, 262, 297, 300, 322, 369, 395, 455, 458, 466, 471, 476, 481 Hertz—Herz—Heinrich Rudolf, Professor of Physics in Bonn University (1857–1894) , 184, 331 Hervart, Joannes Fridericus, “Admiranda Ethnicæ ...,” 15, 106 Hervart, Johann George (1554–1622) , 106 Hevelius—Hevel—Hewelcke Joannes (1611–1687) , 130 (Phil. Trans. 1670, p. 2059) . ”

“ The scientific eminence accorded to a few energetic persons by popular estimate is more or less amusing to those working on the same lines. In the case of Hertz no such mistake has been made. His name is not over well-known, and his work is immensely greater in every way than that of several who have made more noise. ”

“ This experiment was the first to show the propagation of electric current in the form of waves, and Hertz calculated the time of such a wave running back and forth in the wire as the one-hundred-millionth of a second. The possibility of making such rapid oscillations opened up a whole new field of research, which has been greatly exploited in the last twenty-five years. Not only did Hertz show that the current in a wire was propagated in waves, but he also showed that the electromagnetic effects which are able to induce currents in other wires are also propagated across free space in waves. ”

“ The conditions when the discharges of large condensers are passed between spark balls are entirely different from those when the quantity of the spark, or to put it in more exact language, the current passing, is very small. In the case of Hertzian experiments it is necessary, as shown by Hertz, to maintain a high state of polish on the spark balls when they are employed for the production of short waves of small energy, but when we are dealing with large quantities of energy at each discharge, those methods which succeed for laboratory experiments are perfectly impracticable. ”

“ Physicists have busied themselves in measuring the various constants, in refining and perfecting the methods of measurement, or in applying principles already known to technical and practical purposes. Hertz, however, has opened a new and unexplored field, which must eventually bring us into a closer acquaintance with the mysteries which we are daily manipulating. ”

“ And so it was the reading of the discovery of Hertz that started the boy on the train of thought and the series of experiments that ended with practical, everyday telegraphy without the use of wires. To begin with, it is necessary to give some idea of the medium that carries the wireless messages.
It is known that all matter, even the most compact and solid of substances, is permeated by what is called ether, and that the vibrations that make light, heat, and colour are carried by this mysterious substance as water carries the wave motions on its surface. ”

“ These are, however, the fundamental equations of Maxwell's theory in the form given in his memoir of 1868. [47]
That Hertz's deduction is ingenious and interesting will readily be admitted. That it is conclusive may scarcely be claimed: for the argument of Helmholtz regarding the induction of currents is not altogether satisfactory; and Hertz, in following his master, is on no surer ground. ”

“ Certainly, therefore, Hertz is right when he says: 'The rigour of science requires that we distinguish well the undraped figure of Nature itself from the gay-coloured vesture with which we clothe it at our pleasure.' But I think the predilection for nudity would be carried too far if we were to forego every hypothesis. Only we must not demand too much from hypotheses." Boltzmann, Ibid., 413. ↑ The principal opponent of the Maxwell-Boltzmann partition of energies was Lord Kelvin in his "Nineteenth Century Clouds over the Dynamical Theory of Heat and Light." ”

“ We have no space to refer to the whole of the steps of discovery which led up to the invention of all the various forms of the modern electric kumascope or wave detector. Suffice it to say that the researches of Hertz in 1887 threw a flood of light upon many previously obscure phenomena, and enabled us to see that an electric spark, [Pg 50] and especially an oscillatory spark, creates a disturbance in the ether, which has a resemblance in Nature to the expanding ripples produced by a stone hurled into water. ”

“ The means used by Hertz and his immediate followers to detect the waves was simply the little spark which they excited in conductors upon which they fell; electric currents being set up in such conductors by the act of reflection. The effect was often at that time attributed to electric resonance or syntony, but there was very little true resonance in these experiments; the first swing was usually much more powerful than any of the succeeding ones, and was competent to cause the little spark ”

“ This extension of Maxwell’s theory, known as the electrodynamics of moving bodies, was attempted by Hertz, who assumed that matter in motion through the ether would drag the ether along with it in its interior—a hypothesis not so radical, but somewhat in line with that of Stokes. So long as conductors were contemplated, Hertz’s hypothesis seemed to be in accord with experiment; but when we came to consider dielectrics in motion, Hertz’s anticipations were contradicted. ”

“ It may be taken, then, as established that Maxwell’s theory is sufficient, and that the greater generality of Von Helmholtz is unnecessary.
In a later paper Hertz showed that electric waves could be reflected and refracted, polarised and analysed, just like light waves. In his introduction to his “Collected Papers” he writes (p. 19) :—
“Casting now a glance backwards, we see that by the experiments above sketched the propagation in time of a215 supposed action at a distance is for the first time proved. ”

“ While Hertz's mechanics is obviously aimed at presenting the electromagnetic equations as consequences, the relation is directly reversed here. With respect to logical form, the electromagnetically founded mechanics of course cannot compare itself to Hertz's one, just because the system of Maxwell's differential equations has found no precise-critical treatment at all, but it has, as it seems to me, a very remarkable advantage, namely (as it was shown) that it transcends ordinary mechanics, which therefore is only to be described as a first approximation. ”

“ The electrodynamics of Hertz is, in fact, wholly built upon the principle of relativity. It recognizes no absolute motion with regard to empty space. It speaks only of motions of material bodies relative to one another. In accordance with the theory of Hertz, all electrodynamic processes occur in material bodies; if these move, then the electrodynamic processes occurring therein move with them. To speak of an independent state of motion of a medium outside of material bodies, such as the ether, has just as little sense in the theory of Hertz as in the modern theory of relativity. ”

“ Imagining that this would interest Hertz and be successfully attacked by him, Helmholtz specially drew his attention to it, and promised him the assistance of the Institute if he decided to work on the subject; but Hertz did not take it up seriously at that time, because he could not think of any procedure likely to prove effective. It was of course well known, as a necessity of Maxwell’s mathematical theory, that the polarization and depolarization of an insulator must give rise to the same electromagnetic effects in the neighbourhood as a voltaic current in a conductor. ”

“ Furthermore, ever since Hertz’s first discovery, whenever waves had to travel through a metal grid or alongside a plane conductor, it was natural to arrange the electric oscillations so as to be normal to the conducting lines or plane, for if they were tangential they excited electric currents therein, and their energy became wasted in the production of heat. So, in so far as earth and water are conductors, it is desirable to use radiation polarised in a horizontal plane, i.e., with the electric oscillations vertical, if considerable distances are to be traversed by it. ”

“ Fire, water, earth, and air have long been his slaves, but it is only within the last few years that man has won the battle lost by the giants of old, has snatched the thunderbolt from Jove himself, and enslaved the all-pervading ether.”
Of the experiments of Hertz, in inducing vibrations “in ether waves,” Professor Fitzgerald says: “If we consider the possible radiating power of an atom, we find that it may be millions of millions of times as great as Professor Wiedermann has found to be the radiating power of a sodium atom in a Bunsen burner ”

“ She bore on her breast, in the curiously embroidered letter, a specimen of her skill, and her needlework was seen on the ruff of the governor; military men wore it on their scarfs, and the minister on his bands.
As time went on, the public attitude to Hester changed. Human nature, to its credit, loves more readily than it hates. Hester never battled with the public, but submitted uncomplainingly to its worst usage, and so a species of general regard had ultimately grown up in reference to her. ”

“ Consequently, in his equations the state of motion of the ether, as denoting the state of the ether, occurs as well as the electromagnetic field. As is well known, Hertz's extensions cannot be brought into harmony with the results of observation, for example, that [Pg 4] of Fizeau's experiment (Note 2) , so that they excite merely an historic interest as a land-mark on the road to an electrodynamics of moving matter. Lorentz was the first to derive from Maxwell's theory fundamental electrodynamic equations for moving matter which were in essential agreement with observation. ”

“ Theory of H. Hertz.
Hertz's electrodynamics of moving bodies sets the vectors and proportional to and
Accordingly,
where and are considered as constants for a certain material point of a moving body.
Thus it follows from (18)
Hertz's theory doesn't know the concept of electromagnetic momentum. It derives the ponderomotive force from the stresses alone, where it is irrelevant according to (10) , whether one relates the stresses to stationary or to co-moving surfaces. A torque of the relative stresses doesn't arise, and also both sides of (18a) are equal to zero. ”

“ The most obvious interpretation of these experiments was the one given by Hertz—that there was interference between the direct waves given out by the vibrator and those reflected either from the plate or from the ends of the wire, this interference giving rise to stationary waves. The places where the electric force was a maximum were the places where the sparks were brightest, and the places where the electric force was zero were the places where the sparks vanished. ”

“ H. Hertz proving the existence of electric waves in free space, that Edison realized the fact that the fundamental principle of aerial telegraphy had been within his grasp in the winter of 1875; for although the work of Hertz was more profound and mathematical than that of Edison, the principle involved and the phenomena observed were practically identical—in fact, it may be remarked that some of the methods and experimental apparatus were quite similar, especially the "dark box" with micrometer adjustment, used by both in observing the spark. ”

“ The tradition of the goddess Hertha lingered until recently, and perchance lingers still, in the island of Rügen. She had her dwelling, it is believed, in the Herthaburg; and often yet, in the clear moonlight, out of the forest which enfolds that hill, a fair lady comes surrounded by her maids to bathe in the lake at its foot. ”

“ Hertz made an apparatus by which he could produce electric waves of different lengths and this he called an oscillator. It consisted of a couple of wires fixed to the balls of the spark-gap of an induction coil, on the other and free end of which were soldered a couple of sheets of copper. ”

“ It may therefore be compared with a pendulum of any kind which when displaced oscillates with a time period depending on its inertia and on its restoring force.
The study of these electrical oscillations received a great impetus after H.R. Hertz showed that when taking place in electric circuits of a certain kind they create electromagnetic waves (see Electric Waves) in the dielectric surrounding the oscillator, and an additional interest was given to them by their application to telegraphy. ”

“ When electricians, twenty years ago, committed energy to a wire and thus enabled it to go round a corner, they felt that they had done well. The Hertz waves sent abroad by Marconi ask no wire, as they find their way, not round a corner, but through a corner. On May 1, 1899, a party of French officers on board the Ibis at Sangatte, [Pg 122] near Calais, spoke to Wimereux by means of a Marconi apparatus, with Cape Grisnez, a lofty promontory, intervening. In ascertaining how much the earth and the sea may obstruct the waves of Hertz there is a broad and fruitful field for investigation. ”

“ This shows how enormously important was the achievement. Next to steam-power nothing has exerted such a revolutionary influence in all branches as electromagnetism. Without it, the world of to-day would present a totally different aspect. Without it, we should have no dynamos, no electric trams, no telegraphy, no electric-power stations, all of which are due to the work of Arago, Gay-Lussac, Ampère, Faraday, Gramme, and Siemens. Without it, there would be none of the abundance of brilliant discoveries that are associated with the names of Maxwell, Hertz, and Einstein. ”