Marconi’s Spark Telegraphy 1897 – From Larry Dighera

 ABOUT THIS  TRANSLATION PROJECT:
For this project, I used the 1908 first edition: https://books.google.com/books?id=z8xLAAAAYAAJ&pg=PP7#v=onepage&q&f=false
and the 1911 edition: https://dbc.wroc.pl/dlibra/doccontent?id=15666&format_id=2  as source texts.

The AI I employed—Gemini 2.5 Pro via Google AI Studio—produced what appears to be a professional-quality English translation. However, as I am not fluent in German, I cannot fully assess its accuracy. That said, Gemini also demonstrates a strong ability to generate well-placed and relevant footnotes (which are included at the end of the document). With the first chapter now completed, and the workflow established, I anticipate much faster progress going forward. (Gemini 2.5 Pro: Google AI Studio) Google AI Studio. The fastest path from prompt to production with Gemini

It’s truly a delight to have lived this far into the twenty-first century, to witness the freight train of scientific development barrelling forward evermore rapidly, pushing back the veil that has obscured the celestial truths from humankind all these centuries.  The relentless pace of discovery—in cosmology, genetics, physics, and beyond—continues to amaze me. I remember, as a child, reading the Dick Tracy comic strip and doubting that inventions like wrist communicators or personal air-pods would ever become reality. The future seems more exciting than ever. We are indeed fortunate to experience such a unique period in history.

If the totality of human resources presently expended on war and its instruments were redirected from destruction toward monumental creation, the resulting progress would be vast, rapid, and enduring. Hey, everybody’s got to have a dream. 🙂

I can’t wait to get HRM installed: 100X SMARTER Than ChatGPT: This FREE AI Just SHOCKED The AI World

Deny evil the opportunity to plant hatred in your heart. I remain confident that truth, goodness, and justice will ultimately prevail. The pendulum has reached its apogee.

Best regards,
Larry
WB6BBB

Final Compiled Manuscript

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title: “Marconi’s Spark Telegraphy”

author: “Prof. Dr. Adolf Slaby”

date: “1897”

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# Marconi’s Spark Telegraphy

### (1897.)

…as Leverrier in Paris had calculated a short time before from the perturbations of Uranus, this fact was celebrated as a victory of science. The science of electricity has shown similar, no less brilliant successes in the last 50 years.

From purely scientific considerations, William Thomson[^1] derived the laws according to which the discharge of a Leyden jar,[^2] as well as of any two bodies charged with electricity, proceeds. Until then, such a discharge had been seen as a simple transfer of electricity from one body to another, and the phenomenon, accompanied by a loud, brilliant spark, was hardly considered more remarkable than all other electrical processes. Starting from the conventional ideas of the time, Thomson now proved by calculation that, under certain conditions, this discharge must be an **oscillating** one, such that the first transfer of electricity is followed by countless others in alternating direction and with diminishing strength.

The entire phenomenon takes place with such a tremendous velocity that the back-and-forth surge of the electrical forces remains hidden from the eye; rather, the eye is only able to perceive the impression of a single spark as the overall result. A short time thereafter, Feddersen,[^3] through his famous experiment with rotating mirrors, was able to provide the definitive proof that Thomson’s mathematical conclusions corresponded to reality.

Of no lesser importance were the considerations that another physicist, Maxwell,[^4] put forward soon after. Returning to Faraday’s unique interpretation of electrical and magnetic phenomena, he showed that this interpretation, when mathematically developed and deepened, leads to a surprising explanation of the nature and propagation of electrical phenomena. He arrived at the concept that forces emanate from an electric spark, which spread into space in all directions with the characteristics of wave motions and with the speed of light. As the carrier of this wave motion, he presumed the same substance that had already been invoked to explain the propagation of light—the aether—and his theory culminated in the assertion that light itself is an electromagnetic phenomenon, and that light and electric rays obey the same fundamental laws. It is well known how our great countryman Heinrich Hertz,[^5] at the end of the 1880s, demonstrated the correctness of these conclusions—which until then had only been mathematically substantiated—through decisive experiments.

While William Thomson, now Lord Kelvin, still dwells among the living as the celebrated head of the scholarly world and sees before him the astonishing development of the seeds he sowed, fate has unfortunately set an all-too-early end to the lives of Maxwell and Hertz.

It is not the task of this lecture to elaborate on the purely scientific significance of these facts; rather, it is the first technical application of this new knowledge that I wish to demonstrate to you, partly through report and partly through experiment.

With the entry of technology into this field, which is entirely new to it, a phenomenon repeats itself that we have often observed before. Without the rigorous scientific foundation, it would not have been able to make the valuable practical application that shall occupy us today. On the other hand, with its greater resources, it has immediately brought forth such entirely new phenomena that a wide field of work is opened to science. As a technologist, I do not intend to attempt a premature explanation; I will, however, strive all the more to describe the phenomena themselves and the means of producing them in as much detail as possible.

Heinrich Hertz was the first to specify the devices with which one can detect the rays of electrical force emanating from a spark gap. For this purpose, he used so-called resonators (Fig. 75). These are open wire circuits whose ends are fitted with small, polished brass spheres; by means of an insulated adjustment mechanism, the air gap between the spheres can be set with precision to small fractions of a millimeter. If one now places such a resonator in the path of the electric rays, an electrical sympathetic vibration[^6] is excited within it,


which manifests itself by the jumping of sparks across the point of interruption, in a similar manner to how a tuning fork is made to resonate by sound waves. I must refrain from demonstrating this experiment to you. The sparks that one obtains at the electrical resonator[^7] are too tiny to be seen by everyone.

I shall choose a stronger means to convince you of the propagation of electrical forces through space.

Nature, as a spark generator, shows us only widely separated extremes. From the soft crackling you hear on cold winter days when you run a rubber comb through your hair in a heated room, to the flicker of mighty lightning bolts, is a tremendous leap—and yet both are the same phenomenon, from both emanate the same invisible forces. For our purposes, we make use of an artificial spark generation whose strength holds a moderate middle ground between the manifestations of nature. We connect the terminals of an induction apparatus, of a type well-known to you, to solid brass spheres, which are held at a suitable distance by sturdy ebonite plates. When the inductor is set in motion, we obtain an uninterrupted series of thick, white-hot sparks, whose radiative power we can increase by filling the spark gap with oil. In the present apparatus (Fig. 76), this is done with the help of a parchment paper cylinder that surrounds the inner halves of the spheres. Following a procedure first employed by Righi,[^8] we furthermore do not connect the spheres directly to the terminals of the inductor, but rather charge them by means of smaller spheres that are positioned opposite the outer halves of the spheres at a suitable distance.


The parchment sheath conceals the effective spark from your view, yet you can clearly hear the peculiar noise as it breaks through the oil. We shall call this device a **radiating apparatus**,[^9] for from it emanate the rays of electrical force. We are all struck by them; we just do not notice it because our bodies lack the ability to resonate. If we had metallic limbs, it would likely be different.

I now make use of a simple means to substantially amplify the propagative ability of the electrical forces. This method will occupy us frequently this evening; it constitutes what is truly new in the experiments to be demonstrated. It is thin wires, a few meters long, that I have stretched out, insulated, from the feeding spheres of the radiating apparatus—let us call them poles—to both sides. They act like the perforated pipe of a watering cart; from them, the rays of electrical force spray out, as it were, in all directions perpendicular to the wire. They affect a larger portion of the surrounding space.

To demonstrate the propagation of the electrical forces, I will use an arc lamp back there in the hall; I intend to ignite it from here. The arc lamp itself has been stripped of its regulating mechanism. The opposing carbons are connected to the poles of an accumulator battery; as long as they do not touch, the circuit is broken. In the present case, they form a resonator for the electric rays; they are induced to resonate, or more correctly, to co-spark.[^10] This closes the bridge for the direct current, and the white-hot carbon tips bestow their magnificent light. To ensure success, I connect both carbons with thin wires similar to those on the radiating apparatus. I am, in a sense, forming catching arms for the electric rays—sucking proboscises or antennae. Now, I let the radiating apparatus operate—you see the lamp immediately spring into action.

Using the simple means of the resonator, Heinrich Hertz researched the laws that govern the propagation of electric forces. The most remarkable of his experiments shows that the electric rays are reflected by a metal wall, similar to how light is reflected by a mirrored surface. He thereby succeeded in proving the wave-like nature of the phenomenon.

To illustrate, I will draw upon an example that has nothing to do with electricity but makes a wave motion visible. Let us imagine an endless, stretchable cord stretched out in a straight line. If we impart a disturbance to one end, perhaps by striking it, this disturbance propagates along the cord in the form of a wave. We observe a similar phenomenon when a calm water surface is agitated by a thrown stone. The disturbance spreads in ring-shaped waves in all directions from the point of origin. The observation of a cork floating on the water teaches us that the individual water particles themselves do not take part in the outward-striving motion, but only rise and fall. At one moment they are on a wave crest, the next in a wave trough. The same terminology has been adopted for the propagation of the disturbing force in a linear medium, such as our cord. Here too, it is clearly discernible that the individual parts of the cord do not move in the direction of the advancing wave, but only rise and fall perpendicular to it. Such waves are therefore designated as **transverse waves**,[^11] in contrast to **longitudinal waves**, such as those that occur with sound, which propagates its effects through compressions and rarefactions of the sound-carrying medium. In this case, the individual particles of the medium, such as the air, move back and forth in the direction of the advancing wave motion.

Through convincing experiments, it has, as is known, been proven that light propagates by means of transverse vibrations of an unknown medium called the aether. Hertz provided the same proof for the electrical forces that emanate from a spark gap with an alternating discharge. The arrangement of his experiment can be described in a few words.

I draw your attention back to the vibrating cord. Thus far, we have assumed it to be extraordinarily long and have only considered the travel of the wave from the point of disturbance. But at the other end, no matter how long the cord may be, it is again fastened. The waves arriving there do not disappear; they travel back again, they are reflected. Each particle of the cord now receives motions from both types of waves, from the incident and the reflected ones. If the forces at one point are aligned in the same direction, they amplify the motion; if in opposite directions, they diminish it. Points arise where the forces amplify to a maximum value—there, the cord particle must make the largest transverse oscillations; at others, the transverse motion comes to an almost complete rest. After some time, a state develops which is designated as a **standing wave**.[^12]

If one is skillful, one can demonstrate this with a cord fastened at one end, the other end held in the hand. I prefer to rely on artificial aids.

On this vertical slat, a platinum wire is stretched (Fig. 77), its upper end clamped fast, while the lower fastening point is attached to the tine of a tuning fork, which can be excited by electrical means. In this way, the lower end of the wire is set into lively vibration, which propagates upwards and is reflected at the point of fastening. Standing waves are formed, which we can make visible by sending a strong electric current through the wire. The points of rest, called **nodes**,[^13] will heat up to a red glow, whereas the strongly moving parts, the **antinodes**,[^14] will be cooled by the air and remain dark. For better observation, we shall dim the hall. You will now clearly recognize 4 nodes. The fixed distance between two successive nodes is half the length of the wave, because from `a` to `c` the traveling wave has advanced by its full length, consisting of a wave trough and a wave crest. The time that elapses until each particle of the wire has executed one full transverse oscillation is called the **oscillation period**, and the number of oscillations in one second is the **oscillation frequency**.


We can clearly recognize these facts on the apparatus with our own eyes. Let us assume for a moment, however, that we were blind and endowed only with the sense of touch. We could nonetheless convince ourselves of the peculiarity of the phenomenon. We would only need to hold a finger near the wire. We would clearly feel the antinodes through their impacts; at the nodes, by contrast, we would burn ourselves. By now locating these points through the sense of touch, we can not only conclude that wave motions of a medium invisible to us, called wire, are present, but we can even determine the distance between the nodes and thus the length of the waves. Even determining the oscillation frequency by counting the impacts would not be unthinkable.

Hertz did precisely the equivalent of this when investigating electric waves. He directed the invisible rays of electrical force emanating from a spark gap towards a metal wall. There, they were reflected. By now bringing his resonator, like a probing finger, to various points in the path of the rays, he was able to identify locations where it responded most vividly and those where it failed almost completely. My colleague, Professor Rubens,[^15] has even, through more refined measurement methods, determined the magnitude of the electrical impulse for each location and found a regular increase and decrease. With this, the probability has become a certainty that the rays of electrical force bear the characteristic of a wave phenomenon, just like the rays of light.

But there is more. Let us consider the velocity with which a water wave propagates from the origin of the disturbance. The disturbance itself has propagated by one wavelength when a particle of water has oscillated up and down once. If the number of these oscillations is *n* per second, and the length of one wave is *l*, then *nl* is the path by which the disturbance propagates in 1 second, thus the **propagation velocity** of the wave.

The situation with electric waves is exactly the same. Now, according to Thomson’s calculations mentioned at the beginning, one can determine from the dimensions of the spark-generating apparatus the number of alternating discharges that occur in 1 second; one therefore knows the number of impulses in 1 second, i.e., the oscillation frequency. If one further determines the wavelength, as Hertz did, through probing experiments with the resonator after having transformed the waves into standing waves by reflection, then all the means are given for calculating the velocity with which an electrical disturbance, an electrical impulse, propagates through space in all directions. Hertz found, with great approximation, the **speed of light**: 300,000 km in 1 second.

This velocity is so immense that we cannot think of making the travel of the electrical force perceptible to our eyes. Professor Silvanus Thompson[^16] in London showed me this summer a delightful model in which he illustrates the travel of an aether wave using purely mechanical means. He was kind enough to have one made for me (Fig. 78). The radiating apparatus is represented by two heavy brass plates, which hang from threads and possess a specific, relatively long period of oscillation. The “resonator” is an interrupted brass circle and likewise hangs from threads. Both can be adjusted by shortening or lengthening the cord so that they have identical oscillation periods.

To represent the wave-carrying medium, the aether, small lead spheres are used, which hang in a similar manner from V-shaped threads. The successive threads cross over one another, so that no sphere can oscillate without communicating some of its motion to its neighbor. If one sets the radiating apparatus in motion, it imparts transverse oscillations to the spheres, which propagate slowly along the row of spheres. One can clearly follow them with the eye


and see how, after some time, they reach the resonator and cause it to oscillate in sympathy. This is how the propagation of electrical forces through the aether is imagined today.

In conclusion of this physical introduction, one final brief remark. From optical investigations, it is known that the monochromatic rays into which white light is decomposed by refraction possess different wavelengths. Red light has the longest wavelength at 0.8 microns (1 micron is one-thousandth of a millimeter); it decreases towards the violet part of the spectrum, where the wavelength is only about 0.4 microns. The oscillation frequencies behave in the inverse manner: for red light, 400 trillion oscillations occur in 1 second, whereas for violet light, it is 800 trillion. The currently known wavelengths of electrical rays vary in the order of magnitude between centimeters and kilometers; their oscillation frequencies amount to only a few million per second. They thus fall into the **ultra-red**[^17] part of the spectrum. In the extreme ultraviolet part of the spectrum, as is known, one presumes the Röntgen rays[^18] to be. The last years of physical research thus represent a bold push into the borderlands of nature. Who can say if and where we will reach the end? Both of these results of pure research have immediately found important applications for the benefit of humanity.

It would lead me too far from the actual subject of my lecture were I to mention the beautiful experiments by which Hertz and his successors proved that electric rays, just like light rays, obey the laws of refraction, interference, and polarization. As far as is at all possible, they have provided us with the certainty that light and electric rays are phenomena of the same kind, differing from one another only in their scale.

The retina of the eye is the sensitive instrument that enables us to perceive the rays of light; in a corresponding manner, we may now call the apparatuses that show the effects of electric rays **electric eyes**. The Hertzian resonator is a rather imperfect eye; it is weak and short-sighted. We can only recognize the most brilliant effects of the electric rays with it, and estimate their degree of brightness, if I may express it so, only approximately. Today, we have at our disposal a stately number of highly sensitive electric eyes with which the strength of the effect can be precisely measured.

The most sensitive of these presents itself as an ingenious improvement of the Hertzian resonator. The characteristic of the latter was the interruption of a metallic circuit by an air gap of extraordinarily small size. The effect of an electrical irradiation manifested itself in the appearance of visible sparks. We thus had to call upon our human eye for assistance, or in other words, we effected a conversion of the electrical radiation emanating from the spark gap into light radiation. But we can also call upon other aids to detect the infinitely small sparks when the eye fails. The most sensitive means are always electrical; we choose a direct electric current, the faintest traces of which can not only be detected but also measured by galvanometers.

Imagine the metallic knobs of a Hertzian resonator brought so close together that the remaining air gap is no longer discernible even with the finest optical instruments; nevertheless, a complete metallic contact need not yet exist. If we now insert into the wire circuit of the resonator (Fig. 79) a small galvanic battery, perhaps a dry cell of low electromotive force, and a highly sensitive galvanometer, the needle of the galvanometer will remain at rest as long as the circuit at the spheres is interrupted. But if an electrical radiation acts upon the circuit,


the electric waves will thrill through it in electrical resonance, for which the air gap forms no barrier, much like a water wave sprays over an obstacle in billions of dust-like droplets. Thus they spray across here in the form of fine, tiny sparks, and although hidden from the sharpest optical aids, they are nevertheless present for a moment and, like any spark, fill the air gap with metal vapors. These vapors conduct the direct current and close the circuit; the result is a clear deflection of the galvanometer needle. Either the needle now swings back after the radiation has ceased, in which case the insulating air gap has restored itself on its own, and the electric eye is ready to respond to a new radiation, or—and this is the usual case—tiny particles of the metal, re-condensed after vaporization, fill the air gap and form a metallic bridge; then the deflection of the galvanometer is a lasting one. But the slightest vibration causes this loose bridge to collapse and interrupts the metallic contact.

This straightforward explanation of a refined electric eye, based on the properties of the Hertzian resonator, also applies to the eye that Marconi uses to telegraph over long distances with the help of electric rays. It is, however, customary to trace the line of development back to a different source.

In the year 1890, Branly discovered a peculiar property of loose metal grains, such as iron, copper, or brass filings, layered one upon another in a glass tube. Such a tube offers an insurmountable resistance to the passage of an electric current, so that one can connect it, with metallic contact plates or well-conducting spheres embedded therein, to the poles of a galvanic battery without obtaining a current. To demonstrate this effect, Branly placed a sensitive galvanometer in the same circuit. As soon as this tube is struck by electric rays, however, it conducts the direct current, and the galvanometer experiences a deflection. A gentle shake of the tube after irradiation has occurred restores the infinite resistance. Fig. 80 shows such a device, in which the metal filings have been replaced by loosely layered iron nails.[^19]


Here, too, we can trace the explanation back to the Hertzian resonator. In place of the single point of interruption, we have the countless points of contact of the metal filings with their impure, insulating surfaces. The irradiation induces an electrical tremor in the circuit, and countless invisible tiny sparks at the points of interruption bring about the metallic contact.

This simple explanation is also supported by the fact that the effect is not achieved as well with metals whose surfaces remain metallic more easily and for longer, such as platinum, gold, and silver. On the other hand, metals such as copper, brass, aluminum, iron, and nickel are excellently suited, as their surfaces are known to remain metallically pure for only a short time. With carbon grains or carbon powder, the effect is uncertain, which argues against explaining the phenomenon as a purely microphonic one.[^20] Lodge appears to have been the first to use such tubes as electric eyes for the study of Hertzian rays. In his captivating book, “The Work of Hertz and some of his Successors,” he describes various arrangements of this and similar kinds, which he had already used in 1889. From him also originates the name “coherer,” which he derived from “to cohere,” because a more intimate connection of the metal filings, a cohesion as it were, is effected by electrical irradiation. For German use, the ugly word “Kohärer” (more correctly would be “Kohärirer”) has been formed, which one would gladly see disappear again. I have requested Privy Councillor Reuleaux[^21] to exercise his so-often-proven art of coining apt German terms in the present case as well. For “to cohere,” he has proposed the word “**Fritten**.” In technology, this term designates a process in which loose, powdery masses are made to adhere together by superficial melting. This is a perfect fit here, and one could expediently Germanize “coherer” as “**Fritter**” or “**Frittröhre**” (frit-tube). Lodge can probably also be designated as the father of the idea of telegraphing with electric rays and such tubes; however, he specifies the maximum achievable distance as half an English mile (800 m), without, however, having practically tested this.*)

*) In the *Electrician* (Oct. 1, 1897), a statement by Sir William Crookes has also been pointed out. It is found in an essay “Some Possibilities of Electricity” in the *Fortnightly Review*, February 1892, and is very interesting, which is why I report it here.

“Whether longer aether waves, which the eye no longer perceives, are continuously active around us, we have until recently never seriously investigated. But the investigations of Lodge in England and Hertz in Germany reveal to us an almost limitless abundance of aether phenomena or electric rays, whose wavelengths range from thousands of miles to a few feet. Here a new, astonishing world opens up to us, of which we can hardly assume that it should not also contain the possibility of the transmission of thought. Light rays do not penetrate a wall, nor a London fog, as we all know only too well. But electric waves of 1 m length or more will easily pass through such materials; these materials will be transparent to them. Here arises the captivating possibility of a telegraphy without wires, without poles, without cables, without the entire costly paraphernalia. If we assume the feasibility of a few reasonable demands, the question moves entirely into the realm of possibility. We can today generate waves of any desired length, from a few feet upwards, and obtain a succession of such waves radiating in all directions of space. It is also possible, if not with all, then at least with some of these rays, to refract them by suitably shaped bodies acting as lenses and thus to direct a bundle of rays in any given direction; large lens-shaped masses of pitch and similar substances have been used for this purpose. One could also, at a distance, capture some, if not all, of these rays with specially arranged apparatuses and transmit them to another by means of prearranged signals in Morse code… Two friends, living within the transmission range of their receivers, could tune their apparatuses to specific wavelengths and, as often as they pleased, communicate with one another through long and short radiations in the characters of the Morse code. At first glance, one would raise the objection to this plan that the messages could not be kept secret. Let us assume the parties involved were a mile apart from each other; the rays, which the transmitter sends out in all directions, would fill a sphere with a radius of one mile, and anyone within this distance from the transmitter could intercept the message. This could be avoided in two ways. If the positions of the transmitter and receiver were precisely determined, one could focus the rays on the receiver with greater or lesser certainty. If, however, the transmitter and receiver were mobile, so that a lens arrangement is out of the question, the parties involved would have to tune their apparatuses to one and the same wavelength, say, for example, 50 m. I assume here that apparatuses would be invented which, by turning a screw or by changing the length of a wire, could be so regulated that they would be suitable for receiving waves of a prearranged length. If they were set, for example, to 50 m, the receiver would only receive waves of perhaps 45 to 55 m and be insensitive to all others. Considering that a large number of wavelengths are available, from a few feet to thousands of miles, secrecy appears feasible; however tireless a curious person might be, he would surely shy away from the task of trying all the millions of possible wavelengths to finally, by chance, hit upon those which the people to be eavesdropped on are using. Through secret codes, one could exclude even this possibility. These are not mere dreams. All the requirements to realize the plan lie within the realm of possibility, and indeed precisely on the path that research in all the capitals of Europe has already embarked upon, so that we can daily expect to hear that the task has been practically solved. Even today, telegraphy without wires is already possible over the limited distance of a few hundred meters, and a few years ago I myself attended experiments in which telegrams were sent from one part of a house to another without a connecting wire, almost exactly by the means described.”

The news that Marconi had practically carried out this telegraphy over a distance of miles reached us at the beginning of this year. Anyone who had attentively followed the facts to which the study of Hertzian rays led knew that a good deal of truth lay at the heart of the newspaper reports.

Like many others, I too had occupied myself with the task, but had not progressed further than from one end to the other of the long corridors of our university. Even the use of parabolic mirrors and large capacitances did not get us beyond this limit. Marconi, it became clear to me, must have added something else, something new, to what was known, through which the kilometer-long distances were achieved. On short notice, I traveled to England, where the telegraph administration was conducting larger experiments. Through my friend Gisbert Kapp,[^22] I was excellently introduced to Mr. Preece,[^23] the chief engineer of the English telegraph authority, and I was most graciously permitted to participate. I will state this right away: What I saw was indeed something new. Marconi had made a discovery; he worked with means whose full significance no one before him had recognized. Only this explains his success.

I wish to emphasize this right at the beginning of my report, because recently, especially in the English technical press, the attempt has been made to deny the novelty of Marconi’s method. The generation of Hertzian waves, their propagation through space, the sensitivity of the electric eye—all that, they say, was known. Very true, but with these known means, one got 50 meters and no further.*)

*) The author was not yet fully aware at that time (1897) of the pioneering work of Edison, Tesla, Lodge, and Popoff.

First, Marconi devised for the method an ingenious arrangement that achieves a reliable technical effect with the simplest of aids. Then, he showed how, on the one hand, by grounding the apparatuses, and on the other, by using long, vertically extended wires, telegraphy first becomes possible. These wires constitute the essence of his invention; the designation “telegraphy without wire” is therefore actually incorrect. It is more accurately called “**spark telegraphy**” in contrast to the previous “**current telegraphy**.”

First, I will discuss the structural design. The main part of the apparatus is the electric eye, which Fig. 81 shows in half natural size. After many experiments, Marconi identified a metal powder, or more correctly a mixture of metal powders, as the best, consisting of 96% hard nickel and 4% silver. It is produced by filing with clean and dry files. This mixture is enclosed in a glass tube between two silver plugs, whose boundary surfaces are amalgamated with a trace of mercury. The thinner one makes the powder layer, the more sensitive the eye becomes, i.e., it responds to a lower level of radiation energy. The layer is only about ½ mm thick; one can hardly fit more than 20-25 metal grains in it. The specified exact percentage of silver thereby becomes irrelevant; one can only say that a greater abundance of silver grains makes the tube more sensitive, but one exchanges this for a disadvantage: the more silver, the worse the “release capability,”[^24] i.e., the interruption by vibration after a signal has been given. For reliable operation, however, this is the main thing. I therefore omit the silver entirely and use only pure nickel filings. Marconi further recommends evacuating the tube after filling and only then sealing it shut. The first is, according to my observations, of lesser importance; the sealing, on the other hand, is advisable because it secures the correct position of the silver plugs. The connection is made by platinum wires, which are soldered to the silver plugs. Of the utmost importance, however, is that one selects the metal grains to be of as uniform a size as possible with a magnifying glass, preferring the sharp-edged, jagged, and pointed ones, and avoiding the rounded ones as much as possible.


Before filling, they must be carefully cleaned and dried. Despite all this, one is dependent on chance; from a whole series produced in the same way, one always has to cull some, partly due to too little or too great sensitivity, partly due to a lack of release capability.

I will now first explain the arrangement of Marconi’s receiver in a clear overview. The heavily drawn circuit (Fig. 82), which I will designate as the **main circuit**, contains in series a small dry cell *A* of 1.5 to 1.8 volts electromotive force, a sensitive relay *B*, and the frit-tube *C*. A relay, as is known, is a widely used transmitter in telegraphy that responds to very small currents and thereby moves a tongue, which closes a second circuit with a stronger battery, the so-called local battery. If the fritter is released, the circuit is broken; the tongue of the current-less relay rests against the resting contact. After irradiation has occurred, the fritting in *C* allows the formation of a current, which moves the relay tongue to the working contact. This closes the secondary circuit of the local battery *e*, and the Morse writer *b* connected in it, as well as the tapper *d*, are actuated.


At the first strike of the tapper against the fritter, the latter must release, thereby rendering the main circuit current-less; the relay tongue moves back to the resting contact and switches off the local battery. Upon renewed irradiation, the process repeats. It is clear that by intermittently irradiating the fritter, one can generate the characters of the Morse alphabet.

With this simple arrangement, we can telegraph within a room or from one room to another. A standard Morse key is connected into the primary winding of the inductor, with which one closes the circuit for shorter or longer periods. I will demonstrate the handling on the two apparatuses that are set up here on both sides of the hall, about 20 m apart from each other. The frit-tube is cemented with marine glue to a long glass rod, which serves for horizontal mounting on two vertical metal stands. Directly in front of the gap filled with nickel filings is the tapper, a small horn clapper on an armature, which is moved by the electromagnet located behind it in a manner similar to the clapper of an electric bell. The electromagnet of the tapper is here connected in parallel with the Morse writer, or rather with an electric bell, and not, as the diagram indicates for the sake of clarity, in series. I now connect a dry cell to the main circuit and connect the bell in parallel with the tapper in the secondary circuit. As you notice, everything remains at rest, since the main circuit is completely interrupted in the fritter; the tongue of the relay rests against the resting contact. As soon as I now generate an electrical radiation that strikes the frit-tube, the picture changes. The nickel filings form an electrical connection, the dry cell sends a current through the relay, and this closes the secondary circuit.

You hear the ringing signal and the strike of the tapper against the tube, whereby the circuit is again interrupted. If I allow continuously oscillating discharges to pass at the radiating apparatus, each interruption is followed by a renewed irradiation; the process repeats as long as I wish, the bell and the tapper continue to operate. The call signal is given; we switch off the bell, switch on the Morse writer, and the telegraphy can begin.

(The sending and receiving of a telegram follows.)

Thus far, everything is simple and easy to understand. Marconi, a still youthful Italian in his early twenties, began his experiments on his father’s country estate near Bologna, inspired by the lectures of Righi at the University of Bologna. There, he also made the beautiful and momentous discovery of which I have already spoken. He found that the distance he could achieve with the described arrangements was increased more than a hundredfold when he connected one pole of his radiating apparatus to a vertical wire and the other pole to the earth, and made the same arrangement at the frit-tube of the receiver. As late as the middle of this summer, he still believed that capacitances were necessary to achieve good results, which he attached in the form of zinc plates or zinc cylinders to the uppermost ends of the aerial wires. In his English patent specification, written more than a year ago and published a few months ago, he placed particular value on these capacitances. The experiments he conducted in the spring in England and in the summer in Spezia seem, according to a written communication, to have now also brought him to the conviction that the cumbersome capacitances are not as important as he initially assumed: it is mainly the **length of the aerial wire** that determines the crossing of great distances.

The investigation of spark telegraphy is difficult in the limited spaces of a laboratory. For this, one needs kilometer-long distances in the open air, not interrupted by forests, mountains, or houses. The vertical suspension of long, well-insulated wires is no simple matter, especially when, as in Marconi’s first experiments, the upper ends are to be fitted with large capacitances.

Marconi was aided by an exceedingly fortunate circumstance. The chief engineer of the English telegraph authority, Mr. Preece, had for years been striving to connect the lightships on the English coast and small islands lying near them telegraphically with the mainland without the use of cables. He stretched out parallel wires whose ends were led into the water; each of these thus constituted a closed circuit. If strong, intermittent electric currents or alternating currents were now sent through one, they induced, by induction, electric current impulses in the parallel wire, which could be made audible by a connected telephone. As early as 1892, he had established a telegraphic connection in this way between Penarth and Flatholm in the Bristol Channel. Here with us on the Wannsee as well, Messrs. Rathenau[^25] and Rubens have conducted similar successful experiments. However, it seems one did not get beyond limited distances; moreover, the calling signal presented considerable difficulties.

Marconi turned to Mr. Preece; he immediately found understanding and energetic support. On the old experimental field between Penarth and Flatholm in the Bristol Channel, two locations were set up, and on May 10, the memorable experiments began, led by Mr. Preece personally and his engineers Mr. Gavey[^26] and Mr. Cooper.

On the cliff of Lavernock Point, about 20 m high and 1 hour from the pleasant seaside resort of Penarth, a 30 m high mast was erected, held by wire ropes, over whose top a cylindrical zinc hat of 2 m height and 1 m diameter was placed. From the zinc cylinder, an insulated copper wire led down to the foot of the mast to one pole of the receiver. The other pole was connected by a long wire rope, down the cliff, to the sea. In the middle of the channel, 5 km away from Lavernock Point, lies the small isle of Flatholm, bristling with cannons on its high cliffs, and also the site of a lighthouse. That was the transmission site. In a wooden shed stood the radiating apparatus with a relatively small inductor (25 cm spark length), powered by a 10-cell accumulator. The solid brass spheres of 10 cm diameter were brought to within 2 mm of each other and separated by a layer of vaseline oil. The outer spheres, also solid, of about 4 cm diameter, at a distance of 10 mm from the inner spheres, were connected on one side to a capacitance on a mast of exactly the same dimensions as in Lavernock Point, and on the other side to the sea.

On the first day of the experiment, two kilometer-long wires were laid over the cliffs on both sides in order to establish a connection with telephones according to Mr. Preece’s older method, which was also successful after a short time. On the second day, the plan was to telegraph according to the Marconi method. At first, it was not possible to receive any signals at all. The blame was attributed to the iron wire ropes that held the mast and surrounded the receiving wire like a cage. When, on the following day, this wire was extended by about 20 m in order to place the receiver to the side of the mast, the first, though still indistinct, signals arrived. Full success was only achieved the next day, after moving down to the shore with the receiving apparatus, thereby nearly doubling the effective length of the wire. It will remain an unforgettable memory for me how we, huddled together five of us in a large wooden crate because of the strong wind, our eyes and ears fixed with the most intense concentration on the receiving apparatus, suddenly, after the hoisting of the prearranged flag signal, heard the first tick, the first clear Morse signals, carried over silently and invisibly from that rocky coast, perceptible only in indistinct outlines; carried over

`[Image of the first Morse tape from the Lavernock Point – Flat Holm experiment]`

**Figure 83.**

by that unknown, mysterious medium, the aether, which forms the only bridge to the planets of the universe. It was the Morse signals for “V” that came across according to the agreement, and I owe the possession of these first signals, which are reproduced in Fig. 83 by autotype, to the kindness of my hosts.

After my departure, the experiments were continued, and, as Mr. Preece informed me, they succeeded in achieving telegraphic communication between Lavernock Point and Brean Down, right across the entire width of the channel (14.5 km). In this experiment, kites were used at both locations to hold the vertical wires. How long these were, I have not been informed. —

Having returned, I immediately set about resuming my own experiments, using Marconi’s aerial wires.

The first experiment, at the end of June, consisted of the telegraphic connection of this lecture hall with the chemical factory of A. Beringer, located on the Salzufer. A water tower was available there to fasten the transmitting wire. The experiment succeeded immediately, but I chose to break it off swiftly, as an inquiry came in from the telephone exchange asking whether local thunderstorms were occurring at the Salzufer, as all lines there were disturbed. We were thus too close to the telephone wires there with our radiating apparatus.

The next connection was made with the residence of one of my assistants at the corner of Berliner- and Sophienstrasse. The radiating apparatus was set up in a basement room of the one-story house. The distance in a straight line is about ½ km, but there are numerous tall trees in between, which the radiation must penetrate. We shall repeat the experiment this evening.

Here in the hall stands the receiver with the Morse writer. One pole of the fritter is connected to the water main, thus grounded; to the other pole is attached an insulated copper wire, which leads out the window in the next room and is suspended by means of a porcelain insulator from the roof’s edge of the building. Over at the transmission site, a similar wire is well insulated and attached to the top of the flagpole, which also serves as the building’s lightning rod. It runs freely through the air down to near the ground and from here, by means of insulating supports, into the room where the radiating apparatus stands, of the same dimensions as the one here on the table.

(The reception of a telegram follows.)

For the scientific investigation of this remarkable phenomenon, however, such short distances are not sufficient. I was so fortunate as to receive the Highest Permission to conduct experiments on the waters of the Havel near Potsdam and in the surrounding Royal Gardens. I was able to devote almost two months to this research, supported by the crews of the Royal Sailor Station.[^27]

These were the most entertaining, most pleasant studies I have ever undertaken, in the magnificent laboratory of nature under an almost always smiling sky in a paradisiacal setting. The systematically conducted experiments brought us, if not an explanation of the phenomena, then at least a wealth of inspiration and important reference points for the further successful expansion of spark telegraphy.

Our headquarters was at the Sailor Station on the Glienicke Bridge (Fig. 84). The receiving apparatuses were located there. The existing flagpole was significantly heightened, so that the uppermost tip of the bare receiver wire was 26 m above the ground. Our first transmission site


was the Pfaueninsel (Peacock Island), 3 km away. The apparatuses, batteries, inductors, and radiating apparatus were set up in a room of the castle there. On the well-known iron bridge that connects the two towers of the castle (Fig. 85), a mast was attached to support a 26 m long wire led vertically down the castle, which, hanging on insulators, was guided through the window into the room. At both locations, a good earth connection was established by a wire that ran to the Havel and was there soldered to a large zinc plate lying in the water.

The first experiments that were conducted did not yield a satisfactory result. While signals did arrive, they were garbled and illegible. In addition, disturbances of a completely unforeseen nature occurred—irregular signals that were not being sent. The latter, in particular, gave us a great deal of trouble. Since the receiver only indicated them when its pole was connected to the aerial wire, the source of the disturbance had to be presumed to be in the wire. I did not initially think of atmospheric electrical causes; after all, the air was clear and pure and without any thundery humidity. In the English experiments, I had, of course, become acquainted with the effects of atmospheric electricity, but they had been very slight.


As soon as one had disconnected the wire from the receiver and held it insulated in the hand for some time, the frit-tube would respond when one reconnected the copper wire to the pole, and indeed one could repeat the experiment three to four times in succession with ever-weaker effect, until it ceased entirely. Then one had to wait some time before the phenomenon could be repeated. We were obviously dealing with electrical charges from the air as a result of the large capacitance at the tip of the wire. The effects were, however, so slight that they did not interfere with the telegraphy. Here in Potsdam, the phenomena were much stronger, although the large capacitance at the ends of the wires was missing. I had omitted it because I did not believe in its effect from the beginning. Moreover, Captain Jackson[^28] of the English Navy had told me that he was able to telegraph between two ships over a distance of 2 km with simple wires hoisted up the mast without capacitance. I will not weary you with the many unsuccessful attempts that were made to discover the culprit. It was finally established beyond doubt that we were indeed dealing with atmospheric electricity, which, however, only made itself so disruptively noticeable because our electric eye was all too sensitive. It contained powder that was too fine and uneven, and too much silver. This led to a complete redesign of our frit-tubes; since then, we make them with coarser, carefully selected grains and without silver. In the laboratory, our previous fritters had worked excellently; we were delighted with their great sensitivity. In the open, they failed. Nature forced us to put its own, unwanted telegraphic activity out of service by using coarser means.

The other problem, the garbling of our signals, could not be eliminated so quickly. Since Peacock Island cannot be seen from the Sailor Station, communication by flag signals was not possible, and communication by messenger was too time-consuming and laborious. I therefore initially took up my studies with a more favorably located transmission site, the Church of the Redeemer in Sacrow,[^29] which is 1.6 km in a straight line from the Sailor Station and is visible, so that communication by flag signals was possible. Through the kindness of the commander of the Airship Detachment, Major Nieber, I later came into possession of a telephone cable, which was laid through the Havel, so that the experiments could now follow one another more rapidly.

The location of the Sacrow Church is known to you (Fig. 86). To the side of the basilica stands the bell tower, which


carries a platform directly beneath its roof. A mast was attached there, and at its outermost tip, 23 m above the ground, the insulated copper wire was suspended with the help of a porcelain insulator. For the setup of the radiating apparatus, we chose the colonnade of the church in order to be protected in case of rainy weather. That was our good fortune; another arrangement, which was chosen later, would not have led us immediately to our goal.

The telegrams sent from Sacrow arrived at the Sailor Station with impeccable clarity and certainty. The atmospheric disturbances had been definitively eliminated by the less sensitive frit-tubes; the garbling of the Morse dashes had ceased. Only sometimes, when Spree barges with their large, unfurled sails passed in the immediate vicinity of the church, were there some garbled Morse dashes, which were, however, still readable. Once, though, we were thrown into lively consternation by the indistinctness of the signals. It was on the very day that H.M. the Emperor wished to inspect the facilities. Only just before the deadline did we succeed in eliminating the cause of the disturbances. In order to be better protected against possible rain, we had moved the radiating apparatus deeper into the entrance of the church; in doing so, the transmitting wire, which was sagging considerably, had come within about 30 cm of the church’s tiled floor over a length of about 2 m. Later experiments have clearly shown us that any parallel position of a part of the wire in the vicinity of the ground is fateful. There is a certain minimum distance at which the electric rays no longer go into space, but directly to the earth. After we had shortened the wire and pulled it tighter, the disturbance was eliminated. The telegraphy succeeded excellently. H.M. the Emperor himself sent a telegram and was able to convince himself of its reliable arrival upon his return to the Sailor Station.

Further experiments at the Sacrow church yielded an important result. When I led the transmitting wire vertically down the bell tower to the radiating apparatus set up at the entrance of the tower, the signals ceased completely. Only after prolonged experiments was the cause of the obstruction recognized, and with it, an explanation for the initial failure with Peacock Island was gained. In the immediate vicinity of the bell tower were tall groups of trees, which almost completely obscured the vertical wire, so that from the Sailor Station, one could only make out the uppermost piece of the wire with a telescope. The rays emanating from the wire were, just like light rays, swallowed by the group of trees or diverted to the earth. The main condition for the success of spark telegraphy is that all obstacles in the near vicinity in front of the transmitting wire are removed; the two wires, at the transmitter and receiver, must be able to “see” each other, so to speak. Now, what was the situation at Peacock Island? The line connecting the apparatuses was plotted on a survey map from the General Staff. It cut not only through a wooded hill projecting as a headland, but also through a whole group of buildings, the Jägerhof (Hunter’s Lodge) in Glienicke Park. The rays had to pass through this, which explains their conspicuous attenuation.

At first, I had suspected the lightning rod on the castle of Peacock Island as the culprit. I had its earth connection removed—without success. Then, I moved with my receiver further west, to the vicinity of the Marble Bench in the New Garden. On a tall tree, the nimble sailors had soon attached a mast whose tip was 23 m above the ground. Now the wooded and built-up headland no longer lay in the way between the two wires. The result was better, but not yet satisfactory. On Peacock Island, there were still groups of trees in front of the wire, which obscured it. I had the wire led from the mast at the castle with a slight inclination, first to a flagpole directly on the elevated bank of Peacock Island, and from there down to the shore to the radiating apparatus. Now the wire was completely clear; it was visible, but its length had grown to 65 m, while the length of the receiver wire was only about 26 m. The signals again became clearer, but still not completely distinct. When numerous tall sails, or even worse, when steamers with strongly rising smoke came in between, the Morse signals were again garbled. Now I proceeded to the final change. I made the receiver wire of equal length, 65 m. For this, I had to go out onto the Havel; the apparatus was set up on a barge, protected by a tent. Immediately, the signals came through perfectly, no longer garbled by sails or smoke.

Lengthening, making the wires visible, and **tuning** them to the same length had brought about the success. Unchanged, however, had remained the height of the suspension points. What, then, was the essential factor? To decide this, I moved back to the Sailor Station and worked there as well with a wire length of 65 m on a barge. All at once, everything was in perfect order; the signals from Peacock Island came as reliably and precisely as in the rooms of the laboratory.

The experiments have clearly shown that the decisive influence is possessed by the **length and equality of the wires**. Intervening obstacles, while disruptive, can be overcome if one can only make the wires sufficiently long.

Special experiments were conducted to see if vertically stretched wires in front of the receiver wire would disturb reception. The flagpole at the Sailor Station is held by a whole series of iron wire ropes. I placed the receiver, which until then had always been positioned to the side of the flagpole because I feared the influence of the wire ropes, close to the mast, so that the wire ropes surrounded the apparatus like an iron cage. The reliable signaling from the Sacrow church was not disturbed by this. I must note that all wire ropes, with the exception of a single one, were grounded, as was determined by measurement. Only a single one, namely the foremost one, which was fastened close to the shore, had I insulated from the earth by inserting a short piece of hemp rope; a second one immediately behind it, running almost parallel to the first at a distance of a few centimeters, had a good earth connection. I had the forward wire rope insulated in order to be able to use it as a receiver wire if needed. This also succeeded, but the effects were conspicuously weaker and the signals not always entirely complete. Here I first learned of the deficient performance of iron as a material for the receiver wire, as well as the detrimental effect of the twist, of which more will be said below.

A slight twist has no detrimental influence. This was shown by an experiment with bare copper wire, which I wound in a few turns around the wooden flagpole before connecting its end to the apparatus. I received no weakening of the signals, not even when I wound a piece of the wire into a coil of 40 turns.

A resistance of 100 ohms inserted into the receiver wire likewise showed no discernible weakening of the signals. An increase of this resistance to 1000 ohms, however, weakened them considerably and made them almost illegible.

Finally, I would like to mention here one more fact that we encountered several times but could not completely clarify. In the experiments, both with Sacrow and with Peacock Island, in which garbled signals occurred at all, we could notice an increase in the disturbances as soon as the weather became windy. I suspect that the movement of the leaves on the trees, which the rays had to penetrate on their path, brought about a greater and changing resistance. It would also be possible that moving air accelerates the charging of the wire. An influence of air humidity could never be observed; fog or rainy weather did not disturb the signaling.

In the experiments in Potsdam, I solely pursued the purpose of first familiarizing myself more closely with the phenomena of spark telegraphy, of getting to know important basic conditions for success, of developing the apparatuses more suitably, and of practicing their handling. To determine the limits of usability, to overcome great distances—that was not the task I intended to solve in Potsdam. For that, other, more favorable locations and means had been considered from the outset. Therefore, the question of how, for instance, the spark generation at the radiating apparatus could be made more effective was initially disregarded. I always worked in Potsdam with the same modest means: with a spark inductor from Siemens & Halske for a 25 cm spark length, an accumulator battery of 8 cells, and the radiating apparatus standing here, whose dimensions are shown in Fig. 76. The distance between the large spheres was constantly 2 mm in oil; the smaller, outer spheres were at a varying distance of 3 to 15 mm. I could not with certainty discern an influence of the length of the outer spark at the short distance. The adjustment was always made so that the sparks in the oil appeared as uniformly as possible and with a whitish light. —

Before I now move on to the greater distances, I want to briefly report on some experiments that Marconi conducted in July of this year in Spezia with the support of the Italian Navy, and about which detailed reports were published in the September issue of the *Rivista marittima*.

The experiments extended over the period from July 10 to 18. On the first 3 days, experiments were carried out on land; a telegraphic connection over 3.6 km succeeded excellently.

On July 14, they telegraphed from the Arsenal S. Bartolomeo to a tugboat underway. The radiating apparatus stood in S. Bartolomeo with an aerial wire (copper cable of 10 sq mm cross-section) of 26 m length, attached to a mast. Spark inductor of 25 cm spark length, excited by a 4-cell accumulator. The inner spheres of the radiating apparatus had a diameter of 10 cm, the outer ones 5 cm.

The receiver wire on the mast of the tugboat was 16 m long and of 10 sq mm cross-section. Both transmitting and receiving wires had capacitances at their tips in the form of zinc sheets 0.8 x 0.8 m. Earth connection at both locations was via plates in the sea. Telegraphic communication was possible up to a distance of 4 km. As the steamer continued, it failed. The failure was attributed to poor operation of the key at the radiating apparatus as well as to atmospheric electrical influences.

On July 15, the experiment was repeated in the same manner, after the mast in S. Bartolomeo had been raised to 30 m. Upon the departure of the steamer, the receiver continuously gave signals, although the transmitter had not yet been put into operation. This was attributed to storm clouds that appeared in the distance. The experiments were only resumed after the weather had cleared. Readable dispatches were sent up to a distance of 5.5 km. The course of the steamer was then directed so that a headland (Castagna) lay between the transmitter and receiver. The signals immediately became unclear and illegible.

On July 16, they tried under the same conditions as on the 15th. The weather was clear. The signals remained good up to 7 km; up to 9 km, some could still be deciphered.

On July 17 and 18, the battleship S. Martino took the place of the tugboat. The aerial wire in S. Bartolomeo was raised to 34 m; the power source for the inductor was a 5-cell accumulator. The receiver wire on board, attached to the mast, was 17 m high, 22 m above sea level.

On July 17, the battleship was anchored 3.5 km from S. Bartolomeo. The receiver was set up at the most varied locations on the ship; also in the interior of the ship, near the engine. The telegraphic communication was consistently good; even when the apparatus was brought into the lowest rooms of the ship, it was still present, though less good.

The most interesting experiments took place on July 18. The battleship was underway, all other conditions the same as the day before. On the outward journey, telegraphic communication succeeded up to 12.5 km, then it became deficient. The ship turned, but only at 10 km could tolerable signals (buoni se non ottimi ancora)[^30] be received again.

After a pause, the battleship again headed out from S. Bartolomeo, starting from 6 km away. Telegraphic communication was perfect up to 16 km. From then on, interruptions and disturbances occurred, yet they succeeded in deciphering some words even at 18 km. The receiver was positioned at the stern of the ship during this. When they turned, the iron masts and towers of the ship came between the receiver and transmitter. This was suspected to be the reason that the first indistinct signals could only be received again at 12 km. The ship’s course was then steered so that islands (Tino and Palmaria) lay in between; the communication ceased, although the distance between transmitter and receiver was only 7-8 km. Only when the line of sight was clear did good signals return at 6.5 km. —

These experiments fully confirm the experiences I had at Peacock Island. There, too, the intervening headland of the Jägerhof weakened the effect of the rays; only the effect amplified by lengthening the wire permitted the obstacle to be overcome. The increase in transmission range with the lengthening (here exclusively, heightening) of the wires is also instructive.

Based on the experiences gathered in Potsdam, I considered the applicability of spark telegraphy to be completely certain even over greater distances, provided it was possible to use transmitting and receiving wires that were as high and as long as possible.

It is attributable to the most personal suggestion of His Majesty the Emperor that the Airship Detachment made itself available.

A preliminary experiment on the Tempelhofer Feld had the purpose of acquainting the leading officers with the nature and execution of the experiments. At the same time, it was to be determined whether we could send powerful spark discharges up the tethering cable without danger to the airship; for the use of these steel cables as transmitting and receiving wires presented itself as the simplest means. To this end, two airships filled with illuminating gas were attached to ropes whose uppermost parts, for a length of 20 m, consisted of hemp, in order to reliably prevent sparks from jumping to the airship. The middle part of the tethering ropes consisted of 100 m of wire rope, as is commonly used, and the lowest part, down to the winch, again of 20 m of hemp rope, in order to insulate the wire rope from the earth as much as possible. From the lower end of the wire rope, a bare copper wire led to one pole of the apparatuses, which were set up in an open field, and whose other pole was grounded with the help of a saber stuck into the ground. The transmitter was located near Rixdorf, the receiver 3 km away near the training ground of the Airship Detachment in Schöneberg. The connections to the airship were completely identical at both locations. It has often been presumed that the telegraph apparatuses were housed in the baskets of the airships in order to send telegrams from above to below. That would be completely superfluous, as a better connection for the airshipmen to the ground than the currently customary one via telephone is not necessary. The captive airship, in the present experiments, merely took on the role of a carrier for the aerial wires; it did not need to be manned. If one were to place the apparatuses in the basket, a second line to the ground would have to be led down under all circumstances. In a strong wind, both lines could touch and thereby cause disturbances. Moreover, the placement of the radiating apparatus with its powerful sparks in the immediate vicinity of the airship does not seem to me to be without danger. Any metal parts on it could take on the role of an unwanted “resonator” and ignite the gas by forming sparks.

The capacitance of the thick wire ropes was much greater than that of the thin copper wires used hitherto, so that we could only generate relatively weak sparks at the radiating apparatus. An amplification of the spark generator was intentionally omitted. Nevertheless, the setup worked completely satisfactorily; the effects on the receiver were even far too strong, so that we had to use our least sensitive frit-tubes. Disturbances from atmospheric electricity were indeed present, but they were of short duration; they appeared on the Morse tapes as dots and did not interfere with the actual signals, which were formed from short and long dashes.

I was now sure of my ground and decided to immediately move on to distances further than any yet achieved. A suitable location presented itself in Rangsdorf, situated on the military railway line near Zossen and 21 km in a straight line from Schöneberg. The transport of the airship, the hydrogen cylinders, the apparatuses, and the crews was significantly facilitated by the military railway. Furthermore, its command, in a most appreciated gesture, placed a telephone line at our disposal, so that one could easily communicate at any time. Rangsdorf was the transmission site. The actual experiments spanned 3 days and lasted each time from 10 a.m. to 3 p.m. In the following, I will briefly summarize the most important results.

**Tuesday, October 5.**

*Weather.* After moderate precipitation the evening before, the sky had cleared during the night. Cloudless sky until 10 a.m., then slight cloud cover. Heavy dew in the morning. Temperature approx. 8° C. Barometer reading 770.5. Humidity approx. 70%. Stiff east wind.

Due to the strong wind, kite-balloons (Sigsfeld system)[^31] with hydrogen filling were used. 500 m of wire rope was let out from the winch, with 20 m of hemp rope attached at the airship and at the winch. The airship in Rangsdorf was equipped with an altimeter. The fluctuations in altitude were quite considerable; on average, the airship stood 300 m above the ground.

Transmitter and receiver were connected by insulated copper wire of 1 mm diameter to the lower ends of the wire rope. Earth connection in Rangsdorf: a copper plate in the moistened ground; in Schöneberg: a saber stuck into the ground. As a result of the large capacitance of the wire rope, only small sparks could be set at the radiating apparatus. Oil spark 1 mm, outer 2 mm.

When attaching the aerial wires to the poles of the apparatuses, we received violent electric shocks, even when touching the insulation with thick leather gloves. When the wires broke loose, caused several times by the strong wind, there was a wild scattering of the surrounding crew members to avoid being hit by the whipping wire. If one succeeded in catching it, it was immediately grounded with a saber.

The result in Schöneberg was completely unsatisfactory. Some signals did arrive, but they were garbled and indistinct. Even when no one was telegraphing, the apparatus worked incessantly, producing dashes and dots, solely as a result of violently discharging atmospheric electricity. It immediately became clear to us that these disturbances were attributable to the large capacitance of the wire rope, which, moreover, weakened the sparks in Rangsdorf.

**Wednesday, October 6.**

*Weather* generally unchanged. Sky overcast. Temperature 7° C. Barometer reading 769.0. Humidity 63%. Cold northeast wind.

The airships were initially at 300 m of wire rope, and from 1 p.m. onwards at 400 m; their height, according to the altimeter, was 200 m and 280 m respectively. Fluctuations in altitude were still present, but less than on the previous day.

As the receiving wire, a steel telephone cable was used (twisted-pair wire), of the kind used by the Airship Detachment for communication from the airship to the ground. This cable was attached to the basket of the airship with hemp ropes; the lower end was connected to one pole of the apparatus. The tethering rope, this time without the hemp rope extensions, had metallic contact with the winch, whose earth connection was improved by special wire ropes. We hoped through this arrangement to weaken the atmospheric electrical disturbances or, rather, to keep them away from the receiving wire. Nevertheless, they were present in undiminished strength; one could not touch the telephone cables when they hung freely without receiving the most violent electric shocks, though they were less sustained. The effect at the receiver, however, was significantly improved. The individual signals were clearly recognizable, but the Morse dashes were still frequently interrupted and broken. The atmospheric electrical disturbances manifested themselves in numerous dots on the Morse tape. Nevertheless, the improvement achieved by reducing the capacitance of the wires was unmistakable.

Continuing along the path we had taken led to full success on the third day.

**Thursday, October 7.**

*Weather.* Less harsh. Sky completely overcast. Temperature 6° C. Barometer reading 769.4. Humidity 55%. Wind northwest.

Based on the experiences in Potsdam, I attributed the garbling of the signals on the previous day to the steel wire of the telephone cable and its twist. We replaced it with insulated copper wire of 0.46 mm diameter. This was also associated with a further reduction in capacitance.

At the first signal that was received, the success was plain to see. It came through with astounding precision and clarity. We had discovered the culprits and definitively eliminated them: the large capacitance, the iron, and the twist.

The vertical height of the airship, according to the altimeter, was 250 to 280 m. The atmospheric electricity was just as strong as before; one could not touch the free-hanging copper wire without punishment. Nevertheless, it no longer disturbed the incoming signals. Fig. 87 shows one

`[Image of the Morse tape from the Rangsdorf-Schöneberg experiment]`

**Figure 87.**

of the first telegrams; one can clearly recognize the disturbances from atmospheric electricity in it. They are tiny dots that are no longer able to impair the clarity of the Morse signals.

These experiments made the impression on all participants that the limit of transmission possibility with the available means was by no means yet reached. By this, I mean the limit at which a regular dispatch service is still possible. If one now considers that the height of the aerial wire can easily be extended to 1000 m when using captive airships, and that furthermore, almost nothing has been done so far to amplify the sparks at the radiating apparatus, one cannot deny a favorable future for the further expansion of spark telegraphy over great distances.

Hitherto, only inductors whose spark length did not exceed 30 cm have been used for generating the sparks. Here you see an inductor that delivers sparks up to 50 cm; I only refrained from using it in the experiments because it is too heavy. Also, my intention thus far was only to investigate the fundamental conditions, which can be achieved just as well with smaller means. The inductor is a physical apparatus. Electrical engineering has taught us how to generate spark discharges with mechanical aids, the power of which completely puts the thin discharges of inductors in the shade. Since the study of these arrangements is not yet fully complete, I will not go into further detail on them today, but I will demonstrate to you such spark discharges that are generated by a 3-horsepower alternating current machine and a transformer for 25,000 volts. (Experiment.) You can clearly see what powerful forces we are dealing with here.

I have frequently been asked in what direction and to what extent an application of spark telegraphy will be possible. Our knowledge of the phenomena in question is as yet very modest; we are in the very earliest beginnings. Who would venture to say today how far and where the path will lead us? I will certainly refrain from unfurling visions of the future before you, yet I believe I can assert with certainty that the new telegraphy is already mature and noteworthy for certain applications. The most important of these seem to lie in the military domain. Besieged fortresses, advancing armies that have the enemy between them, could already today make use of spark telegraphy as a means of communication that works equally reliably in broad daylight as it does in night and fog—though admittedly only with the use of airships, as the distances achievable with towers, masts, or tall trees would hardly suffice in this case. Larger army masses are, as a rule, already equipped with this important means of observation today.

Equally apparent is the benefit for the navy. Experiments last summer have placed the usability of captive airships on the high seas beyond question. It would surely be valuable if, in a case of war, the ships of the North and Baltic Seas could remain in constant telegraphic communication.

Just as obvious is the application for lighthouses and lightships. The receiving apparatuses can easily be designed in a handy form, no more voluminous than a chronometer. Upon approaching a lighthouse, they would not only give signals but could also write down the name of the lighthouse. It even seems feasible to provide the receiving apparatuses with an adjustable control for sensitivity, which would permit the reading of the distance to the lighthouse. But I am beginning to unfurl visions of the future, and you will prove me a liar.

More modest, but not unimportant, are some applications that are being planned in England. There are individual islands there near the mainland, some of which have seaside resorts or defensive works and require a means of telegraphic communication for short periods or to a limited extent. The laying of a cable would be too costly, especially considering the destruction caused by ebb and flow, which would cause rapid wear and tear of the cable. Thus, Mr. Preece intends in the near future to connect the islands of Guernsey and Sark by means of the spark telegraph. I consider spark telegraphy between Dover and Calais to be entirely possible. As the newspapers report, the English telegraph administration is eagerly occupied with such experiments.

Now I come to a question that is also frequently discussed. The electric waves emanating from a transmitting wire spread out uniformly in all directions of space. Every receiving apparatus is struck by them, and with suitable sensitivity, it will respond. Every telegram is thus actually communicated to the whole world. This is indisputably correct, and therein lies the weakest side of spark telegraphy, which limits its applicability to very special cases.

For practical use, the only recourse that remains for the time being is the use of prearranged codes, if one wishes to secure the dispatches against being read by others. Telegraphy in war would, of course, be immediately rendered impossible if an enemy radiating apparatus caused a permanent disturbance of the signals. It would be an interesting battle in the waves of the aether.

Despite these undeniable shortcomings, however, let us not allow our joy in the new spark telegraphy to be diminished. We stand before entirely unique phenomena that are only just now opening up a new field of technical application. Here, too, progress will not fail to materialize. —

In the experiments discussed, the poles of the transmitter and receiver were always connected to an aerial wire or, respectively, to the earth. The connection to the earth need not be a particularly intimate one; a saber stuck in the ground, a wire placed in water—even with insulation, as long as the cross-section at the outer end is exposed—are sufficient. If one omits the earth connection entirely, however, the effect on the receiver is significantly weakened. Between the Sailor Station and Sacrow, we were able to give clear signals even without an earth connection; with Peacock Island, it did not succeed—the signals broke up and became incomplete. To establish a sufficient earth connection, it was also enough for the well-insulated earth wire to lie loosely on the wet floorboards of the barge. —

I have conducted some experiments to see if the vertical orientation of the aerial wire is necessary under all circumstances. That is not the case. The following experiment will convince you of this. If I use the interruption spark of this small house bell as a transmitter, the frit-tube responds when I generate the sparks in its immediate vicinity. One meter, however, is the utmost distance to which I may go. If I now connect the poles of the fritter on one side, and the spark gap of the bell on the other, to freely stretched, horizontal wires of about 5 m length, insulated at the other end, I can reliably activate the receiver from the farthest end of this hall. We are now not in the immediate vicinity of the ground. If one repeats the experiment outdoors, one notices that the transmission range decreases as one approaches the ground with the horizontal wires. If the distance is over 2 m, however, one can go to considerable distances. When we were significantly disturbed by atmospheric electrical phenomena during the initial experiments with Peacock Island, I used four such horizontal wires of 0.46 mm diameter, each 100 m long, which were suspended freely on insulators about 2 m from the ground or, respectively, from the water’s surface. With these, we were able to send clear signals over 3 km, although numerous obstacles, such as trees and the aforementioned headland, lay in between. From this arises the possibility of overcoming great distances even without the costly assistance of airships. One would, however, have to place the horizontal wires so high that they can, so to speak, “see” each other over their entire extent. Two opposing coasts could probably be connected telegraphically in this way most simply, if no obstacles stand in the way of stretching kilometer-long lines on high masts.

A parallel alignment of the wires is, however, required as much as possible. A simple experiment will show this. I connect stiff copper wires of about ½ m length to the poles of the receiver and the bell’s spark gap. I now position myself with the bell in front of the receiver so that the wires are parallel; at this distance, it responds reliably. But if I turn, so that the parallel alignment of the wires ceases, the receiver fails already at an angle of about 30°.

After all these observations, I am inclined to the view that the essential factor is the **length of the wires and not their height**. The latter need only be great enough so that intervening obstacles remain below it at a reasonable distance. This arrangement would have the not-to-be-underestimated advantage that atmospheric electrical disturbances can be reliably excluded, for at the same height from the ground, the electrical potential of the air is the same, so that discharges of the two wires through the fritter are avoided. The setup of the receiver would, however, have to be insulated from the ground. —

In my experiments, I have also made an observation that opens up various prospects. It relates to the role of a wire situated in the direction of the progressive wave motion of the aether. When we were conducting experiments last winter in the long corridors of the Technical University with our then still imperfect arrangements, it struck us one day that we could achieve significantly greater distances than usual, although our apparatuses were unchanged and operating in the same way. We discovered the cause. It was a piece of thin wire, about 10 m long, that had been left lying fairly straight on the floor from previous experiments in the direction of our transmission. When we picked it up, the effectiveness of our apparatus was again significantly worsened. Further experiments led to the realization that electric waves travel along wires with much greater ease than through the air; indeed, that they seem to seek out the wires and prefer them on their path, if they extend in the direction of the propagation of the rays. At the Sailor Station, we stretched out 160 m of well-insulated wire, about 1 m from the ground. Tiny bell-sparks, generated near one end, acted upon the receiver, which was set up near the other end of the wire. It was like a speaking-tube effect.[^32] I repeated the experiment with the 10-times-longer telephone wire that had been sunk into the Havel to connect the sites. I achieved not the slightest effect, not even when I metallically connected the wire itself on one side to the pole of the receiver and on the other to the sphere of the radiating apparatus and sent the strongest discharge sparks into it. It was solely the effect of the nearby earth, which deflected the rays through the insulation of the wire. Only at a certain, albeit not large, distance from the earth does propagation along the wire become possible.

Upon this, one could perhaps found a new type of telegraphy with only one wire and without an earth connection. If one were to connect the ends of the wire to one pole each of the transmitter and receiver, a tiny spark would surely carry its effects for miles. It would, however, have to be determined whether the usual insulation of the support points could prevent the waves from passing into the earth as effectively as they prevent the passage of direct currents in the ordinary method of telegraphy.

Another consideration leads to remarkable consequences. The effects of direct current, as is known, propagate only in conductors; any insulation impedes their course. To what astonishing degree this happens, we have seen with the frit-tubes, which, despite their metallic filling, completely prevent the formation and propagation of a direct current due to the tiny air gaps between the loosely adjacent grains. The behavior of the electric waves that emanate from a spark gap with rapidly alternating discharges is precisely the opposite. They penetrate with ease precisely through the best insulators, such as air, yet they are impeded by metals; they are reflected by them like light from a mirrored surface. The waves running along a wire therefore do not penetrate into its interior; their road is the free aether-space all around.

Now, every wire divides space into two parts, an outer and an inner space; one could logically call them the outer and inner tube. If the effects of the direct current now fill the inner tube, the outer one remains free for the unimpeded progress of electric waves. It must therefore be possible to convey two telegrams on a single wire: one with direct current, the other with spark current, if this expression is permitted.

An experiment will convince us of the correctness of these conclusions. Along those three walls of this hall, a thin insulated copper wire of 0.4 mm diameter is stretched and attached to porcelain insulators. The total length is about 60 m. Here on the front long side of the hall are the free ends of the wire, about 20 m apart from each other. For the execution of ordinary current telegraphy, there is on one side a small accumulator battery, one pole of which can be connected to the line by means of a key, while the other pole is grounded by connection to the water main in the next room. On the other side, a Morse writer is connected, and the line is likewise grounded. You notice how, by pressing the key for a longer or shorter time, I can activate the Morse writer.

In the immediate vicinity of the end of the wire, there is also on one side a small electric house bell, operated by two dry cells. We will use its tiny interruption spark as a transmitter of electric waves. On the other side, our Marconi apparatus is moved close to the wire. As soon as I generate a spark, you hear the noise of the tapper and the ticking of a connected second Morse writer. We will now send two telegrams at the same time: the word “Strom” (Current) with the key, the word “Funke” (Spark) with the bell. (Experiment.) You see, both telegrams have arrived quite clearly, without interfering with each other.

A small precaution must, however, be observed. The interruption spark at the key of the current telegraph would act on the Marconi apparatus; I have rendered it ineffective by means of a 2000-ohm shunt.

Before this experiment can gain practical significance, however, a trial on longer lines would have to be carried out.

May this example, however, show that the application of electric rays is not exhausted with Marconi’s invention. Nature has opened a new gate for us. The task of science is, for now, to illuminate the newly opened space.

A captivating train of thought imposes itself upon us. We stand at the end of a century whose beginning brought us the discovery of the electric current. For more than 50 years, we knew only one useful application for it: telegraphy. Who, at the beginning of the century, would have guessed its full significance? From the fleet-footed mediator of thoughts, it became the bestower of the most brilliant light, the load-bearing Hercules of transport and industry.

The sea of electric waves is only now opening up. Again, it is for now only a light ship that we see being carried. But it seems to us more than a captivating dream that one day, heavier vessels will also travel upon its waves. For does not the water wave carry not only the lightest feather, but with equal willingness the laden iron ship from shore to shore; has not the sun, for thousands of years, been sending countless millions of horsepower to the solidifying, power-poor Earth with the waves of the aether!

—

### Footnotes

[^1]: **William Thomson (1824-1907).** Later Lord Kelvin. A towering figure in British physics. The work Slaby refers to is Thomson’s 1853 paper, “On Transient Electric Currents,” where he mathematically proved that the discharge from a capacitor (like a Leyden jar) through an inductor would be oscillatory. This is the fundamental principle behind generating radio-frequency waves.

[^2]: **Leyden Jar.** The earliest form of electrical capacitor, invented in the mid-18th century. It was the essential component for storing the electrical charge needed to produce the powerful sparks for these early experiments.

[^3]: **Berend Wilhelm Feddersen (1832-1918).** A German physicist who, in 1859, provided the first experimental proof of Thomson’s theory. He photographed the reflection of a spark from a rapidly rotating mirror, which visually separated the individual oscillations of the discharge, proving it was not a single event but a rapid back-and-forth surge of current.

[^4]: **James Clerk Maxwell (1831-1879).** A Scottish physicist whose equations for the electromagnetic field (published in the 1860s) unified electricity, magnetism, and light. His theory predicted the existence of electromagnetic waves that travel at the speed of light, providing the complete theoretical foundation that Hertz would later prove experimentally.

[^5]: **Heinrich Hertz (1857-1894).** A German physicist who, between 1886 and 1888, was the first to conclusively generate and detect the electromagnetic waves predicted by Maxwell. He is the “father” of experimental radio science.

[^6]: **Electrical Sympathetic Vibration** (German: *elektrisches Mitklingen*). “Mitklingen” literally means “to co-sing” or “to resonate acoustically.” Slaby uses this musical analogy to explain the concept of electrical resonance in a way that is intuitive to a general audience.

[^7]: **Electrical Resonator** (German: *elektrischen Mittöner*). Another musical analogy. “Mittöner” translates to “co-toner” or “sympathetic sounder.” This is Slaby’s creative term for the Hertzian resonator, emphasizing its function as a device that “sounds” in sympathy with the transmitter.

[^8]: **Augusto Righi (1850-1920).** An Italian physicist who was a professor at the University of Bologna. Righi made significant improvements to Hertz’s oscillator, particularly the four-sphere, oil-immersed spark gap that Slaby describes here. Righi’s lectures and demonstrations were a direct inspiration to his young student, Guglielmo Marconi.

[^9]: **Radiating Apparatus** (German: *Strahlapparat*). Slaby’s term for the spark-gap transmitter or oscillator. “Strahl” means “ray” or “beam,” so “Strahlapparat” literally translates to “ray apparatus,” emphasizing its function as the source of the invisible electric rays.

[^10]: **Co-spark** (German: *Mitsprühen*). Another of Slaby’s intuitive, non-technical terms. “Sprühen” means “to spray” or “to spark.” By adding the prefix “mit-” (with, co-), he creates a word that means “to spark in sympathy with,” perfectly describing the action of the receiving spark gap.

[^11]: **Transverse vs. Longitudinal Waves** (German: *Querwellen* vs. *Längswellen*). This is a fundamental concept in physics. In transverse waves (like light or the cord analogy), the oscillation is perpendicular to the direction of energy transfer. In longitudinal waves (like sound), the oscillation is parallel to the direction of energy transfer. Hertz’s proof that electric waves were transverse was a key piece of evidence supporting Maxwell’s theory that light is an electromagnetic phenomenon.

[^12]: **Standing Wave** (German: *stehende Schwingung*). A standing wave is a stationary wave pattern that does not appear to move through space. It is formed by the interference between two waves traveling in opposite directions—in this case, the incident wave from the tuning fork and the wave reflected from the fixed end. Understanding standing waves is crucial for understanding resonance in antennas and transmission lines.

[^13]: **Nodes** (German: *Knotenpunkte*). The points along a standing wave where there is minimum amplitude or zero motion. In Slaby’s demonstration, these are the points that do not move, are not cooled by the air, and therefore glow red from the electric current.

[^14]: **Antinodes** (German: *Bäuche*, lit. “bellies”). The points along a standing wave where the amplitude of oscillation is at its maximum. These are the points that move the most, are effectively cooled by the surrounding air, and thus remain dark in the demonstration.

[^15]: **Heinrich Rubens (1865-1922).** A prominent German physicist known for his work in infrared radiation. His experiments, which confirmed Maxwell’s predictions about the refractive index of various substances at very long wavelengths, were crucial in bridging the gap between radio waves and light, further solidifying the electromagnetic theory of light. Slaby’s mention of him here highlights the close-knit and collaborative nature of the German physics community at the time.

[^16]: **Silvanus P. Thompson (1851-1916).** A distinguished British physicist, electrical engineer, and author. He was a gifted educator and known for creating ingenious mechanical models to illustrate complex physical principles, such as the wave machine described here. His book *Elementary Lessons in Electricity & Magnetism* was a standard textbook for decades.

[^17]: **Ultra-red** (German: *ultraroten*). This is the older term for what we now call **infrared**. Slaby is correctly placing the newly discovered radio waves on the electromagnetic spectrum, far beyond the red end of visible light. This organization of the spectrum was a monumental scientific achievement of the late 19th century.

[^18]: **Röntgen Rays.** Now known as X-rays, discovered by Wilhelm Conrad Röntgen in 1895. At the time of this lecture, their exact nature was still a topic of intense debate. Placing them at the other extreme end of the spectrum, beyond ultraviolet, was a common and ultimately correct hypothesis. Slaby’s mention of them shows how he is framing his work within the most cutting-edge physics of his day.

[^19]: **Iron Nails Coherer.** This is a wonderful, large-scale demonstration of the coherer principle. Instead of microscopic filings, Slaby uses macroscopic objects (nails) to show that the phenomenon relies on the creation of conductive paths across many loose, high-resistance contact points. This would have been a very effective and easily understood visual aid for his audience.

[^20]: **Microphonic Phenomenon.** A microphonic effect is one where a mechanical vibration causes a corresponding electrical signal (the principle of a microphone). Some researchers believed the coherer worked because the sound or vibration of the incoming spark caused the filings to settle, rather than it being a direct electrical effect of the radio wave itself. Slaby correctly argues against this, noting that carbon, which is used in microphones, works poorly as a coherer.

[^21]: **Franz Reuleaux (1829-1905).** A prominent German mechanical engineer and a key figure in the development of kinematics. He was also a respected academic and linguist, known for his ability to coin precise German technical terms for new inventions, a skill Slaby clearly admired and utilized. His suggestion of “Fritter” is based on the industrial process of “sintering,” where a powder is heated to make it coalesce into a solid mass.

[^22]: **Gisbert Kapp (1852-1922).** An Austrian-born electrical engineer who spent much of his career in Britain and Germany. He was a leading expert in the design of electrical machinery and a respected figure in the international engineering community. His introduction would have been invaluable for Slaby.

[^23]: **Sir William Preece (1834-1913).** The Chief Engineer of the British General Post Office (GPO). Preece was a major proponent of new technologies and had been conducting his own wireless experiments using an inductive method. When Marconi arrived in England in 1896, Preece immediately recognized the superiority of Marconi’s Hertzian wave system and provided crucial institutional support, resources, and publicity, including the famous demonstrations Slaby was invited to witness.

[^24]: **Release Capability** (German: *Auslösungsfähigkeit*). This is Slaby’s technical term for the ability of the coherer to “decohere” or return to its high-resistance state after a signal. A coherer that was very sensitive (cohered easily) was often “sticky” and difficult to reset with the tapper, while a less sensitive one might reset more reliably. This trade-off between sensitivity and reliable operation was a central challenge in coherer design.

[^25]: **Walther Rathenau (1867-1922).** An industrialist, politician, and son of Emil Rathenau, the founder of AEG. Before his prominent political career, Walther Rathenau was an engineer and researcher. His collaboration with the physicist Heinrich Rubens on these early induction experiments on the Wannsee lake near Berlin shows the deep integration of German industry and academic science.

[^26]: **John Gavey (1842-1923).** An engineer with the British GPO who worked closely with William Preece. He succeeded Preece as Chief Engineer in 1899. Gavey was present at and supervised many of Marconi’s key early demonstrations for the Post Office.

[^27]: **Royal Sailor Station** (German: *Königliche Matrosenstation*). A unique Royal Prussian institution located in Potsdam. Housed in a romantic, mock-Norman style building, it was crewed by sailors who served the Royal family on the surrounding lakes and waterways. Its location on the Glienicke Bridge, with access to open water and royal properties like Peacock Island, made it an ideal and secure headquarters for Slaby’s extensive experiments.

[^28]: **Captain Henry Jackson (1855-1929).** A pioneer of radio in the British Royal Navy. Independently of Marconi, Jackson began experimenting with Hertzian waves in 1895 and had developed a functional ship-to-ship wireless system. When Marconi came to prominence, he collaborated with him, sharing knowledge and providing the crucial support of the Royal Navy. He later rose to become the First Sea Lord, the head of the Royal Navy.

[^29]: **Church of the Redeemer in Sacrow** (German: *Sacrower Heilandskirche*). A famous church located on a peninsula jutting into the Havel river. Its picturesque setting and prominent Italian-style bell tower (Campanile) made it an ideal, and visually striking, location for one of Slaby’s transmission sites. Its clear line of sight to the Sailor Station was a significant advantage over the obstructed path from Peacock Island.

[^30]: **(buoni se non ottimi ancora)** – An Italian phrase meaning “good, if not yet excellent.” Slaby includes the original phrase from the Italian report, indicating the signals were usable but not perfect at that range.

[^31]: **Kite-balloons (Sigsfeld system)** (German: *Drachenluftschiffe (System von Sigsfeld)*). This refers to a type of tethered observation balloon, a *Drachenballon*, developed by August von Parseval and Rudolf von Sigsfeld for the German military. Unlike spherical balloons, these were sausage-shaped and had fins, which made them much more stable in high winds, acting like a kite—hence the name. Their stability made them ideal for lifting an antenna wire to a consistent height.

[^32]: **Speaking-tube effect** (German: *Sprachrohrwirkung*). This is a brilliant analogy. A speaking tube physically guides and contains sound waves, allowing them to travel a long distance with little loss. Slaby is describing what would later be known as a **surface wave** or **Goubau line**, where an electromagnetic wave is guided along the surface of a single conductor. His observation that this “speaking tube” for radio waves only works when the wire is some distance from the ground is a key insight into how such transmission lines function.