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High Frequency Currents:  Oudin, Tesla, d'Arsonval, Piffard, Violet Rays, Auto-Condensation, Auto-Conduction
Excerpt from Medical Electricity, Röntgen Rays, and Radium by Dr. Sinclair Tousey

High Frequency Currents Chapter, Pages 518 - 532.

All photos and references can be found in the above links to the scanned version of the book.

 

IT will be remembered that when a discharge of electrostatic energy takes place from a Leyden jar the spark does not represent a single exchange of the exact amount required to equalize the electric condition of its two armatures. On the contrary, the state of equilibrium is reached by a series of oscillations back and forth at the rate of about 500,000 a second. This is somewhat analogous to the experiment with the pith-ball suspended between a positively and a negatively charged body. The ball swings back and forth, carrying each time a fraction of the charge from one and taking it to the other body, where it neutralizes that amount of electricity of the opposite sign. This back-and-forth transference continues until both bodies are in the same electric condition. The oscillations occurring in the case of a discharge between the positively and negatively charged coatings of a Leyden jar, or of a battery of Leyden jars (acting as the condenser of an induction-coil, for example) are infinitely more rapid than the oscillations of the

pith-ball in the illustration. The relative electric condition of the two armatures undergoes 500,000 alternations a second, and if the human body is connected with both armatures the application is quite different from any form of galvanic or faradic current. It is more analogous to the static spark or breeze than to anything else, but at the same time with the best high-frequency apparatus a current of from 100 to 500, or sometimes 1000 or more, milliamperes passes through the patient. This current is of incomparably greater volume or amperage than that which passes between the poles of the most powerful static machine. The effect upon the patient is due to the self-induction in the coil uniting the two Leyden jars, which forms an essential part of all high-frequency apparatus.

The oscillations in the currents, usually referred to as high-frequency currents and as the d'Arsonval, Oudin, and Tesla currents, are of the type above described and are called damped oscillations. This is because they quickly diminish in extent and die out, while undamped oscillations are uniform in extent. High-frequency currents with undamped oscillations are referred to under the heading of DeForest Needle and Duddell's Singing Arc (page 618).

The Fleming Rectifier for High Frequency Currents.-This consists of an incandescent electric lamp in which there is a little metal cylinder besides the carbon or metallic oxid filament. Alternating high-frequency currents can pass through such a lamp in practically one direction only. When the filament is incandescent the partial vacuum in the globe becomes much less resistant to the passage of a current. The filament acts as a cathode, while the metal cylinder has a comparatively small surface for the radiation of cathode rays during the period when the current seeks to flow in the other direction. The incandescent lamp is lighted up by the current from a storage-battery.

It is necessary to recharge the Leyden jars each time that they are discharged, so as to produce a certain continuity of effect in therapeutics.
The rate at which the Leyden jars are charged and discharged is only a few hundred or a few thousand times a minute. The rate of oscillation in each individual discharge is millions of times a second. It is the latter rate that gives the name "high frequency" to these currents.
At the present time it is not possible to obtain directly from any make of static machine or induction-coil a high-frequency current. In order to obtain a high-frequency current from either the static machine or induction-coil it is necessary to have an additional piece of apparatus. The term "high-frequency current" should always have in addition the name which designates its particular type, such as d'Arsonval high frequency current or Tesla high-frequency current. In both of these the frequency is high, but the physical characters of the current are entirely different. Fig. 324 illustrates a complete arrangement such as will be necessary to produce the d'Arsonval current from the 110volt direct current; positive and negative indicate the 110-volt direct current, then comes an ordinary double knife-switch with fuse.

The positive wire is conducted to the platinum point of the Wehnelt interrupter. This consists of a glass or porcelain jar containing a 10 per cent. solution of sulphuric acid. Mounted on the cover is a porcelain stem having an opening at the lower end through which is passed a piece of platinum wire. This usually has a mechanism for regulating the length which it extends beyond the porcelain stem. In addition there is a connection with the plate of lead. The plate of lead is connected with one terminal of the rheostat; the other terminal of the rheostat with one terminal of the ammeter; the other terminal of the ammeter with one terminal of the primary; the other terminal of the primary back to the negative terminal of the 110-volt current.

The primary has a core consisting of a bundle of soft iron wires. This is held together by insulating materials, and on this is wound the primary wire, which may consist of one or more layers of copper wire of any desired diameter. This is placed inside of the insulating tube which may be made of hard rubber or micanite. On this insulating tube is mounted the secondary winding of the coil; the ends of the secondary winding are now connected with two sliding rods; these in turn are connected with the inside coatings of two Leyden jars. The outside coatings of the Leyden jars are connected by means of a coil of heavy copper wire which is known as the small solenoid of d'Arsonval. The patient is connected with the two terminals marked D. The strength of the current as applied to the patient is regulated by means of the spark-gap and by the strength of current used in the primary of the induction-coil. The current which passes through the patient is what is known as the d'Arsonval high-frequency current.

In place of the electrolytic interrupter a mechanic interrupter may be used. In order to obtain the d'Arsonval high-frequency current it is absolutely necessary, using the usual induction coil and 110-volt direct current, to have the above-described arrangement.

d'Arsonval and Oudin High-frequency Apparatus.- d'Arsonval also made what is known as the large solenoid. Dr. Oudin found that by connecting one end of the large solenoid of d'Arsonval with one end of the small solenoid of d'Arsonval, as shown by Fig. 325, that from the terminal 0 he obtained a current entirely different in character from the ordinary d'Arsonval current. He also found that by adjusting the contact point between the large solenoid and the small solenoid he was able to regulate the discharge from the terminal 0. This led him to construct what is now known as the Oudin Resonator (Fig. 326). This you will see is simply a combination on one tube of the small solenoid of d'Arsonval and the large solenoid of d'Arsonval. In this construction, however, it is arranged so that the contact E is adjustable and it is found that when it is placed at a particular point the discharge from terminal 0 is at its maximum. As this contact-point is moved above or below this particular point the discharge decreases. When it is adjusted to produce its maximum effect the apparatus is said to be in resonance.

Another arrangement for obtaining high-frequency currents consists in what is known as a high-frequency set. This is designed especially
to operate from the 110-volt alternating current (Fig. 327). It makes a somewhat more simple construction than the usual induction-coil arrangement, as it does away with the electrolytic or mechanic interrupter, owing to the fact that the current is alternating. In this
arrangement, instead of the usual open magnetic circuit type of induction-coil, the closed magnetic circuit type is used. The alternating current is conducted to the double pole knife-switch; then one terminal is carried to either the metallic rheostat or what is known as an inductance regulator.  This is then connected with one end of the primary, the other end of the primary to one terminal of the ammeter, the other terminal of the ammeter back to the main line. The secondary circuit is connected with the Leyden jars, which are connected with the Tesla coil. The current is regulated by means of the inductance and the length of spark-gap. In place of a Tesla transformer the secondary can be connected with an Oudin resonator. At the present time it is not possible to obtain a high frequency current in any other than by the above or similar means. You cannot obtain a high-frequency current direct from either the induction-coil or the static machine. With either of these it is necessary to have the arrangement of d'Arsonval, the arrangement of Tesla, or that of Oudin in addition to the static machine or coil. I call attention to this particularly, as some manufacturers claim that their static machine will give a high-frequency current direct. They use in conjunction with the static machine a vacuum electrode, and, as a rule, it is connected up as shown by Fig. 329. When the vacuum electrode is placed in contact with the patient it will light up with a violet color the same as it would if attached to a high-frequency apparatus, but the sensation produced in the patient is entirely different, being of a vibratory character; it is, in fact, when used in this way in conjunction with a static machine simply a method of applying the wave-current by means of vacuum electrodes. This current has a certain therapeutic value, but should not be called a high-frequency current. It will be referred to as vibratory current (Figs. 329 and 330).

One very simple test to demonstrate physically the difference between this current and either form of high-frequency current is to have the subject come in contact with the metal part which holds the vacuum electrode. When this is connected with the static machine as above described, you will experience a very disagreeable shock, whereas, when it is connected with a high-frequency current no sensation other than that of having a slight feeling of warmth will be experienced. Vacuum electrodes are used in this same way with an induction-coil, the strength of current being regulated by the distance A and B are separated.

In order to demonstrate the fact that this current is not a high-frequency one, it is only necessary to insert between the electrode and the apparatus a little instrument known as the oscilloscope. Fig. 331 shows this in circuit with a Tesla current. With the static machine you will notice that the violet color is all on one side of the center, whereas when connected with the Tesla current it shows the violet color on both sides of the center.

An induction-coil, such as is suitable for x-ray work, is very desirable for high-frequency apparatus. A 12-inch coil is about the best, and can be used no matter what the nature of the interrupter and the source of the primary current are. The primary winding of the coil should have a large number of turns so as to give great self-inductance and a proportionately heavy secondary discharge. In this case the actual spark length seems to be of less importance than the "fatness" of the spark, and in my own apparatus the best results are obtained with an adjustment which will produce a 6-inch flame between the poles of the coil when the high-frequency apparatus is disconnected from them. Every x-ray- coil should have a variable primary winding, and if this is the case it will be easy to adjust it for the best high-frequency work. A desideratum is an interrupter which will produce a sufficiently heavy spark with only one, two or three, four, or five amperes of primary current. This means less wear upon the apparatus and longer continuous use without detriment. With alternating currents an x-ray coil with one of the rectifiers described on page 699 works very well, or Gaiffe's transformer outfit may be used.

Gaiffe's transformer outfit, without any interrupter, for x-ray and high-frequency apparatus, is described in detail on page 719. The ordinary alternating electric-light current passes through a primary wire, which surrounds one part of the circumference of a magnet which forms a complete ring. Around another or the same part of the ring is wrapped the secondary wire. The voltage in the secondary wire is as many times the original 110 volts as its number of turns of wire is times the number of turns in the primary wire. The magnetic ring, with its primary and secondary windings, constitutes a transformer; in this case a step-up transformer, since the voltage is increased by it. The switches and liquid rheostats and condensers are all arranged as for x-ray work, but the two ventril tubes need not be used. Connection is made from the two x-ray terminals to the high-frequency apparatus.

Such an outfit will work continuously for an indefinite length of time and with absolute uniformity. It is the very best for use with an alternating current, and may prove to be so much better than an induction coil and interrupter that, even with a direct current, it will be advantageous to use this outfit in connection with a motor generator by which the direct current is made to produce an alternating one.

The d'Arsonval transformer is one of the simplest and best forms of apparatus for the production of high-frequency currents. In this apparatus the poles of an ordinary induction-coil, such as an x-ray coil, are connected with the inner coatings of two large Leyden jars, and these inner coatings are further connected with the two terminals of an adjustable and enclosed (rnuffled) spark-gap. The outer coatings of the Leyden jars are connected with each other by a solenoid, which is a coil of heavy wire wound in the form of a hollow cylinder. The turns of this wire, about twenty in number, are about half an inch apart, and require no further insulation from each other. Conducting cords also pass to the patient from turns near the ends of the solenoid. One of these cords terminates in an ordinary metal handle, which is usually held by the patient. The other sometimes terminates in an insulated handle held by the operator. This has a metallic socket, into which fit electrodes of metal or of glass; the latter are vacuum tubes of various kinds, or this wire may terminate in the metallic plate of an autocondensation couch, or neither wire may go to patient, but they may lead to opposite extremities of an autoconduction cage.

The poles of the x-ray coil are widely separated; the points of the spark-gap of the d'Arsonval transformer are separated about one-third or one-half inch and a sufficient current is turned on to cause a rapid and uniform succession of sparks across the spark-gap. The latter is muffled, enclosed in a glass cylinder or vulcanite box to deaden the noise. Nitric acid fumes are generated by the passage of these sparks through the nitrogen of the air and a metallic nitrate is deposited upon the interior of the glass, which eventually interferes with the spark-gap by short circuiting and requires to be cleaned out. The patient, holding one of the handles in one hand and a vacuum electrode in the other, will experience no sensation but that of a gradually developing warmth from the vacuum electrode. This is true even with a current of 200 to 500 milliamperes passing through the patient. The vacuum electrode becomes lighted up by waves of violet light passing down inside the tube, succeeding each other at a rate which seems to be the same as that of the sparks across the spark-gap. This is ordinarily at the same rate as the interrupter. A hot-wire milliamperemeter, placed in series with the patient, shows the strength of the current. If the electrode is not in good contact with the skin, sparks may be seen beginning at some little distance and passing along the outside of the glass to the skin. There is also a production of ozone from the same sparks. There is no spark-gap in circuit with the patient. He is on a shunt circuit with the solenoid, and the fact that he gets any current at all is due to the heavy impedence in the solenoid developed by its self-induction.

To light an incandescent lamp by direct conduction of high-frequency currents two persons hold each a metallic electrode from one pole of the d'Arsonval transformer and each by his other hand holds one of the wires leading to an electric lamp suspended between them.

The lamp may light up brightly and still the persons experience no sensation from the current passing through their bodies.
The author's vacuum electrodes, with a vacuum of about 1/1000 of an atmosphere, are made with a leading-in wire passing just through the
thickness of the glass at the point where the tube has a screw thread. The tube is screwed into a metal socket well up inside of a special handle of hard rubber, which is completely insulated. No current can be received by either the patient or the operator from any part of the handle. The glass electrode is the only bare part, and contact with that is not disagreeable at all, although the current may be sufficient to light up a 16-candle-power lamp placed in circuit with the patient. Those for the surface of the body are simple tubes with a dome-shaped extremity, while some of those for the mouth, rectum, or vagina have an insulated stem where they enter the cavity and where sparks might occur from the contact being less perfect than further in where it is surrounded by mucous membrane. This insulation is accomplished by having the vacuum tube very small along this portion of its length, and having an air-space between it and an outer tube of glass, which is of uniform caliber with the portions of the electrode above and below it. The waves of light may be seen in the upper and lower and the narrow central portion, but are absent from the outer jacket surrounding the latter, and no current is obtained by touching this outer jacket.

Other vacuum electrodes are made without any wire, the current being of sufficiently high tension to penetrate glass of any reasonable thickness. In this case, to obtain a sufficient current the glass should be quite thin and there should be a large area of contact with the metal handle to avoid overheating the glass at that place. Different forms of metal and glass electrodes for various parts of the surface and for the different orifices of the body are made, and will be considered in detail in the section upon the Therapeutic Application of High-frequency Currents.

The autocondensation couch consists of a sheet of metal or a flat mass of wires connected with one pole of the d'Arsonval transformer, on top of which is a thick insulating mattress upon which the patient lies. The handle from the other pole of the d' Arsonval transformer is held in the patient's hand, and when the apparatus is in operation a current of 100 to 400 milliamperes is indicated by the meter which is in circuit with the patient. The patient becoming charged with one kind of electricity and the metal plate with electricity of the opposite sign, and the insulating mattress intervening, form a complete condenser on the same principle as a Leyden jar. The patient corresponds to the external metallic coating or armature of the Leyden jar, and each time the patient and the metal sheet become overcharged and a discharge takes place across the muffled spark-gap of the d'Arsonval apparatus the patient undergoes a very great number of electric oscillations.

In another couch which the author has used the principle is rather that of autoconduction. The couch consists in some cases of a ii^-11V mattress in two parts, very heavily insulated, each end being connected with one of the poles of the d' ArsonvaL Iligh-frequency currents are produced in the patient by induction from the wire couch without any metallic connection reaching the patient.

Another couch consists of indurated fiber an eighth of an inch thick, upon the back of which is a sheet of x-ray metal, and this covered again with a light insulating cloth. This is made in two sections, hinged together with quite a wide insulated separation, the wire from one pole of the d'Arsonval passes to one metal sheet, and the wire from the other pole to the other metal sheet. A convenient way to use it is to place it on an ordinary chair so that one Dart forms the seat and another the back. There should be no metallic parts to the chair except the ordinary nails and tacks. Before the patient is seated upon this the current shown by a milliamperemeter in circuit with the couch may be 150 milliamperes, and tho moment the patient sits down it may increase to over 400 milliamperes. This is without any sensation. Through the patient's back he receives an induced charge from one metal sheet, and through the lower part of the body and the thighs he receives an induced charge of the opposite sign from the other metal sheet. Thus, an extremely rapid series of condenser discharges is produced through the patient's body. If a stronger current is turned on, 500 or 600 milliamperes, considerable brush discharge passes to the patient through the indurated fiber. While this is not disagreeable or harmful for a short time, it is better to avoid it in general.

With the autocondensation couch used by the author the current may be between 400 and 500 milliamperes when the patient is seated upon it and thus by a conductor effect facilitates the discharge. And when the patient leaves the couch the current will be seen to diminish to about 100 miiliampercs. It will be remembered that if two Leyden jars are hung from the prime conductors of a static machine and a metal rod connects the outer layers of the jars, tremendously powerful white sparks pass between the poles of the coil. These are a thousand times louder than the discharge which takes place when the rod is disconnected from the outer layers of the Leyden jars. The wonderful discharge which takes place between the poles of the static machine when the rod is in place is accompanied and, one can almost say, produced by a similar discharge which passes through the rod. In the autocondensation couch in question the lead plates to which the wires lead from the high-frequency coil correspond to the inner coatings of the two Leyden jars in the experiment with the static machine. The patient's body corresponds to the outer layers of the two Leyden jars and the rod connecting them. The difference between the number of milliamperes going through the wires passing to the autocondensation couch, with and without the patient, shows roughly the amount of electricity induced in and discharging through the patient.

• The autoconduction cage is a hollow cylinder formed by a coil of wire the turns of which are widely separated. The cage may be placed vertically, and the patient stand or sit inside of it, or it may be horizontal and surround a table top on which the patient lies. Its two extremities are connected with the two poles of the d'Arsonval transformer, and when in operation high-frequency currents are produced in the patient without his being in metallic connection with any part of the apparatus.

Measurement of High-frequency Currents in Auto Conduction.-The most practical measurement of the strength of the current induced in the interior of the autoconduction cage is in Gausses, as described by Doumer, and depends upon the amount of current induced in a loop of wire placed inside the autoconduction cage and parallel with its turns. The currents are alternating, and the ampererneter is usually a thermic or hot-wire instrument. The graduations may be directly in Gausses.

The frequency of the oscillations in high-frequency currents may be measured by Ferrie's ondometer. This has a certain length of wire, which may be placed parallel with and close to the wire through which the oscillatory current is passing. The wire mentioned forms part of a circuit which also contains a self-induction, a condenser of adjustable capacity, and a hot-wire milliamperemeter. The capacity of the condenser in the ondometer is regulated so that the maximum current is registered, indicating oscillations synchronous with those in the circuit to be tested. The condenser is graduated in figures representing the number of oscillations per second. This is between 300,000 and 600,000 for most high-frequency work.

Effects of Autoconduction and Autocondensation.-With both the autocondensation couch and the autoconduction cage the patient does not feel any electricity, but its presence may be proved by drawing sparks from any part of his body and even a slight violet brush discharge may take place between the patient's two hands if one finger of each are brought lightly together. A variety of experiments may be performed with incandescent lamps or telephones to demonstrate the presence of electricity on every portion of the patient's surface.

To light an incandescent lamp by autoconduction it is only necessary to connect it by a loop of wire held inside a solenoid traversed by high frequency currents. A vacuum tube approached to the solenoid lights up. Any body inside a solenoid is itself traversed by high-frequency currents.

Piffard's Hyperstatic Transformer (Fig. 333).-This apparatus is devised to obtain high-frequency currents from the static machine. Two medium-sized Leyden jars have their inner coatings connected with the two prime conductors of the static machine. The.spark-gap is obtained by separating the poles of the static machine about an inch. The outer layers of the Leyden jars are connected with the extremities of a small solenoid, at the ends of which are binding-posts. With the plates revolving at the rate of 300 or 350 times a minute there is an efl3uve to be felt from both binding-posts, that corresponding to the positive pole of the static machine being the stronger. For mild applications a vacuum electrode is connected with only one (the positive) pole of the hyperstatic transformer. For a more active effect the patient holds a metal electrode connected with one pole while a vacuum or a metal electrode from the other pole is applied to the region to be treated. Piffard's own belief is that the hyperstatic current is chiefly valuable for a local effect, as in chronic eczema, and that it cannot take the place of the d'Arsonval current, with its vastly greater amperage, for the production of constitutional effects. The static machines usually found in Europe scarcely amount to more than laboratory toys. It is only the large American machines with eight or more pairs of plates, 30 inches or more in diameter, that are suitable for this therapeutic application.

THE OUDIN RESONATOR

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