US1980534A - Gas arc lamp - Google Patents

Description

Nov. 13, 1934. K. F. J. KIRSTEN 1,980,534

GAS ARC LAMP Filed March 4, 1932 2 Sheets-Sheet 1 f TJ y E f: 5, C131 T "tiff 3:31:35? 7 'INVENTOR w FJ/fiwm/Y ATTORNEY Nov. 13, 19 4- K. F. J. KIRSTEN 1,930,534

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ATTORNEY Patented Nov. 13, 1934 UNITED STATES PATENT OFFICE GAS ARC LAMP Washington Application March 4, 1932, Serial No. 596,753.

1 Claim.

This invention relates to the art of electrical illumination and it has reference particularly to gas are lamps of low voltage suitable for purposes of general illumination as distinguished from what are commonly known as corona lamps" or glow lamps.

Before going into a detailed explanation of the present invention, it is thought advisable, for purposes of better explanation, and clearer understanding, to recite briefly the characteristics of corona lamps, glow lamps and are lamps; also to give a brief discussion of rare gas arc lamps as disclosed in the prior art.

It is a well known fact that any electrical circuit can give rise to the phenomenon known as corona provided that certain conditions are satisfied. Corona is descriptive of the leakage of electrical energy from the positive side of the circuit to the negative side, or vice versa, through an insulating medium when the potential gradient of the medium is sufliciently high to ionize said medium.

The potential gradient is proportional to the voltage between the parts of the circuit in question; the diameter of the electrical conductor, or the surface per unit length of the conductor; and to the dielectric characteristic of the medium. The dielectric characteristics include the density of the medium. A transmission line may not show corona near sea-level, but sometimes shows considerable corona when passing over a mountain range. Therefore, the lesser the density of the medium, the more readily corona appears. The surface condition of the conductor also has a bearing uponthe readiness of formation of corona. A smooth conductor will give corona less readily than one with a rough surface or with points protruding. It may be stated, however, that corona does not appear unless the voltage of the circuit is sufiiciently high to start ionization of the medium surrounding the conductor. This voltage is called critical corona voltage. The critical corona voltage for a three-fourths inch diameter transmission line is approximately one hundred seventy five thousand volts.

When corona is formed in gaseous media, a glow of comparatively low intensity can be seen surrounding the conductor. an electrical energy change to heat energy and is accompanied by a rise in temperature of the medium.

Rare gases, such as helium, neon, argon and xenon have a greater conductivity than air and hence they show corona at far lower voltage, especially when their density is considerably lower This glow represents,

relative to normal atmospheric pressure. Consequently, these gases lend themselves very readily to the manufacture of corona lamps, which consist mainly of a glass bulb containing a rare gas under very low pressure. This gas surrounds suitably spaced electrodes upon which a difference of electrical potential is impressed. Such lamps show adecided corona at very low voltages (one' hundred twenty volts and less) but this type of glow lamp has a very small luminous intensity and it cannot be used for practical illumination.-

As stated above, the amount of energy discharged from the electrical conductor, known as a corona discharge, is proportional to the voltage impressed. Consequently, the circuit may be said to have a positive resistance characteristic, by which is meant that the greater the voltage the greater is the current flow.

The corona phenomenon above described has a very important function in the invention herewith submitted, as will appear later.

With respect to glow lamps, it is well known that a transparent container charged with a rare gas and having two electrodes which are subjected to an electrical potential shows a glow from terminal to terminal if the impressed potential upon the terminals or electrodes is suificiently high. Such tubes are well known today in the art of the electrical display-sign industry. The gases most commonly used in the art of luminous tube advertising are neon, helium, argon and mercury vapor. Each of these gases glows in its characteristic color when under electrical influence.

These glow tubes which have an internal diameter of approximately fifteen millimeters or less operate under anelectrical potential of approximately one thousand volts per meter of length between electrodes. The current flow in these tubes is approximately thirty milliamperes. It is common practice in the manufacturing industry of display signs to connect several tubes in series so that the whole circuit of tubes will operate on a potential of about sixteen thousand volts. This comparatively high voltage is obtained by the use of a transformer, the primary of which is arranged to operate from a one hundred twenty volt circuit. An important feature of these tubes is the fact that they possess a negative resistance characteristic. By that is meant that, after the tubes are once functioning, the current therethrough has a tendency to rise rapidly to a large magnitude on the same voltage. In order to avoidthis rapid growth of current in-these tubes the transformers are provided with a comparatively large leakage reactance so that, automatically, as

the current begins to flow through the transformer, the voltage of its terminals decreases to values which limit the current flow inthe tube.

As a consequence of this relatively high internal leakage reactance of the transformer, the power factor of the circuit whichcarries these luminous tubes is in the neighborhood of forty per cent. Since a low power factor is undesirable from the standpoint of eflicient transmission of electrical energy, it will be necessary to use condensers connected across the high potential side of the tube circuit in order to correct for this low power factor when the load taken by luminous signs becomes large enough to warrant such demands forelectrical operating characteristics are undesirable from the standpoint of a low power factor, and their requirements for a very high potential for operation will limit them to installation outside of buildings in places which cannot be touched by human hands, or be safeguarded by other means.

The invention herewith submitted is related to the glow tube inasmuch as it contains all the elements of a glow tube and can be operated as such if its energizing current is properly limited. However, it contains additional features which produce glow at low voltage and change the glow of an arc of comparatively large current values.

If the electrodes in a closed glow tube are 'so shaped as to stimulate, either by material makeup or by special electrical circuit connection, the emission of electrons, the glow between electrodes changes to a distinct arc of extraordinary brilllancy. At the same time the voltage required to maintain this arc is far lower than the voltage required for the maintenance of the glow, so that an arc tube will operate at a voltage of forty to sixty volts instead of four hundred to six hundred volts as required for the glow tube. The current consumption at the same time rises from thirty milliamperes to approximately six, seven and up to ten amperes. This brilliant arc at once compares very favorably with the luminous intensity of the tungsten filament lamp from the standpoint of energy consumption and light emitted.

The are tube, however, again has negative resistance characteristics, that is, the current has a tendency to grow as the voltage remains constant and in order to prevent a flash-over from terminal to terminal, it is necessary to introduce a resistance or reactance element which automatically has a voltage drop comparable to the decrease in voltage required to maintain the arc, so that the terminal potential on which the tube is operating rises slightly as the current consumption of the tube increases.

The rare-gas arc lamps of the prior art differ from the corona lamps and glow lamps inasmuch as they contain a means of stimulating electronic emission from the electrode; a means of starting the arc and a means of stabilizing the arc after it has been established.

The means of stimulating electronic emission consists either of a glowing filament or of a material such as an oxide of a metal. The glowing filament has long' been known in the art of radio tubes for its characteristic of emitting a stream of electrons. It has also been known that some metallic oxides, such as oxides-of potassium, borium, and strontium also readily emit electrons when under electrical stimulation, or when sufliciently heated. Therefore, the electrodes of some are tubes of the prior art are made of this metallic oxide.

All low-voltage are tubes of the prior art require a high voltage are starting device. Although conditions maybe satisfied to maintain a low-voltage arc, this arc does not kindle on that same low voltage on which the tube operates. The initial ionization. of the gas between electrodes requires a high voltage such as is necessary for the glow tubes. The same eifect, namely the stimulation of ionization, may be accomplished by a high-frequency, high-potential electrical discharge in the neighborhood of the tube. Consequently, the low-voltage tubes of the prior art are equipped with a high voltage kicking coil which is connected to the tube circuit only during the starting period of the arc; or they are exposed to the effect of a tesla coil for the arcstarting period. The above starting means may not be the only means of starting an arc in a glow tube, but any sudden high potential impulse,

such as the collapse of a magnetic field or of a dielectric field may also be used.

The stabilization of the arc is necessary betube, so that the total voltage of the tube circuit includes the voltage drop of the resistance, the

circuit as a whole may be made to have a positive resistance characteristic. Similarly, a reactance drop may be produced by a reactance which provides automatically a voltage drop in excess of in the negative drop of the arc, so that the ohmic drop of the whole tube circuit increases with the growth of the current in the circuit.

The above three requirements of the low voltage arc tubes of the prior art introduces special and costly materials in the make-up of the tube electrodes, necessitating the-use of special circuits for cathode heating and of other auxiliary eqgipment for the proper functioning of the arc tu ev 1 The present invention belongs to the class of low-voltage arc lamps and the object of the invention has been to provide a low voltage gas are lamp suitable for purposes of general or special illumination, operating on either direct or alternating current, and being'free from all external means or equipment for starting the arc, that is, a lamp which within itself, or by means of a very simple and permanent external circuit connection, contains all of'the necessary elements for kindling and maintaining a steady are from a low but constant potential or direct current source of electrical energy. a

It is also an object of this invention to produce a lamp in accordance with the above statement,

the life and efliciency of which, from an illuminating standpoint, are greater than the life and efiiciency of all arc lamps of the prior art, and

which can be produced economically in commerial quantities.

Other objects of the invention reside in the construction of the electrodes and in the provision and use of a special arc kindling means.

In accomplishing these and other objects of the invention I have provided improved details of construction, the preferred forms of which are illustrated in the accompanying drawings, wherein- Fig. l is a graphic illustration in which curves have been plotted to illustrate current and voltage relationship of a rare gas arc lamp.

Fig. 2 is a side view of a preferred form of gas are lamp embodying the present invention.

Fig. 3 is the top view of a modified form of the lamp of Fig. 2.

Fig. 4 is an enlarged sectional view of one of the terminal portions of the lamp of Fig. land of the electrode contained therein.

Fig. 5 is a circuit diagram showing the manner in which electrical energy is taken from a standard electrical low-potential main and conducted to the different parts of the lamp.

Referring more in detail to the drawings- First, with reference to Fig. 1, this plot illustrates the current and voltage relation of a lamp filled with a rare gas, such as neon. When a difference of potential exists, between the two electrodes of the lamp placed sumciently close together and this difference of potential is made to rise from zero to larger values as read along the abscissa OX, a very small current is observed to flow. This current increases almost in proportion to the increase in voltage. A faint glow'is observed to envelope the electrodes which is a visual indication of corona. As the voltage is increased to the critical value (abscissa of point 1) the gas between the electrodes becomes luminous and the current in the lamp increases while the voltage across the lamp terminals decreases. The lamp has changed its corona performance as depicted by curve A to glow performance shown by curve B. The glow of the lamp persists although its voltage may decrease to the value of abscissa of point 2. At the same time, the current in the lamp assumes considerable proportions as compared to the corona current. If this current is large enough to heat the electrode sufficiently for electronic emission, the glow changes to an are. If this emission does not occur, the lamp will cease to function. When the arc strikes, the current changes instantly to a much larger value (ordinate of point 4) and the performance of the lamp is now described by curve C.

Not only does the electrical performance change very strikingly when the arc begins to function, but the luminous brilliancy also changes from a weak glow to a light of remarkable intensity. The lumens per watt emitted compare favorably with the tungsten filament lamp with the added advantage of a greatly decreased intrinsic brilliancy. That is, in the tungsten lamp, all the light flux emanates from a very small space so that direct visualization of it is painful and harmful to the human eye, whereas the light flux from the gaseous arc lamp emanates from all the space within the lamp. Consequently, a tungsten lamp necessitates the use of a dispersing shade which absorbs approximately 15 per cent of the total emitted light flux, while all of the light flux from the arc lamp is available for direct illumination without disagreeable or harmful visual sensations.

The operation of the lamp of this invention is similar to that of the arc lamps above described when once the arc is started, but it differs from all arc lamps of the prior art inasmuch asthe construction of its electrodes is fundamentally different. It is the particular arrangement and construction of the electrodes that makes it possible to kindle and maintain an are at a voltage only slightly in excess of the normal arc voltage.

In Fig. 2 is illustrated one form of low voltage are lamp embodied by the present invention. This lamp comprises an airtight, tubular, transparent vessel 1, provided at its opposite ends with terminal electrodes which are designated in their entirety, respectively, by reference numerals 2 and 3. Electrode 2 is provided with sealed in terminal connections 4 and 5. Likewise, electrode 3 is provided with terminal connections 6 and 7. The connections 4 and 5, also 6 and '7, lead to a suitable source of electrical energy, as later described. Also, there are sealed in connections 8 and 9 associated, respectively, with the terminal electrodes 2 and 3 and these connections 8 and 9 are joined by a connector 16 including a suitable resistance or reactance, as designated at 16' in Fig. 5.

Fig. 3 illustrates a modification of the lamp of Fig. 2. In this modification, the terminal connections 8 and 9 have been omitted and in the place of exterior connector 16, there is a high resistance conductor 10 internally of the tube.

The details of construction of a terminal portion of the tube of Fig. 2 and electrode contained therein is illustrated in Fig. 4. The tubular vessel 1, as illustrated in Fig. 2, is provided at each of its electrode ends with a two wire seal 11. At

one end of the tube, the seal 11 supports the terminal connections 4 and 5, and at the other end, the seal 11 supports the terminal connections 6 and 7. The two metallic terminal connections 45 and 6-7 are connected together at their extremities within the tube by wire coils 12 of semi-circular loop form located approximately centrally within tubular metallic screens 13 that are supported coaxially within the terminal portions of the tube. One of these screens has an electrical connection at its outer end with the terminal connection 8 and the screen at the other end of the tube likewise is attached'to the tenninal connection 9, and the inner ends of these tubular screens are supported by wire prongs 15 extending therefrom into contact with the walls of the tube, as seen in Fig. 4.

In the circuit diagram of Fig. 5, shown in connection with the tube of Fig. 2, the terminals 8 and 9 are shown connected together through the connector 16, including the resistance or reactance 16'. The terminals 4 and 5 are connected by wires 30-31 to the opposite ends of a coil 1'1. Likewise, the terminals 6 and '7 are connected by wires 3233 with opposite ends of a coil 18. The coils 1'1 and 18 are located about the opposite side portions of the iron core 19 of a transformer, designated in its entirety by reference numeral 34. This iron core, which for the purpose of better illustration has been shown cross hatched, also carries a reactance coil 20 and primary coil 21 on its opposite end portions. The coil 21 is energized on the closing of a switch 22 which connects the transformer with a standard low potential alternating current main M. The transformer core 19 is also provided with a magnetic shunt 23 with an air gap 24. The circuit, which consists of the coil 17 and that part of the electrode associated with the terminal connections 4 and 5, for the purpose of clearer explanation, will be designated as the filament circuit A, and the corresponding circuit of coil 18 and terminal connections 6 and 7 will be designated as the filament circuit B.

The operation of the low voltage lamp of Figs. 2 and 3 is as follows:

Upon closing the switch 22, see Fig. 5, coil 21 will be connected through the medium of the switch and wires 36 and 37, leading therefrom to the opposite ends of the coil, with the main M. 'When the coil 21 is energized by the closing of the circuit, a magnetic fiux is then established in the transformer core 19. This flux must pass through the coils 17, 18 and 20 establishing therein an electromotive force. This electromotive force is proportional in magnitude to the number of turns in each coil, the amount of flux in the core and frequency of the circuit. The number of turns in the coil 20 is such that the induced voltage of coil 20 when added to the voltage of the main is sufficient to kindle an arc between the terminal connections 4 and 6 at the opposite ends of the lamp.

Fig. 5 illustrates coils 20 and 21 connected in series to the terminals 4 and 6. As soon as the arc is established between the terminal connections 4 and 6, the arc current must fiow through the coils 20 and 21. This current in the coils 20 and 21, by virtue of their mutual inductance and the comparatively large leakage flux between the coils through the flux shunt 23 of the coil, generates a counter electromotive force in the arc circuit which is proportional to the current in the circuit. The transformer of Fig. 5 assumes the characteristics of a reactor.

The internal reactance of a transformer is proportional to the leakage flux between the primary and secondary coils. In Fig. 5 the primary coil is the coil 21 and the secondary coil is the coil 20. The leakage fiux is proportional to the coil spacing and inversely proportional to the reluctance of the magnetic shunt 23 with its air gap 24. Therefore, by the proper constructim of the transformer core 19, and the provision of a sumcient number of turns in coil 20, the arc circuit may be stabilized so that the voltage of the circuit rises as the current in the circuit increases; or the negative resistance of the arc is more than offset by the positive reactance of the transformer. The circuit above described satisfies all conditions required for the stable operation of an arc when the arc is once established, but the arc does not kindle unless the electrodes of the lamp are stimulated so that they function under what is now known as electronic emission." This electronic emission is created by either of two well known methods, namely, by heating the electrode or by using some oxides of metals which are known to readily emit electrons under electric impulses. Both methods may be used simultaneously by coating the electrode with these oxides, and by heating the electrode.

The present invention functions best when filament 12 (see Fig. 4) is coated with a metallic oxide, and when at the same time the temperature of filament 12 is increased.

For the purpose of heating filaments 12, the filament terminals 4 and 5 of filament circuit A are connected to coil 17 (see Fig. 5) and the terminals 6 and '7 of filament circuit B to coil 18 of the transformer. Coils 17 and 18 are wound on the same magnetic circuit, as coil 20, so that as soon as the arc current is established, the voltage generated in coils 17 and 18 suffers a drop similar to that of coil 20. This drop in voltage reduces the current in the electrode filaments which are now sufficiently heated by the arc itself. The heating of filaments 12 is required only for the kindling of the arc since .the arc itself generates sufficient heat for continued electronic emission. The decrease of the filament current in circuit A and B is desirable also from the standpoint of most efiicient operation of the lamp.

The two circuits above described would ordinarily be sufllcient to'kindle and maintain an are at low voltage of the order. of one hundred ten or two hundred twenty volts if the electrodes were spaced only 'a very short distance apart. But, when the electrodes are installed at the ends of long tubes, the voltage between terminals for kindling the arc is very high.

In order to decrease this arc kindling voltage to a practical minimum, a third circuit is required. This circuit consists of the cylindrical screens 13 which are electrically connected to terminals 8 and 9,,and which also are connected together on the outsideof the lamp through a conductor 16. This circuit, hereafter called the kindling circuit", forms a shunt around the arc circuit if sufiicient voltage. exists between electrode 12 and screen 13 to create a flow of current through the space between the screen and electrode. When this space is occupied by neon gas or any highly conductive gas under low pressure, a small current will flow at a comparatively low voltage. This current is usually called "corona current.

The kindling circuit, therefore, stimulates the flow of a small current from electrode 2 to electrode 3 through screens 13 and conductor 16. When this current is suiliciently large to create a glow between screen and electrode, the resistance of the gap assumes a negative characteristic and the current rapidly .increases to such proportions as to heat the filament 12 and to powerfully stimulate electronic emission from the filaments to the screens and between the filaments 2 and 3.. The are kindles at much reduced voltage, a voltage which is but slightly greater than that of the are between the electrodes 2 and 3.

The energy transformations in the lamp circuits when the'switch is closed upon the supply circiut of, say one hundred twenty volts, are

as follows:

The auto transformer connection of coils 20 and 21 of the transformer increases this voltage so that it rises to one hundred eighty volts between terminals 4 and 6 of lamp 1 Immediately a small current fiows from electrode 2 to electrode 3 through thekindling circuit which consists of screens 13, terminals 8 and 9 and conductor 16 including the reactance 16'. Corona is observed surrounding the electrodes and screens. This corona current rapidly increases to a glow current, and the space between the screen and electrodes is filled with a luminous glow of low intensity. Meanwhile the current.

in the filament circuits A and B has gradually increased the temperature of the filaments and when these filaments have reached a cherry red appearance, the arc flashes from filament of electrode 2 to filament of electrode 3.

voltage by virtue of the internal reactance of the transformer. The current in the filament circuit also decreases because of the decreased induction in coils 17 and 18. Furthermore, the reduction of the terminal voltage also decreases Imme-. diately the arc current decreases the terminal the current flow in the kindling circuit. The are voltage drops to one hundred twenty volts.

The above processes follow each other so rapidly that the arc appears almost instantly when switch 22 is closed. However, the phenomena above described can be readily observed in experimental set-ups with all circuits under separate control.

It has been found by many experiments that for best operation of a low voltage are lamp, the above described three circuits must be delicately inter-related. For instance, with a given tubular lamp of fixed geometrical proportion containing a given rare gas or a given mixture of such gases at a fixed pressure, the minimum kindling voltage depends upon-the following circuit characteristics:

Coil 20 must contain a sufficient number of turns so that, for optimum conditions in the other circuits the arc will kindle and then stabilize at the desired arc current density; The filament circuits A and B must also be proportioned so that. the filaments receive the amount of current for the lowest possible kindling voltage. That is, the current density in the filament may be both too high or too low for optimum kindling conditions. Also the kindling circuit must be properly adjusted for proper kindling of the lamp. If the reactance 16 is too large, the corona current is too small to stimulate electronic emission; if it is too small, an arc is established between filaments and screens, instead of between filaments alone. This condition prevents the formation of the arc. The reactance 16 may be inductive, condensive or it may be a resistance, for the circuit functions differently for resistance than for an inductance or condenser of the same ohmic drop. The values of the optimum ohmic drop of resistance or reactance 16 depends upon, and varies greatly with, the internal gas pressure in the lamp, the geometric relations of the electrodes, the length and size of the lamp and with the kindling potential of the arc. It has been found that for a short tube, terminals 8 and 9 can be short circuited and reactance 16 omitted. It is also possible that the electrodes may be so proportioned as to permit the short circuiting of terminals 8 and 9 for all sizes of lamps.

In order to convey an idea of quantitative relations involved in the coordination of the circuits of the present invention, the following measurements are here given:

A tube of twenty eight mm. inside diameter and of length between filaments 2 and 3 of ten inches, when filled with pure neon at a pressure of six mm., will kindle at ninety volts between terminals and will establish a steady arc of two and five tenths amperes with an arc voltage of approximately eighty. A tube twenty inches long of the diameter and with the same gas charge will kindle at one hundred twenty volts and burn at one hundred five volts when the arc current is two and five tenths amperes.

The circuits above described may be modified considerably without influence upon the general principles of this invention. The kindling circuit may be placed wholly within the lamp as shown in Fig. 3. For this arrangement the potential drop in conductor 10, due to the corona or glow current which flows from the filaments through the gas and into the screens, must be less than the potential drop of the arc in the positive column.

The oxide treatment of the filaments may alsobe omitted without seriously affecting the operation of the lamp. Under this condition of operation the filament must be made of a material which does not readily disintegrate under high temperatures. It has been found that the required filament circuit power is greater than for an oxide treated filament in order to kindle-the are at the same voltage.

The screens 13 which surround the filament and which are shown in Fig. 4 to be made up of wire mesh may be made of sheet metal and of different shape, as long as the principle involved, namely the provision of a conductor in the close vicinity of each filament and their interconnection for the facilitation of corona formation, is not violated. Other means of heating the filaments by external circuits than the means shown in Fig. 5 may be used or this filament circuits may be entirely omitted if suflicient corona or glow currentcan be created in the kindling circuit to stimulate the arc.

The transformer of Fig. 5 may be made in a variety of ways. It may have additional coils on the leakage path 23, which, when connected in series with the filament coils 1'7 and 18, will decrease the filament current to zero when the arc is established. A separate transformer and reactor may be used, or the transformer may be entirely omitted when the supply circuit potential is greater than the kindling voltage of the arc.

The circuit of Fig. 5 shows only one lamp connected to the supply main. It is evident that a plurality of lamps may be connected in series on one transformer or-reactor, provided the secondary-pr imary ratio is sufficiently large to kindle all the lamps. A series connection of lamps naturally requires a greater number of filament coils. It is also evident that the lamps of the present invention may be operated in delta or star connection on a three-phase circuit. The advantage of this three-phase operation would be the elimination of flicker in the composite set up.

The lamps may also be operated on a direct current source. For this operation only one electrode may be constructed as per Fig. 4, the other being merely a metal rod or sleeve which serves as an anode. The heating of the filament circuit of the cathode maybe accomplished by a sepa-. rate source of either direct or alternating current.

The electrical circuit characteristics within the low voltage are lamp are far more complicated than those of ordinary electrical circuits which may be readily analyzed by the application of Ohms law. Since all the circuit constituents, within the lamp are enveloped by a conductive medium, namely the rare gas in the lamp, there is a slight leakage of current from all parts of the metallic conductors from one point of the circuit to other points of different potential. This phenomenon makes mathematical calculations of performance practically impossible .and necessitates, therefore, the evaluation of the circuit variables by experimentation. It is also apparent that the variables are many in number, as for instance, the kind of gas or gas mixtures for best operation; the gas pressure in the lamp; length and diameter of lamp; the geometric dimensions and relations of the different parts of the electrodes; the kind of materials best suited for the different parts of the electrodes, etc. Although the invention is based upon a great many of such experiments, it is expected that slight modifications of its present form and of its constituent parts will suggest themselves as arc lamp having electrode filaments at opposite ends, a shield enclosing each filament in spaced relation thereto, a conductor a connecting said shields and forming a. shunt across the arc 'clrcuit and a transformer. reactor connected with the source of electricity for supplying current to the arc and filament circuits.

KURT F. J. KIRSTEN.

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