Is Ohm's law applicable to arc lamps?

The singing or speaking arc lamp.


1 The mercury vapor lamps. The singing or speaking arc lamp. (The wireless telephony.) By Dr. techn. Ernst Kraus, assistant at the electrotechnical institute at the technical university. Lecture, held November 14th (With experiments.) With 17 illustrations in the text.


3 Beautiful assembly! Ladies and gentlemen! When the glowing red sun leaves the horizon in the evening, the moon and stars send their pale light down to the earth, then the desire awakens in us, through our own strength, to illuminate the dark night in an artificial way. How wonderfully the people succeeded in this can be seen from the lighting in this hall, in which we are enveloped in a dazzling artificial flood of light by the numerous electric light bulbs. On a very peculiar basis, we see light phenomena come about with these incandescent lamps, which are called upon to play an outstanding role in lighting technology due to their principle of origin. However, if we take a closer look at such an incandescent lamp and take energy measurements on it, we shall find that the incandescent lamp is actually a very imperfect device; because of the total energy supplied to this incandescent lamp, only 5/0, i.e. only 1/20, are converted into light, everything else is uselessly lost as heat. One has therefore always endeavored to find cold light sources, which

4 90 thus converting the electric current into light without generating heat at the same time. It has been known for a long time that there are cold sources of light in nature. When we indulge in God's free nature on sultry summer evenings at Midsummer, we see here and there a faint light phenomenon like a will-o'-the-wisp. The locust worm or firefly (PyropJiorus noctilieus) emits energy that is almost entirely converted into light; only a small part of the energy is lost as heat. But the origin of its light is shrouded in mysterious darkness, one only suspects that the light emitted comes from a slow oxidation of a substance produced by the beetle. The glow of the sea, that wonderful natural phenomenon occurring in the southern seas, may also be attributed to a similar cause. Tremendous amounts of infusoria combine their dull light into a shimmering shimmer, which at first flares up here and there like a will-o'-the-wisp and gradually enlarges into a splendid light phenomenon. The physicist also endeavored to create such cold light sources. A step in this direction was taken with the vacuum lamps, in which a gas took over the transmission of the current. You probably still know the so-called Geissler tubes from school (experiment), evacuated glass tubes or glass tubes filled with various gases, which are operated by Rhumkorff induction apparatus with high-voltage electrical currents, with various colored magical light

5 91 light up. By touching such a glass tube with your hand one can convince oneself that the temperature of the tube is only a low one, that we are actually dealing with an almost cold source of light. "The operation of these Rhumkorff induction apparatus, however, involves such great losses The fact that these Geissler tubes could not yet be used in practice.Rather, practical successes with vacuum lamps were only achieved when mercury vapor lamps were used, because they could be operated with the low voltages customarily supplied by electricity companies. The mercury vapor lamps are in their most general form vessels made of glass, which have a high air void and have two electrodes made of mercury. The first mercury vapor lamp of this type was designed by Arons. The Aron see mercury vapor lamp (Fig. 1) consists of a spherical

6 92 gene glass vessel which has two sack-like, mercury-filled attachments A i A 2. To ignite this lamp, shake it a little, so the mercury flows from one electrode Aj to the other A 2. In this way, the mercury forms a coherent thread that connects the power supply lines to the lamp for a short time. When this thread breaks off immediately, an arc is formed, part of the mercury evaporates, the vessel fills with highly conductive mercury vapors and a voltage of around 20 volts is already able to send a continuous current through the lamp. (Experiment.) On closer inspection of the lamp, we see on the negative electrode, that is, at the point where the current from the gas enters the mercury, a brightly shining point, which eagerly moves to and fro on the surface of the mercury, and one more Millimeter deep pit digs into the mercury. In order to be able to operate lamps with higher voltage, the line resistance of the lamps was increased by making the diameter of the vessel smaller and the length larger. This led to such lamps of tubular shape which are activated by tilting or tilting them. (Experiment.) The inconvenient way of starting it meant that Aron's mercury vapor lamp never got beyond the stage of the laboratory apparatus. The further development of the mercury vapor lamps was by the American Cooper-Hewitt

7 93 pending. While both electrodes of the Aron mercury vapor lamp are formed by mercury, the mercury vapor lamp from Cooper-Hewitt has only one mercury electrode inside the evacuated glass tube; the second electrode A 2 at the top is made of steel (FIG. 2). In the vicinity of the positive pole one can also see a spherical extension X, the so-called cooling chamber, which is partly located outside the light column. This makes it possible to maintain the gas pressure in the tube that is necessary to maintain the most favorable current strength. Like the two lamps discussed above, this lamp can only be used for direct current; it also has the characteristic property that it can only be ignited when the mercury

8 negative pole and the positive pole is placed on the steel electrode above. In order to ignite this lamp in a convenient way without shaking, Cooper-Hewitt uses what is known as voltage ignition. In this case, a high voltage is generated by quickly interrupting the current in a self-induction coil S connected in series with the lamp, that is, a coil with many turns wound around an iron core, e.g. B. by means of a vacuum arranged under r breaker u (Fig. 3). In the vicinity of the cathode, the Cooper-Hewitt lamp now has a metal coating m, which is connected to the positive pole of the lamp by a metal wire d. The high voltage that occurs when the switch u is opened at the ends a and & of the coil S is now balanced in FIG. 3 via the battery and the metal wire d from the metal coating m to the mercury surface. As sparks jump to the surface of the mercury, part of the mercury evaporates, the tube fills with highly conductive mercury vapors and the direct current voltage present at the terminals of the lamp forms an arc. In order to get to know the mode of operation of the Cooper-Hewitt lamp and the mercury vapor lamps a little better, I would like to allow myself to adhere to the explanations that Prof. Dr. Johann

9 95 Sahulkain gave his recently published work Explanation of Gravitation, Molecular Forces, Heat, Light, Magnetic and Electrical Phenomena from a Common Cause. "You will certainly have heard of the fact that light comes from a wave-like movement of the world ether should exist, that fine, imponderable body that fills the whole universe and penetrates all bodies. Prof. Dr. Sahulka now imagines that the electric current is an etheric flow that behaves exactly like the flow of an ordinary gas. If we now think of the two poles of the Cooper-Hewitt lamp with a direct current voltage applied, e.g. the positive pole at the top and the negative pole below, we must assume, in the spirit of the ether theory, that the pole at the positive pole Ether present has a greater tension than at the negative electrode. However, an ether flow through the gaseous medium filled with mercury vapor is n ot possible because the outer ether particles, which are buzzing in all directions of space, prevent the creation of a current. However, when the electrodes evaporate and the relatively large vapor particles move perpendicular to the surface of the electrodes, these vapor particles form a protective wall against the outer ether particles. Since the ether emerges easily at the positive electrode due to its overvoltage, evaporation is only necessary at the negative electrode. So in some way, e.g. B.

10 96 by skipping sparks; the negative electrode, the so-called cathode, evaporates, then a continuous flow of ether can take place from the positive to the negative pole, that is, an arc can be formed. To maintain the flow in the direction from the steel electrode to the mercury electrode, a much lower voltage is required than for the reverse direction of the current, because the mercury evaporates easily, but the steel electrode only with great difficulty. We shall come back to this property of the Cooper-Hewitt lamp of only allowing the current to pass in one direction from the steel to the mercury in the case of the mercury vapor rectifiers to be discussed later. A further improvement of the mercury vapor lamps was given by Bastian and Salisbury in London. The turning on of this lamp is done by tilting it like the lamp by Ar on, but the tilting is not done by hand, but automatically by means of an electromagnet. If the lamp is not in operation, the meandering tube H lies horizontally and the mercury connects both supply poles a and b (FIG. 4). If the circuit is closed, an iron core is drawn into the coil S and the tube B is brought into an inclined position by means of a double-armed lever. The mercury now flows to the lower part of the pipe. At the moment when the mercury thread breaks, an arc is formed and the mercury vapor is able to push

11 97 Fig. 4. The vapor tension of the mercury into the tube attachment A at the end. (Experiment.) When we light such a mercury vapor lamp and extinguish the incandescent lamps used to illuminate the hall, we see a strange phenomenon. Colored items appear all over the club. Know 47 vol. 7

12 98 different color. In particular, the color of all bodies that appear reddish in daylight is changed. The faces and hands of the people appear bluish green and almost pale as a corpse. A red sheet of paper looks chocolate brown, these red roses appear almost black, a bouquet of fir branches, on the other hand, shines as freshly as in the forest after refreshing rain. We involuntarily have to ask ourselves what is the reason for this strange light phenomenon. To answer this question, we want to analyze the light from a mercury vapor lamp and break it down into its individual parts. You all know that the light that appears white to us and that we receive from the sun is actually not a uniform light, but comes about through the mixture of differently colored light. In order to separate the different types of light of sunlight from one another, we let the sunlight fall through a fine gap onto a glass prism, which deflects the different types of light to different degrees. The red light is deflected the least, the violet light the most. On a white screen we get a wonderful band of colors, the so-called light spectrum, similar to the rainbow, in which, however, instead of the prism, the raindrops cause the sun's rays to be broken down into the individual types of light. One color gradually changes into the other, we get what is known as a continuous spectrum. However, when we develop the spectrum of the mercury vapor light, we look up

13 99 on the screen there is no continuous band of color, but only an intense yellow, green and, somewhat further away, a purple line (Fig. 5). (Experiment.) The red color, however, is entirely absent; therefore, when illuminated with mercury vapor, all red bodies appear black. The face and hands take on an unaesthetic color, which prevented the mercury vapor lamp from being used any further. To remedy this inconvenience, keflectors have been used which fluoresce reddish under the influence of the mercury vapor light, e.g. B. silk soaked with rhodamine. Furthermore, the mercury has been given various additives, e.g. B. ff, 1 r «Strontium, lithium and potassium preparations, which mainly emit red rays. In pj 5, mercury vapor lamps have also been combined with incandescent lamps, the red rays of which complement the bluish-green light of the mercury vapor almost to white. Here you see such a combination lamp in which the carbon filament incandescent lamps of the mercury vapor lamp are partly connected in front of and partly in parallel (Fig. 6). The mercury vapor lamp is activated by simply tilting it. (Experiment.) Recently, zinc has been added to mercury, so that zinc amalgam is used as an electrode. The zinc line, which is intensely red in the spectrum, complements the pale light of the mercury vapor lamp, making it almost white. However, the light from the mercury vapor lamp not only stimulates our 7 *

14 100 optic nerves. When we let the light fall on our hand, it brings about sensations of heat; on a photographic plate the silver salts are broken down by the same light. Accordingly, one speaks of light, heat and chemical rays. As in Fig.

15 101 to convert only those ether waves into light sensations whose number of vibrations is between 500 and 700 trillion per 1 second. Ether waves with a smaller number of vibrations are only felt as heat, those with a higher number of vibrations produce only chemical effects. The mercury vapor light now contains a large amount of chemical rays called ultraviolet rays. These are rays in which the ether particles have such a large number of vibrations that our eyes can no longer perceive them as light. However, the ultraviolet rays have a great chemical effectiveness, which is why the mercury vapor lamps are used for copying purposes, portraits and light healing purposes. The ultraviolet rays can also be detected in the light spectrum. If you hold a screen coated with barium platinum cyanur above the violet line of the spectrum, we see two lines fi 2 and (j, s light up The barium platinum cyanur screen converts the invisible ultraviolet light into physiologically visible light. The previously discussed mercury vapor lamps made of ordinary glass give only very small amounts of ultraviolet light, since ordinary glass absorbs almost all of the ultraviolet radiation. In order to obtain larger amounts of ultraviolet light, has the glass

16 102 works Schott in Jena Lamps made of uviol glass, which is barium phosphate chrome glass, which lets most of the ultraviolet light through. This UV lamp (Fig. 7) is ignited by simply tilting it not too quickly, with mercury flowing in a thin beam from the positive to the negative electrode, thus establishing contact. (Experiment.) Even more intense ultraviolet light is emitted, as Mr. Hofrat Eder, Prof. of the local technical university, has shown, from the quartz glass lamp from out in Hanau (Fig. 8). Quartz glass is obtained by adding rock crystal

17 103 Fig. 8. a temperature of 2000 Celsius in the oxyhydrogen blower melts. The quartz glass obtained in this way is extremely tough, withstands very high temperatures and allows ultraviolet rays to pass through almost entirely. This quartz glass lamp is ignited by means of an inductor which is placed on the one hand on the negative pole and on the other hand on the metallic cooling device UT attached near the negative pole. The ultraviolet rays from the quartz glass lamp cause painful conjunctivitis in the eyes. It is therefore necessary to protect the eyes with glasses made of ordinary glass which absorbs the ultraviolet rays. Furthermore, the air is ozonated by the ultraviolet rays, so that you immediately feel the odor of ozone when you switch on such a lamp. The ultraviolet rays are very damaging to smaller living things. Thousands of dead insects were found the following morning under a quartz glass lamp that was kept in operation during the night with the window open.

18 104 The main advantage of mercury vapor lamps is their low power consumption or watt consumption.With normal designs, there are approximately 0 * 6 watts per 1 normal candle strength, while-. rend you have to use 3 to 3 * 5 watts per normal candle with the usual carbon filament incandescent lamps. With the mercury vapor lamps there is only * / 5 of the power consumption of the carbon filament incandescent lamps. The reason for this favorable economy is that the mercury vapor arc converts about 40/0 of the total energy used into light, while with arc lamps only 10/0, with incandescent lamps only 5/0 and with Auerbrenner only 1.5/0 is converted into light. The remaining part of the supplied energy is not emitted as light, but in the form of heat rays and chemical rays. The mercury vapor light also has the property that it is very pleasant for the eyes, is much less tired than any other artificial light source and in this property comes closest to daylight of all artificial lighting sources. The cause is probably mainly in the diffuse generation. While z. For example, in an arc lamp the entire amount of light seems to come from almost one point, in the case of the mercury vapor lamp the amount of light is distributed over the entire tube filled with luminous mercury vapor. The mercury vapor lamp allows an interesting application due to its property of converting alternating current into rectified current, i.e. as direct

19 105 judge or converter to act. In the case of the Cooper-Hewitt mercury vapor lamp, it was emphasized that this lamp can only be put into operation when the positive pole is connected to the steel electrode; the negative pole is placed on the mercury electrode below, i.e. the easily atomized mercury is the cathode (Fig. 2). This mercury vapor lamp thus has the property of only allowing the current to pass in one direction from the steel to the mercury; so the lamp acts as it were like a valve, i. H. it only allows the current to pass in one direction from steel to mercury. Therefore, this lamp cannot easily be used in this arrangement for AC operation. Despite the valve action, the Cooper-Hewitt mercury vapor lamp can still be used for alternating current. One only has to arrange the circuit in such a way that both alternating current waves, the current wave flowing in one direction and the current wave flowing in the opposite direction, are passed through the lamp in the same direction, but the lamp itself takes on the rectification by virtue of its valve action. If the lamp is then designed in such a way that it consumes even a low voltage, but is able to carry relatively strong currents, one arrives at rectifiers or converters, devices that convert the current changing in its direction into rectified current. These mercury vapor rectifiers specified by Cooper-Hewitt consist of an evacuated glass vessel (Fig. 9),

20 106 which has two steel electrodes A] A 2 and a mercury electrode K} in the lower part. If the two steel electrodes A] Ao are connected to an alternating current source, e.g. B. to a transformer, you can take rectified current between the center of the transformer winding and the mercury electrode Kj; Tc is an auxiliary electrode that is only used to ignite the converter. The balloon B serves as a cooling chamber, the purpose of which was already discussed when discussing the Cooper-Hewitt lamp. The one available here

21 107 Mercury vapor rectifier converts 440 volt alternating current, which changes direction loom times in one second (alternating current of 50 periods), into rectified current of 220 volts, the energy of which is converted into light and heat in a bulb resistor. (Experiment.) The quality ratio of the mercury vapor rectifier is very favorable, depending on the size / 0. In the converter itself, only 5 or 2/0 are lost. In America these converters are already widely used in places where only alternating current is available. If you wanted z. B. charging the batteries of an electric vehicle, then you could not use alternating current. A mercury vapor rectifier can be used to convert the alternating current into rectified current and then charge the batteries with this *. The mercury vapor lamp has met with great interest among experts due to its low wattage consumption and has been used sufficiently as an artificial source of lighting for a number of years. They are used because of their calm, eye-less tiring light in drawing rooms, precision mechanic workshops, because of their unusual light color for stage and effect lighting, because of their high ultraviolet radiation for photochemical purposes and in dyeing shops to test the colors for lightfastness. In America, mercury-vapor lamps with automatic ignition are being used with success in street lighting

22 108 applied. That the mercury vapor lamp still clings to various imperfections, such as the pale light color, is well understandable in the short time since the effects of the mercury vapor light have been known. However, the improvement of the mercury vapor lamps is constantly being worked on, automatic ignitions have been created, numerous patents pursue the purpose of complementing the bluish green color of the mercury vapor light to white, and over time the public will probably become familiar with the characteristics of the lamp, its advantages and Familiarize weaknesses. With this we want to conclude the discussion of the mercury vapor lamps and turn to the second part of this lecture, the singing or speaking arc lamp. Ladies and gentlemen! You certainly know all those hissing and grumbling spirits that sometimes animate a direct current arc lamp, and you may remember Having dined now and then in a restaurant in which an arc lamp caused your annoyance with its hissing noise. This AC arc lamp that I want to light also hums with a pitch that depends on the speed with which the current changes its direction . (Experiment.) But the thinking spirit of man has understood how to tame these hissing and grumbling spirits and to force them into the service of mankind,

23 109 to transform the vices of this arc into virtues. Instead of allowing inarticulate sounds to be heard, as is otherwise the case, the arc has learned to speak an educated language; he declaims, sings, speaks, whistles, plays every musical instrument, in short, he behaves as befits a well-bred member of our society. The first person who knew how to tame these hissing and grumbling ghosts was Prof. Simon in Erlangen. Prof. Simon once experimented with an arc lamp, which every time a Rhumkorffian inductor was started in a neighboring room, a peculiar crackling noise could be heard. Prof. Simon investigated the matter and found that line a & of inductor B lay parallel to arc lamp line AB for a short distance (Fig. 10). The cause was soon cleared up. A current of rapidly changing intensity flows in the line a b of the inductor B, depending on the speed with which the circuit breaker u operates. As you know, a current i is induced in the adjacent direct current line A B, which changes its direction just as often

24 110 changes its intensity like the current in the line a b. The fact that a direct current J is already flowing in line A B does not hinder the induction effect in any way. A direct current of constant strength J and the induced current i of alternating direction and strength, a so-called alternating current, thus flows in the electric circuit of the arc lamp. In spite of their different characters, the two streams J and i go well with one another; the induced current i}, which is the weaker one, is superimposed by the direct current J and so both flow together through the arc lamp L. What is happening here now? The current i, which changes in its direction, flows once in the direction of the current J, after a fraction of a second in the opposite direction, then again in the direction of the current J and so on. The direct current J, which always runs in the direction from the positive to the negative pole of the Current source flows, so it is alternately amplified and weakened by the alternating current i. In the first case, the flame arc gases of the arc L get a higher temperature and therefore expand. However, if a weaker current flows through the arc, the temperature drops and the volume of the flame arc gases decreases accordingly. With the change in current, there are therefore rhythmic changes in the volume of the flame arc gases. The arc behaves like a spherical membrane that expands and contracts again in rapid succession. There are therefore air vibes on all sides.

25 illusions emanate which, given sufficient strength and number of vibrations, are perceived by our ears as tones or as noise. Despite the low strength of the induced alternating current i, the acoustic effect is significant. This prompted Prof. Simon to use a microphone to make the arc speak. A microphone (Fig. 11) consists in principle of a carbon plate K, which carries a piece of coal Jci on the rear side; kg is a second piece of coal that is loosely attached to kj. The property of carbon is that the resistance to the electric current, which is always present at the touch of two conductors, is considerably reduced when the pressure is increased and increases again when the pressure is released. With a reduced resistance the current strength increases and with a higher resistance it decreases. If we now speak against V Fig. 11. Carbon plate K, this vibrates with a number of vibrations which is equal to the number of vibrations of the spoken tone. The transition resistance at the point of contact a is now increased and decreased as often as the carbon plate ^ makes vibrations. If the microphone is connected to the circuit of a battery, a current flows through the microphone, which changes its intensity as often as the number of vibrations of the tone spoken into the microphone. To achieve a greater induction effect, used

26 112 one has a transformer T, consisting of an iron core over which two windings are given (Fig. 12). The microphone current m of rapidly changing strength just discussed flows through the left winding Sj. An alternating current i is now induced by induction in the same way as previously discussed in the other winding # 2 of the transformer T, which is exactly the same. its direction often changes as the microphone current changes its strength. An alternating current i is thus superimposed over the I Fig. 12. Direct current J of the arc lamp L, which alternately amplifies or weakens the direct current J. The temperature of the flame arc gases and thus the volume suffer analogous fluctuations, which are propagated as sound waves in the surrounding air masses. These thus have a number of vibrations which is equal to the number of vibrations of the induced alternating current i, i.e. the number of vibrations of the microphone diaphragm K, which is identical to the

27 113 Number of vibrations of the tone spoken into the microphone. I now want to demonstrate the experiment. The arc L must be made as large as possible so that a strong sound effect is achieved. It is also advisable to use coals impregnated with various salts, so-called M Fig. 13. Effect coals, instead of the usual coals, because you can use them to form a longer arc. To keep the dazzling light of the arc lamp from your eyes, I place a pane of red glass in front of the arc lamp. The microphone M (Fig. 13), which is in a distant room of the institute, is airtight through a rubber hose K with a gramophone Gr Verein nat. Keontn. 47 vol. 8

28 114, which was kindly loaned to me by the Odeon company in Kärtnerstrasse. If I now let the gramophone play, the sound waves are transmitted to the microphone plate of the electric arc and from the arc lamp the piece of music produced by the gramophone will echo out with unchanged timbre. The sound effect is so significant that even in the top rows of the bench the price song from Meistersinger "sung by the court opera singer Leo Slezak" is not difficult to recognize. If you switch off the microphone current, the sound effect disappears immediately. (Experiment.) In order to find practical applications of the singing and speaking arc lamp, to force the tamed grumbling spirits into the service of humanity, we only need to let our imagination run wild. Perhaps one day the preacher in the church will be replaced by a speaking arc lamp, which then speaks as the church light in the truest sense of the word to the devout congregation. It is also not impossible that the professors, comfortably seated in their armchairs, will speak against a microphone in their private room, while the arc lamps in the lecture halls let their light sound, louder or quieter, depending on the strength of the current, the high one Ministry of Education permitted.

29 115 The speaking arc has an interesting application in light telephony or telephony without wire. It has already been discussed above that the sound effect of the arc is caused by the temperature changes of the flame arc gases of the arc lamp L. From the laws of physics it follows that the temperature changes of the arc cause exactly corresponding fluctuations in brightness, which, however, because of their rapid succession, are no longer perceived by our eyes. If we now imagine a speaking arc lamp L in the transmitting station (Fig. 14), we can direct the speaking light of this arc lamp by means of a spotlight or a parabolic mirror Pj as a parallel light beam in a certain direction. In the receiving station z. B. At the upper end of the hall we collect the light through a parabolic mirror Pg, in the focus of which we put a body that reacts to the rapid fluctuations of the speaking light. 8th*

30 116 The chemical element selenium is such a body. This element, selenium, which belongs to the sulfur group, has the strange and hitherto unexplained property of changing the electrical conduction resistance through exposure to light. So z. For example, under favorable conditions, a selenium cell conducts electricity ten times better in daylight than in the dark. In order to show the sensitivity of selenium to light, I switched a mirror galvanometer into the circuit of the selenium cell, the light image of which will be visible on the opposite scale. If I light a match, the exposure will immediately reduce the resistance of the selenium and thus increase the current strength, the mirror galvanometer will show a larger deflection angle, the light image will move to the right. When the match is extinguished, the light gradually goes back to its resting position. (Experiment.) So we put a selenium cell Z in the focal point of the parabolic mirror Pg (Fig. 14) and switch a telephone T into the circuit of the selenium cell. Under the influence of the speaking light, the selenium cell Z will change its resistance as often as the speaking light changes its intensity. With a constant terminal voltage of the battery B, the current n flowing through the telephone T will change its intensity just as often, i. H. the telephone generates sound waves whose number of vibrations is equal to the number of vibrations of speaking light. In the telephone T of the receiving station we hear the conversation that goes into the microphone M of the

31 117 transmitting station was spoken into. As a transmitting station I use a spotlight (Fig. 15), which mainly consists of an arc lamp and the parabolic mirror. The microphone M belonging to the transmitting station (Fig. 14) and the other auxiliary devices are exactly the same as in the case of the singing arc lamp discussed above. I just switch on the headlamp's arc lamp instead of the singing arc lamp. In the receiving station (Fig. 14) I gave a Fig. 15. Vessel, a so-called cuvette K, filled with water from the selenium cell Z. It is namely in the focal point of the parabolic mirror Pg because of the low in

The distance available to this room developed such a heat that the selenium cell would burn. However, the water-filled vessel it absorbs the heat rays and thus protects the selenium cell from melting. With regard to the headlight, I should like to remark that I tried to lock it up in a soundproof manner; The spotlight's arc lamp sings along so loudly that you can hear the singing or the conversation clearly here in the lecture hall. I now use the gramophone to play the price song from "Meistersinger" sung by Slezak and transmit it wirelessly to the receiving station through the microphone and spotlight in the manner discussed above. I would now like to ask one of the gentlemen to listen to the telephone above. that we are really dealing with a wireless transmission, I would like to ask you to block the light falling on the selenium cell with your hand. Immediately the playback of the telephone goes silent. (Experiment.) The physicist Rhumer, who is responsible for the training of the Light telephony has achieved great merits, it has already been possible to conduct wireless calls on 15 hm with great clarity.One might think that the experiments are only possible in the dark. However, the experiments succeed in sunshine as well as at night; you just have to block out the sun's rays with a screen. Even in rain and fog, the attempts were accompanied by success. Practical use

33 119 light telephony is likely to be found primarily in the navy. It will probably not replace the spark telegraphy introduced there, but it will be able to replace it here and there. For communication between the warships lying in the harbor or when maneuvering them, the radio telegraphy is not well applicable, because the signals interfere and a good coordination is not possible. In all these cases, light telephony takes its place. No conversation or command can be intercepted by unauthorized persons, only someone can hear something whose apparatus is hit by the bill of the transmitting apparatus. So far we have seen how the electric arc was made to speak or to sound using the microphone. However, the English physicist Dudell has succeeded in making the electric arc also sound B without a microphone, i.e. without an external sound source. If you switch Fig. IG. to an arc lamp (Fig. 16) in points a and d a capacitor G, z. B. a larger number of Leydner bottles, and a wire roll or a self-induction coil L, so be

34 120 the arc 2 starts to sound loud with a pure tone. The connection of a capacitor C and a self-induction coil L creates an electrical oscillation, i.e. H. a current i is formed in the circuit ah da, which changes direction in rapid succession many thousands of times in one second. If this alternating current * flows in the direction of the current J, it amplifies it. On the other hand, if the current flows in the opposite direction, it weakens it. In the first case we have a strong current and a correspondingly high temperature of the arc, in the second case, however, a low temperature. The temperature and thus the volume of the flame arc gases is therefore subject to rhythmic changes. The surrounding air masses are set in vibrations which, if strong enough, are perceived as a sound by our ears. The number of oscillations of the alternating current i and thus the number of oscillations of the tone depends on the self-induction of the wire roll L and the capacitance of the capacitor C. 1) If you change the self-induction or the capacitance, the pitch also changes. One can now use a fixed self-induction L, e.g. B. the wire roll present here, and assume a number of l) The self-induction of the wire roll L is increased by placing the individual turns of the wire roll close together. The capacity or the capacity of a capacitor is increased by increasing the number of Leydner bottles connected in parallel or by increasing the occupancy of the Leidner bottles

35 121 Arrange capacitors C in such a way that the number of oscillations produced when a capacitor is switched on corresponds to the tone of an octave. If you now connect the capacitors to a keyboard, melodies can be played on the arc and an arc piano can be created in this way. I now want to turn on the arc lamp. At a certain arc length and current J, which is set with the resistor W (Fig. 16), you will hear a relatively pure sound, which, however, changes its height immediately if you change the capacitance of the capacitor G by means of a plug. By pulling the wire roll L apart, the self-induction of the same is reduced. Since the change in self-induction occurs continuously, the pitch also changes continuously. With this arrangement given by Dudell, a maximum current change of current i is achieved in one second. However, it was not possible to obtain currents of greater intensity with a larger number of alternations or oscillations of the current i. Engineer Poulson recently made the discovery that an electric arc burning in a hydrogen atmosphere significantly increases the intensity of the alternating currents *. An even more effective device is obtained if the arc burning in the hydrogen is arranged between the poles Np, Sp of an electromagnet (FIG. 17). The favorable effect of hydrogen on the electric light

36 122 arcs is related to the high efficiency for heat and the resulting high cooling capacity. The first experimental results of this discovery were published by Ingenieui 'Poulson last week. I have now tried to show the behavior of the arc in hydrogen gas with the arrangement presented here. You can see here a glass balloon Gr (Fig. 17), in which the carbon pins kj Tc 2 -T Fig. 17 are inserted airtight. Instead of hydrogen gas, you can also use luminous gas, which is supplied to the pipe socket a and ignited at the opening ß. Instead of the wire roll that was switched on earlier, I am using several turns of thick wire D, which are wound on a cylindrical glass vessel. Inside the vessel, which is completely filled with oil, there is a coil d, which consists of many turns of thin wire. The whole apparatus T is called

37 123 as a Tesla transformer. The capacitor C consists of a large number of Leydner bottles that are built into a sheet metal box. After the arc has been formed and with a suitable current J in the abdsla circuit, an alternating current i is obtained which has a greater intensity than the direct current J and a number of oscillations of up to several hundred thousand, even several million per second. In this way we arrive at currents such as those used in wireless telegraphy to generate electrical waves. You can see from the following experiment that we are really dealing with an alternating current with a high number of oscillations. The voltage at the ends of the thick-wire coil D is significantly increased by the coil d located inside the glass cylinder. I now let this high-tension electrical current of several thousand volts pass through my body between the terminals e f. (Experiment.) You see that the electric current enters my body through a pair of pliers and leaves the body again through a piece of metal held in the other hand. From the length and strength of the arc between the metal objects held in the hand and the terminals ef of the coil d, one can conclude that the voltage is several thousand volts and the current is a few tenths of an ampere, so it is large enough to kill a person . The reason why this current is completely safe is that the current because of its high oscillation

38 124 movement number does not go through the body, but over the surface of the body. With his discovery, engineer Poulson pursues the goal of achieving a great improvement in wireless telegraphy. With this arrangement, one is able to generate continuous electrical waves (undamped electrical), while with the arrangements used so far the intensity of the electrical waves sank to zero after just a few oscillations, i.e. the individual wave trains were separated by long pauses. Wireless telephony by means of electric waves should also be realized by the arrangement given by Poulson. Finally, I would like to thank His Magnificence Senior Building Officer Prof. Hoc hen egg for providing the teaching materials of this institute, as well as Prof. Dr. Reithofer, the engineers Sartori and Libesny and finally the Austrian Siemens-Schuckertwerke for the kind provision of test materials to express my thanks.