High frequency apparatus, design, construction and practical application; a practical treatise for electrical engineers, electricans, physicians, students and experimenters

Front matter

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Preface

This volume has been prepared in response to a general demand created by a series of articles which appeared in Electrician and Mechanic, Popular Electricity and Modern Mechanics, and 7 he World's Advance. The articles covered briefly the apparatus employed in an experimental study of high frequency current phenomena over a period of several years.

In this w^ork, I have spared no efifort to produce a treatise of practical value. Theory has been ignored chiefly because 'it would serve merely to confuse the non-technical reader. .The designs offered are more than theoretical — they are the result of actual construction and experiment. In many cases, the entire oscillation transformer has been rebuilt and rewound many times before satisfactory results were obtained.

The work has been divided into six basic parts. The first ^two chapters tell the uninitiated reader what the high frequency current is, what it is used for, and how it is produced. The second section comprising four chapters describes in detail the principles of the transformer, condenser, spark gap, and oscillation transformer, and covers the main points in the design and construction of these devices as applied to the work in hand. The third section covers the construction of small ihigh frequency outfits designed for experimental work in the home laboratory or in the class room. The fourth section is devoted to electro-therapeutic and X-Ray apparatus. The fifth describes apparatus for the cultivation of plants and Ivegetables. The sixth section is devoted to a comprehensive discussion of apparatus of large size for use upon the stage in spectacular productions. i 3

4 PREFACE

I wish to acknowledge my indebtedness to the following concerns and individuals for assistance rendered in the preparation of this volume: Victor Electric Company for illustrations of standard electro-therapeutic apparatus; Clapp-Eastham Company for illustrations and the list of parts and materials ; Mr. Melville Eastham for a practical working knowledge of magnetic leakage transformer design and construction; and, last, hut not by any means least, Prof. Wm. C. Houghton, for many ideas and suggestions, and much unselfish manual labor during the course of experiments which made this treatise possible.

THOMAS STANLEY CURTIS.

Preface To The Second Revised And Enlarged Edition

During the absence of the author of this volume, Mr. Thomas Stanley Curtis, the writer was called upon to prepare the second revised edition. The first edition of the book was made- so complete and the development work done with high frequency electricity since the first edition was prepared has been so small that there was really little new matter to choose from. However, a few thousand words of Mr. Curtis' later|| writings on the subject of high frequency, which appeared in past issues of ''Everyday Engineering Magazine," were found to be suitable and they have been included in the present edition together with their accompanying illustrations.

RAYMOND FRANCIS YATES.

July, 1920.

Chapter I The Alternating Current At Low And High Frequencies

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Introduction. What the Alternating Current Is. Change of Frequency. Effects of Change in Frequency. The High Frequency Current. Characteristics of the High Frequency Current. Spectacular Demonstrations. The High Frequency Current in Medicine. Generation of Ozone and the X-Ray. Electrical Cultivation of Plants. Radio Telegraphy and Telephony 15 to 26

Chapter II How The High Frequency Current Is Produced

Three Practical Methods. The High Frequency Alternator. Advantages and Disadvantages. The Direct Current Arc Generator. Condenser Discharge Generator. Principles Involved. The Kicking Coil Method. Limitations and Unique Advantages 27 to 30

Chapter III The High Potential Transformer Or Induction Coil

jSome Points in the Construction of High Frequency Apparatus. . Principle of the Commercial Transformer. Transformers for Condenser Charging. How Arcing is Prevented. Development of the Eastham Magnetic Leakage Transformer.

The Question of Proper Secondary Potentials. Advantages of Relatively High and "Low Voltage. Transformer Construction. Transformer Designing. How to Calculate

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Number of Turns, Size of Core, etc. Core Volume.

Changes Necessary for Use on Various Frequencies. Proportions of Core. Induction Coils for High Frequency Work. How they Differ in Design and Proportion. Induction Coil Design. Kicking Coils. What they Are. 31 to 4f

Chapter IV The Oscillation Condenser

Function of the Condenser. What It Is. The Glass Plate Variety. Considerations of Weight, Capacity, and Space Occupied. A Simple Method of Determining Capacity.

Forming a Standard Unit. Condensers for Portable Coils. The Use of Mica and Micanite. Relative Costs. The Murdock Moulder Condenser. Capacities, Sizes and Weights. The Oil-Immersed, Glass Plate Condenser for Permanent Installation 49 to 53

Chapter V The Spark Gap

The Simple Open Gap. Addition of Cooling Flanges. Use of Air Blast. The Rotary Spark Gap. Various Types and Advantages of Each. Number of Studs or Points Required. Speed of Motor. Air Gap between Sparking Points. The Quenched Gap. Principles of Operation.

Simple Types for Amateur Construction. Importance of Regulation. Characteristics of the Discharge when Quenched Gap is Used. The Rotary Quenched Gap. Production of a High-Pitched Musical Note on 60-Cycle Current. Advantages in Radio Telegraphy . . . . 54 to 59

Chapter VI Oscillation Transformers

Various Types of Air-Insulated High Frequency Current Transformers. The Simple Oudin Coil. Various Shapes and Proportions for the Secondary. Cones, Cylinders, Cages, Spirals, and the Advantages of Each. Various Primary Types. Round Conductor, Edgewise-Wound Copper Strip, Hollow Tubing, Flat Copper Ribbon, and Stranded Con-

\ J _ / CONTENTS

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ductor. Couplinig^; The Tesla Type of Coil. How it Differs from the Qwdin. Advantajges to be Gained. Tesla Secondaries. Means of Mechanical Support. Tesla Primaries. Proportions and Ratio of Diameter to Length. Combined or Double Resonator Type. Coupling. Oil and Wax Insulation for High Frequency Coils. Advantages and Disadvantages. Advantages of Close Coupling Possible. Spirally Wound and Wax Impregnated Coils for Portable Outfits. Large Oil Insulated Coils for Testing and Other Permanent Installations 60 to 70

Chapter VII Induction Coil Outfits Operated On Battery

CURRENT

Ideal Apparatus for the Experimenter. Simple Oudin Reso- I nator for Use with a Wireless Transmitter. Interesting I Results Obtained with Mediocre Apparatus. Operation of t the Outfit. How to Tune the Oscillatory Circuits. Induc- ' tion Coil Construction. How to Build a Coil Giving a Thick, Hot Spark. Core and Primary. Insulation. Secondary Winding. Simple Winding Apparatus. Assembly.

Interrupter and Condenser. Use of Silver Contacts in Lieu ^' of Platinum. High Tension or Secondary Condenser. 71 to 85

I CHAPTER VIII

Possibilities of this Type of Apparatus. Use on Either Direct or Alternating Current Circuit. What the Kicking Coil Is. Design for Portable Outfit Giving Seven Inch Spark. Construction of the Interrupter. The Choke Coil. Data for Cores and Windings. The Condenser. Use of Lantern Slide Cover Glasses. The Oscillation Transformer. How the Pancake Coil is Wound. Variable Primary for Tuning. Assembly of the Apparatus. Testing and Using. Electro-therapeutic Work. Construction of D'Arsonval Attachment 86 to 99

CHAPTER IX ONE-HALF KILOWATT TRANSFORMER OUTFIT Advantages of a Transformer for Use on Alternating Current

PAd

Winding. Data for All Commercial Voltages and Fre- Circuit. Design for a One-Half Kilowatt Magnetic Leakage Transformer. Construction of the Core. Primary quencies. Secondary Winding. Assembling and !Mounting. Oudin and Tesla Coils to Give Eighteen Inch Spark. Construction of the Coils. Condenser and Spark Gap.

Connecting and Using. Protection from "Firing Back" on the Line 100 to 11^

CHAPTER X ^

QUENCHED GAP APPARATUS "

Peculiar Characteristics of Sparks Produced with the Quenched Gap. Increase in Thickness or Volume and Decrease in Length. Production of a Flame as Thick as a Broomstick. Design for a Practical Form of Gap. Simple Patterns Required. Machine Work. Assembly of the Gap.

Quenched Gap Transformers. Peculiar Characteristics. Low Secondary Potential. Data for a Two-Kilowatt Quenched Gap Transformer. Specifications for All Commercial Voltages and Frequencies. Construction of the Transformer. Caution to be Observed. Danger of Shock from the Low Resistance Secondary Winding. Suitable Secondary Condenser. General Hints 114 to 12^

CHAPTER XI PHYSICIAN'S PORTABLE APPARATUS

Electro-Therapeutic and X-Ray Apparatus. Requirements of the Ideal Outfit. Good Workmanship Required. Dangers of a Short Circuit Within the Cabinet. Importance of Establishing Confidence of the Patient. Transformer Outfit not Practicable for Amateur Construction. Design for Kicking Coil Outfit Within Reach of Builder. Standard Electro-Therapeutic Apparatus. Various Types and what they Cost. Possibilities and Limitations. Special Direct Current Outfits. Apparatus Suitable for Dentists. Large Portable Outfits. ' Technical Description and Capabilities 125 to 131

CHAPTER XII PHYSICIAN'S OFFICE EQUIPMENT

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Powerful and Efficient Equipment for the Physicians' Office. Design for a One-Kilowatt Outfit with Apparatus Mounted upon a Table. Advantages of this Form of Construction. Imposing Appearance. Accessibility of the Component Parts. Construction of the Magnetic Leakage Transformer. Rotary Spark Gap. Stationary Spark Gap. Oscillation Condenser. Transformer for Vacuum Tube Work. Oil- Immersed Oscillation Transformer for X-Ray Work.

D'Arsonval Treatment Transformer. Assembly of the Apparatus. Connecting and Using 132 to 144

CHAPTER XIII

A PHYSICIAN'S OFFICE EQUIPMENT MADE WITH STANDARD MATERIALS

Design. Explanation of Operations. Directions for Making High Frequency Transformer. Construction of Cabinet. Coil for Thermo. Faradic Currents. Price of Alaterials Necessary. Design of Impedence. L^se of Apparatus.

CHAPTER XIV HOT WIRE METER CONSTRUCTION

I Principle of the Hot Wire Meter. Ease and Cheapness of Construction. Measurement of Both Low and High Frequency Currents with One Instrument. How to Build a

j Simple Hot Wire Meter. Calibration and Use. . .160 to 165

CHAPTER XV

NOTES FOR THE BEGINNER IN ELECTRO- THERAPEUTICS I Discussion of the Apparatus and the Principles upon which It Operates. Relation of Transformer to the Condenser and Oscillatory Circuit. The High Potential or Tesla Current. Physiological Effects of the High Frequency Current. Re-

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duction of Blood Pressure. Treatment of Diseases of the Skin and Scalp. True Merit of the High Frequency Current in the Practice of Medicine. Stimulation of the Growth of Hair. Restoration of the Original Color to Grey Hair. Cumulative Effects. The Value of Persistent Administration. 166 to 171

CHAPTER XVI

PLANT CULTURE WITH HIGH TENSION CURRENT

Practical Electro-Horticulture or the Cultivation of Plants with Electricity. Scarcity of Available Data. Investigation Mostly Private. Great Progress Made by Agricultural Departments of Schools and Colleges. The Art in the Experimental Stage. Electro-culture ^lethods. High Tension. Direct Current. High Tension, Low Frequency Alternating Current. High Frequency Alternating Current. Cultivation of a Bed of Lettuce. The Aerial Conductor. Caution Must Be Observed. Construction of the High Potential Transformer. Data for All Commercial Voltages and Frequencies. Assembly of tlie Apparatus. Actual Results Obtained. Report on Experiments at the Moraine Farm. Table of Comparative Results Obtained with Various Processes of Electro-Culture. . . 172 to 181

CHAPTER XVII HIGH FREQUENCY PLANT CULTURE

Generation of High Frequency Current for Long Continued Periods of Time. The Problem Involved. Careful Workmanship Essential. Construction of the Generating Apparatus. Data for Various Commercial Voltages and Fre- | quencies. Building of the Transformer. Assembling and Mounting. Construction of the Condenser. Provision for Cooling. The Self-Cooling Spark Gap. The Oscillation Transformer. Installation of the Apparatus. The Transformer Shed. Switches and Control Devices. Protection from Accidental Shock. Wiring the Plot to be Cultivated. Ground Connection and Overhead Net Work. Operation of the Apparatus. Time of Treatment. Value of Comparative Data 182 to 20v^ I

CONTEXTS 11

CHAPTER XVIII FURTHER NOTES ON PLANT CULTURE

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How to Use a Standard Radio Transmitter for Plant Culture Work. The Distributing System. Construction Difficulties. Alaking Wire Net Work. Vegetables to' Plant.

Apparatus Required. jMushroom Growing. . . 204 to 211

CHAPTER XIX

A FOREWORD OX THE CONSTRUCTION OF ELECTRI- CAL APPARATUS FOR THE STAGE

High Tension Electrical Stagecraft. Opportunities of High Potential Electricity for the Professional Entertainer. Chance to Improve upon Past Offerings. Importance of High Frequency Apparatus. Points to Consider before Starting Work. Cost and Weight of Apparatus. Difference Between the Lecturer and the Vaudeville Artist. Current Required and Difficulties of Obtaining It. Where and How to Build the Apparatus. The Home Workshop and Its Equipment. Some Work Done Outside if Large and Expensive Tools are , not Available. Advantages of Doing Work at Home. Working Drawings and Blueprints. Need for Practical Working Knowledge of Subject. How to Obtain this Knowledge. ^Mathematics Unnecessary 212 to 217

CHAPTER XX

CONSTRUCTION OF LARGE HIGH FREQUENCY APPARATUS

Design for a Resonator Producing a Five-Foot Spark. Details of Construction. Building the Secondary Cylinder. The Winding. Building the Primary. Assembly of the Coil. Connecting Cable and Clips. The High Potential Transformer. Design for a Four-Kilowatt Magnetic Leakage Instrument. Building the Core. Forms for Winding Primary and Secondary. Insulation. Assembly of the Transformer. Construction of the Rotary Spark Gap.

Spark Gap Muffler. The Oscillation Condenser. Coating the Plates. Building Up Units. Connections. Setting Up

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and Operating the Apparatus. The Switch Board. Prevention of Kick Back. Tuning and Adjustment of the Apparatus 218 to 238

CHAPTER X'XI LARGE TESLA AND OUDIN COILS FOR THE STAGE

Specifications for Large Oscillation Transformers of the Portable Air-Insulated Type. Tesla Transformer for the Production of a Fifty-Inch Spark. Details of Construction. Oudin Resonator for the Production of a Short but Very Thick Discharge. Mounting the Apparatus. Provisions for Packing and Shipment 239 to 246

CHAPTER XXII CONSTRUCTION OF A WELDING TRANSFORMER

Transformer to Deliver a Current of Low Voltage and very Great Amperage. Heating a Quarter-Inch Iron Rod to Incandescence. Building the Transformer. Suggestions for Handling the Heavy Secondary Wire. Insulation.

Assembly and Mounting. Experiments Using a Current of 250 Amperes. Special Copper Tongs or Pliers. Alaking Flexible Cable to Carry the Heavy Current. Burning Up a Heavy Bar of Steel. Welding Two Pieces of Iron Rod Held in the Hands. Spot Welding of Sheet Iron. Melting Metals in a Crucible to Show Principle of Electric Furnace. Suggestions for Effective Stage Setting. Particularly Startling and Spectacular Experiments to Close the Entertainment 247 to 25S

CHAPTER XXIII HINTS FOR THE ELECTRICAL ENTERTAINER

Preparation of the Lecture. Snap and Vigor Necessary. Education of the Public Far Advanced in Recent Years. Class of Audience Must Receive Careful Consideration. Comparison of Well-Read Chautauqua Assembly with Audience Found in High Class Vaudeville Theatre. Vaudeville Audience Demands to be shown. Experiments must Speak

CONTENTS

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for Themselves. Method of Presentation for Typical Lecture Audience. Touch of Comedy of Great Value with Theatre Audience. Short Introduction Preferable. Impressive Opening Necessary. Suggestion for Successful Program. "Trying it on the Dog." The Matter of Rehearsals. Selection of Experiments. Time of Act. How to Present the Offering on the Stage or Lecture Platform. Specimen Program with Outline of Experiments and

Lecture 256 to 263

Useful Tables 264 to 266

Chapter I. The Alternating Current At Low And High Frequencies

While the manuscript for this book was being prepared, the author was approached by a caller who introduced himself as an enthusiastic experimenter and a reader of all manner of practical books. This gentleman explained that he was an armature winder by trade, and that he wished to take up high tension work solely as a hobby. He was possessed of but little knowledge of mathematics and had been unable to understand the many books on trans- ( former design and construction that he had purchased. I A few minutes' conversation with this caller brought

I to light some important points which since have prompted a radical and wholesale change in the method of treat- I ment. Half a dozen pointed questions suggested the introduction to the general -subject that is offered in the next few paragraphs.

What the Alternating Current is. — An alternating current is one that periodically changes its direction of flow a I certain number of times per second. It is the reverse of the I direct current which is assumed to leave the battery or dy- ; namo at the positive pole and return by way of the negative pole. With the alternating current, the terminals of the machine are alternately positive and negative. This char- I acteristic is well shown in the diagram, Fig. 1, which may be assumed to show the course taken by a current leaving

IS the terminals of an alternating current generator having four field poles and having its armature or ' rotor'* driven at 1800 R.P.M. This machine v^ould be termed a 60-cycl alternator because the current it delivers v^ould make 60 complete cycles or 120 alternations in a space of one second.

With reference to Fig. 1, let us assume that A represents the current as it starts from one collector ring of the machine. Following the direction indicated by the arrow, we find the current rises in voltage until it reaches its peah at 5. The value then falls back to zero as the current returns to the other collector ring, C At this point the armamoA/mam 'J[ \ potent /a/ zero poteJif/at ma//mi/rr> jXftent/a/

Fig. 1. — Diagram showing how an alternating current periodically reverses its

direction of flow ture or rotor of the machine passes to the next set of field or stator poles and the current starts out over its circuit again, but in the reverse direction. For convenience, this is shown as below the zero line in the illustration. Leaving C, the current rises to the maximum at D and then returns to £.

The period of time taken in -the passage from A to B is just 1/60 second ; in this space of time the current has made a complete cycle of two alterations, one in a positive and the other in a negative direction. In one second of time, it will have made 60 complete cycles ; it i > therefore called a 60-cycle current.

Change of Frequency. — Now let us assume that the alternator be supplied with eight field or stator poles instead of four. As a reversal of current occurs when the rotor windings pass from the influence of one pair of stator poles to the next pair, it is obvious that to double the number of stator poles is to double the frequency, if the speed at which the armature is driven remains the same in each case. On the other hand, precisely the same result is obtained if the number of poles remains fixed and the speed of the rotor is doubled. Therefore, the matter sums itself up into a simple formula which will be useful to the worker if he will but understand it and not fear it as some intangible form of ''mathematics." The formula is:

2X60 ' Frequency :=

R.P.M. X Number of Poles

Therefore, if we know the number of poles of a given machine and the speed at which it is driven, we may multi- Jply the number of revolutions per minute by the number ^f poles and divide this product by 120 to find the frequency of that particular machine.

I On the other hand, suppose we know the number of poles and we are required to produce a certain frequency from a given machine; we must determine the number pf revolutions at which the rotor must be driven. This ormula is:

2 X 60 X Frequency R.P.M. =

Number of Poles

To simplify the first formula into a form where it i ready for use at a moment's notice without any calculation, we may say that the number of cycles per revolution will be equal to the number of poles divided by 2. To use this, let us take the case of the four pole machine. Four di vided by 2 is 2. Therefore, the machine will deliver two cycles to every complete revolution of the rotor. If the speed is 1800 revolutions per minute or 30 per second, the frequency is 2 times 30 or 60 cycles per second.

Effects of Change of Frequency. — For commercial use such as lighting lamps and operating motors, the 60-cycle

Fig. 2. — A motor-gcneratur lor cl.angir.g direct current to alternating current

current is in general use in the United States. Certain parts of the country still use 125 and 133-cycle currents and in Canada the 25-cycle current is much in evidence.

A change in the frequency of the current necessitates profound changes in the apparatus it is intended to operate. It is not within the province of this work, however, to touch upon the alterations necessary in motors in order that they may be adapted for various frequencies. Suffice it to say that in the case of transformers, which ^Tc closely identified with the apparatus described, any change in the frequency of the current necessitates a corresponding change in the windings of the transformer.

Generally speaking, one of the higher frequencies is to be preferred for transformer work, for the core may be lighter and smaller, and the instrument is consequently cheaper and easier to build. Therefore, if the worker intends to generate his own alternating current, he may well employ an alternator producing a 120-cycle current at moderate speed. As a rule, however, some form of alternating current supply is available and, in such event, the experimenter will, of course, find it cheaper and better to so design his apparatus that it will operate in a satisfactory manner on the circuit at hand.

In the various descriptions of transformers w'hich follow in later chapters, the data for all standard frequencies are given in order that the worker need not make computations unless he so desires. In addition to this, one entire chapter is devoted to a simple explanation of the principles of transformer design, and, from this explanation, the average worker will be enabled to w^ork out any special design that may appear desirable.

In the case of direct current supply a motor-generator of the type shown in Fig. 2 is sometimes used. This consists of an alternating current generator driven by a direct current motor. Both armatures are mounted on the same jShaft in the machine illustrated.

I The High Frequency Current. — When an alternating 'current is made to change its direction of flow many thousands of times per second, it is termed a "high frequency current.'' The precise figure at which this term is properly jappHed is not very clearly defined but it is usually placed at the mark of 10,000 cycles per second. From this, it may extend into the hundreds of thousands or perhaps ^millions of cycles per second. How this current, w^hich oscillates with such inconceivable rapidity, is produced will be duly explained in the next chapter, but first of all let us consider the peculiar characteristics of which it partakes and the uses to which it may be put.

Characteristics of the H. F. Current. — For the serious experimenter and student of modern electricity, there is no more fascinating study than that of the electric current at high potential and high frequency. The phenomena which may be exhibited through its agency are at once spectacular and startling, of inconceivable beauty and grandeur, and, in practical applications, of the greatest utility and importance. While the larger types of apparatus demand that the utmost care and the finest materials be- used in the construction, the youthful experimenter may satisfy his craving for immediate results by building temporary apparatus of the crudest construction imaginable and still obtain effects bordering upon the marvelous. I

When the electric current is made to oscillate or change * its direction of flow several thousand times per second, it partakes of some astonishing characteristics. All of the preconceived theories of electricity as applied to the com-' mercial current are overthrown and the phenomena exhibited are contradictory in the extreme to the conventional ideas of the everyday electrical worker. For example, if an alternating current of the commercial sort having a frequency of 60 or 125 cycles per second, be passed through the human body, a muscular contractive effect is produced and the sensation of an electric '*shock" is felt. If the voltage of the applied current should be higher than the hundred mark, the shock is unpleasant and perhaps dangerous ; let it reach 1,000 volts or perhaps even half that amount, and the shock is in most cases fatal. On the other hand, if the current be made to oscillate or change its direction of flow with a frequency of 10,000 or more cycles per second, it may be applied to the body without danger or even discomfort at potentials running well into the tens of thousands. Let the frequency be increased still further, say into the millions, and the sensation of shock and muscular contraction is quite absent. Its place is taken by one of gentle warmth.

Spectacular Demonstrations. — The importance of this one peculiarity alone will be appreciated by those who have seen the self-styled electrical marvels upon the stage. Their claims to the effect that they are ''taking thousands of volts through their bodies'' are perhaps well founded for the presence of a spark several inches long is pretty good evidence of a very high potential. It is usually con- , ceded that every inch of spark between points through . the air represents a potential of between fifteen and twentyfive thousand volts. The secret of the performer's apparent power rests solely with the high frequency current.

I Perhaps the reader has seen one of these entertainers

I charge the body of an assistant to the point where a spark < several inches in length may be drawn from the fingers, chin, elbow, or even the tongue. A tuft of cotton or tissue paper held in the spark is immediately ignited, or perhaps the performer may light the tip of his cigarette with the spark taken between his finger and the body of the assistant. Possibly the performer may grasp the terminal of his machine with one hand while the other holds a wire leading to an ordinary incandescent lamp ; the assistant touches the remaining terminal of the lamp and the current is turned on. The lamp filament becomes red and perhaps white hot, finally burning out completely with the current passed through the bodies of the performer and his man.

The stage may be darkened and the terminal of the apparatus connected with the body ; as the current is turned on, the extremities of the body are seen to glow with a weird blue light. As the hand is raised above the head, streamers of purplish fire dart from the finger tips. A vacuum tube brought to within a distance of several feet from the body lights up with its characteristic glow even though there is no connection with the performer's body or the apparatus.

All of these experiments and hundreds of others may be performed with comparatively simple and inexpensive apparatus that is well within the reach of the average amateur mechanic. If the reader aspires to greater heights, he may build apparatus with which great, long sparks may be produced.

The High Frequency Current in Medicine. — The high frequency current, when applied to tlic human body through suitable electrodes and other appurtenances, can be made to produce the most profound physiological effects. Applied through a glass electrode from w^hich the air has been exhausted, the current stimulates the circulation of the blood, bringing it to the surface and increasing nutrition. Persistent application of the vacuum electrode to the scalp at certain intervals will restore tlie original color to grey hair. On the scalp of a partially bald patient, repeated applications will promote the Lrowth of new hair if the roots have not been totally destroyed.

Placing the patient in a chair having a metallic plate beneath its seat and behind the back, the physician may administer the high frequency current in the form of treatment known as auto condensation and thereby reduce the blood pressure in cases of arteriosclerosis. The same treatment is being successfully used in the reduction of superfluous flesh.

The general effect on the patient is a tonic one and in practically every case reported, the patient has been brightened up, given added vieor and cheerfulness, and, in fact, has exhibited all of the favorable efifects of a powerful tonic without sustaining any of the unfavorable after effects of a stimulant.

While on the subject of the medical application of the high frequency current, it may be well to point out the fact that while no ill effects are likely to be experienced from the treatment in the hands of an unskilled operator, continued applications intended to produce a medicinal effect upon the body should certainly not be given by the layman without first having had the advice of a physician. The two primary modes of treatment, i. c, the vacuum electrode and the auto condensation, produce diametrically opposite eft'ects. The electrode treatment tends to increase the blood pressure while the auto condensation tends to reduce it. It is obvious, therefore, that the auto condensation should never be applied except in cases where normal

( or hyper tension is indicated. After the examination has been made and the treatment prescribed, there is no reason why the actual administration should not be given by the

\ layman if the physician keeps a watchful eye on the progress at suitable intervals between treatments.

The Generation of Ozone and the X-Ray. — For the physician or the experimenter, there is perhaps no form of X-Ray apparatus better adapted to light office or laboratory use than the high frequency coil. It is safe, convenient and powerful and for all cases where very short exposures through the heavier portions of the body are unnecessary, it will meet the requirements admirably. True, the X-Ray is never quite safe in the hands of anyone other than a skilled operator having years of experience on his shoulders. The ray generated by a tube excited with a high frequency current is, however, less liable to produce the characteristic burn than is that produced by any other means. Just why this is so, is not definitely known, but the experience of the past few years indicates beyond a doubt the truth of the statement.

A high frequency coil to produce an eight-inch spark of a quality adapted to light X-Ray work can be built in the home workshop at only a fraction of the cost of an induction coil to do the same work. Furthermore, the high frequency apparatus is simple in construction and operation and it can be depended upon to do its work without the annoying delays incident to the usual induction coil with its troublesome interrupter and the ever-present danger of a serious breakdown of the insulation.

As a generator of ozone for medicinal purposes, the high frequency coil is particularly energetic and efficient. When the discharge terminals of the coil are separated beyond the normal sparking distance, great volumes of ozone are liberated in the space filled with a crackling brush discharge. When the vacuum tube electrode is passed over the body, the ozone is liberated at the point of contact. For purposes of inhalation, a simple apparatus consisting of vacuum electrode surrounded by an outer wall of glas: with an air space between can be made to produce the gas in ample quantities and with the additional advantage that it may be collected and administered to the patient through a suitable rubber tube and mouthpiece. Furthermore, this simple appliance permits one to pass the gas through small quantity of oil of eucalyptus which tends to remov' the nitrous oxide that invariably accompanies ozone generated by the electric spark.