GNITION 
 
 CarlA.PfanstiJW 
 

 AU. j 
 
 GIFT OF 
 
 ^"/ 
 
I G N IT I O N 
 
 BY 
 
 CARL A. PFANSTIEHL 
 
 President Pfanstiehl Electrical Laboratory 
 
 SECOND EDITION 
 
 With Original Diagrams 
 and Photographs 
 
 $1.00 
 
 Penton Publishing Co 
 Cleveland, O 
 

 
 Copyright 1912 
 
 by 
 
 The Penton Publishing Co 
 All rights reserved 
 
GJ0 tlf* mrmurit of 
 
 iflntltrr 
 
 464513 
 
IGNITION 
 
CARL A. PFANSTIEHL 
 
Introductory 
 
 Before entering upon the study of electric ignition, it 
 will be well to mention a few facts concerning electricity 
 itself. What is this wonderful agent which can be sent 
 through a small wire many miles long, then made to run 
 our heaviest machinery or to do almost anything from 
 carrying the delicate vibrations of the human voice from one 
 city to another, to the more difficult task of rendering visible 
 to the physician the broken bones of his patient, and last, 
 but by no means least, to enter the cylinders of our engines 
 and ignite the charge at the proper instant? To this, science 
 as yet has no definite answer. However, enough is known 
 regarding its action to enable it to be handled with at least 
 some degree of certainty. 
 
 There are two principal forms of electricity : Elec- 
 tricity at rest, known as "Static Electricity'' and electricity 
 in motion, or "Current Electricity!' Matter may be divided 
 into two classes with respect to electricity insulators 
 through which it cannot pass, and, therefore, must remain 
 where it is placed, and conductors through which it can pass 
 or flow. 
 
 Static electricity can be produced by friction; for in- 
 stance, by rubbing some good insulator, such as a glass or 
 hard rubber rod, with a piece of dry silk or woolen cloth. 
 Its presence on the rod can be shown by the latter's power 
 of attracting small bits of paper, wood, etc. It is easy to 
 show that this electricity is static, by rubbing only a part of 
 
 1 
 
Ignition 
 
 the rod with a cloth and observing that the power of attract- 
 ing the paper is found only on that part of the rod which 
 is actually rubbed. If a conductor, such as a brass rod, is 
 held in the hand and rubbed with a cloth, it exhibits no 
 such power of attraction. The electricity which is thereby 
 produced, passes from the rod through the body, a conduc- 
 tor, into the earth. It does not remain static on the rod, but 
 passes off as a current. If the conducting rod is provided 
 with an insulating handle and rubbed as before, the elec- 
 tricity so produced will flow to all parts of the rod, and 
 when it has spread over the entire surface, it ceases to flow 
 and becomes static. Thus the entire rod possesses the 
 power of attraction, even though one part only is rubbed. 
 The rod is now said to be charged with static electricity. 
 We will have occasion to refer again to static electricity 
 when discussing the action of the condenser in a jump 
 spark coil. 
 
 Our concern here will be mostly with the phenom- 
 enon of electricity in motion, or current electricity. 
 
 It can be seen from the above that, in order to maintain 
 a current of electricity, it is necessary that the part or cir- 
 cuit, through which it flows, be composed entirely of con- 
 ductors. If the conducting circuit is broken in any place 
 and an insulator interposed, the flow of current is thereby 
 stopped and it then remains static in the circuit. As a mat- 
 ter of fact, however, it does not remain static very long 
 unless the circuit is unusually well insulated. It leaks out 
 and finds its way to the earth, where it is neutralized. 
 
 The force which tends to move electricity must also be 
 present in the circuit if the current is to be maintained. 
 This is called Electro-Motive-Force, abbreviated, E. M. F. 
 
Introductory 
 
 Only the two principal methods for producing the E. 
 M. F. will be considered, viz. : Galvanic and Dynamic. The 
 former is a chemical action, the latter a mechanical one, 
 consisting of a conductor being made to pass across a mag- 
 netic field. The former method includes all kinds of bat- 
 teries the latter dynamos and magnetos. We will con- 
 sider first the Galvanic method, later taking up the Dy- 
 namic, under the head of "Dynamic Electricity". 
 
Photos showing a cast lead grid, for a storage battery, 
 before and after filling the pockets with 
 the active material. 
 
Forewoid 
 
 This book was written in response to a growing demand for an 
 explanation of the fundamental principles of Electric Ignition. 
 
 The author aims to show the real simplicity of a subject too 
 generally considered obscure, and he believes that the most 
 inexperienced gas engine operator, after carefully reading 
 these pages, will be greatly aided in solving the mysteries of 
 his ignition system. 
 
 Chapter Fourteen on low-tension, built-in, gear-driven, make- 
 and-break magnetos will be found especially timely and 
 helpful to the progressive manufacturers of stationary farm 
 engines, many of whom already have adopted as standard 
 equipment this type of ignition in which all batteries and 
 high-speed friction-driven generators are eliminated and the 
 entire ignition system made an integral and permanent part 
 of the engine. 
 
 The writer presents with special pleasure the oscillograph 
 tests made by him in his laboratory, which show with absolute 
 accuracy the action of vibrating and make-and-break coils, 
 and the current wave-forms of various magnetos. These 
 original and new experiments enable him to give information 
 that will prove to be of particular interest and value to the 
 student of ignition. 
 
 The author wishes to express his thanks to Mr. Oscar Bell, 
 who prepared the drawings. 
 
CONTENTS 
 
 Introductory. 
 
 Chapter I. Batteries. Primary Batteries Edison Pri- 
 mary Cell Gordon Cell Dry Cell Secondary or Storage 
 Batteries Edison Storage Battery. 
 
 Chapter II. Electrical Units and Laws Governing 
 the Flow of Electricity. Volt Ampere Ampere 
 Hour Ohm Watt Ohm's Law Series Connections 
 Parallel Connections Joint Resistance Current in 
 Branch Circuits Resistance of Different Materials 
 Table of Comparative Resistances. 
 
 Chapter III. Connecting, Testing and Care of Bat- 
 teries. Testing Dry Cells E. M. F. of Cells Amperage 
 of Cells Testing Storage Batteries Installing Batteries 
 Voltage and Amperage of Set of Cells Current from Cells 
 in Multiple Tests of Cells in Multiple. 
 
 Chapter IV. The Simplest Form of Electric Ignition. 
 
 Make and Break Ignition. Electric Inertia and Momen- 
 tum Magnetic Field The Igniter. 
 
 Chapter V. Construction and Operation of Make and 
 Break Coils. Make and Break Coils General Form of 
 Igniter Loss of Compression Igniter Points Duration 
 of Spark Time Length of Contact. 
 
 Chapter VI. Oscillograph and Tests. The Oscillograms 
 of Make and Break Coils E. M. F. of Spark Magnetic 
 Plug System. 
 
 Chapter VII. Theory of the Jump Spark Coil. Spark 
 Voltage Theory of Jump Spark Coil Theory of Con- 
 denser Theory of Vibrator Complete Action of Coil. 
 
 Chapter VIII. Practical Construction and Operation 
 of the Jump Spark Coil. The Primary The Vibrator 
 The Condenser Secondary Winding Pancake Wind- 
 ing Balance of Parts. 
 
 Chapter IX. Oscillograph Tests. Non-Vibrating Jump 
 Spark Coils. 
 
Contents 
 
 Chapter X. Dynamic Electricity. How an Electric 
 Current is produced by mechanical Means in Dynamos 
 and Magnetos Magnetism Magnetic Strength Mag- 
 netic Density Collecting Brushes Commutator Mag- 
 netic Circuit Armature Difference between Magnetos 
 and Dynamos Shunt Wound Series Wound. 
 
 Chapter XI. Low-Tension Dynamos Direct and 
 Alternating Current Low-Tension Magnetos. The 
 
 Low-Tension Dynamo The Commutator The Direct- 
 Current Magneto The Alternating Current Magneto 
 The Inductor Type Alternating Current Magneto. 
 
 Chapter XII. High-Tension Magnetos Their Theory 
 and Construction. High-Tension Magnetos Theory 
 of the Pure High-Tension Magneto. 
 
 Chapter XIII. The Installation and Care of High- 
 Tension Magnetos. Timing the Magnetos Care of 
 High-Tension Magnetos The Magnetic Circuit Wind- 
 ing the Armature Collecting Ring and Brush The 
 Condenser The Interrupter High Tension Distributor 
 Safety Spark Gap. 
 
 Chapter XIV. Low Tension Positively Driven Make- 
 and Break Magnetos for Stationary Engines. 
 
 Operation of System Construction of Magneto Field 
 Magnets Armature Grounding Brush Collecting Ring 
 and Brush Bearings Current Waves Timing the Mag- 
 neto Relation of Engine and Magneto Speeds Multiple 
 Cylinder Engines Wear of Igniter Points Insulation 
 of Igniter Heat of Arc Sizes of Magnetos Oscillating 
 Make-and-Break Magnetos. 
 
Chapter One 
 Batteries 
 
 Batteries are divided into two general classes, namely, 
 Primary and Secondary. In the former the current is pro- 
 duced by a chemical decomposition of the active materials. 
 Tn the latter by a kind of chemical change of the active ma- 
 terials, which change can be reversed, thereby restoring the 
 elements to their original state. \ 
 
 Cross section of ordin- 
 ary dry cell. Fig. B 
 shows cross section 
 of carbon rod, which 
 has large surface area 
 insuring good con- 
 tact with the granu- 
 lated carbon. 
 
 Diagrammatic view of a simple galvanic 
 cell. 
 
5 ^ L c H^ c ^' t fc * **** Ignition 
 
 PRIMARY BATTERIES. 
 
 Primary batteries consist essentially of a chemical solu- 
 tion, called the electrolyte, in which are placed two conduc- 
 tors, one of which will be attacked more rapidly by the solu- 
 tion than the other. During this process the element which 
 is acted upon most, usually receives a negative charge of 
 electricity, and if a wire is connected between the elements, 
 a current flows through it from one to the other. This cur- 
 rent continues to flow until either the solution or one of the 
 elements is exhausted or until the chemical action is tem- 
 porarily checked by bubbles of hydrogen gas which form 
 and collect on the negative element, thereby insulating it 
 from the solution. In this case, the wire connecting the 
 plates must be disconnected and the cell allowed to stand or 
 recuperate until the bubbles pass off, thereby allowing the 
 chemical action to proceed. This process is known as 
 "polarization" and is one of the most important factors to 
 be considered in the construction of primary batteries. It 
 is obvious then, that, if the current is to be maintained, this 
 polarization must be entirely prevented. 
 
 This is accomplished only in certain types of batteries, 
 known as "closed circuit." When a current is wanted for 
 only a few seconds at a time, as in ignition apparatus, where 
 the intervals of rest between current impulses are compara- 
 tively long, batteries in which the polarization is only par- 
 tially checked, are satisfactory and somewhat easier and 
 cheaper to make. These are known as "open circuit bat- 
 teries." 
 
 While there are a great many varieties of primary bat- 
 teries employing different elements and solutions, most of 
 them are more or less unsuitable for ignition purposes, 
 
 6 
 
Batteries 
 
 chiefly for mechanical reasons. The solutions are easily 
 spilled, the glass jars are large and readily broken, and the 
 active elements are more or less expensive and troublesome 
 to renew when exhausted. The internal resistance of these 
 types of batteries is usually quite large, which, as we shall 
 see later, reduces the available current output. 
 
 There are, however, two types of liquid cells, known as 
 the Edison Lalande, now called Edison Primary, and the 
 Gordon, which have been found to be a satisfactory source 
 of current in isolated places, where there is plenty of space 
 and no great vibration, and where it is inconvenient to have 
 a storage battery recharged. 
 
 It may be well to give a brief description of these cells 
 which are of the closed circuit type, and, therefore, suitable 
 for electric lighting as well as ignition. The active elements 
 are zinc and copper oxide in a solution of caustic potash 
 (potassium or sodium hydrate). 
 
 THE EDISON PRIMARY CELL. 
 
 In the Edison Primary cell the copper oxide with some 
 magnesic chloride added to it, is molded under pressure into 
 plates of the proper size and then baked ; the magnesic chlor- 
 ide serving to bind the mass together. The black oxide 
 plate thus formed is suspended in a copper frame between 
 two thick plates of zinc. Polarization is done away with in 
 this case, since the hydrogen as fast as it forms, combines 
 with the oxygen of the copper oxide, forming water, thus 
 gradually reducing the oxide to red metallic copper. The 
 amount of black active oxide left in the plate at any time 
 can be ascertained by picking into it with a pen knife. If 
 the plate is red throughout the entire mass, it is exhausted 
 and requires renewal. If, however, there is a layer of black 
 
 7 
 
Ignition 
 
 in the interior, there is some life left, the amount depending 
 upon the thickness of the layer of black oxide still remain- 
 ing. 
 
 It is very important that a layer of heavy paraffine oil 
 about Y4 inch thick be kept floating on the surface of the 
 solution to prevent corrosion and to protect it from a de- 
 teriorating chemical action with the air. If this is not done, 
 the life of the battery will be reduced over one-half. It 
 is also necessary to have the oxide plate kept one inch 
 below the surface of the solution. This cell gives an E. M. F. 
 of 0.7 volts and can furnish a current continuously dur- 
 ing its life of from two to seven amperes, depending, of 
 course, upon the size of the active elements. These cells 
 range in size from 150 to 600 ampere-hour capacity. 
 
 THE GORDON CELL. 
 
 In the Gordon type of cell, the oxide is powdered or 
 flaked and contained in a perforated sheet iron can. The 
 zinc takes the form of a cylinder placed around the oxide 
 can and held in place by porcelain lugs. The containing jars 
 are either porcelain or enameled steel, and with the latter, a 
 tight fitting compressed fiber cover is used, which is prac- 
 tically liquid tight, thus making the cell suitable for portable 
 engine and marine work. It is extremely easy to renew the 
 exhausted elements of this cell, as the loosening of one 
 screw will permit the exchange of both the oxide can and 
 the remains of the zinc for fresh elements. A layer of 
 paraffine oil must be kept on the surface of the solution as in 
 the Edison Primary cell. Both the Edison and the Gordon 
 batteries have the advantage of never freezing and while 
 severe cold slightly reduces their efficiency, it by no means 
 
Batteries 
 
 prevents their satisfactory action. Gordon cells have 
 worked satisfactorily at a temperature of 15 to 20 degrees 
 below zero. 
 
 THE DRY CELL. 
 
 The most popular primary battery is the well known 
 dry cell. 
 
 The active elements of the dry cell are zinc and carbon 
 in an electrolyte, consisting principally of ammonium mur- 
 iate. The containing can is made of sheet zinc, which also 
 forms an efficient positive element, as the active surface is 
 large. The inside of the zinc can is lined with some absorb- 
 ent material such as blotting paper, and to prevent internal 
 short circuit great care must be exercised that no cracks or 
 holes are left to allow the zinc to come into direct contact 
 with the carbon. A rod of solid carbon carrying a binding 
 post, is placed in the center and the space around it is filled 
 with a solidly packed mass of granular carbon, forming a 
 negative element. With this carbon is mixed some manga- 
 nese dioxide as a depolarizer. The fibrous lining is satur- 
 ated with a solution consisting principally of ammonium 
 muriate, which forms the electrolyte. The cell is then her- 
 metically sealed with some kind of sealing wax. In this 
 way the elements present large active surfaces without un- 
 duly increasing the size of the cell. 
 
 When the cell is put to work, it starts to polarize ; that 
 is, hydrogen gas is formed in quantities depending prin- 
 cipally upon the rate at which the cell is discharged, and, un- 
 less the gas is absorbed in some way, it will not only inter- 
 fere with the chemical action, but will cause the cell to swell 
 or puff out, sometimes even bursting it. If the hydrogen is 
 not formed too rapidly, however, it is disposed of by com- 
 
Ignition 
 
 bining with the oxygen of the manganese dioxide which was 
 mixed with the carbon. If the cell is discharged at a rate 
 high enough to cause hydrogen to be produced more rapidly 
 than the manganese dioxide can absorb it, the cell will soon 
 be ruined unless it is given frequent intervals of rest long 
 enough to allow the gas to be absorbed. This is how a cell 
 recuperates. If, on the other hand, the rate of discharge is 
 kept so low that the gas will be absorbed as fast as it is 
 produced, the cell will not need to recuperate as much and 
 can be used on closed circuits such as electric lighting. 
 The closed circuit discharge limit for most good dry cells 
 is about one-quarter ampere and better results are obtained 
 with even less. This is why the life or efficiency of a dry 
 cell is so dependent upon the rate of discharge. The greater 
 the discharge rate, the longer and more frequent must be 
 the intervals of rest, and the less will be the total efficiency. 
 This will be considered later more in detail when the meth- 
 ods of caring for and connecting cells are described. 
 
 The success of a dry cell depends not only upon the 
 selection and purity of the elements used but upon the man- 
 ner and uniformity with which they are handled during the 
 process of manufacture. For instance, an impurity on the 
 inside surface of the zinc will usually be all that is needed 
 to constitute a tiny local cell, which causes a current to flow 
 from the impurity to the zinc and back again through the 
 electrolyte. This will continue until the speck of foreign 
 matter is set free by the surrounding zinc being eaten away 
 or until the electrolyte around it is exhausted. This process 
 is known as "local action" and, fortunately, in the better 
 grades of dry cells is practically prevented. A careful 
 manufacturer of dry cells uses machinery largely in the 
 
 10 
 
Batteries 
 
 work, thus eliminating the variable personal factor, and sev- 
 eral tests for voltage and amperage are made during the 
 process of construction. The cells are then allowed to sea- 
 son for four days and after a final test are packed for ship- 
 ment. 
 
 SECONDARY OR STORAGE BATTERIES. 
 A brief mention only can be made of the principle of 
 the secondary or storage battery. In this cell, as stated be- 
 fore, the current is the result of a chemical change, which 
 takes place within the cell. This change differs from that 
 in the primary cell, in that, when the active elements are 
 exhausted, it is not necessary to replace them with new ones, 
 but the old ones can be re-formed or reconstructed, as it 
 were, by passing a current of electricity from some outside 
 source, through the cell. The direction of the charging 
 current is, of course, opposite to that during discharge. A 
 storage battery, then, is not, as most people believe, a reser- 
 voir, into which electricity can be pumped and held for 
 a time then drawn off as desired. What is actually stored 
 in the cell is not electricity, but chemical energy in a poten- 
 tial state. With this fact clearly fixed in mind, the opera- 
 tion and care of storage batteries becomes a comparatively 
 simple matter. 
 
 While there are several kinds of materials, which can 
 be employed, the combination most universally used is that 
 of lead plates in an electrolyte of dilute sulphuric acid. 
 The active material on the positive plate is peroxide of lead 
 (Pb O 2 ), and on the negative, spongy lead (Pb). The 
 plates usually consist of a cast lead framework or grid, hav- 
 ing many pockets, which are filled with the active material. 
 Several of both kinds of plates, always one more negative 
 
 11 
 
Ignition 
 
 than positive, are alternately assembled together, but insu- 
 lated one from another by thin strips of rubber or wood, the 
 positive and negative plates being respectively connected to 
 the positive and negative terminals of the cell. In the igni- 
 tion type of batteries there are usually three positive and 
 four negative plates, the capacity of the cell depending upon 
 the total area of the plates. The containing jars are glass 
 or hard rubber and the electrolyte is a ten per cent solution 
 of sulphuric acid in distilled water. A good storage battery 
 will last for several years if properly cared for, but it must 
 be guarded against several diseases to which it is susceptible. 
 
 I EDISON STORAGE BATTERY. 
 
 How about the new Edison storage battery upon which 
 the great inventor has been experimenting the last eight 
 years at an enormous expense ? It is undoubtedly a success, 
 and, were it not for the excessively high cost of production, 
 would soon replace the lead cell, being free from the list of 
 diseases which beset the lead battery. The active elements 
 are oxides of nickel and iron in an electrolyte of potassium 
 hydrate (KOH). 
 
 The grids are made of nickel-plated pressed steel, the 
 positive containing nickel oxide mixed with flaked metallic 
 nickel, the latter material reducing the resistance of the 
 oxide. The negative grid contains iron oxide, commonly 
 known as iron rust, and the containing cans are made of 
 nickel-plated steel, having all seams welded. This cell will 
 stand a great deal of abuse. 
 
 12 
 
Chapter Two 
 
 Electrical Units and Laws Governing 
 the Flow of Electricity 
 
 In the preceding chapter a few general principles of 
 electricity were discussed. Consider now a few laws which 
 govern its rate of flow, and learn how an understanding of 
 these laws can aid us in the proper installation and care of 
 batteries. We have seen that there are two conditions that 
 must be fulfilled before a current of electricity can be pro- 
 duced, namely, a complete circuit, composed wholly of con- 
 ductors, and included as a part of that circuit, some source 
 or sources of Electro-Motive-Force. 
 
 VOLT. 
 
 The unit of E. M. F. is called the Volt, and represents a 
 certain specific amount of that force zuhich tends to move 
 electricity. The volt, therefore, signifies electrical pressure 
 only, and does not designate any particular quantity of elec- 
 tricity. 
 
 AMPERE. 
 
 The unit of volume or size of an electric current is 
 called the Ampere and represents a certain specific rate of 
 How. The ampere, therefore, signifies volume of current 
 only, and not any particular quantity of electricity. Volts 
 correspond to pounds pressure in a water pipe, and amperes 
 to the size or volume of the stream. 
 
 13 
 
Ignition 
 
 AMPERE HOUR. 
 
 In order to measure any particular quantity of current 
 electricity, we must introduce the factor of time. Static 
 electricity can be stored, that is, held for a while in con- 
 densers, and its quantity then measured ; but not so with 
 current electricity. If a fixed number of amperes flows past 
 a given point in a wire for a definite period of time, a cer- 
 tain specific quantity of electricity will have passed that 
 point. The unit quantity of electricity is determined when 
 one ampere flows for one second, and is called a cou- 
 lomb. As the coulomb is a very small unit, it has been re- 
 placed, in practical work, by the ampere-hour, which is one 
 ampere flowing for one hour, or the equivalent. One am- 
 pere-hour, then, equals 3,600 coulombs. 
 
 We have already pointed out that electricity can only 
 pass through certain substances known as conductors and 
 not through others called insulators. Further experimenting 
 would have disclosed the fact that there is no such thing as 
 a perfect conductor* or perfect insulator, and that the 
 power of conducting electricity by different materials greatly 
 varies. Silver is the best known conductor, but even it 
 offers some opposition to an electric current. Therefore, 
 when a current is forced through a conductor, the attending 
 "friction" produces heat, and, if sufficient current is used, 
 the conductor can actually be melted. 
 
 OHM. 
 
 Since a current encounters resistance in its passage 
 through a conductor, it is easy to see that a given E. M. F. 
 
 *An Electron the absolute unit of electricity may be a perfect con- 
 ductor within itself. For an interesting and authoritative treatise on this 
 and similar subjects, see "Electrons," by Sir Oliver Lodge, D. Sc., F. R. S., 
 and also "Electricity and Matter," by Sir J. J. Thomson, D. Sc., F. R. S. 
 
 14 
 
Electrical Units and Laws Governing the Flow of Electricity 
 
 is capable of forcing a given current through only a certain 
 definite resistance. The logical unit of resistance, therefore, 
 is that amount of resistance through which a pressure of 
 one volt can force a current of one ampere, and is called 
 the Ohm. 
 
 WATT. 
 
 One other unit must be mentioned, namely, that of 
 electrical energy or power. It is easy to see that a cer- 
 tain current, propelled by a high E. M. F., repre- 
 sents more power than the same current propelled by 
 a low E. M. F. The unit of electrical power, therefore, is 
 that amount of power exerted when one ampere Hows under 
 a pressure of one volt, and is called a Watt. It follows that 
 a watt is a volt-ampere, and that the power in watts exerted 
 in a direct current circuit is equal to the total number of 
 volts multiplied by the amperes, acting in that circuit. The 
 readings of voltage and amperage must, of course, be taken 
 simultaneously. This relation can be expressed algebraic- 
 ally thus : 
 
 W = I E (1) 
 
 where W stands for watts, / for amperes, and E for volts. 
 
 Having clearly fixed in mind the meaning and values of 
 these various units, their numerical relations can be dis- 
 cussed. 
 
 OHM'S LAW. 
 
 Many years ago, Dr. Ohm, after whom the unit of 
 resistance was named, discovered that, in a circuit of con- 
 stant resistance the current increases as the voltage is in- 
 creased; and with a constant E. M. F. the current decreases 
 as the resistance is increased. This fact is known as "Ohm's 
 Law" and is the fundamental law of electricity, since it 
 
 15 
 
Ignition 
 
 governs the rate of current flow in direct current circuits. 
 Its importance, therefore, cannot easily be over-estimated. 
 Ohm's Law may be stated as follows: 
 
 The current in a direct current circuit varies directly 
 as the total E. M. F. and inversely as the total resistance 
 acting in that circuit; 
 
 or: 
 
 E. M. F. in volts 
 Strength of current in amperes = - 
 
 resistance in Ohms 
 and expressed algebraically : 
 E 
 
 / = - (2) 
 
 R 
 
 where R stands for Ohms. By simple transposition we have : 
 E 
 
 *W- (3) 
 
 / 
 and 
 
 E = IR (4) 
 
 It is evident that if two of the factors are known, the 
 third can easily be calculated. s . v 
 
 SERIES CONNECTIONS. 
 
 A word now about series and parallel circuits before 
 we take up the practical application of these principles. If 
 we join a number of conductors together, end to end, in a 
 circuit, so that the entire current will have to pass through 
 each one successively, they are said to be connected in series, 
 
 16 
 
Electrical Units and Laws Governing the Flow of Electricity 
 
 DIAGRAM NO.I 
 
 SERIES CONNECTIONS 
 
 18 VOITS- 
 
 L/IMP 
 POWEft- t x/Q- 
 
 WATTS 
 
 and it is obvious that the total resistance will be the sum of 
 their respective resistances. Series connections are illus- 
 trated in diagram No. 1. 
 
 PARALLEL CONNECTIONS. 
 
 If, on the other hand, we connect several conductors 
 together, so as to provide a number of separate paths 
 through which the current can flow from one point to 
 
 DIAGRAM 
 
 MULTIPLE 
 
 N0.2 
 
 I AMP REQV/RE5 . AMP. AT 6 VOLTS 
 - /. X 6 - 9 WATTS 
 
 another, they are said to be joined in parallel or multiple; 
 and each separate conductor is known as a Shunt on the 
 others. Multiple connections are shown in diagram No. 2. 
 
 JOINT RESISTANCE. 
 
 To figure the joint resistance of several conductors, con- 
 nected in multiple, as between points "A" and "B" in dia- 
 
 17 
 
Ignition 
 
 VlftGRKM NO 5. 
 
 
 "R= 5 OHMS 
 
 A A A A. 
 
 N 
 
 
 vvw 
 
 s\ 
 
 
 60AMP 
 
 R=li> OHMS 
 
 60/^MP. 
 
 ft 
 
 / V Wv 
 
 la flMPETR ES 
 
 B 
 
 
 B - 3O OHMS 
 
 
 *SPECT,V 6 loNDll S TNCt 5 KS^ HJ> 3 \ 
 
 WHICH ABE TO E/1CH 0THET? flS 6, 3 /1NX> 1 
 
 gram No. 3, first find the joint conductance by adding the 
 respective conductances of the various branches; the word 
 "conductance" meaning the precise opposite of resistance, 
 and equal numerically to the reciprocal of the resistance in 
 ohms. The joint resistance, of course, is the reciprocal of 
 the joint conductance. Therefore, the joint resistance in 
 ohms of a number of conductors joined in multiple, is equal 
 to the reciprocal of the sum of their respective conductances. 
 For example to find the joint resistance between points "A" 
 and "B", the resistance of the various shunts is respectively 
 5, 10 and 30 ohms. Therefore, their conductances are 1/5, 
 1/10 and 1/30, which, added together, equal the joint con- 
 ductance of 1/3. The reciprocal of their joint conductance 
 
 3 
 is or 3. Hence, the joint resistance is 3 ohms. 
 
 1 
 
 CURRENT IN BRANCH CIRCUITS. 
 
 Referring again to diagram No. 3 ; notice that the cur- 
 rent flowing from the battery divides when it reaches 
 point "A" and part of it flows through each branch, the cur- 
 rent, of course, dividing in direct proportion to the conduct- 
 
 18 
 
Electrical Units and Laws Governing the Flow of Electricity 
 
 ances of the several branches. , This .principle is used to 
 advantage in the multiple connecting of batteries. 
 
 We have discussed these various electrical units and their 
 relations to one another at considerable length, because we 
 wish to urge upon the reader the importance of his becom- 
 ing thoroughly familiar with these fundamental principles, 
 especially Ohm's Law, for he will find that a knowledge of 
 the basic principles involved, along with a little thought, is 
 all that is needed to make the locating and correcting of 
 faults in his electrical equipment a very simple matter. 
 
 RESISTANCE OF DIFFERENT MATERIALS. 
 
 The table herewith, shows the approximate re- 
 sistance of different materials, as compared with that 
 of pure copper, which is taken as "I". 
 
 Since there is no known perfect insulator, we can, 
 according to Ohm's Law, force a current through even the 
 best insulator, provided we sufficiently increase the voltage, 
 but, when this is done, the current takes the form of a jump 
 spark and burns its way through the insulator, thereby de- 
 stroying it. This phenomenon is known as "disruptive dis- 
 charge" and is what takes place between the points of a 
 spark plug in the jump spark system of ignition. 
 
 19 
 
20 
 
Electrical Units and Laws Governing the Flow of Electricity 
 
 TABLE OF COMPARATIVE RESISTANCES. 
 
 (MATTHIESSEN'S STANDARD.) 
 
 COPPER = i. 
 
 RELATIVE 
 MATERIALS. RESISTANCE. 
 
 Silver annealed 0.925] 
 
 Copper 1.00 \ 
 
 Gold (99% pure) 1.38 
 
 Aluminum (99% pure) 1.61 J 
 
 GOOD 
 CONDUCTORS 
 
 Zinc 3.62 
 
 Platinum, annealed 5.65 
 
 Iron 5.70 
 
 Nickel 7.78 
 
 Tin 8.28 
 
 Lead 12.8 
 
 Antimony 22.1 
 
 Mercury 59.3 
 
 Bismuth 82.2 
 
 Carbon (arc light) 2510.0 
 
 FAIR 
 CONDUCTORS 
 
 Sea water 
 
 Ordinary water 
 
 Dampness 
 
 Damp wood 
 
 Partly carbonized oil. . 
 Dirt of any kind, etc. 
 
 Leather, cured 
 
 Ordinary dry wood 
 
 Black vulcanized or hard fibre. 
 Red fibre 
 
 POOR 
 CONDUCTORS 
 
 POOR INSULATORS FOR VOLT- 
 AGES HIGHER THAN 1,000 
 BUT FAIRLY GOOD FOR 
 LESS VOLTAGE 
 
 White vulcanized or hard fibre 
 
 Ditto Boiled in paraifine 
 
 Kiln dried wood 
 
 Ditto Boiled in paraffine 
 
 "Electros" or composition materials.... 
 
 Asbestos (dry) 
 
 Various dry oils 
 
 "Empire" oiled fabrics. . , , 
 
 Card board and paper boiled in paraffine 
 
 Shellac (dry) 
 
 Insulating varnishes 
 
 Micanite cloth and paper 
 
 Rubber (soft) 
 
 Rubber (hard) 
 
 Porcelain 
 
 Paraffine, beeswax, rosin, etc 
 
 Sulphur 
 
 Glass 
 
 Mica . 
 
 GOOD 
 INSULATORS 
 
 21 
 
Chapter Three 
 
 Connecting, Testing and Care 
 of Batteries 
 
 Consider now the purely practical side of the subject. 
 Suppose one wants to buy some dry batteries. He should 
 not accept any cell the clerk in the store gives him. He 
 ought first to ask for some well-known make. Then look 
 at the date stamped on the cell, and, if it is several months 
 old, the chances are ten to one that the small amount of 
 moisture or electrolyte originally in the cell is already half 
 dried up. 
 
 TESTING DRY CELLS. 
 
 After finding a cell, bearing a recent date, test it for 
 amperage with a pocket "battery tester" or ammeter, which 
 should have been previously compared with a larger instru- 
 ment for accuracy. Hold the ammeter in contact only the 
 fewest possible seconds necessary to obtain a reading, for, 
 since the resistance of the ammeter is extremely low in 
 fact practically nothing the cell while being tested is dis- 
 charging at its maximum possible rate. 
 
 The cell showing the highest amperage is not neces- 
 sarily the best. This reading is not an indication of the 
 amount of electricity in the cell, but, rather of the highest 
 possible rate of chemical action that the active elements and 
 the depolarizer can undergo. By the use of extra strong 
 
 22 
 
Connecting, Testing and Care of Batteries 
 
 chemicals in the construction, a standard No. 6 cell can be 
 made to show 40 amperes or more, but, when this is done, 
 the chemicals will soon burn themselves out, without doing 
 useful work, and greatly reduce the life of the cell. It has 
 been found that the combination of chemicals best suited 
 for long life and efficiency, under ordinary conditions, in the 
 standard No. 6 cell, is that which will cause the latter to test 
 16 to 20 amperes. However, this may vary slightly with dif- 
 ferent good makes of cells. As severe cold temporarily 
 checks chemical action, dry cells will not show their full 
 strength when chilled through ; and, on the other hand, cells 
 should not be kept too warm, as their chemical action would 
 be unduly stimulated, thereby shortening their life. 
 
 Should we be without an ammeter, a rough test can be 
 made by holding a nail or a key firmly against the zinc 
 binding post, screwed up tight, and touching the surface of 
 the carbon rod with the smallest point possible. Owing to 
 the high contact resistance of carbon, if the cell is quite new, 
 a tiny red spark or arc, accompanied by a little puff of 
 smoke, will form at the point of contact; if, however, just 
 a little black ring forms on the carbon around the point of 
 contact, there is some life left, sufficient usually to run the 
 engine a few hours at least. With a little experience, a 
 fairly accurate test can be made in this way. If a cell in a 
 set will not pass this test, or show 4 or 5 amperes on an 
 ammeter, it is dead and should be thrown out, as it adds 
 to the resistance of the circuit, and thereby tends to check 
 the current flow from the rest of the cells. 
 
 E. M. F. OF CELLS. 
 
 The E. M. F. of a primary cell depends upon the charac- 
 ter of the active elements, and not upon the size of the cell. 
 
 23 
 
Ignition 
 
 Dry cells, regardless of size, should, when new, show about 
 1.5 volts, which figure, however, is rarely ever reduced even 
 to 1.2 when the cell is exhausted, provided the reading is 
 taken on "open circuit," viz. : when there is no current 
 being drawn from the cell. The voltage of an exhausted 
 cell will, however, drop to nearly nothing the instant an 
 attempt is made to draw a current from it. An ammeter, 
 however, is much to be preferred in ascertaining the condi- 
 tion of dry cells. 
 
 AMPERAGE OF CELLS. 
 
 The amperage, which can be drawn from a cell, in- 
 creases directly with the size or rather the area of the active 
 elements. Should we find ourselves dependent for a few 
 hours run upon a newly exhausted set of dry cells, we can 
 coax them into action for a while longer by breaking out the 
 sealing wax on the top and pouring in as much water as 
 will be absorbed, as this tends to reduce the internal 
 resistance. The internal resistance of a No. 6 dry cell, 
 when new, is about 0.064 ohm. 
 
 In setting up wet or liquid cells, follow the directions 
 given by the maker, being careful not to get any dirt into 
 the electrolyte. 
 
 TESTING STORAGE BATTERIES. 
 
 An ammeter should never be used to test a storage bat- 
 tery, for, owing to the extremely low internal resist- 
 ance of both, a current of 100 or 200 amperes would flow, 
 which would not only wreck the ammeter, but ruin the 
 plates of the cells as well. A low reading voltmeter should 
 be used to test storage batteries, and should show two volts 
 per cell when pretty well charged, and when the voltage per 
 cell drops to about 1.8, it should be recharged. The voltage 
 
 24 
 
Connecting, Testing and Care of Batteries 
 
 should never be allowed to drop below 1.7. These readings 
 should be taken when the battery is discharging under nor- 
 mal conditions. A lead storage battery should not remain 
 long in an uncharged condition, as lead sulphate (Pb SO 4 ) 
 will form on the plates. As this material has a high resist- 
 ance, it tends to insulate the plates from the electrolyte, 
 thereby greatly increasing the internal resistance of the 
 battery, which, of course, reduces the available current. 
 This process is known as "sulphation," and is the most 
 common disease of the lead battery. The remedy for a 
 mild case of sulphation is a very long charge at about one- 
 fourth or less of the normal charging rate. 
 
 INSTALLING BATTERIES. 
 
 A word upon the installing of batteries. Referring to 
 the table of comparative resistance of materials notice that 
 water, dampness, and dirt of any kind are partial conductors. 
 Therefore, to avoid leakage and consequent waste of cur- 
 rent, install the batteries in a clean, dry, cool, but not cold, 
 place, as free from vibration as possible. If dry cells are 
 used, nail together several strips of wood to separate the 
 cells one from another, and hold them off the bottom of the 
 box in which they are placed. It is a good plan to boil the 
 strips of wood in paraffine, or, at least, to give them a good 
 coat of shellac, as this prevents, them from absorbing 
 moisture. 
 
 If the regular portable type of storage battery is used, it 
 should frequently be thoroughly rinsed with cold water, by 
 placing it under the faucet, and then wiped. Be sure 
 that the rubber corks are in place, so that no water or 
 dirt will get washed into the electrolyte. During the process 
 of charging, a storage battery gives off a certain amount of 
 
 25 
 
Ignition 
 
 acid spray, which, if allowed to remain, rapidly corrodes the 
 terminals and destroys the wooden case. No trouble need 
 be experienced from the acid, if the battery is thoroughly 
 washed after each charge, or oftener. Cleanliness is the 
 main thing to observe in the care of batteries. 
 
 In connecting cells together, flexible conductors should 
 be used, or better yet, the little copper battery connectors 
 that are made for the purpose. Be sure to see that the bind- 
 
 -NO. 4. 
 
 SERIES CONNECTIONS. 
 
 OPEN C1R6UI T VOL TAGE AB OUT /. 
 
 >$ RIES-MULTI PLE CONNECTIONS. 
 
 WORKING VOL TA6E JBOUT 6.S 
 C/ffGU/r VOLTJ6 ABOUT 7.3~ 
 
 26 
 
Connecting,. Testing and Care of Batteries 
 
 ing nuts are tight, and particularly that the screw attached 
 to the carbon rod in a dry cell is very tight, so as to reduce 
 the contact resistance of the carbon to a minimum. 
 
 A loose contact with the carbon rod is a fault often very 
 troublesome to locate, for it does not completely shut off 
 the current, as does a broken wire, but, owing to the high 
 resistance, permits only a part of the current to flow. 
 
 When several cells are joined together, to form a single 
 source of E. M. F., the whole is called a battery. It is well 
 to use cells of the same make and necessary that they be of 
 the same age and in the same condition. It is not economy 
 to connect a new cell with several old ones. 
 
 VOLTAGE AND AMPERAGE OF SET OF CELLS. 
 
 When cells are connected in series, and the entire cur- 
 rent thereby made to flow through each one successively, it 
 is easy to see that no more current or amperage can 
 economically be drawn from the set than from one cell. 
 The E. M. F., however, will be increased as the current pro- 
 ceeds from one cell to the next ; therefore, the total voltage 
 of a number of cells connected in series is equal to the sum 
 of the voltage of the separate cells and the total amperage 
 is no greater than that of one cell. 
 
 It is important that we learn the voltage best suited 
 economically to operate our electrical apparatus ; this infor- 
 mation can best be had from the manufacturers. While 
 most ignition apparatus is designed for use with six volts, 
 there is some apparatus which requires eight, and others 
 work more satisfactorily and efficiently on four. Taking 1.5 
 volts per dry cell, we see that four cells in series will give 
 an E. M. F. of six volts, but, because the internal resistance 
 
 27 
 
Ignition 
 
 of dry cells increases as the cells are used, reducing the 
 available or working E. M. F., five cells instead of four, 
 are usually used for six-volt apparatus. 
 
 Since the life of a dry cell depends almost entirely upon 
 the rate of discharge, it is desirable to keep the current flow- 
 ing through the cells, as low as practicable. By connecting 
 a number of batteries, of equal voltage, in multiple, the cur- 
 rent divides, as we have seen, and only a part flows through 
 each branch, thereby reducing the demand on each battery. 
 
 CURRENT FROM CELLS IN MULTIPLE. 
 
 The number of amperes flowing in a circuit governs the 
 number of sets of cells to be connected in multiple. A low 
 reading ammeter should be included in the main circuit to 
 show the amperage, and a sufficient number of batteries 
 should be placed in multiple to reduce the current in each 
 branch to J4 ampere, or less, if they are to work on closed 
 circuit, as in operating electric lights. This is illustrated in 
 diagram No. 4. 
 
 The demand for current made by a single-cylinder en- 
 gine, if an efficient coil is used, is not too great to be effi- 
 ciently furnished by one set of cells in series. For operat- 
 ing multiple cylinder engines, much more efficiency is to be 
 had from ten cells, connected in series-multiple, than if they 
 were used in two separate sets of five in series. It would be 
 well to have as many sets in multiple as there are cylinders, 
 but this is often impracticable. 
 
 The results of many careful tests, made to show the in- 
 crease in efficiency of dry cells, when connected in series- 
 multiple, are given below. Tests were made on a four- 
 cylinder automobile engine, in severe service, as well as in 
 many other ways. 
 
 28 
 
Connecting, Testing and Care of Batteries 
 
 TESTS OF CELLS IN MULTIPLE. 
 
 When dry cells are connected in series-multiple, four in 
 series will usually have sufficient working voltage to operate 
 six-volt apparatus, since the internal resistance of a battery, 
 composed of cells in series-multiple, is much less than in one 
 
 RESULTS OF PRflCT/C/IL TEST 0N D1RV CELLS. 
 
 c 
 
 2 
 3 
 4 
 
 HOURS seRVjce 
 
 > 2O 40. 6O SO /<*? 120 140 160 180 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 NO. 
 
 WRftNGEMENT OF DT^r CELL S. 
 
 
 I 
 
 
 SET OF4JN SEKIES. 
 
 
 2 
 
 2 SETS OF 4- W SE"RIS-MULTIPL. 
 
 
 3 
 
 3 SETS OF 4 IN SERIES-MULTIPLE. 
 
 4 
 
 4SET5 OF 4 IN SEtt/HS-MULTlPLE. 
 
 
 
 set of cells in series. For some apparatus, however, par- 
 ticularly electric lights on closed circuit, it is well to have 
 the battery composed of sets of five cells in series, which 
 will insure an average working E. M. F. of about six volts. 
 
 29 
 
Chapter Four 
 
 The Simplest Form of Electric 
 Ignition 
 
 Having a fairly good idea of an electric current, its 
 production in galvanic batteries and mode of travel, we shall 
 now see how it ignites the charge in gas engines. Clearly 
 fix in mind just what the requirements are. 
 
 First The work must be done inside the cylinder, and 
 consequently the current must be led through the cylinder 
 walls ; this must be accomplished without leaving any cracks 
 or leaks through which the gas can escape. , 
 
 Second Enough heat must be developed to instantly 
 ignite the charge under all conditions. 
 
 Third The ignition must occur at a certain fixed time, 
 without a variation of so much as a hundredth or even a 
 thousandth part of a second. 
 
 Fourth The apparatus must be very reliable and there- 
 fore simple. 
 
 Fifth It must be efficient. 
 
 Electric ignition may be divided into two general classes 
 the Jump Spark or High Tension, and the Touch Spark or 
 Low Tension systems. We will confine ourselves in this 
 chapter to the Touch Spark system. 
 
 MAKE AND BREAK IGNITION. 
 
 There are three principal parts to Touch Spark ignition, 
 namely, a source of E. M. F., a Touch Spark or Primary 
 coil, and an Igniter. 
 
 30 
 
The Simplest Form of Electric Ignition 
 
 The source of E. M. F. may be any suitable galvanic 
 battery of usually four to six volts, such as a set of four or 
 
 Photograph showing magnetic field, generated around a copper wire carrying 
 
 a current of 120 amperes. The wire passes through a piece of paper and 
 
 the magnetic lines are formed by iron filings sprinkled on the paper. 
 
 five dry cells ; or a low tension Dynamo or Magneto. In 
 some special forms of magnetos, the primary coil is com- 
 bined with the armature of the machine itself. This latter 
 system will be described in detail in the last chapter. 
 
 Before the action of the Touch Spark coil can be under- 
 stood, mention must be made of a most important charac- 
 teristic of current electricity. 
 
 An electric current does not confine its influence solely 
 to the conductor through which it passes, but sets up a kind 
 of rotary disturbance, in the nature of whirls, at right angles 
 
 31 
 
Ignition 
 
 Series of diagrams showing various steps in increasing the magnetic field 
 
 surrounding a current carrying wire. With a properly constructed coil 
 
 as in Diagram 4 the apparent momentum of the current can be 
 
 increased many times, which results in a hot spark when the 
 
 circuit is broken. 
 
 Diagram No. 1 
 
 Shows the beginning of the 
 magnetic lines forming around 
 the wire instantly after the 
 circuit is closed. 
 
 Diagram No. 2 
 
 Shows how the_magnetic lines 
 combine an instant later. 
 
 Diagram No. 3 
 Shows how the magnetic density is increased by 
 placing a piece of iron in the center 
 of the coil. 
 
 32 
 
The Simplest Form of Electric Ignition 
 
 N 
 
 Diagram No. 4 
 
 Shows how the magnetic density is still further in- 
 creased by placing the coil in an iron box- 
 
 to and around the wire, in the all-pervading Ether-of- 
 Space. 1 This phenomenon is the same as that near the poles 
 of an ordinary magnet and is known as Magnetism ; in other 
 words, an electric current magnetizes the space around it. 
 
 ELECTRIC INERTIA AND MOMENTUM. 
 When a circuit is completed, the current starts to flow, 
 but is held back for an instant by its growing magnetic field, 
 and consequently does not reach its full value, as determined 
 by Ohm's Law, until its magnetic field has ceased to grow 
 and become constant ; and, conversely, a current does not 
 instantly stop on breaking a circuit, but is maintained for a 
 moment by the collapsing or shrinking of the magnetic lines. 
 An electric current, therefore, appears to possess inertia and 
 momentum, 2 and it is this tendency to persist or apparent 
 
 1 See an article by the author in POWER BOATING for July and August, 
 1910. 
 
 2 (For an interesting and non-mathematical treatise on Electricity and 
 Magnetism, see "Modern Views of Electricity," by Sir Oliver Lodge, F. R. S. 
 This book is obtainable through The Penton Publishing Co., Cleveland, O.) 
 
 33 
 
Ignition 
 
 momentum of an electric current which causes it to burst 
 through the intervening air space, thus producing the spark 
 seen on breaking a circuit. This is the way the spark is 
 produced in make-and-break ignition. 
 
 MAGNETIC FIELD. 
 
 The magnetic field around a current-carrying wire can 
 be shown by sprinkling iron filings on a cardboard, through 
 which the wire is passed at right angles. Since magnetism 
 finds a much easier path through iron than air, the filings 
 will arrange themselves in concentric circles around the 
 wire, as the photograph shows. 
 
 In order to secure a large, "fat" spark, when the circuit 
 is broken, the apparent momentum of the current must be 
 increased, which can be done by increasing the surrounding 
 magnetic field. This, in turn, can be accomplished by wind- 
 ing the wire into a compact coil, making the current circulate 
 around a small space many times, thereby greatly concen- 
 trating the magnetism. In this case the magnetic lines 
 around each turn of wire tend to open up and include the 
 other turns. The magnetic density can still further be in- 
 creased by placing a piece of iron in the center of the coil. 
 With a properly constructed coil of this kind, the apparent 
 momentum of a current can be increased many times, re- 
 sulting in a fat, hot spark when the circuit is broken. 
 
 THE IGNITER. 
 
 The igniter is simply a means for making and breaking 
 an electric circuit inside the cylinder, and usually consists 
 of two electrodes, insulated from each other, one fixed in 
 position and the other moveable into and out of contact 
 with' it. Usually a lever, extending from some moving part 
 
 34 
 
The Simplest Form of Electric Ignition 
 
 of the engine, engages the moveable electrode, causing a 
 separation at the instant ignition is required. 
 
 Having now a general idea of the theory of make-and- 
 break ignition, we will in the next chapter turn our atten- 
 tion to the practical construction and operation of its parts. 
 
 35 
 
Chapter Fvie 
 
 Construction and Operation of 
 Make-and-Break Coils 
 
 The Make-and-Break coil consists of a few hundred 
 turns of insulated copper wire, varying in size from No. 14 
 to 20 B. & S. gage, wound around an iron core, about an 
 inch in diameter, and from 3 to 10 inches long. Since mag- 
 netism does not penetrate to the center of and saturate a 
 thick bar of iron as readily as a thin one, the core is made up 
 of a bundle of small iron wires. If the best results are to be 
 obtained, the iron wires must be thoroughly annealed, to 
 make them as soft as possible, otherwise the magnetic 
 lines cannot easily rise and fall through them. The turns 
 of copper wire must be well insulated one from another, to 
 prevent leakage or short-circuits. 
 
 Some kinds of Make-and-Break coils are placed in an 
 iron box, which provides a nearly complete circuit of iron, 
 through which the magnetic lines can pass. This tends to 
 increase the time required for the magnetic field, and conse- 
 quently the current, to build up to its maximum. In this 
 construction, however, a small space should be left between 
 the ends of the core of the coil and the iron box, in order to 
 make the magnetic lines jump a small air gap, for, if the 
 magnetic circuit were composed entirely of iron, the path 
 would be so good that the magnetic lines would keep on 
 
 36 
 
37 
 
Ignition 
 
 spinning around in it and would not shrink or collapse when 
 the current is broken as quickly as they should. The 
 proper amount of gap in the magnetic circuit is a matter 
 to be carefully determined. 
 
 Whether the coils are mounted in an iron box, paper or 
 vulcanized fiber tube, they should be filled in with an insu- 
 lating waterproof wax, having a high-melting point. Some 
 Make-and-Break coils are insulated by winding a narrow 
 strip of paper around the bare wire, as the latter is being 
 
 Types of make and break coils. 
 
 wound on the coil, and, when the winding is completed, the 
 coil is finished by gluing a layer of paper around it. A coil 
 made in this way will give fairly good -results, provided it 
 is kept perfectly dry and free from moisture and not con- 
 nected with too strong a battery. The only advantage in 
 this kind of coil is that a few cents can be saved on the 
 cost; but this saving in no way offsets the risk sustained 
 by its use. 
 
 GENERAL FORM OF IGNITER. 
 
 The general form of the Igniter can be seen by the illus- 
 tration. "A" is a cast iron member, carrying an insulated 
 stationary electrode, "B," and a grounded, moveable elec- 
 trode "C." 
 
 The electrode "B" must be very carefully insulated from 
 all other parts. A built up mica washer, J^ inch, or better, 
 f$ inch thick, should be used at "D." Irregular and weak 
 explosions can often be traced to a faulty insulation of this 
 
 38 
 
Construction and Operation of Make-and-Break Coils 
 
 part. If the mica washers become loose and begin to sepa- 
 rate, dirt will get in between them and cause a partial short 
 circuit. In this event it does little good to tighten the old 
 washers ; new, clean ones should be substituted. 
 
 Loss OF COMPRESSION. , 
 
 The moveable electrode should have a long, well made 
 bearing, or better, be provided with a ground taper joint 
 on the inside end in order to prevent the escape of the com- 
 pressed charge ; in fact, the whole igniter must be con- 
 structed and bolted to the cylinder in such manner as to pre- 
 vent any leakage of gas. A leaky igniter is often a cause of 
 poor compression and consequent loss of power. 
 
 The constant breaking of a circuit, with the attending 
 spark, has a strong tendency to disintegrate and burn the 
 contact surfaces ; in fact, the current seems to tear off ex- 
 
 Make and break ignition system. 
 
 39 
 
Ignition 
 
 ceedingly small particles of the metal and project them in a 
 stream between the separating contacts. This provides a 
 fairly good conducting path, over which the current con- 
 tinues to flow for a moment, and, since the current-carrying 
 capacity of this stream of particles is small, the current 
 heats it and partially burns it up, as it would a small wire. 
 The surrounding gas adds fuel to this burning stream of 
 particles and is thereby ignited. The metallic particles that 
 are not consumed, are either lost or deposited on the nega- 
 tive contact. This accounts for the "pitting" of the positive 
 and building up of the negative contact points. For this 
 reason the igniter points must be made of some metal that 
 will not readily disintegrate and burn. 
 
 IGNITER POINTS. 
 
 Platinum and iridium are the best metals for this pur- 
 pose. Points of pure platinum, however, are not quite hard 
 enough to withstand the mechanical strain of being con- 
 stantly beaten together, and pure iridium is so hard and has 
 such a high melting point that it cannot be drawn into a 
 wire or made into a rivet, but can only be formed into 
 little globules or spheres, by allowing a drop of the molten 
 metal to cool while falling. This iridium drop must be 
 brazed or hard-soldered to the contact arms. A rivet made 
 of an alloy of these metals, containing 15 to 20 per cent of 
 iridium, is very satisfactory, and can easily be riveted to 
 the contact arms. A form of hard nickel can be used with 
 fair satisfaction for the igniter points where the mechanical 
 wear and current are not too great. 
 
 There are several special alloys of nickel-steel, etc., 
 made for this purpose, which are a great deal cheaper than 
 
 40 
 
Construction and Operation of Make-and-Break Coils 
 
 platinum and iridium, but they are in no way as satis- 
 factory. 
 
 DURATION OF SPARK. 
 
 The apparent momentum of an electric current is ex- 
 pended in a very short time after the -contact points begin 
 to separate ; that is, the life of the spark or arc in Make-and- 
 Break ignition apparatus, under working conditions, is ap- 
 proximately from 0.0008 to 0.005 second, as shown by the 
 Oscillograph. This makes it necessary to separate the con- 
 tact points very suddenly, in order to draw the arc out to 
 about -j^ inch before it dies out. To accomplish this sudden 
 break, regardless of engine speed, a spring and tripping 
 mechanism is used. Every make of engine has its own 
 particular design of igniter, but a glance at any one, with 
 the requirements in mind, will make it clear. 
 
 In order to insure even and accurate timing, the tripping 
 mechanism should be so made that wear on any of its parts, 
 as \vell as on the igniter points, will not affect the time the 
 spark occurs. The difficulty of meeting this requirement is 
 one of the main reasons why Make-and-Break ignition is 
 not suitable for high-speed multiple-cylinder motors. 
 
 So long as the igniter points are in contact the cur- 
 rent flows ; therefore, to save the battery, the contact should 
 be as brief as possible. The circuit should be closed just 
 long enough to allow the current to build up almost to its 
 maximum, for it is evident that the spark will be strongest 
 if the circuit is broken instantly after the current has 
 reached its full strength, and will be no stronger no matter 
 how long after that the circuit is kept closed. 
 
 41 
 
Ignition 
 
 TIME LENGTH OF CONTACT. 
 
 The time required for the current to build up in Make- 
 and-Break coils, depends upon the E. M. F. of the battery 
 and the construction of the coil. With four new dry cells, 
 the time required with different makes of coils is from 
 0.015 to 0.10 second. These figures are not the results 
 of theory or guess, ' nor even of mathematical calculation, 
 but are taken from the record made by the rising current 
 itself, in an oscillograph, a description of which is given in 
 the next chapter. 
 
Chapter Six 
 The Oscillograph and Tests 
 
 THE OSCILLOGRAPH. 
 
 In the oscillograph, very rapidly changing electric cur- 
 rents are made to trace a permanent record of themselves 
 on a photographic film. Two thin strips of silver 1/2000 
 of an inch thick, are suspended very close together in a 
 strong magnetic field, and a tiny glass mirror, 0.001 of an 
 inch thick and about -^ f an i ncn square, is cemented to 
 the strips. A current of electricity sent up one ribbon and 
 down the other reacts upon the magnetic field, tending to 
 push one ribbon forward and the other backward, thereby 
 slightly rotating the mirror, the amount of rotation being a 
 measure of the current strength. A cylinder, with a pho- 
 tographic film wound around it, is supported about twenty 
 inches from the silver strips, and a tiny beam of light from 
 an arc lantern is focused on the mirror and reflected back 
 from it through a slot in a partition to the cylinder. The 
 whole is inclosed in a light-tight box. The cylinder is rotated 
 at a known speed and an electrically operated shutter allows 
 the beam of light to strike the film for one revolution only. 
 If the current to be measured, or a certain proportion of it, 
 is sent up and down the strip, the mirror and beam of light 
 will oscillate according to the variation of current. This 
 motion of the spot of light, combined with the rotation of 
 the film, w r ill trace a curve on the latter. The loop of silver 
 
 43 
 
Ignition 
 
 ribbon with the mirror is inclosed in a glass tube, containing 
 the damping liquid, and is so sensitive that it will respond 
 over 6,000 times a second. 
 
 The oscillograph, a very sensitive instrument which makes an accurate 
 record of rapidly changing electric currents on a photographic film. 
 
 The oscillograph the author has in his Laboratory has 
 been specially arranged by him for particular research work 
 along other lines, and being extra sensitive it is peculiarly 
 adapted for investigating ignition apparatus. 
 
 OSCILLOGRAMS OF MAKE-AND-BREAK COILS. 
 
 The accompanying "oscillograms" were carefully traced, 
 from the original film, on squared paper, properly calibrated 
 
 44 
 
A series of records taken from the oscillograph, showing how the 
 
 current builds up in various coils. The current was furnished by 
 
 four dry cells working through a regular igniter arranged 
 
 to make a very long contact. 
 
 45 
 
Ignition 
 
 for time, from the diameter and speed of rotation of the 
 film ; and amperes, by the deflection of the beam of light by 
 a constant current of known strength. They were taken 
 with several different kinds of coils and four dry cells 
 working through a regular igniter, the latter, however, for 
 convenience, was arranged to make a very long contact, 
 namely about 0.1 of a second. 
 
 A thoughtful study of these curves will develop many 
 interesting facts ; for instance, in curve "C-12," we see that 
 the current builds up to one ampere during the first 0.005 
 second and becomes 1.6 amperes in 0.01 second, finally 
 reaching its maximum of 2.2 amperes, as determined by 
 Ohm's Law, after 0.03 second. The time length of contact 
 
 o-f Oscillograph. 
 
 for this particular coil should be between 0.015 and 0.020 
 second. The current remains constant at about 2.2 amperes 
 until the circuit is broken, when the arc begins and the steep 
 descent of the curve indicates the current passing through 
 the arc. In this instance, the arc lasts a little longer than 
 
 46 
 
The Oscillograph and Tests 
 
 0.001 second and dies out when the current, passing through 
 it, drops to about 1 ampere. 
 
 Curve "C-ll" is taken from the same coil as "C-12," 
 excepting that the coil is placed in an iron box. Note how 
 much slower the current rises and falls. In this, case, the 
 arc lasts nearly 0.003 second. This type of coil will, as a 
 rule, consume less current than open core types, because it 
 will permit a greater variation of time length of contact 
 without using too much current. The time length of con- 
 tact for this coil should be between 0.02 and 0.04 second. 
 Since the time length of contact varies with the speed of 
 the engine, and the accuracy with which the igniter is made, 
 the advantage of an iron clad coil from a standpoint of 
 current consumption, is obvious. 
 
 Curve "C-13" was taken from a coil not having an iron 
 core. Curve "C-14" was taken from the same coil with an 
 iron core, showing the difference there is between the 
 two. A comparison of these curves proves the great im- 
 portance of the iron core. 
 
 E. M. F. OF SPARK. 
 
 The momentary voltage produced in Make-and-Break 
 coils has to the writer's knowledge heretofore been only 
 estimated, for it is very difficult to make an accurate meas- 
 urement, due to the many conditions affecting it. To obtain 
 an accurate measurement of this the author constructed a 
 commutator which connected a special electrostatic volt- 
 meter across the arc for about one hundred thousandths part 
 of a second. Various coils were tried, and it was found 
 th;t the momentary E. M. F. was from 60 to 200 volts, de- 
 pending upon the battery and coil. 
 
 47 
 
Ignition 
 
 Make-and-Break ignition is very satisfactory for single- 
 cylinder, low-speed engines, provided the igniter is properly 
 insulated and equipped with iridium or iridium-platinum 
 points and designed to give a very sudden break, and proper 
 time length of contact to suit a well made coil. Most of the 
 trouble with Make-and-Break ignition is in the rapid burn- 
 ing and corroding of the igniter points, requiring frequent 
 renewal and in defective insulation of the stationary elec- 
 trode. Points of proper material, when used with an 
 efficient coil, will last a whole season, and often very much 
 longer. 
 
 Make-and-Break ignition may be said to be complicated 
 mechanically and simple electrically, and the Jump Spark, 
 simple mechanically, but complicated electrically. The ab- 
 sence of levers and heavy moving parts makes the Jump 
 Spark system superior for high-speed multiple-cylinder 
 engines. 
 
 MAGNETIC PLUG SYSTEM. 
 
 A form of Make-and-Break ignition, known as the 
 Magnetic Plug system, has been devised to meet the condi- 
 tions in medium speed multiple-cylinder engines. In this 
 system, the igniter is made very small and light and is oper- 
 ated by an electro-magnet, the whole being enclosed in a 
 metal shell not a great deal larger than the high-tension 
 spark plug, and is screwed into the cylinder in the same 
 way. When ignition is required an impulse of current is 
 sent to the magnetic plug, across the igniter points through 
 the electro-magnet, which then attracts its armature thereby 
 separating the contacts. 
 
 48 
 
Chapter Seven 
 Theory of the Jump Spark Coil 
 
 We have already pointed out that, in order to produce 
 the spark or arc in tnake-and-break ignition, it is necessary 
 that the igniter points touch each other, then rapidly sepa- 
 rate. Since this involves considerable mechanical action, 
 this system is unsuitable for high-speed motors. In order 
 to properly ignite medium and high-speed engines, it is 
 necessary to eliminate all heavy moving parts. This is 
 accomplished in the jump spark system, wherein the igniter 
 points are placed a short distance apart and held stationary, 
 and the arc is started between them without previous con- 
 tact. As stated in a previous chapter, this is accomplished 
 by increasing the E. M. F. sufficiently to force a current 
 against the high resistance of the gas lying between the 
 points of the igniter or spark plug, as it is called in this 
 case. The instant a current starts to flow between the 
 points, an arc is formed, very similar to the arc in the touch 
 spark system, except that the amperage or volume of cur- 
 rent, passing through it, is very much less. After the arc 
 has been started, only a few volts are required to maintain 
 it, for the- resistance of the arc 1 itself is only a few ohms, 
 and, in some cases, less even than one ohm. 
 
 1 For methods of measuring the resistance of arcs of various kinds, and 
 the E. M. F. required to start them, see "The Principles of Electric Wave 
 Telegraphy," by J. A. Fleming, F. R. S., pages 178 and 152. 
 
 49 
 
Ignition 
 
 HEAT OF SPARK. 
 
 The heat of an arc depends largely upon the amperage 
 flowing through it. A high voltage is needed only to start 
 the arc, which, when started, should be fed with considerable 
 current. The E. M. F. required to start an arc depends 
 upon several conditions, the principal ones being : Distance 
 between terminals or length of spark; kind of surrounding 
 gas its pressure, its temperature ; nature and form of ter- 
 minals between which the spark jumps. We can only briefly 
 mention the manner in which these conditions influence 
 spark potential. 
 
 In sparks, from 1-64 inch to J4 inch long, the E. M. F. 
 increases almost directly as the length. The resistance of 
 various gaseous mixtures used in internal combustion 
 motors, at atmospheric pressure, is not very different from 
 that of air. 
 
 SPARK VOLTAGE. 
 
 The E. M. F. necessary to produce a spark other 
 things being equal, varies almost directly as the absolute 
 pressure. This law is quite accurate up to 200 pounds per 
 square inch. Increasing the temperature of the gas lowers 
 the necessary voltage. The writer knows of no accurate 
 law expressing this relation ; however, it has been shown 
 that there is no simple inverse law, as the voltage decreases 
 less rapidly than the temperature increases. The shape of 
 the terminals between which the spark jumps, influences 
 the necessary voltage. For instance, much less voltage is 
 required to produce a spark between two sharp points or 
 from a point to a flat surface than between smooth surfaces 
 or spheres. 
 
 50 
 
Theory of the Jump Spark Coil 
 
 Many practical tests were made to determine the dis- 
 tance a spark should jump in air at atmospheric pressure, 
 to insure its jumping between the points of the spark plug 
 while igniting the engine. It was found that, for compres- 
 sions not exceeding 80 pounds, a spark that would jump 
 from fV inch to J4 inch between needle points in air, would 
 insure a jump between the points of a plug under compres- 
 sion in the cylinder. Many persons have made "tests" on 
 coils and spark plugs by screwing the latter in a box, in which 
 the air was compressed to 60 or 80 pounds, but these tests 
 are of little value, unless the temperature of the air is raised 
 to equal that of the gases in the cylinder. It is not easy 
 to determine the exact voltage necessary to produce this 
 spark, but it has been shown that the average jump spark 
 ignition coil is capable of producing a momentary open cir- 
 cuit E. M. F. of from 10,000 to 25,000 volts. 
 
 THEORY OF JUMP SPARK COIL. 
 
 Let us see how the jump spark coil produces this enor- 
 mous E. M. F. A jump spark coil consists essentially of an 
 iron core, around which is wound a few turns of rather 
 large wire, called the primary, and an entirely separate 
 winding of many turns of fine wire called the secondary, 
 and some means for making and breaking the primary cir- 
 cuit. This is really a make-and-break coil, having two sepa- 
 rate windings. When a current is sent through the primary, 
 a magnetic field is formed around the core, as we have seen, 
 and the magnetic lines, when expanding or collapsing, cut 
 through the turns of wire in the secondary winding, thereby 
 producing in it an E. M. F. The value of this "induced" 
 E. M. F. depends upon the density of magnetic lines, the 
 speed at which they expand or collapse, and the number of 
 
 51 
 
Ignition 
 
 turns of wire through which they cut. The current, or am- 
 perage, in the secondary circuit, depends upon the value of 
 the induced E. M. F., and the resistance of both the sec- 
 ondary winding and spark gap. 
 
 It is desirable to use as little current as possible and 
 keep the resistance of the secondary winding as low as can 
 be done. Therefore, in order to produce the necessary 
 E. M. F. with a limited number of both magnetic lines and 
 turns of wire in the secondary, the magnetic lines must be 
 made to collapse as quickly as possible. 
 
 We have seen that the arc, which forms when the pri- 
 mary circuit is broken, allows the current and consequently 
 the magnetic field, to die down rather slowly. If this arc 
 were prevented, the current would suddenly be stopped and 
 
 Diagram showing action of the jump spark coil. 
 
 a very rapid collapse of the magnetic lines would follow. 
 While there are several ways for preventing the arc, such 
 as directing a blast of air against it, or placing it in a strong 
 magnetic field, the best method is to absorb, in a condenser, 
 
 52 
 
Theory of the Jump Spark Coil 
 
 the momentary "extra" current, which would otherwise 
 form the arc. 
 
 THEORY OF CONDENSER. 
 
 A condenser consists essentially of two thin, metal 
 strips, of considerable area, placed a short distance apart, 
 but carefully insulated from each other. If these metal 
 strips are connected respectively to the contact points, be- 
 tween which the primary circuit is broken, the "extra" cur- 
 rent, which would otherwise form the arc, finds it easier 
 to rush on to the strips and spread itself over their sur- 
 face, thereby charging them with static electricity. After 
 the magnetism has subsided, the condenser discharges 
 through the primary winding, and is then ready to receive 
 the sudden rush of current at the next break. As a matter 
 of fact, however, the discharge of the condenser has a slight 
 tendency to cause a more complete collapse of the magnetic 
 lines, thereby slightly increasing the E. M. F. in the sec- 
 ondary. While it is impracticable to entirely eliminate the 
 spark at the contact points it can be so far lessened as to 
 reduce the wear on them to a minimum. The contact points 
 in this case, as in the make-and-break system, must be made 
 of iridium-platinum. 
 
 The secondary winding must have several thousand 
 turns, therefore a very small wire must be used. The tre- 
 mendous voltage produced demands a very careful insula- 
 tion and arrangement of the turns. The secondary winding 
 is, perhaps, the most important part of the coil. 
 
 THEORY OF VIBRATOR. 
 
 In order to produce a stream of sparks, the primary 
 circuit must be rapidly made and broken. In the vibrating 
 
 53 
 
Ignition 
 
 type of coil, this is accomplished by supporting a thin piece 
 of iron, having a contact point on it, near one end of the 
 core. The current, from the battery, on its way to the 
 primary winding, is made to pass through a stationary con- 
 tact point, into the point on the iron head. When the core 
 becomes magnetized the iron head is attracted ; the circuit is 
 thus broken, and the core loses its magnetism, allowing the 
 vibrator to spring back into contact again. This process is 
 repeated several hundred times a second. Since the vibrator 
 is operated automatically by the magnetic attraction of the 
 core whenever a current is sent through the primary, means 
 must be provided for closing the primary circuit at the 
 instant ignition is required. This is accomplished by the 
 use of a contact maker, called the timer or commutator, 
 which is operated by the cam shaft of the engine. 
 
 Having now a general idea of the theory of a jump 
 spark coil, let us follow it through a complete cycle. 
 
 COMPLETE ACTION OF COIL. 
 
 Contact having been made at the timer, the current 
 from the battery starts flowing across the points on the 
 vibrator through the primary winding, where it circulates 
 around the iron core, then back to the battery. The instant 
 the current starts, it begins to magnetize the space around 
 it, which effect is greatly concentrated in the primary in the 
 manner already described. As the magnetic field is expand- 
 ing, the lines of force cut through the many turns of sec- 
 ondary winding, thereby producing in it an E. M. F. which, 
 owing to the comparatively low rate of expansion, is too 
 feeble to force a current across even a very small air gap. 
 When the magnetic field has grown strong enough to attract 
 the vibrator armature against the tension of its spring, the 
 
 54 
 
Theory of the Jump Spark Coil 
 
 circuit is broken, and the "extra" current which would other- 
 wise maintain itself for an instant by arcing between the 
 points, is absorbed by the condenser and thus suddenly 
 choked off. The magnetic lines accordingly shrink very 
 rapidly, cutting through the secondary turns with sufficient 
 speed to cause a considerable E. M. F. strong enough this 
 time to overcome the resistance of an air gap and force a 
 current across it in the form of the familiar jump spark. 
 This spark lasts only until the energy of the shrinking lines 
 is expended, when the vibrator is no longer attracted by the 
 core and it springs back into contact again. The whole 
 process is repeated with surprising rapidity. 
 
 55 
 
Chapter Eight 
 
 Practical Construction and Oper- 
 ation of the Jump Spark Coil* 
 
 Having in the last chapter described the theory of the 
 Jump Spark Coil, the manner of its practical construction 
 will now be given. 
 
 THE PRIMARY. 
 
 The core consists of a number of soft Norway iron 
 wires, Nos. 20 or 22 gage, packed tightly into a card board 
 tube from 4 to 8 inches long, and ^ to J4 i ncn m diameter. 
 Around this are usually wound two layers of insulated cop- 
 per wire, varying in size, according to conditions, from No. 
 16 to No. 20 gage. It is important that the iron wires be 
 thoroughly annealed to make them as soft as possible, and 
 also to give them a coat of scale which tends to insulate them 
 one from another, thereby preventing a loss of energy 
 through the production of Foucault or Eddy currents. A 
 turn of oiled paper or cloth should be placed between the 
 layers of wire, and it is well to dip the whole primary in 
 paraffine, or better, an insulating compound having a higher 
 melting point. 
 
 THE VIBRATOR. 
 
 The vibrator is, perhaps, the most troublesome part of 
 the coil to correctly design, consequently there are many 
 different forms on the market. Since no fixed rule can be 
 
 *(For a treatise on the practical construction of coils, see ''Induction 
 Coils," by A. Frederick Collins.) 
 
 56 
 
a. 1 
 
 IB 
 
Ignition 
 
 laid down for its construction, we will briefly mention a few 
 things that go to make up a good vibrator. 
 
 In the first place, it should be very simple and free from 
 delicate adjustments, particularly if it is to be used by a 
 novice, as is usually the case. It is considered good practice 
 by many manufacturers to have both contact points station- 
 ary and effect the adjustment by regulating the tension of 
 the spring supporting the soft iron head. This permits a 
 uniform distance between the core and vibrator at all times, 
 and also increases the life of the contact points, for, after 
 they have become worn to fit each other, their relation is not 
 disturbed by adjustment as would be the case if one point 
 were mounted on an adjusting screw. Good sized points, 
 made of the best grade of iridium-platinum, should be used 
 for the contacts. 
 
 Some vibrators, known as "Hammer Break," have one 
 platinum point, mounted on a spring separate from the iron 
 head. A hook or catch, mounted on the latter, after it has 
 begun to move, strikes this spring, effecting a very sudden 
 and positive separation of the contacts. While this tends to 
 give a slightly longer spark, it is more complicated, and, as 
 a rule, not quite as responsive or rapid as some other styles, 
 and also generally consumes more current. 
 
 It is well to, have the adjustment so designed as to pre- 
 vent the possibility of "freezing" the vibrator ; viz., bringing 
 the contacts together so tightly that they cannot vibrate, 
 thereby rendering the coil inoperative and causing an ex- 
 cessive waste of current. As a rule, the current consump- 
 tion is lessened by placing the vibrator closer to the core, 
 and particularly by reducing the pressure between the con- 
 tact points; this, of course, also reduces the strength of 
 
 58 
 
Practical Construction and Operation of the Jump Spark Coil 
 
 spark. Therefore, to adjust a vibrator to be economical in 
 current, reduce the pressure between the points as much as 
 possible, without causing the engine to miss fire. 
 
 THE CONDENSER. 
 
 There are several ways for making a condenser, but 
 only one of the best will be mentioned. 
 
 Two strips of very thin tin foil, separated by a double 
 thickness of special paper, are wound into a compact roll, 
 then soaked for several hours in hot wax. After the paper 
 is thoroughly impregnated, the condenser is placed under a 
 pressure of several tons, which squeezes out all surplus 
 
 Condenser shown on the left before soaking in wax. 
 
 Finished condenser on the right, after it has 
 
 been impregnated and subjected to 
 
 several tons pressure. 
 
 59 
 
Ignition 
 
 wax, and, after cooling, it is as compact as a board. This 
 does away with troublesome air spaces between the layers 
 of paper and foil, and insures a minimum and uniform dis- 
 tance between the tin foil sheets. The importance of this is 
 apparent when we remember that the capacity of a con- 
 denser, other things being equal, varies inversely as the dis- 
 tance between the tin foil sheets. It is also desirable for 
 the condensers to be of uniform capacity. The connecting 
 wires are soldered respectively to the folded edges of the 
 two tin foil strips, as the photograph shows. 
 
 As the condenser of an ignition coil is subjected to sud- 
 den surgings of potential reaching several hundred volts, 
 the insulation between the tin foil strips must be very good 
 to prevent a breakdown. The actual capacity of con- 
 densers used in various ignition coils, is from 0.1 to 0.4 
 Microfarad. 
 
 SECONDARY WINDING. 
 
 When it is realized that a current under a pressure of 
 10,000 to 20,000 volts is produced and made to circulate 
 many times in the secondary of an ignition coil, it is needless 
 to say that the most careful arrangement and insulation 
 of the turns are necessary. The conventional method of 
 making the secondary consists in winding a fine insulated 
 wire in even layers around a paper tube, just large enough 
 to slip over the primary, the layers of wire being separated 
 one from another by one or two turns of thin paper. When 
 the required number of layers are wound, which is usually 
 between 30 and 50, the coil is soaked for several hours in 
 melted wax. In order to insure thorough and uniform 
 insulation, it is best to use the vacuum impregnating process, 
 
 60 
 
Practical Construction and Operation of the Jump Spark Coil 
 
 A group of secondary windings. The three on the left are wound 
 
 by the Pancake system. The small winding in the foreground 
 
 is taken from a very cheap coil. A pile of iron core wires 
 
 with a finished primary are shown on the right. 
 
 which consists essentially of thoroughly drying the winding 
 in an oven in which a partial vacuum is created. The 
 melted wax is then allowed to flow into the oven under 
 pressure. This helps to force the insulating compound 
 into the center of the winding, and also drives out all trace 
 of moisture. Where the layer method of winding is used, 
 it is almost necessary to employ the vacuum process to se- 
 cure satisfactory insulation. In order to lessen the danger 
 of a breakdown or "burnout" of the secondary, it is usually 
 wound in two separate parts, which are connected in series. 
 To prevent a spark passing from one section to the other, a 
 space is left between them which is filled with wax. 
 
 "PANCAKE" WINDING. 
 
 There is a patented method of winding, in which the 
 secondary is wound in 10 to 16 little rubber spools or sec- 
 tions, which are slipped over the primary and connected in 
 series. The wire used has a special cotton covering. The 
 spools are actually wound in a bath of melted wax, which 
 is constantly kept at a temperature just above the boil- 
 
 61 
 
Ignition 
 
 rass Packinct. 
 
 G-rcutfd 
 E lectrode . 
 
 Showing general scheme of 
 high tension spark plug. 
 
 ing point of water. This insures the complete saturation 
 of every inch of wire and also makes air spaces and moisture 
 within the winding impossible. In this construction, known 
 
 Steel 
 Keller 
 
 White 
 Fibre. 
 
 Timer for vibrating coil (4-cyl.). 
 
 62 
 
Practical Construction and Operation of the Jump Spark Coil 
 
 as the "pancake method/' the insulation runs at right angles 
 to the core, making the difference of potential increase with 
 the length of the winding, instead of its height, which latter 
 is the case in the layer method, where the insulation runs 
 parallel to the core. In the layer winding, the maximum 
 difference of potential exists between the top and bottom 
 layers, which are not often separated more than % inch, 
 and, if there is a flaw in the insulation, particularly at the 
 ends, a breakdown may occur. This, however, does not often 
 happen in a modern well made vacuum impregnated coil. 
 In the "pancake" winding, the greatest difference of poten- 
 tial is between the two ends of the winding, which are from 
 3 to 5 inches apart. A breakdown in this winding is prac- 
 tically impossible. 
 
 There are several other advantages to be gained by 
 the "pancake method" of winding ; among others, the elimi- 
 nation of electrostatic capacity and self-induction of the 
 winding which tends to produce a very responsive and quick 
 acting coil.* 
 
 The secondary windings of ignition coils contain from 
 8,000 to 25,000 turns, depending upon the make of coil. 
 The size of wire used is between No. 34 and No. 38 B. &.S. 
 gage. 
 
 BALANCE OF PARTS. 
 
 All parts of a coil must be carefully designed to work 
 well together. For instance: If the condenser is too small 
 or sluggish in action, the contact points will often flash and 
 quickly burn, and, on the other hand, if it is too large, the 
 secondary spark will be shortened and tend to hesitate be- 
 
 *See "Induction Coils," by Armagnat, pp. 41, 44 and 78. 
 
 63 
 
Ignition 
 
 fore jumping, particularly if made to pass between round, 
 smooth surfaces. The size and number of turns of wire on 
 the primary is determined largely by the quickness and re- 
 sponsiveness of the vibrator. Many other things have to 
 be worked out, for it is not a simple matter to correctly de- 
 sign a coil. 
 
 After the coil and condenser are assembled in a box 
 or hard fiber tube, the latter should be filled with a good in- 
 sulating waterproof compound that will not melt in hot 
 weather or if installed in a hot place. 
 
 64 
 
Chapter Nine 
 Oscillograph Tests of Vibrating Coils 
 
 It is well known that an ammeter, connected in series 
 with a vibrating coil and battery, will indicate from % to 1 
 or more amperes. Since the vibrator is constantly interrupt- 
 ing the current, it is evident that the current passing through 
 the coil is not steady, but is a series of separate impulses, 
 and that the ammeter simply indicates their average value. 1 
 The oscillograph 2 is the only instrument that is quick and 
 sensitive enough to accurately record the current impulses. 
 The accompanying oscillograph tests were made on several 
 well known makes of coils, operated by a regular roller timer 
 and storage battery. Each group of lines indicates one con- 
 tact at the timer, and each line shows the current used each 
 time the vibrator breaks the circuit. A careful study of 
 these records will develop many interesting facts. For 
 lack of space, brief mention only of a few of the most 
 important will be made. 
 
 The first thing noticed is the fact that, in some cases 
 nearly five amperes are required to operate the vibrator ; in 
 other words, a series of current impulses, each reaching a 
 maximum of 2 to 5 amperes, is needed to operate a vibrating 
 coil. This explains why a battery will not work after its 
 
 1 This reading may not be the same with all types of moving coil am- 
 meters. A hot wire ammeter will give the root mean square (square root 
 of the average square). 
 
 2 See Chapter Six, page 43. 
 
 65 
 
Ignition 
 
 amperage is reduced below a certain limit, and also that 
 comparatively large wires, namely No. 12 or No. 14 gage, 
 should be used to make the connections, and still larger 
 wires if the battery is placed more than a few feet from 
 the coil. 
 
 It also will be noticed that in some coils the first im- 
 pulse of the vibrator requires more current than the suc- 
 ceeding ones, and in others less current is required. The 
 vibrator breaks the circuit several times during one contact 
 
 s .0 .01 .02 .03 ,04- .05 .06 -07 .08 .09 JO .11 ./2 .13 
 
 Seco n ds. 
 
 Oscillograph records of the current in the primary circuit of various 
 vibrating coils. 
 
 66 
 
Oscillograph Tests of Vibrating Coils 
 
 at the timer, causing as many separate sparks at the plug. 
 If the first spark, which occurs the first time the vibrator 
 breaks the circuit after contact is made at the timer, is too 
 weak to ignite the charge, ignition will be delayed until the 
 second or third interruption occurs. This partly accounts for 
 the so-called "lag" in some kinds of coils. Curve "B 2" 
 illustrates this kind of a vibrator. Curve "B 3", on the 
 other hand, is from a coil that takes more current for the 
 first impulse of the vibrator than the succeeding ones ; con- 
 
 a 
 
 .Ol .02 .03 -O-f .05 ,O6 .07 .08 
 
 Secon ds. 
 
 IQ II .12 
 
 Oscillograph records of the current in the primary circuit of various 
 vibrating coils. 
 
 67 
 
Fio.3 
 
 Contact Breaker for non-vibrating 
 coil, which cannot stop on con- 
 tact and gives a uniform 
 length of contact at all 
 speeds. 
 
 68 
 
Oscillograph Tests of Vibrating Coils 
 
 sequently the spark, resulting from this first impulse, will 
 be stronger than the following ones, and will invariably ig- 
 nite the charge. In this case the several following sparks do 
 no good and it will also be noticed that the current required 
 for these extra sparks is comparatively small. This type 
 of coil has very little "lag," and is, therefore, particularly 
 good for high-speed motors. It will not work, however, 
 quite as well on an old battery low in amperage as the other 
 type (B 2), unless a multiple battery is used. Curve "B 6" 
 represents the very irregular action of a poorly designed 
 vibrator working on an improperly balanced coil. 
 
 NoN-VlBEATING JlJMP SPARK CoiLS. 
 
 A mechanical circuit breaker is often substituted for the 
 vibrator, and geared to the engine, so as to break the circuit 
 the instant ignition is required. In this system only one 
 spark occurs at the plug, but, if it is strong enough, it is all 
 that is needed. Fig. 6 illustrates this type of timer, as used 
 
 Platinum TWAs. 
 
 036"Thic/< 
 
 Si-eel Burton. 
 
 Case Hardened. 
 
 End of Half- 
 Time 
 
 Fig. 6. Timer for non-vibrating coil. 
 
 on motorcycles and many types of small stationary engines. 
 The fact that this timer can stop with the points in con- 
 tact is an objection, because when this happens, the battery 
 
 69 
 
Ignition 
 
 is rapidly used up. Figs. 1, 2 and 3 clearly show a contact 
 breaker which can never stop with the points together. The 
 time length of contact, and therefore the strength of spark, 
 is the same at all engine speeds. This apparatus uses very 
 little current. 
 
 70 
 
Chapter Ten 
 Dynamic Electricity 
 
 How AN ELECTRIC CURRENT is PRODUCED BY MECHANICAL 
 MEANS IN DYNAMOS AND MAGNETOS. 
 
 In the Introductory it was stated that there are two 
 principal methods for producing an electric current, viz. : 
 Galvanic or chemical, and Dynamic or mechanical. Con- 
 sider now how an electric current can be produced by 
 mechanical means. 
 
 As already mentioned, electricity and magnetism are 
 very closely related. An electric current magnetizes the 
 space around it ; in other words, an electric current produces 
 magnetism. This process can be reversed and magnetism 
 made to produce an electric current. It is well right here to 
 call attention briefly to a few facts concerning magnetism, 
 and clearly fix in mind just what is meant by the phrase 
 "magnetic lines of force. " 
 
 MAGNETISM. 
 
 There is no known insulator of magnetism. It passes 
 quite freely through the air, and, with practically equal free- 
 dom, through all other substances, with the exception of 
 iron and its various modifications nickel and cobalt. 
 These latter metals offer a better path than air. Iron, being 
 the best, will, according to its chemical and physical proper- 
 ties, conduct magnetism from 100 to about 10,000 times bet- 
 ter than air. Magnetism, like electricity, can flow only in 
 
 71 
 
Sparks from a 30-inch induction coil playing around a glass plate five 
 
 feet square an artificial thunder and lightning storm, making 
 
 a noise like a broadside of gattling guns. 
 
 72 
 
Dynamic Electricity 
 
 closed circuits. Every magnetic line of force is assumed to 
 pass out -from the north ( + ) pole, and make a complete 
 circuit through the surrounding medium and return into 
 the south ( ) pole, then through the magnet to the north 
 pole again, and so on. The path through which the lines 
 
 Diagram showing the path or circuit taken by the magnetic 
 lines of force around a bar magnet. 
 
 of force travel, is called the magnetic circuit, and, like an 
 electric current, the amount of magnetism that will flow, 
 other things being equal, depends upon the resistance or 
 reluctance, as it is called, of the magnetic circuit. The 
 region near the poles of a magnet, traversed by lines of 
 force, is spoken of as a magnetic field. The directions taken 
 by the lines of force can be shown by placing a small com- 
 pass in the magnetic field. The needle will swing around so 
 as to be parallel (or tangent) to the lines of force, and its 
 north pole will point in the direction of the magnetic lines. 
 
 73 
 
Ignition 
 
 
 Diagram showing the induced current and the direction it takes in a wire, 
 
 as the latter is being moved across a magnetic field in the direction 
 
 shown by the arrow. The compass needle will turn in the 
 
 direction indicated. 
 
 MAGNETIC STRENGTH. 
 
 In order to compare magnetic fields of different 
 strengths, the following unit was adopted : The unit mag- 
 netic pole is a pole of such strength as will repel a similar 
 pole of equal strength ivhen placed in air, one centimeter 
 away, with a force of one dyne. Imagine a magnetic pole 
 of unit strength, placed in the center of a sphere having a 
 radius of one centimeter; a certain quantity of magnetism 
 will pass through every square centimeter of the surface of 
 the sphere. This particular amount has been adopted as the 
 unit quantity of magnetism, and is known as one line of 
 force. The name "Maxzveli" after J. Clerk Maxwell the 
 first great mathematical electrician is often substituted for 
 the phrase "line of force," and so a magnetic field, through 
 which 20 lines of force pass, may be said to have a strength 
 of 20 maxwells. Since the surface area of a sphere of 
 radius "r" equals 47rr 2 , the area of a sphere having a radius 
 of one centimeter is 12,57 square centimeters. From this it 
 
 74 
 
Dynamic Electricity 
 
 follows that every magnetic pole of unit strength sends out 
 12.57 lines of force or maxwells. 
 
 MAGNETIC DENSITY. 
 
 The unit of magnetic or "flux" density is called a gauss, 
 and is that density resulting when one maxwell passes at 
 right angles through an area of one square centimeter; hence 
 a magnetic field may be spoken of as having a flux density 
 of, say 5,000 gausses, meaning that 5,000 maxwells pass, 
 at right angles, through every square centimeter. 
 
 In the light of the above facts, the following statement 
 of the fundamental principle of dynamo electric generators 
 will be readily understood : Whenever a conductor and mag- 
 netic lines of force are made to intersect one another, an 
 E. M. F. is produced in that conductor, and, if its ends are 
 connected, thereby completing the circuit, an electric current 
 will How. This phenomenon can easily be illustrated by 
 passing between the poles of an ordinary horseshoe magnet, 
 a wire having a galvanometer included in its circuit. If a 
 galvanometer is not handy, make one by winding a few turns 
 of insulated wire around a pocket compass, as shown in 
 Fig. 2. Note that the compass needle will swing in one 
 direction when the wire is entered between the poles of the 
 magnet, and in the opposite direction when it is zvithdrawn. 
 This shows that the direction taken by the so-called "in- 
 duced" current depends upon the relative direction of mo- 
 tion of the wire through the magnetic field. 
 
 The value of the E. M. F. so produced, depends directly 
 upon the three following conditions : The density of mag- 
 netic flux, through which the wire passes; the length of 
 "active" wire that part of the wire that actually cuts 
 through the magnetic flux; and the speed with which the 
 
 75 
 
Ignition 
 
 wire is passed across the magnetic field. The current or 
 amperage depends, as we already know by Ohm's Law, 
 directly upon the E. M. F. and inversely upon the resistance 
 of the circuit. 
 
 Fig. 3 illustrates the principles of a direct-current elec- 
 tric generator. The magnetic field is furnished, in this case, 
 by a permanent magnet. The wire which cuts through the 
 lines of force is a single turn, rectangular in shape, and 
 mounted on a shaft. When the latter is rotated in the direc- 
 
 Ficj.3. 
 
 Diagrammatic view of simple generator, showing, respectively, the 
 
 direction of rotation, magnetic lines of force, 
 
 and induced current. 
 
 76 
 
Dynamic Electricity 
 
 tion indicated by the arrows, both long sides of the winding 
 will cut through the lines of force in such manner as to 
 cause a current to flow in the direction shown by the arrows. 
 In Fig. 3, the armature is in the most advantageous position, 
 that is, the maximum number of lines of force are being 
 cut, and, consequently, the current is at its maximum. As 
 the armature continues to rotate, the number of lines of 
 force being cut becomes gradually less and less, until, after 
 revolving a quarter of a turn the position shown in Fig. 4 
 is reached where no lines of force are being cut and the 
 current accordingly has dropped to zero. As rotation con- 
 tinues, the winding begins again to cut the lines of force, 
 
 Ficj.4. 
 
 Same as Fig. 3, except armature has advanced 90 degrees and is NOT~ 
 
 cutting any lines of force, therefore no 
 
 current is produced. 
 
Ignition 
 
 reaching a maximum at the next quarter revolution, when 
 the current is once more strongest. In this manner, the 
 current fluctuates between maximum and zero values, two 
 impulses of current being produced every revolution. 
 
 COLLECTING BRUSHES. 
 
 The current from the armature winding is collected by 
 means of two copper brushes, bearing against a split copper 
 ring, each half of which is connected to an end of the 
 armature winding. Observe that, as the armature revolves, 
 the current produced in the winding reverses its direction 
 twice in a revolution. In order to make the current, taken 
 away from the machine by way of the brushes, flow in one 
 direction, it becomes necessary to reverse the connections 
 between the armature winding and the brushes twice in 
 every revolution. This is precisely what takes place as the 
 brushes slide from one copper segment to the other during 
 rotation. 
 
 COMMUTATOR. 
 
 These copper segments are called the commutator and 
 serve the double purpose of leading the current away from 
 the armature winding and making it uni-directional. 
 
 A current constantly fluctuating in strength is not, as a 
 rule, as desirable as if it were of uniform value. If several 
 coils, instead of one, are wound on the armature and their 
 ends properly connected to a commutator, having as many 
 segments as there are coils, the current will be quite uni- 
 form in strength ; since, no matter in what position the 
 armature may happen to be, a few of the coils will always 
 be cutting the lines of force. The greater the number of 
 coils there are, the more steady will be the current. 
 
 78 
 
Dynamic Electricity 
 
 MAGNETIC CIRCUIT: 
 
 We have already seen that the value of the induced 
 E. M. F. depends among other things upon the strength of 
 the magnetic field. In order to make the magnetic field as 
 strong as possible, the reluctance of the magnetic circuit 
 must be reduced to a minimum. Obviously, most of the 
 reluctance of the circuit is in the air gap between the pole 
 pieces. If this air gap were filled with soft iron, the reluct- 
 ance would be very greatly reduced, and the magnetic 
 density thereby increased many times. The only way this 
 can be accomplished, for obvious reasons, is by winding the 
 coil around an iron cylinder or drum, and allowing it to 
 rotate with the armature. The drum, or armature core, is 
 made to fit the pole pieces, allowing only the necessary 
 clearance, and the winding is placed in grooves, parallel to 
 the axis of rotation. In order to prevent so-called Eddy 
 
 Fig. 5 Photograph of a "drum" wound armature, showing 
 
 commutator and several coils, and two types 
 
 of soft iron armature discs. 
 
 currents from being produced and circulating around in the 
 iron core, the latter is usually built up of many thin, soft 
 iron discs, coated with varnish, to insulate them one from 
 another. 
 
 79 
 
Ignition 
 
 ARMATURE. 
 
 The accompanying photograph shows a finished "drum" 
 armature, taken from a small six-volt dynamo. The greater 
 the number of turns of wire in each coil of the armature the 
 higher will be the voltage. In small, low-tension machines 
 for ignition service, giving four to ten volts, there may be 
 anywhere from 10 to 50 turns in each coil. Of course, 
 the voltage increases with the speed of rotation. There are 
 a few other ways for winding an armature, but the princi- 
 ples involved are exactly the same. The drum armature, 
 however, is the most popular. If some one could design a 
 generator that would give a uniform voltage, regardless of 
 speed, and without complicated governors, etc., a long-felt 
 want in the ignition field would be filled. 
 
 DIFFERENCE BETWEEN MAGNETO AND DYNAMO. 
 
 When the magnetic field is furnished by a permanent 
 magnet, as shown in the illustrations, the machine is know r n 
 as a Magneto, and when an electro-magnet is employed, it is 
 called a Dynamo. In the dynamo, part of the current gen- 
 erated by the armature is used to energize the field magnet. 
 When the two ends of the field winding are connected re- 
 spectively to the two brushes, the current from the arma- 
 ture divides, a small part flowing through the field coil and 
 the rest out and away through the main circuit. This is 
 known as a Shunt Wound dynamo. 
 
 If a dynamo of this type were short-circuited, a power- 
 ful rush of current would take place, lasting, however, only 
 a moment, then all generation of current would cease. This 
 is due to the fact that the current would no longer divide 
 at the brushes, but all of it would flow across the short cir- 
 cuit and leave nothing to energize the field magnet, which 
 
 80 
 
Dynamic Electricity 
 
 would then rapidly lose its magnetism, when, of course, no 
 current could be generated by the- armature. When the 
 machine is at rest, there is practically no magnetism in the 
 field ; a very little only is retained by the soft iron of the 
 field core. When the dynamo is started, this "residual" 
 magnetism is usually strong enough to produce, in the arma- 
 ture, a feeble current, which flows into the field winding, 
 thereby strengthening the magnetic field. 
 
 SHUNT WOUND. 
 
 Quite often a dynamo, particularly if it has been idle 
 for a long time, will not, when started up, begin to generate 
 current or "pick up" at once. This may be due to a lack 
 of residual magnetism, and, if a battery is connected for a 
 moment to the field coil, the machine will invariably pick 
 up immediately. The polarity of the battery may have to be 
 reversed, before meeting with success. If a Shunt Wound 
 Dynamo is connected to a circuit of too low resistance, most 
 all of the current will flow 7 over this circuit, and there will 
 not be enough left to properly excite the field. Under these 
 conditions, the dynamo will give out only a fraction of its 
 capacity. In this event, the resistance of the main circuit 
 should be increased or a dynamo, wound for a lower volt- 
 age, used. 
 
 SERIES WOUND. 
 
 If the field winding is of large size ware, and connected 
 in series with the armature, the total current will flow 
 through the field coil on its way to the main circuit. A 
 dynamo, connected in this way, is said to be series wound. 
 The Shunt connection is generally used, however, as it is 
 less troublesome. 
 
 81 
 
Ignition 
 
 The variation of voltage with speed is greater in a 
 dynamo than in a magneto, because, in the former the 
 strength of the field changes with the speed, and in the latter 
 the magnetic field is always constant. For this reason, a 
 magneto generator is not so dependent upon the circuit with 
 which it is connected. 
 
 82 
 
Chapter Eleven 
 
 Low- Tension Dynamos Direct and 
 Alternating Current Low- 
 Tension Magnetos 
 
 Having discussed the fundamental principles of dyna- 
 mos and magnetos we will now see how they are made and 
 operated. There are several different classes of low-tension 
 machines, viz. : Dynamos, generating direct current, a part 
 of which is used to energize the electro-magnet fields, and 
 therefore permanent magnets are not used ; magnetos, hav- 
 ing permanent magnets for the field, generating either 
 direct or alternating current; and a few odd types of mag- 
 neto generators which produce intermittent impulses of 
 current by a reciprocal or oscillatory movement of some 
 part of the machine. 
 
 THE LOW-TENSION DYNAMO. 
 
 The low-tension ignition dynamo is built along practi- 
 cally the same lines as the large dynamos used in power sta- 
 tions. The electro field magnet, having its poles shaped to 
 fit the armature, may assume several different forms. For 
 stability and appearance it is well to have it so shaped as to 
 act as a housing for enclosing the whole machine. The pole 
 pieces are cast integral therewith as inside projections, 
 around which are placed the field windings. The armature 
 is usually of the "drum" type and may have from six to 
 
 83 
 
84 
 
Low-Tension Dynamos Direct and Alternating Current 
 Low-Tension Magnetos 
 
 twelve coils wound with double cotton covered wire, care- 
 fully insulated from the armature core. The coils should 
 be given a thick coat of some oil and heatproof insulating 
 varnish. If the winding of the armature is not carefully 
 done, one or more of the coils will, sooner or later, become 
 short-circuited or grounded, and the output of the machine 
 seriously impaired. If the armature is run at high speed as 
 is usually the case, binding wires should be placed around 
 the armature to prevent the coils from flying out of place by 
 centrifugal force. 
 
 THE COMMUTATOR. 
 
 The commutator is another delicate part to manufac- 
 ture. The copper segments must be securely held in place 
 and insulated one from another and the ground, by a special 
 form of mica. The ends of the coils are placed in grooves 
 in the commutator segments and soldered. The armature 
 is then placed in a lathe and the commutator turned per- 
 fectly smooth and polished. The brushes are usually made 
 of copper gauze, rolled or folded under pressure into a 
 short rod, one end of which is dipped into melted solder, 
 to keep it from unravelling. A spiral spring is also attached 
 to it. These brushes are often made with a little graphite, 
 which reduces the wear on the commutator and prevents 
 cutting. Carbon rod, made with graphite, wears better than 
 any other material, but, owing to its comparatively high 
 resistance, it is not often used for low-tension machines. 
 This objection, however, can be overcome, to a large extent, 
 by heavily copper-plating the carbon. Care should be taken 
 that good electrical contact is always maintained between the 
 brush and the brush holder. Missing explosions can often 
 be traced to a brush that is not in good contact with its 
 
 85 
 
Ignition 
 
 holder. The spring should be just stiff enough to hold the 
 brush firmly against the commutator. If it is not stiff 
 enough, sparking is likely to occur, which will burn and 
 roughen the commutator, making good contact impossible. 
 In this case the armature should be placed in a lathe and 
 the commutator smoothed up with very fine sand paper, 
 and then rubbed with a piece of oily waste, if a stick of 
 regular commutator compound is not handy. 
 
 Since the brushes and commutator are responsible for 
 nine-tenths of the trouble with direct-current dynamos and 
 magnetos, a frequent inspection of these parts is greatly 
 desirable. If the commutator is well made, protected from 
 dust and dirt, and large brushes are used and inspected once 
 in a while, there is no excuse for trouble of any kind. 
 
 Where current for ignition only is needed, the dynamo 
 has been largely replaced with the direct-current magneto, 
 but where it is also required to furnish current for several 
 small electric lamps, as for an electrically lighted automobile 
 or small launch, the dynamo is usually used. 
 
 In order to get the best results from a spark coil, and 
 particularly from low voltage tungsten lamps, it is neces- 
 sary to keep the voltage applied to them uniform in value. 
 This is often accomplished, to a certain extent, by building 
 a governor into the machine, which does not allow the arma- 
 ture to rotate above a certain speed. Most governors, how- 
 ever, do not work accurately enough to keep the voltage 
 as uniform as it should be for tungsten lamps. To further 
 regulate the voltage, the dynamo is often connected to a 
 storage battery in such a manner as to be constantly charg- 
 ing it while the battery is supplying current for the ignition 
 and lamps. A switch worked by an electro-magnet, or by a 
 
 86 
 
Low-Tension Dynamos Direct and Alternating Current 
 Low-Tension Magnetos 
 
 governor on the dynamo, must be provided to disconnect 
 the battery from the dynamo, when the latter is stopped 
 or not up to speed, otherwise the battery would send a cur- 
 rent through the winding of the dynamo and rapidly dis- 
 charge. If, on the other hand, the dynamo is allowed to 
 run all the time, continually charging the battery, when the 
 
 Zonii'ion Systems. 
 
 Diagram showing the connections for a combination ignition 
 
 and lighting system known as "floating the 
 
 battery on the line." 
 
 lights are not turned on, the battery will become over- 
 charged, and, if prolonged, it will be injured. There are 
 storage batteries with liquid electrolytes, made especially for 
 
 87 
 
bO 03 
 g 6 
 
 88 
 
Low-Tension Dynamos Direct and Alternating Current 
 Low-Tension Magnetos 
 
 this service, that will stand considerable overcharging. The 
 water in the electrolyte will, however, be "boiled" out and 
 must be replaced, from time to time, with pure, distilled 
 water. It is very, important to keep the electrolyte well 
 above the plates of the cells at all times. It is a very good 
 thing to install a low-reading zero-center ammeter in series 
 with the battery, and a voltmeter in multiple with it, as 
 shown by the diagram. When the pointer of the ammeter 
 swings to the right, the battery is being charged, and to 
 the left, discharged. The voltmeter will indicate the condi- 
 tion of the battery. If a regular six-volt battery is used 
 and the voltmeter shows 7 to 7.5 volts, while the battery is 
 charging, at a rate of 2 to 4 amperes, the dynamo should 
 be disconnected, since the battery is fully charged. This 
 system is known as " floating --the battery on the line," and 
 will give excellent results if a little care is used in han- 
 dling it. 
 
 There are several special methods for regulating the 
 output of dynamos, such as having the governor, instead of 
 regulating the speed of the armature, control a variable 
 resistance, in series with either the field winding or the 
 main circuit ; or by having a compound winding on the field 
 so arranged with an electro-magnetic mechanism that, when 
 the voltage exceeds a certairi value, the field windings will 
 oppose each other. We cannot, for lack of space, go into 
 the details of these various systems, as the manufacturers 
 furnish descriptive matter and instructions for their own 
 particular systems. 
 
 THE DIRECT-CURRENT MAGNETO. 
 
 The direct-current magneto is exactly the same as the 
 dynamo, except that permanent magnets are used for the 
 
 89 
 
90 
 
Low-Tension Dynamos Direct and Alternating Current 
 Low-Tension Magnetos 
 
 field. The armature, commutator and brushes require the 
 same care as in the dynamo. 
 
 Direct-current magnetos are usually made a little 
 smaller and cheaper than dynamos, and are more popular 
 where current is wanted for ignition only, or for one or two 
 small tungsten lamps. The magneto has an advantage over 
 the dynamo, in that the strength of the field magnet is the 
 same at all speeds. This allows the magneto to generate 
 current at a slightly lower speed than the dynamo, and the 
 variation of voltage with speed is not as great. If the 
 magnets are carefully made by up-to-date methods, from the 
 best special magnet steel, they will last for several years, 
 without recharging. It is very important in installing a 
 magneto, to make sure that the voltage it gives is suited to 
 the coil that is to be used with it. If the voltage is too high, 
 the contact points on the coil will soon burn up, and, if too 
 low, the vibrator will not work and the engine will miss fire. 
 If the magneto and spark coil are purchased from two dif- 
 ferent concerns, one or both of the manufacturers should 
 be consulted, as to whether or not the combination will work 
 satisfactorily. Some magnetos will give current enough to 
 operate the coil when the engine is cranked over, but, in 
 many cases it is best to provide a battery for starting. 
 
 THE ALTERNATING CURRENT MAGNETO. 
 When an electric current is constantly changing in 
 strength and periodically reversing its direction, it is known 
 as an alternating current. Alternating current magnetos 
 cannot, under any condition, be used to charge storage bat- 
 teries. Some alternating current magnetos have one coil 
 only on the armature, and give one positive and one nega- 
 
 91 
 
92 
 
Low-Tension Dynamos Direct and Alternating Current 
 Low-Tension Magnetos 
 
 tive impulse of current every revolution. This type of 
 magneto must be geared to the engine in such a manner that 
 the current wave will be at its maximum value at the instant 
 ignition is required. One end of the winding is usually 
 grounded on the armature core, and the other end is brought 
 to an insulated copper ring, against which bears a collecting 
 brush. While this collecting ring and brush is less trouble- 
 some than a regular commutator, it should occasionally be 
 cleaned and inspected. 
 
 THE INDUCTOR TYPE ALTERNATING CURRENT MAGNETO. 
 There are a few patented alternating current magnetos 
 on the market, which have no commutator, brushes, collect- 
 ing rings or moving wires of any kind. An alternating cur- 
 rent is induced in a stationary winding by rapidly shifting 
 the magnetic lines of force through it. The only moving 
 part of the machine is a soft iron member called the induc- 
 tor, which is so shaped as to cause the magnetism to alter- 
 nate through the coil four times in one revolution, thereby 
 producing four impulses of current two positive and two 
 negative. Referring to the drawing, the full line shows 
 one path taken by the magnetic lines through 'the soft iron 
 inductor and stationary winding, and the dotted line shows 
 the other path in the reverse direction. Inductors were tried 
 which gave six and even eight alternations of magnetism 
 per revolution, but it was found that, at high speed, the 
 magnetic lines could not reverse through the inductor 
 rapidly enough and so the current impulses were too weak 
 to satisfactorily operate a coil. Four impulses of current 
 per revolution is the most satisfactory. Care must be taken 
 in designing an inductor type magneto to see that the pole 
 pieces and inductor are so shaped as to cause the magnetic 
 
 93 
 
Ignition 
 
 reversals through the winding to be as uniform as possible, 
 in order to insure what is known as a "Sine Wave." While 
 there are four impulses of current per revolution, there are 
 also four times when the current is zero. It is evidently 
 desirable, then, to have the time during which little or no 
 current is being produced, as short as possible. The two 
 oscillograms show the current wave forms of two different 
 inductor type machines. Notice that one wave is more 
 "peaked" than the other. 
 
 If a machine, giving four impulses of current per revo- 
 lution, is speeded up to 2,000 revolutions per minute, there 
 will be 8,000 impulses of current per minute, or 133 every 
 second. When this is used as a source of current for a 
 vibrating coil, working through a regular timer, it is evi- 
 dent that the timer may happen to make contact at the in- 
 stant when little or no current is being produced. When 
 this happens, the vibrator must wait until the next impulse 
 or wave becomes strong enough to operate it. This will de- 
 lay ignition for an instant, but, owing to the rapidity with 
 which the impulses follow one another, the delay is too short 
 to cause any appreciable loss of power, except, perhaps, 
 in some very high-speed motors. 
 
 All styles of coils will not, as a rule, work satisfactorily 
 on the inductor type magneto, since the vibrators and pri- 
 mary windings will not respond on the rapidly alternating 
 current. A special coil, or at least a special master vibrator, 
 designed to work on alternating current, should be used with 
 inductor type magnetos. 
 
 These machines can be driven by the flywheel with a 
 friction pulley, or belt, and should always be kept up to 
 speed as recommended by the manufacturers. About the 
 
 94 
 
Low-Tension Dynamos Direct and Alternating Current - 
 Low-Tension Magnetos 
 
 only advantage an inductor type magneto has over a direct 
 current machine is the entire absence of all brushes, com- 
 mutators, collecting rings and moving wires. The variation 
 of voltage with speed is also less than on direct-current ma- 
 chines, due to the more rapidly increasing impedance of the 
 winding with speed. On the other hand, they have the dis- 
 advantage of not being able to work successfully on all 
 types of coils, or to charge storage batteries. 
 
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 Oscillograph records, showing the current wave forms of inductor type 
 
 magnetos. At 2,000 revolutions per minute of the machine 
 
 there are 133 of these impulses every second. 
 
 95 
 
Chapter Twelve 
 
 High-Tension Magnetos Their 
 Theory and Construction 
 
 Having described a few different types of low-tension 
 machines it remains to speak of the high-tension magneto. 
 It combines in one machine first, a source of low-tension 
 current; second, a commutator or timer, to allow the cur- 
 rent to flow at the instant ignition is required ; third, a high- 
 tension coil or transformer, to increase the E. M. F. of the 
 low-tension current to several thousand volts sufficient for 
 a jump spark; and fourth, a distributor, to connect the high- 
 tension current respectively with the several cylinders in the 
 order of firing. 
 
 HIGH-TENSION MAGNETOS. 
 
 There are two types of magnetos commonly known as 
 high-tension, but one of them only is, strictly speaking, a 
 purely high-tension machine, combining within itself all four 
 of the above mentioned parts. The other type contains 
 within itself all of the parts except the high-tension coil or 
 transformer, which, in this case, is placed in a separate 
 mahogany box or hard fiber tube and mounted as near the 
 magneto as convenient. A low-tension current is generated 
 in the armature and sent across the timer or breaker points, 
 where it is cut up into properly timed impulses of current. 
 These low-tension impulses are sent into the primary wind- 
 ing of the separate transformer coil, where they are changed 
 to high-tension in the secondary winding and sent back 
 
 96 
 
High-Tension Magnetos Their Theory and Construction 
 
 through a heavily insulated wire to the distributor of the 
 magneto, where they are sent again through heavily insu- 
 lated wires to the respective cylinders. 
 
 It is possible, in this system but not in the pure high- 
 tension machine to substitute the current from a battery 
 for that produced by the armature, when, of course, a good 
 spark is produced, no matter how slowly the machine is 
 turned over. This should be spoken of as a Dual system, 
 and is highly satisfactory and very popular, but should not 
 be confused with pure high-tension machines. 
 
 THEORY OF THE PURE HIGH-TENSION MAGNETO. 
 
 Permanent magnets are always used to furnish the field 
 magnetism in high-tension magnetos. A common two-pole 
 or "H" armature is commonly used, 1 the central core of 
 which consists of a number of soft iron stampings. As we 
 already know, an armature of this type produces two im- 
 pulses of current in a revolution one positive and one nega- 
 tive. 
 
 In a previous chapter it was shown that, other things 
 being equal, the voltage produced by an armature increases 
 directly with the number of turns of wire in its winding. 
 Why not, then, wind an armature with a sufficient number 
 of turns of fine wire to produce a high-tension current, 
 capable of jumping the spark gap at the plug? This has 
 been tried, but, owing to the small space available for wind- 
 ing, it is impossible to get on anywhere near the required 
 number of turns ; in fact, only a few hundred volts can be 
 reached. We also remember that a high voltage is needed 
 only to start an arc, and only a few volts are necessary to 
 
 1 There are a few special types of high tension magnetos employing 
 either a stationary winding and inductor, or a magnetic shield arrangement, 
 which give four impulses of current in P revolution. In all other respects, 
 however, the principles are the same. Such a machine would be good for 
 a multiple-cylinder, two-cycle motor. 
 
 97 
 
* bfl 
 
 ss 
 
 be 
 rj <u 
 
 98 
 
High-Tension Mrgnetos Their Theory and Construction 
 
 maintain it. We must, therefore, provide some other means 
 for obtaining a momentary impulse of high voltage, capable 
 of starting the arc, which can then be maintained for a 
 short time by the comparatively low voltage produced in the 
 armature. As we have already learned, other things being 
 equal, the voltage produced in an armature varies directly 
 with the speed at which the magnetic lines are cut or made 
 to reverse through the armature winding. As the armature 
 revolves, the magnetic reversals do not take place instan- 
 taneously, but are more or less gradual, thus tending to 
 lower the voltage, yet, at the same time, prolonging the cur- 
 rent impulses. 
 
 Wind, on the armature, two or three layers of rather 
 coarse wire <say No. 24 and call it the Primary ; around it 
 wind as many turns as possible of carefully insulated, fine 
 wire say No. 36 to No. 40 and call it the Secondary. 
 Now, short-circuit the primary winding and rotate the arma- 
 ture. The magnetic lines of force begin to cut through the 
 windings, producing a current in the primary which grad- 
 ually increases until a position is reached where the maxi- 
 mum number of lines of force is being cut. This induced 
 current in the primary tends to strengthen the magnetism 
 in the armature core. When the current in the short-cir- 
 cuited primary is at its maximum, suddenly interrupt it by 
 opening the circuit and an almost instantaneous collapse 
 of part of the magnetic lines in the armature will follow. 
 This very rapid change of magnetism through the secondary 
 winding will induce in it a momentary impulse of several 
 thousand volts, sufficient to start an arc between the points 
 of the spark plug. The arc is then maintained for a short 
 time by a current of lower voltage, produced in the second- 
 ary winding by the rotation of the armature. A condenser 
 of small capacity is connected across the breaker points to 
 
 99 
 
d p M 
 
 Sal 
 
 cog's 
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 *.*5 w 
 
 cj^w <u * 
 
 MCJ 
 TJ 
 
 ro <u I 
 
 l 
 
 
 |9 
 
 100 
 
High-Tension Magnetos Their Theory and Construction 
 
 prevent the platinum contacts from burning and to assist in 
 the rapid collapse of the magnetic lines. 
 
 Fig. 1 shows three different positions of an "H" arma- 
 ture during rotation, and clearly illustrates how the mag- 
 netic lines are made to reverse their direction through the 
 armature. The curve at the bottom of the figure is an oscil- 
 lograph record of the current wave, showing the two im- 
 pulses of current during one revolution one positive and 
 the other negative. The positions on the curve marked A', 
 B' and C' correspond to the three positions of the armature 
 shown at A, B and C. A careful study of the relative posi- 
 tions will be of interest, as we can briefly mention only one 
 or two of the most important points. 
 
 Suppose the cam to be set so as to open the primary 
 circuit when the armature has reached the position indicated 
 at "B" (Fig. 1). The wave is at its maximum height, so 
 that the induced current in the Primary winding will be 
 strongest. Also notice that, as the armature continues to 
 rotate from position "B" to "C," the curve does not rapidly 
 descend. The armature, therefore, cuts the lines of force at 
 almost a uniform rate during that period, and, consequently, 
 the current produced thereby in the secondary winding, will 
 maintain a strong arc for a short time. Again, suppose 
 the cam to be set so as to open the primary circuit when the 
 armature has reached position "C" ; the curve has begun to 
 descend, and, consequently the arc will not jump as far or 
 be as strong as in the first case. Position "B" corresponds 
 to extreme advance, and "C" extreme retard, of a high- 
 tension magneto having a spark advance range of 40 de- 
 grees. This explains why the spark is stronger when the 
 magneto is advanced than when retarded, particularly at 
 low engine speeds. 
 
 101 
 
Ignition 
 
 If the cam should be a trifle too far advanced so as to 
 open the primary circuit before the armature reaches the 
 position shown at "B," say at "d" (indicated on the curve), 
 it is evident that the spark will be very weak and will not 
 
 V} 
 
 fc 
 x 
 
 QJ 
 ^ 
 
 E 
 
 t 
 
 te^ 
 
 A/o.3/. 
 
 Complete Revolution of the 
 
 A series of oscillograph records of the current forming 
 
 the arc between the points of a spark plug. The first 
 
 two are taken from the same magneto No. 28 at 
 
 extreme retard and No. 29 at extreme advance. 
 
 Note that the arc does not immediately 
 
 begin to die out on the advance 
 
 position as it does on the retard 
 
 102 
 
High Tension Magnetos Their Theory and Construction 
 
 always jump between the points of the plug, causing the 
 engine to miss fire. If the cam or facing against which it 
 rubs, or the platinum points should be badly worn, or the 
 platinum tipped contact screw backed out farther than it 
 should be, the effect is the same as if the cam were advanced 
 too far, and a short, weak spark will be the result. To 
 avoid this trouble and to allow for a slight variation in 
 manufacture, it is best to set the cam so as to open the cir- 
 cuit at a point well up on the curve, in order that a slight 
 advance, due to wear or improper adjustment of the plati- 
 num points, will not weaken the spark. 
 
 Fig. 2 is a series of oscillograph records of the current 
 forming the arc between the points of a spark plug. The 
 first two are taken from the same magneto 'No. 28 at ex- 
 treme retard and No. 29 at extreme advance. Note that 
 the arc does not immediately begin to die out on the advance 
 position, as it does on the retard. No. 30 is from a different 
 make of pure high-tension magneto and No. 31 is from a 
 special form of Dual magneto, employing a separate high- 
 tension winding in the form of a transformer, so designed 
 with sufficient magnetic lag, etc., as to prolong the arc prac- 
 tically the same as a pure high-tension machine. There is 
 no object in maintaining the arc too long; in fact it simply 
 tends to burn up the points of the spark plug. The charge 
 is, most likely, thoroughly ignited before the position marked 
 "X" on curve No. 28, is reached. 
 
 103 
 
Chapter Thirteen 
 
 The Installation and Care of 
 High-Tension Magnetos 
 
 All high-tension magnetos must be positively driven. 
 They cannot, under any condition, be driven by belt or fric- 
 tion. Since the spark occurs only when the armature is in a 
 certain position, the magneto must be so timed that the spark 
 will occur at the instant ignition is required. The magneto 
 is usually connected with some form of universal joint, 
 directly to one end of the cam or pump shaft, or a special 
 short shaft extending from one of the cam shaft gears that 
 runs at the proper speed. The following table shows the 
 different speeds at which magnetos should be driven relative 
 to the speed of the motor : 
 
 Number of 
 
 cylinders. Cycle. Speed. Form of cam. 
 
 4 4 Crank shaft Double 
 
 2 4 Crank shaft Single 
 
 3 4 iy 2 x crank shaft Single 
 6 4 iy 2 x crank shaft Double 
 
 4 2 2 x crank shaft Double 
 
 2 2 2 x crank shaft Single 
 
 3 2 iy 2 x crank shaft Double 
 6 2- 3 x crank shaft Double 
 
 Fig. 6 shows several forms of couplings. No. 1 is the 
 popular Oldham universal coupling ; No. 2 is a fairly satis- 
 factory device, consisting of two> pins in one end of the 
 coupling, working in two corresponding slots in the other 
 end. No. 3 shows a device for slightly changing the timing 
 after both ends of the coupling are secured to the shafts. 
 When the two hexagon bolts are loosened, the magneto end 
 
 104 
 
-EP 
 
 Fig. 6 shows several forms of couplings. No. 1 is the popu- 
 lar Oldham universal coupling; No. 2 is a fairly satisfac- 
 tory device, consisting of two pins in one end of the 
 coupling, working in two corresponding slots in the other 
 end. No. 3 shows a device for slightly changing the 
 timing after both ends of the coupling are secured to the 
 shafts. No. 4 consists of two similar "T" shaped members, 
 loosely joined together, with a star-shaped steel stamping, 
 having its edges folded over. No. 5 shows a very poor 
 coupling which does not permit of any misalignment of 
 magneto and driving shaft. 
 
 105 
 
Ignition 
 
 of the coupling can be turned as far as the slots, through 
 which the bolts extend, will permit. No. 4 consists of two 
 similar "T"-shaped members, loosely joined together, with 
 a star-shaped steel stamping, having its edges folded over. 
 No. 5 shows a very poor coupling which does not permit 
 of any misalignment of magneto and driving shaft. It is 
 not economy to use a poor coupling, as it will strain and 
 sometimes bend the armature shaft and cause an undue 
 wear of the bearings. 
 
 A rigid shelf, made of some non-magnetic material, 
 such as brass or aluminum, should be provided, upon which 
 to mount the magneto. If an iron shelf is used, a part of 
 the magnetic lines will pass through it, which tends to 
 weaken the spark. It is best to locate the magneto on the 
 shelf with dowel pins and hold it in place with a strap of 
 sheet brass passing over the top of the magnets. This 
 makes it easy to remove the magneto for cleaning and in- 
 specting. 
 
 TIMING THE MAGNETO. 
 
 The following are the general rules for timing a high- 
 tension or dual magneto. 
 
 Turn the engine over until cylinder No. 1 is on the upper 
 dead center, just before the firing stroke. Secure one end 
 of the coupling to the driving shaft or magneto, whichever 
 is the most convenient, and place the magneto and other 
 parts of the coupling in position. Turn the spark advance 
 lever to the position of extreme retard, which will be in the 
 same direction as the armature runs. Remove the cover of 
 the interrupter or breaker box, so that the contact points 
 can be seen, and slowly turn the armature in the direction 
 it is to run until the contact points just begin to separate. 
 
 106 
 
The Installation and Care of High-Tension Magnetos 
 
 This point should be carefully determined. Now secure 
 both ends of the coupling to the shafts with taper pins. Re- 
 move the front plate or cover of the distributor and see with 
 what segment the distributor hand is in contact. Connect 
 this segment with high-tension wire to the spark plug of 
 cylinder No. 1, then connect the remaining terminals with 
 the rest of the cylinders in the proper order of firing, bear- 
 ing in mind that the distributor hand, in most cases, revolves 
 in the opposite direction to that of the armature. 
 
 There is usually a binding post on pure high-tension 
 machines, which, when connected through a switch to 
 ground on the engine frame, will short-circuit the primary 
 winding, thereby shutting off the spark. Dual magneto con- 
 nections are more complicated and the wiring diagrams 
 furnished by the makers should be carefully followed. Care 
 must be exercised in connecting dual magnetos, not to get 
 the battery connected directly across the armature winding, 
 even for a second, as 'this would make an electro-magnet 
 out of the armature which, likely, would oppose the field 
 magnets and weaken them. It is convenient sometimes with 
 dual magnetos to connect an electric bell and dry battery in 
 series with the contact points, to determine when the separa- 
 tion occurs. Unfortunately, this cannot be done with pure- 
 high-tension machines. 
 
 CARE OF HIGH-TENSION MAGNETOS. 
 
 A few hints regarding the care of high-tension mag- 
 netos may be helpful. It is often a very good thing to cover 
 the machine with a rubber or leather hood, made especially 
 for the purpose, since dust, dirt, grease and particularly 
 water, are all enemies of the magneto. The glass or 
 porcelain knob, which covers the safety spark gap (if there 
 is one), should be kept clean and free from grease and dirt. 
 
 107 
 
Ignition 
 
 The distributor should be kept clean and dry and the path, 
 over which the carbon distributing brush slides, ought to be 
 wiped off occasionally with a clean cloth, moistened with 
 gasoline, for a slight carbon deposit will, in time, form be- 
 tween the segments and cause misfiring. The spiral spring 
 behind the carbon distributing brush must not be too stiff; 
 it should be just stiff enough to hold the brush in very 
 light contact with the surface over which it slides. 
 
 Fig. 3 is a diagrammatic view of a pure high-tension 
 magneto and shows the connections and relations of the sev- 
 eral parts. At the left is a sectional view of the heavily 
 insulated collecting ring for leading the high-tension current 
 from the secondary winding on the armature, to the distrib- 
 uting hand, from which it is sent to the different cylinders. 
 When tracing out the connections, note that one end each 
 of the primary and secondary windings is grounded to the 
 armature core. A safety spark gap is provided, over which 
 the spark can find an easy path, should a wire come off of 
 a spark plug, thereby preventing unnecessary and dangerous 
 strain on the insulation of the secondary winding. 
 
 Fig. 4 is a sectional drawing of a special form of dual 
 magneto, which has the high-tension winding made in the 
 form of a transformer and placed under the arch of the 
 magnets. In this machine as in all dual magnetos, the arma- 
 ture has just one primary winding of coarse wire. 
 
 A high-tension magneto is not an easy piece of appa- 
 ratus to manufacture. The greatest care, both mechan- 
 ically and electrically, must be exercised throughout the 
 entire construction. 
 
 THE MAGNETIC CIRCUIT. 
 
 The magnets should be carefully made of the best mag- 
 net steel and strongly magnetized and seasoned before plac- 
 
 108 
 
The Installation and Care of High-Tension Magnetos 
 
 ing on the machine. In order to make the magnetic circuit 
 as good as possible, the inside surfaces of the magnets 
 should be ground bright and smooth after hardening, but 
 before magnetizing, and the pole pieces smoothed and all 
 
 To Spark Pluqs. 
 
 Secondary 
 Collecting 
 Brush, t- 
 
 'Distributing 
 
 hand. 
 
 Secondary 
 D i stri butinrj. 
 Brush. 
 
 ecortdary 
 Windinq. 
 
 Primary 
 W'mdinq 
 
 'Thick J.rtsu\atioti. 
 
 Soft Iron 
 Qrmal'ure Core. 
 
 Cam' 
 
 Screw. 
 
 Fig. 3, a diagrammatic view of a pure high-tension magneto, which 
 clearly shows the connections and relations of the several parts. 
 At the left is a sectional view of the heavily insulated 
 collecting ring for leading the high-tension cur- 
 rent from the secondary winding on the 
 armature, to the distributing hand, 
 from which it is sent to the 
 different cylinders. 
 
 109 
 
Ignition 
 
 scale removed so as to make a perfect fit with the magnets. 
 The armature should be made with only a few thousandths 
 of an inch clearance, but must not be close enough to the 
 pole pieces to drag after the bearings have become slightly 
 worn. With good ball bearings and workmanship, a clear- 
 ance of about six thousandths of an inch on a side is all 
 that is necessary. 
 
 WINDING THE ARMATURE. 
 
 The winding of the armature is the most delicate part 
 of the work, requiring a great deal of patience and skill. 
 Many layers of very fine insulated wire are used on the 
 secondary, each layer being separated from its neighbor by 
 a turn of very thin oiled silk gauze. The whole winding 
 must be saturated with a good, flexible, heat-resisting, moist- 
 ure-proof insulating varnish, and covered over with a thick 
 insulation of oiled silk. 
 
 COLLECTING RING AND BRUSH. 
 
 The problem of leading the high-tension current away 
 from the armature is not an easy one, and the collecting ring 
 should be made of the best grade of hard rubber, ample in 
 size, with as great a sparking distance to ground as possible. 
 It must also be protected from oil and dirt. The carbon 
 brush should bear lightly on the brass ring and be carefully 
 insulated from ground. 
 
 THE CONDENSER. 
 
 The condenser, in many machines, is made of alternate 
 washers of tin foil and mica, assembled over the shaft at 
 one end of the armature, and should be protected by a thin, 
 brass case. In other machines it consists of alternate sheets 
 of tin foil and mica, assembled in a brass or aluminum case, 
 placed under the arch of the magnets. 
 
 110 
 
The Installation and Care of High-Tension Magnetos 
 
 THE INTERRUPTER. 
 
 The interrupter or breaker assumes many different 
 forms, but the principle in all cases is the same. In many 
 pure high-tension machines, it is -made to rotate with the 
 armature and two stationary fiber pieces act as cams to 
 effect a separation of the platinum points. The main thing 
 about an interrupter is to have it light and responsive, so 
 that, at high speeds, it will not miss contact as some earlier 
 forms are apt to do. There are, unfortunately, a few of 
 these still on the market. Dual magnetos have the inter- 
 rupter mounted stationary and effect a separation of the 
 contacts by a cam attached to the armature shaft, bearing 
 against a steel roller, or steel or fiber facing attached to the 
 interrupter arm. 
 
 SAFETY SPARK GAP. 
 
 The wire or spring clip, which connects the collecting 
 brush with the distributing hand, must be widely separated 
 and insulated from the ground or metal parts of the mag- 
 neto. The safety spark gap is often placed under this strip 
 and protected from dirt and water by a glass or porcelain 
 insulator. The gap is usually about T % inch long, and, if it 
 is wet or dirty, or too short, the spark will jump or creep 
 across it rather than take the gap between the points of the 
 spark plug, particularly if they happen to be rather widely 
 separated, and irregular missing of explosion will result. In 
 some pure high-tension machines, the safety gap is located 
 on one end of the armature near the winding. 
 HIGH-TENSION DISTRIBUTOR. 
 
 There are two general forms of distributor, the passing 
 contact, where the spark is made to jump a small air gap 
 between the distributing hand and brass segments ; and the 
 
 111 
 
112 
 
The Installation and Care of High-Tension Magnetos 
 
 rubbing contact, where a carbon brush is made to slide 
 from one brass segment to the next. The passing contact 
 is cheaper to manufacture than the other, but is not consid- 
 ered as good because some, energy is lost in forcing the 
 spark across the air gap. If this gap could be kept less 
 than 1-64 inch at all times, this objection would be over- 
 come, but it is impracticable, for mechanical reasons, to do 
 so. It is well to mold the brass segments into a block of 
 special hard rubber and then smooth up in a lathe the sur- 
 face against which the carbon brush rubs. The distributing 
 hand must be driven by gears from the armature shaft at 
 such a speed that it will be in contact with a brass segment 
 at the instant the interrupter points are separated. 
 
 Fig. 5 is a photograph of a pure high-tension magneto 
 partly disassembled. A is the high-tension winding on the 
 armature ; B the collecting ring ; C the carbon collecting 
 brush and hard rubber holder ; D the hard rubber protector 
 and brush that leads the high-tension current into the dis- 
 tributing hand ; E the distributing hand and carbon brush ; 
 F the special form of interrupter that rotates with the arma- 
 ture; G the spark advance lever, showing the stationary 
 fiber cams ; H the porcelain safety spark gap protector, and 
 7 the small carbon brush which leads the primary current to 
 the switch for grounding to stop the magneto. The con- 
 denser is mounted on the left hand end of the armature and 
 does not show. 
 
 The contact points should not separate more than the 
 thickness of an ordinary, rather thin business card, and 
 should they become badly pitted, they must be made smooth 
 with a very fine file or replaced with new ones. 
 
 113 
 
53 rt 
 
 6 bo 
 
 e-S 
 
 ill 
 
 114 
 
The Installation and Care of High-Tension Magnetos 
 
 Most magnetos are provided with three or more oil 
 holes, which should receive a few drops of high grade thin 
 oil several times a season, according to how much the ma- 
 chine is used. It is not well nor necessary to flood the ma- 
 chine with oil, neither should it be run dry. The ball bear- 
 ings are packed with hard grease before the machines leave 
 the factory, and so very little oiling is necessary for the 
 first few months' use. 
 
 There is nothing difficult about caring for a magneto. 
 If these few simple things are systematically looked after, 
 trouble with the magneto is not likely to develop. 
 
 115 
 
Chapter Fourteen 
 
 Low- Tension Positively Driven 
 
 Make-and-Break Magnetos 
 
 for Stationary Engines 
 
 The newest type of ignition receiving the attention 
 of progressive manufacturers of stationary farm en- 
 gines, is a gear-driven magneto, the armature of which 
 is designed to act as a make and break coil as well as 
 to perform its regular function of generating the cur- 
 rent. With this type of magneto the make-and-break 
 coil and batteries are entirely eliminated and the mag- 
 neto made a permanent part of the engine, thereby 
 making the system extremely simple. 
 OPERATION OF SYSTEM. 
 
 A two-pole or "H" armature is made to revolve 
 between the poles of a permanent magnet. The arma- 
 ture has a single winding, one end of which is grounded 
 to the armature core. The other end is brought out 
 to a collecting ring against which bears a collecting 
 brush. This brush is connected to the insulated point 
 of the igniter on the engine. The armature is posi- 
 tively driven from the crank or cam shaft so that the 
 current impulses will be at their maximum strength 
 the instant ignition is required. When the armature 
 starts to revolve a current is produced in its winding, 
 
 116 
 
Low-Tension Positively Driven Make-and-Break Magnetos 
 
 for Stationary Engines 
 
 which passes out through the collecting ring and brush 
 to the igniter points, which are now in contact, then 
 to the ground and back through the frame of the en- 
 gine and magneto to the grounded end of the winding. 
 The current begins to build up and strengthens the 
 magnetism in the armature. When the current has 
 reached its maximum the igniter points separate, 
 after which the armature acts as a make-and-break 
 coil and delivers the energy stored in it to the igniter 
 points in the form of an arc similar to that produced 
 by a battery and make-and-break coil. This process 
 is repeated for every ignition, and the armature is con- 
 stantly changing from acting as a generator of current 
 to a make-and-break coil. This system as a whole is 
 very simple, but great care must be taken in properly 
 designing all of the parts. 
 
 CONSTRUCTION OF MAGNETO. FIELD MAGNETS. 
 
 The best grade of permanent steel magnets should 
 be used for furnishing the field magnetism. The pole 
 pieces must be fitted perfectly to the magnets and 
 should be made of the best grade of soft "magnetic" 
 cast iron. 
 
 ARMATURE. 
 
 The armature core should be cast from a special 
 grade of soft magnetic iron having a high magnetic 
 permeability at low densities. In order to reduce 
 the reluctance of the magnetic circuit as much as pos- 
 sible, the cross sectional area of the core must be made 
 large enough to easily carry all the magnetic lines 
 
 117 
 
bo 
 
 <u C 
 
 118 
 
Low-Tension Positively Driven Make-and-Break Magnetos 
 for Stationary Engines 
 
 from one pole piece to the other, and the clearance 
 between the pole pieces and armature should not 
 exceed eight thousandths of an inch. On the other 
 hand, the armature must not run close enough to the 
 pole pieces to rub should the bearings become slightly 
 worn. 
 
 The armature has a single winding of silk insu- 
 lated wire, varying with different makes of machines 
 from No. 22 to No. 32 B. & S. gage. One end of the 
 winding is grounded by soldering to the armature core, 
 and the other end is connected to the insulated collect- 
 ing ring. 
 
 GROUNDING BRUSH. 
 
 The current is led away from the machine by the 
 collecting ring and brush, and the return circuit passes 
 through the engine frame into the frame of the mag- 
 neto and back to the grounded end of the armature 
 winding. The bearings, however, must not be depend- 
 ed upon for carrying the current to the armature 
 winding. The film of oil which surrounds the shaft 
 acts as a high resistance and prevents a steady flow 
 of current. If the current is forced across this film of 
 oil a sort of electrolysis of the steel shaft w r ill take 
 place, which will not only destroy the oil but will 
 roughen the shaft and bearing. 
 
 There are various forms of grounding brushes 
 such as plain copper gauze brushes, gauze brushes 
 saturated with graphite, and carbon brushes. These 
 brushes are usually round and are made to bear against 
 the bronze end of the armature cap. The graphite 
 saturated copper gauze brush is very satisfactory. 
 
 119 
 
120 
 
Low-Tension Positively Driven Make-and-Break Magnetos 
 for Stationary Engines 
 
 COLLECTING RING AND BRUSH. 
 
 It is not easy to design a collecting ring and 
 brush that will operate continuously without any 
 attention. There are several different methods which 
 have been used with more or less satisfaction. 
 
 In some machines one end of the armature shaft 
 has a hole bored lengthwise through it, in which 
 is placed an insulated copper or steel rod, the outer 
 end of which terminates in a copper button or better, 
 a steel disc. If steel is used, it should be highly 
 polished and glass hard. A gauze or carbon brush 
 is arranged to bear against the center of the steel 
 button. It is better, however, to place two smaller 
 brushes near the outside edge of the steel disc, so 
 that the wear on the brushes will be more uniform 
 and the surface will be kept cleaner than if one larger 
 brush were used against the center of the disc. In 
 some constructions the steel disc is replaced with a 
 short length of steel shaft and one or two brushes 
 made to bear on the side of this shaft. This is not 
 as satisfactory, however. 
 
 Good electrical contact between the brush and the 
 surface over which it slides is necessary, because if 
 the brush starts sparking it will rapidly wear, and the 
 sparking action will roughen the surface and cause 
 imperfect contact. A very satisfactory arrangement 
 is a special carbon brush about 5/16 of an inch in 
 diameter bearing lightly against the surface of a flat 
 ring made of hard commutator copper. Brass or 
 steel is in no way as good as this particular form of 
 
 121 
 
Ignition 
 
 copper. The carbon brush can be greatly improved 
 by having it made with a little graphite which acts 
 as a lubricant, thereby reducing friction and wear. 
 It should also be heavily copper plated to reduce the 
 electrical resistance. The copper ring must be care- 
 fully insulated from ground. Washers of hard white 
 fiber, 1/16 of an inch thick are good for this purpose. 
 Figure 1 is a drawing showing the detailed construc- 
 tion of the collecting ring and brush holder. The 
 brush holder must also be well insulated and firmly 
 fastened so as not to work loose. It is very important 
 that the brush make a good electrical contact with 
 its holder, and at the same time be free to slide in and 
 out so that a light spiral spring will be sufficient to 
 hold it firmly against the copper ring. 
 
 BEARINGS. 
 
 Needless to say the bearings should be provided 
 with an oil chamber of ample capacity so that fre- 
 quent attention will not be necessary. In order to 
 protect the armature from dust and moisture a tight 
 fitting cover over the housing should be provided. 
 This also will prevent iron filings from being drawn 
 in between the pole pieces by the magnetic attraction. 
 A felt washer fitted snugly over the shaft between 
 the bearing and the collecting ring will help materially 
 in keeping oil away from the armature and brush. 
 CURRENT WAVES. 
 
 The armature does not give a steady flow of cur- 
 rent like a battery or dynamo, but gives two sep- 
 arate impulses of current every revolution one posi- 
 tive and one negative. These impulses or current 
 
 122 
 
Low-Tension Positively Driven Make-and-Break Magnetos 
 for Stationary Engines 
 
 waves, as they are called, build up gradually and die 
 down still more gradually. From this it follows that 
 the armature must be positively driven by the engine 
 so that a current wave will be at its maximum strength 
 at the instant the igniter points separate. The cur- 
 rent wave must not be "peaked" but should be as 
 "flat" as possible so that any lost motion in the driv- 
 ing gears, or wear of igniter points, will not cause 
 the latter to separate when the wave is weak or at 
 zero value. 
 
 In order to take care of the advance and retard 
 of spark the wave must be flat enough to permit the 
 necessary variation, or the whole magneto must be 
 mounted so that it can be revolved through as many 
 degrees as there is spark advance. With this latter 
 system when the engine is being started, the mag- 
 neto is tilted in the same direction the armature runs 
 and the spark lever retarded. This shifts the cur- 
 rent wave so that it will be at its maximum when 
 the igniter points separate. The form of the current 
 wave depends principally upon the shape of the arma- 
 ture core and pole pieces, the magnetic permeability 
 of the iron from which they are cast, and the winding 
 on the armature. 
 
 Following is an oscillograph record of the cur- 
 rent and open circuit E. M. F. waves of a well-designed 
 magneto. The current wave, of course, does not follow 
 the shape of the E. M. F. wave, but is materially flat- 
 tened, due to the reactance of the armature winding. 
 If the resistance of the armature winding is too high 
 
 123 
 
124 
 
Low-Tension Positively Driven Make-and-Break Magnetos 
 for Stationary Engines 
 
 the current will be choked and will not respond as 
 rapidly as it should. On the other hand, if it is too 
 low the current will not persist long enough, thereby 
 shortening the duration of the arc. The amperage 
 will also be increased, which will more rapidly destroy 
 the igniter points. The current wave on this magneto 
 is strong enough to produce a good spark during 
 about 40 degrees of revolution. This is ample to per- 
 mit a considerable variation of adjustment between 
 the armature and igniter points. 
 
 TIMING THE MAGNETO. 
 
 Any good coupling such as is used for high 
 tension magnetos, or a set of gears, can be used 
 to drive the magneto. There is usually a mark placed 
 on the magneto armature, by the manufacturer, to 
 show the position it is in when the current wave is 
 at its maximum strength. This occurs at the instant 
 the edge of the armature core has pulled away from 
 the edge of the pole piece about 1-16 of an inch. 
 
 The timing is very simple. Turn the engine over 
 slowly until the igniter points just snap apart; then 
 turn the magneto in the direction it is to run until 
 the armature has pulled away from the pole piece 1-16 
 of an inch, or as shown by the marks on the armature. 
 Now secure the magneto in place and connect a wire 
 from the collecting brush to the igniter. The mag- 
 neto can be run in either direction. 
 
 If the magneto is not mounted on a metal base 
 which is in good electrical contact with the engine 
 frame, it will be necessary to ground it by connecting 
 a wire from the body of the magneto to the frame 
 
 125 
 

 A typical installation the magneto is gear driven at engine 
 speed from the cam shaft. 
 
 126 
 
Low-Tension Positively Driven Make-and-Break Magnetos 
 for Stationary Engines 
 
 of the engine. The shut-off switch can be put in series 
 with the wire leading to the igniter, or it can be 
 arranged to ground the magneto by short circuiting 
 the armature, thereby cutting off ignition. 
 
 RELATION OF ENGINE AND MAGNETO SPEEDS. 
 
 It is not necessary to use every current wave 
 that is produced. A four-cycle single cylinder engine 
 calls for one spark every other revolution of the crank 
 shaft; therefore, if the magneto is run at engine speed, 
 only one out of every four current waves will be used. 
 A single cylinder two cycle, and a two cylinder four 
 cycle engine will use every other wave ; a four cylin- 
 der, four cycle engine, which requires two sparks 
 every revolution, will use every impulse. It is often 
 necessary with low speed engines to run the mag- 
 neto twice engine speed in order to increase its effi- 
 ciency and make starting on the magneto easier. This, 
 of course, doubles the number of current waves, which 
 is immaterial, but also reduces by one-half the avail- 
 able spark advance. A magneto giving a current wave 
 strong enough to ignite the charge during 60 degrees 
 of armature revolution, will allow the same number 
 of degrees spark advance on the crank shaft if run at 
 engine speed, and only half as much or 30 degrees if 
 driven twice engine speed. 
 
 MULTIPLE CYLINDER ENGINES. 
 
 This type of magneto will give good results on 
 engines of more than one cylinder provided it is cor- 
 rectly timed. The igniters on the different cylin- 
 
 127 
 
Ignition 
 
 ders are all connected to a common wire leading to 
 the collecting brush on the magneto. The two princi- 
 pal things to observe are: First, the magneto must 
 be driven at such a speed that a current wave will be 
 at its maximum every time any of the igniter points 
 separate; second, the igniters must be so arranged 
 that at the instant any one of them snaps causing 
 ignition all the others will be out of contact. It is 
 easy to see that if any of the other igniters are in 
 contact when ignition is required in cylinder No. 1, the 
 current will flow across them rather than produce an 
 arc in the first cylinder. 
 
 It is often a good plan with single cylinder engines 
 to run the magneto at 1% engine speed. This makes 
 use of some positive and some negative waves, caus- 
 ing the current to reverse its direction across the 
 igniter points every time they separate. Under these 
 conditions "pitting" of one point and "building up" 
 on the other is impossible and the wear is uniform. 
 
 WEAR OF IGNITER POINTS. 
 
 The igniter points will last considerably longer 
 with this type of magneto than with battery sys- 
 tems. This is due, in part, to the fact that much 
 less amperage passes across the arc when a magneto 
 is used than with a battery and coil. The oscillograms 
 on page 45 show that with battery systems from 1 to 
 4 amperes pass through the arc, while the maximum 
 current possible with the magneto giving the current 
 wave shown on page 124 is 0.25 of an ampere. The 
 several different makes of magnetos, however, differ 
 somewhat in this respect. Some machines having 
 
 128 
 
Low-Tension Positively Driven Make-and-Break Magnetos 
 for Stationary Engines 
 
 armatures of less resistance give twice as much am- 
 perage, but even then the wear on the igniter points 
 is very slight. 
 
 INSULATION OF IGNITER. 
 
 The successful operation of the magneto depends 
 to a large extent upon the insulation of the stationary 
 igniter point. Two or three times the insulation ordi- 
 narily used is necessary, particularly since a lack of 
 sufficient insulation at this point is so common a fault 
 with battery systems. The reason for this is simple : 
 The voltage of the magneto is several times that of 
 a set of 4 or 6 dry cells, and so if a greasy carbon 
 deposit collects on the surface of the insulation, which 
 usually happens sooner or later, the higher voltage 
 of the magneto finds an easy path across it to ground. 
 The lower curve on page 124 shows that the open circuit 
 E. M. F. rises to about ISO volts. Since several of 
 these voltage impulses occur between successive igni- 
 tions when the igniter points are separated, the insula- 
 tion is subjected to a strain of 150 volts as against 
 about 6 volts with battery systems. If mica washers 
 are used, they should be extra large and not less than 
 J4 or % of an inch thick. The voltage will not punc- 
 ture the mica but will "skate" or slide a considerable 
 distance over the surface, particularly if it is blackened 
 with even a slight carbon deposit; therefore, the "dis- 
 tance to ground" must be kept comparatively great. 
 
 Built up thick mica washers are not entirely sat- 
 isfactory. They are quite sure to loosen in time and 
 the heat and pressure of constant explosions will drive 
 
 129 
 
130 
 
131 
 
Ignition 
 
 grease and carbon in between them. A form of mold- 
 ed composition or so-called "lava" bushings are very 
 good. If the bushings are thoroughly annealed, to 
 make them less sensitive to sudden changes of tem- 
 perature, and are correctly shaped and installed, they 
 will be very durable and entirely satisfactory. A cone- 
 shaped lava bushing, fitted in a ground taper joint 
 in the igniter casting, will be so well protected me- 
 chanically that breakage will be very unlikely. 
 
 When kerosene is used as fuel, the problem of 
 insulation is more difficult. Mica washers seem to 
 break down sooner and are even less satisfactory than 
 with gasoline. 
 
 HEAT OF ARC. 
 
 The temperature the arc attains is not as important 
 as its duration, viz. : the actual time it lasts. Almost 
 any kind of an electric spark is hot enough to ignite 
 the charge, but often fails to do so because it does 
 not last long enough. A piece of paper can be passed 
 through a flame without catching fire, provided it is 
 done quickly. The gas in the cylinder ignites very 
 quickly, to be sure, but some kinds of sparks are even 
 quicker, and ignition fails on that account. 
 
 The arc from this type of magneto is of ample 
 duration to ignite the most .stubborn mixture, in fact 
 its duration is, as a rule, longer than that of bat- 
 tery systems. The applied voltage is higher, the 
 inductance of the winding is greater, and the arma- 
 ture continues to generate current for a part of a sec- 
 ond after the igniter points separate, all of which tends 
 to prolong the arc. 
 
 132 
 
Low-Tension Positively Driven Make-and-Break Magnetos 
 for Stationary Engines 
 
 SIZES OF MAGNETOS. 
 
 Make-and-break magnetos of this type are made in 
 two principal sizes, generally known as "Two Magnet*' 
 and "Three Magnet." The larger machine is a trifle 
 longer than the smaller and has one more magnet. 
 This extra magnetic strength and length of armature 
 makes the three - magnet machine more efficient at very 
 slow speeds. A good two-magnet magneto will give 
 a spark strong enough to start the engine at 22 revo- 
 lutions per minute, while the larger machine of same 
 make will give as good a spark at 12 revolutions per 
 minute. For engines up to 6 or 8 H. P. that can be 
 easily turned over, the two-magnet magneto is satis- 
 factory, but for starting larger engines the three-mag- 
 net machine should be used. Where starting is accom- 
 plished with a battery and cheap coil, and the mag- 
 neto run not less than 500 revolutions per minute, the 
 two-magnet machine will operate successfully on 
 engines of 30 or more horsepower. 
 
 OSCILLATING MAKE-AND-BREAK MAGNETOS. 
 There are a few special forms of magnetos 
 arranged to be attached directly to the igniter plate. 
 The armature is fastened to the movable igniter point 
 so that it will oscillate across the magnetic field. Syn- 
 chronism between the armature and igniter is absolute 
 since they are both operated by the same tripping 
 mechanism. The tendency in designing this type 
 of magneto, so far, has been to make it too small and 
 the magnetic circuit of too high reluctance, resulting 
 in a lack of reserve spark strength to meet adverse 
 
 133 
 
Ignition 
 
 conditions, and in the magnets losing their strength 
 after being in service a few months. This type is stili 
 in the experimental stage, but the idea of making the 
 magneto a part of the igniter itself is correct, and 
 the practical difficulties attending its achievement will, 
 without doubt, soon be overcome. 
 
 Since reliable ignition apparatus can be had today, 
 which was not so a few years ago, the far greater 
 part of present-day ignition trouble is due to no other 
 cause than the tinkering and guessing of the man who 
 DOESN'T KNOW. 
 
 134 
 
A 
 
 ALTERNATING CURRENT 91, 93; Magneto 91. 
 
 AMMETER 22, 24, 89; substitute for, in testing dry cells 23; hot wire 
 65 (foot note). 
 
 AMPERE definition of 13. 
 
 AMPERE HOUR definition of 14. 
 
 ARC (see spark). 
 
 ARMATURE 77, 78, 79, 80, 117; "drum" 79, 80, 83; winding of, for 
 dynamos 85; "H" 97, 100, 101, 116; winding of, for high tension 
 magneto 99, 110; winding of, for make-and-break magneto 119, 
 123, 125; position of, when spark occurs 104; position of relative 
 to current strength 100, 101, 125; short circuiting of, to cut off 
 ignition 127; re-actance in 123; clearance of 110, 119; high ten- 
 sion 113; for make-and-break magneto 116, 117; acting as make 
 and break coil 117; strengthening magnetism in 117; energy 
 stored in 117; protecting of from dirt, etc., 122. 
 
 B 
 
 BATTERIES Ch. 1 ; primary, definition of 5 ; theory of 6 ; internal re- 
 sistance of 7 ; polarization of 6 ; closed and open circuit, definition 
 of 6; E. M. F. of 23, 27; amperage of 24, 27; installing of 25; 
 connecting of 26; "local action" of 10. 
 
 Dry 9, 10; E. M. F. of 24; amperage of 24; current from 28; ef- 
 ficiency tests of 29; internal resistance of 24; life of 28; 
 polarization of 9; recuperation of 10; test for amperage of 22, 
 23; "local action" of 10; connecting of 27, 28. 
 Edison Primary 7, 8. 
 Edison Storage 12. 
 Gordon 8. 
 
 Secondary or Storage definition of 5; theory of 11, 12; care of 25, 
 
 26; testing of 24; "floating on the line" 87; sulphation of 25. 
 
 BEARING passing current through 119; for make and break magneto 
 
 122; ball 115. 
 
 BRUSHES Collecting 78, 93; carbon 85; copper plated carbon 85, 122; 
 for dynamo 85 ; copper gauze 85 ; trouble with 86 ; graphite satur- 
 ated 85, 122; for high tension magneto 110, 113, 116; grounding 
 119; for make and break magneto 119, 121, 122; sparking and 
 wear of 121, 122; contact with its holder 85, 122. 
 BUSHING lava 132. 
 
 C 
 
 CAPACITY electrostatic, of secondary winding 63 ; of condensers 60. 
 CARBON for brushes 85; rod for dry cell 5, 9, 27; granular for dry cell 
 
 9 ; resistance of 21 ; loose contact with 27. 
 CELLS (see Batteries); connected in series 27; in multiple 28; in series 
 
 multiple 29. 
 
 COBALT as a conductor of magnetism 71. 
 COIL make-and-break 32. 36, 38, 42; oscillograms of 44 to 47; E. M. 
 
 F. of spark from 47. 
 
 Jump Spark theory of 51, 52, 54; construction of Ch. 8; oscillograph 
 tests of Ch. 9; E. M. F. of 51; producing sparks five feet 
 long 20. 
 Non Vibrating 6'9. 
 
 COLLECTING BRUSHES (See Brushes.) 
 
 COLLECTING RING for high tension magneto 108. 110, 113; for A. C. 
 
 magneto 93; for make-and-break magnetos 116, 119. 121, 122. 
 COMMUTATOR 54, 78; construction of, for dynamos 85; burning and 
 
 roughening of 86. 
 COMPASS 73, 75. 
 COMPRESSION loss of 39. 
 
CONDENSER 2, 52, 53 ; construction of for coils 59 ; capacity of 60 ; 
 
 if too large or small 63; for high tension magneto 99, 110, 113.. 
 CONDUCTANCE definition of 18. 
 
 CONDUCTORS definition of 1; best known 14; table of 21. 
 CONTACT poor on dry cells 27; time length of 42, 46, 47, 70. 
 
 Points. Theory of wear and burning of 39, 40 ; for igniter 40 ; wear of 
 igniter 41, 48, 123, 125, 128; adjustment of, for make-and- 
 break magneto 127, 128; adjustment of, for high tension mag- 
 neto 113; for vibrating coils 53, 54, 58, 63; adjustment of for 
 vibrating coils 58, 59. 
 CORE-IRON 36, 51; importance of 32, 47; construction of 56; for 
 
 armature 79. 
 
 COULOMB definition of 14. 
 
 COUPLING for driving magnetos 105; Oldham 104, 105. 
 CURRENT 1; alternating 91, 93; wave in magneto 95, 100, 124; in 
 primary of vibrating coils 52, 54, 65, 66, 67, 69; in secondary of 
 vibrating coils 52, 55, 60 ; in make-and-break coils 45, 46, 47 ; 
 current producing magnetism 31, 32, 33, 71; momentum of 33, 34; 
 inertia of 33, 34; Foucault or Eddy 56, 79. 
 
 D 
 
 DISRUPTIVE DISCHARGE definition of 19. 
 
 DISTRIBUTOR for high tension magneto 96', 97, 111, 113; care of 108. 
 
 DRY CELL 9, 10; (see Batteries). 
 
 DUAL SYSTEM 97, 103, 111. 
 
 DYNAMIC ELECTRICITY definition of 3, 71, Ch. 10. 
 
 DYNAMO 80, 81, 82; shunt wound 80, 81; series wound 81; making it 
 "pick up" 81; variation of voltage in 82; construction of low 
 tension 83 to 89 ; regulating voltage of 86, 87, 89 ; governor for 
 86, 89. 
 
 DYNE^-74. 
 
 E 
 
 EDDY OR FOUCAULT CURRENTS 56, 79. 
 
 ELECTRICITY 1, 2, 3; 
 
 Current-definition of 1 ; (see current). 
 Dynamic-definition of 3, 71, Ch. 10. 
 Galvanic-definition of 3. 
 Static-definition of 1, 2, 14, 53. 
 
 ELECTROMOTIVE FORCE (E. M. F.) definition of 2; unit of 13; of 
 cells 23, 27 ; production of by magnetism 75 ; variation of in mag- 
 neto 91, 95; required to start an arc 50, 97, 99; produced in 
 armature 97, 99; produced in secondary winding 51, 60, 99. 
 
 ELECTROLYSIS 119. 
 
 ELECTROLYTE definition of 6; for dry. cells 9; for Gordon and Edison 
 primary cells 7; for secondary or storage batteries 11, 87, 89; for 
 Edison storage battery 12. 
 
 E. M. F.' (see Electromotive Force). 
 
 ETHER OF SPACED- 33. 
 
 F 
 
 FIELD (see Magnetic Field). 
 
 "FLOATING BATTERY ON LINE" 87, 89. 
 
 FLUX magnetic 75. 
 
 FOUCAULT OR EDDY CURRENTS 56, 79. 
 
 G 
 
 GALVANIC ELECTRICITY 3. 
 GALVONOMETER 75. 
 
GAUSS definition of 75. 
 GENERATOR electric, principle of 75. 
 GOVERNOR for dynamos 86, 89. 
 
 H 
 
 "H" ARMATURE 97, 100, 101, 116. 
 HEAT produced by current in wire 14; of spark or arc 50, 132. 
 
 I 
 
 IGNITER 34, 37, 38; points for 40; wear of 41, 48; insulation of 129. 
 
 IGNITION make-and-break 30, 48; jump spark 49. 
 
 INDUCTION coil, producing spark five feet long, 20. 
 
 INDUCTOR of alternating current magneto 92, 93 ; type magneto 93, 95. 
 
 INERTIA (electric) 33. 
 
 INSULATORS definition of 1; table of 21. 
 
 INTERNAL RESISTANCE of batteries 7, 24, 27, 28, 29. 
 
 INTERRUPTER ^for vibrating coils 53, 54, 56', 57, 58; for non-vibrating 
 
 coils 68, 69; for high tension magneto 96, 101, 111, 113. 
 IRIDIUM 40, 58. 
 IRON as a conductor of magnetism 71 ; for core (see Core). 
 
 J 
 JUMP SPARK 49; (see Spark). 
 
 K 
 
 KEROSENE as fuel 132. 
 
 L 
 
 "LAG" in coils 67, 69; magnetic 103. 
 LAVA BUSHING 132. 
 LINES OF FORCE definition of 71, 73, 74; unit of 74; forming around 
 
 a coil 32; around a wire carrying a current 31; producing E. M. 
 
 F. by "cutting'' 51, 75, 76, 77. 
 "LOCAL ACTION" in galvanic cells 10. 
 LODGE Sir Oliver 33 (foot note.) 
 
 M 
 MAGNETIC CIRCUIT definition of 73; reluctance of 79, 117, 133; for 
 
 high tension magneto 108, 109. 
 
 Field definition of 73; surrounding wire carrying a current 31. 33; 
 34 ; between poles of a magnet 74, 75 ; increasing strength 
 of 79. 
 
 Density definition of 75 ; increasing by use of iron core 32, 33. 
 Lines of Force see "Lines of Force". 
 Strength 74. 
 Plug System 48. 
 
 MAGNETISM 71, 75; around wire carrying a current 31, 32, 33; insu- 
 later of 71 ; circuit of (see Magnetic Circuit) ; conductor of 71 ; 
 unit quantity of 74 ; density of (see Magnetic Density) ; strength 
 of 74 ; producing electric current from 75 ; residual 81 ; strengthen- 
 ing of, in armature 99, 117. 
 
 MAGNETO definition of 80; variation of voltage in 82, 91; direct cur- 
 rent 89, 91 ; alternating current 91 ; inductor type 93, 95 ; varia- 
 tion of voltage in inductor type 95 ; theory of high tension 96', 97, 
 99, Ch. 12; timing of high tension 106, 107; timing of make-and- 
 break 125, 127. 128; dual type 97, 108, 114; connecting of 107; 
 diagram of high tension 109; oiling of high tension 115; for make- 
 and-break engines 116. Ch. 14; sizes of make-and-break 113; 
 oscillating types 133, 134; interrupter or timer for high tension 111. 
 
MAKE-AND-BREAK IGNITION 30, 48. 
 
 MAXWELL 74, 75; J. Clerk, 74. 
 
 MICA as an insulator 21 ; for insulating commutator 85 ; washers for 
 
 insulating igniter 38, 39, 129, 132; for condenser of high tension 
 
 magneto 110. 
 MICROFARAD 60. 
 
 MOMENTUM of electric current 33, 41. 
 MULTIPLE CONNECTIONS 17; joint resistance of 17, 18; current in 
 
 branch circuits of 18. 
 
 N 
 
 NICKEL resistance of 21; as a conductor of magnetism 71; for igniter 
 points 40. 
 
 O 
 
 OHM definition of 14, 15. 
 
 OHM'S LAW definition of 15, 16; mentioned 46. 
 
 OLDHAM-COUPLING 104, 105. 
 
 OSCILLOGRAPH 43, 44; diagram of 46. 
 
 OSCILLOGRAMS of make-and-break coils 45; of vibrator coils 66, 67; 
 of current waves of inductor type magnetos 95 ; of current in "H" 
 armature 100; of current passing through arc 102; of current 
 waves in make-and-break magneto 124; of E. M. F. waves in 
 make-and-break magneto 124. 
 
 P 
 
 "PANCAKE WINDINGS" for jump spark coils 61, 63. 
 
 PARALLEL CONNECTIONS (see Multiple Connections). 
 
 "PITTING" of contact points, theory of 39, 40, 48, 58, 63, 113, 
 
 PLATINUM 40, 58. 
 
 PLUG spark, 51, 62. 
 
 Magnetic, system 48. 
 
 POINTS contact (see Contact Points). 
 
 POLARIZATION explained 6; .prevention of in Gordon and Edison 
 primary cells 7; prevention of in dry cells 9, 10; effects of in 
 dry cells 9. 
 
 POLE PIECES -79; for dynamo 83; for inductor type magneto 93; for 
 high tension magneto 109; for make-and-break magneto 117. 
 
 POWER unit of electrical 15; loss of in gas engine 39, 94. 
 
 PRIMARY of jump spark coil 51, 56; of armature of high tension mag- 
 neto 99. 
 
 R 
 
 RELUCTANCE definition of 73 ; of magnetic circuit 79. 
 
 RESISTANCE unit of 14; of different materials (table of) 21; of arc 
 or spark 49; of spark gap 52, 55; internal of batteries 7, 24, 27, 
 28, 29; of circuits in multiple 17, 18; of circuits in series 16'; of 
 gases 50 ; of secondary winding 52 ; of carbon brushes 85. 
 
 S 
 
 SAFETY SPARK GAP for high tension magneto 107, 108, 109, 111, 113; 
 causing missing explosions 111. 
 
 SECONDARY theory of 51; illustration of 61; winding of 53, 60; cur- 
 rent in 52; E, M. F. in 51, 53, 54, 6'0 ; insulation of 60-63; 
 number of turns in 63; "pancake" winding 61-63; of high tension 
 magneto armature 99. 
 
 SELF-INDUCTION of secondary winding 63. 
 
 SERIES CONNECTIONS 16; total resistance of 17; of cells 27. 
 
SHELF or base on which to mount magneto 106, 125. 
 
 SPARK Jump 49; E. M. F. of 49, 50, 51; duration of 55; current pass- 
 ing through 102, 103; heat of 50; resistance of 49, 52; tests of 
 in air 51 ; preventing spark at contacts 52, 53 ; shortening of 63, 
 64; number of during one contact of timer, 65, 66, 67; timing of 
 in high tension magneto 104 ; shutting off of in high tension mag- 
 neto 107; maintaining of in high tension magneto 99, 101. 103; 
 strength of in high tension magneto 101, 103; playing around glass 
 plate 72. 
 
 Make-and-Break theory of 33, 34; E, M. F. of 47; duration of 41, 
 125, 132; current passing through 45. 46, 128; heat of 132; 
 resistance of 49 ; preventing of at contacts 52, 53 ; at low 
 speed of make-and-break magneto 133; advance and retard 
 of, in make-and-break magneto 123, 127; timing of, in make- 
 and-break magneto 125, 127, 128; occurring on breaking a 
 circuit 34. 
 
 Safety Gap (see Safety Spark Gap). 
 Plug 51, 62. 
 SULPHATION of storage battery, cause and remedy for 25. 
 
 T 
 TABLE of comparative resistance of materials 21 ; of life of dry cells 
 
 29; of driving speeds for high tension magneto 104. 
 TIME LENGTH OF CONTACT 70; in make-and-break battery system 
 
 41, 42, 46, 47. 
 TIMER for vibrating coils, 54, 62; for non-vibrating coils, 68, 6*9, 70; 
 
 working with alternating current magneto 94 ; for high tension 
 
 magneto 96, 111, 113. 
 TIMING of high tension magneto 106, 107: of make-and break magneto 
 
 125, 127, 128; of igniter 41. 
 TRANSFORMER 96, 103, 108, 114. 
 
 V 
 VACUUM IMPREGNATING PROCESS 60, 61. 
 
 VIBRATOR theory of 53; construction of 56, 57, 58; illustrations of 
 57; "hammer break' 58; "freezing" of 58; current required to 
 operate 65, 66, 67 ; substitute for 69 ; working with alternating 
 current magneto 94 ; adjusting of 59. 
 
 VOLT definition of 13. 
 
 VOLTAGE (see Electromotive Force). 
 
 VOLTMETER 24, 89; electrostatic 47. 
 
 W 
 
 WASHERS mica, for insulating igniter 38, 39, 129, 132. 
 WATT definition of 15. 
 WAVES current, in alternating current magnetos 93 ; "sine" 94 ; number 
 
 of, in inductor type magneto 93 ; oscillograph records of (see 
 
 "Oscillograms"). 
 WIRE heat produced in. by current 14; size of for connecting coils 66; 
 
 iron for core 56; size of for winding make-and-break coils 36; 
 
 size of for winding primary 56; size of for winding secondary 63; 
 
 size of for winding high tension magneto armature 99. 
 
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