*** LIBRARY UNIVERSITY OF CALIFORNIA. Deceived APR 13 1893 . /*P ^Accessions No'. 5*0 Q.P 6" . Ctes A^o. DYNAMO CONSTRUCTION. WORKS ON ELECTRIC LIGHTING BY THE SAME A UTHOR. ELECTRIC LIGHT : Its Production and Use. Embodying Plain Directions for the Treatment of Dynamo- Electric Machines, Batteries, Accumulators, and Electric Lamps. By J. W. URQUHART, C.E., Author of "Electric Light Fitting," "Electroplating," c. Fourth Edition, care- fully Revised, with Large Additions and 145 Illustrations. Crown 8vo, 7>r. td. cloth. \Just published. " The book is by far the best that we have yet met with on the subject." Athenceum. " It is the only work at present available, which gives in language intelli- gible for the most part to the ordinary reader, a general but concise history of the means which have been adopted up to the present time in producing the electric light. ' ' Metropolitan. " The book contains a general account of the means adopted in producing the electric light, not only as obtained from voltaic or galvanic batteries, but treats at length of the dynamo-electric machine in several of its forms." Colliery Guardian. ELECTRIC LIGHT FITTING: A Handbook for Working Electrical Engineers, embodying Practical Notes on Installation Management. By JOHN W. URQUHART, Electrician, Author of "Electric Light," &c. With numerous Illustrations. Crown 8vo, $s. cloth. \Just published. "This volume deals with what may be termed the mechanics of electric lighting, and is addressed to men who are already engaged in the work, or are training for it. The work traverses a great deal of ground t and may be read as a sequel to the same author's useful work on ' Electric Vght.' " Electrician. " Eminently practical and useful. . . . Ought to be in the hands of every- one in charge of an electric light plant." Electrical Engineer. "Altogether Mr. Urquhart has succeeded in producing a really capital book, which we have no hesitation in recommending to the notice of working electricians and electrical engineers." Mechanical World. CROSBY LOCKWOOD & SON, 7, STATIONERS' HALL COURT, E.G. DYNAMO CONSTRUCTION A PRACTICAL HANDBOOK FOR THE USE OF ENGINEER-CONSTRUCTORS AND ELECTRICIANS-IN-CHAR GE FRAMEWORK BUILDING, FIELD MAGNET AND ARMATURE WINDING AND GROUPING, COMPOUNDING, &c. ; WITH EXAMPLES OF LEADING ENGLISH, AMERICAN, AND CONTINENTAL DYNAMOS AND MOTORS BY JOHN W. URQUHART, ELECTRICIAN AUTHOR OF "ELECTRIC LIGHT" AND "ELECTRIC LIGHT FITTING" tf) $um*rou Hlurftratton* LONDON CROSBY LOCKWOOD AND SON 7 STATIONERS' HALL COURT, LUDGATEJHILL 1891 \All rights reserved] U7 Engineering Library PREFACE. A FEW words may be given here in explanation of my aim in offering this Handbook of the Dynamo- electric Machine. Much has been done by several well-informed writers towards disseminating a knowledge of the principles of the dynamo, but I could not attempt to decide whether the course of study laid down by these learned authorities has commended itself generally to engineers. It is, however, beyond dispute, that although the excellent works of two or three English authors have done a great deal towards spreading correct views of the theory of the dynamo, their labours have not covered the technical requirements of ordinary engineers and mechanics. The electro- technical journals of this country, recognising this fact, have of late begun to devote a good deal of atten- tion to the mechanics of the dynamo. They have engaged the best known writers, consisting mostly of practical men, to throw light upon the jealously- guarded " mysteries " of the dynamo-builder's art, and doubtless with great success. But while this important work of instruction is in progress in those journals, there are numerous engineering stu- dents who will, no doubt, welcome a fairly complete Handbook upon the subject. It is to this class that I look for readers. A long practical acquaintance, not only with the VI PREFACE. subject, but with the kind of men who devote their lives to it, has convinced me that a treatise of the kind, to be acceptable at the outset to the minds of ordinary engineers, must have some of the following characteristics : It must be very plainly worded ; it should explain as much as possible of the theories of the dynamo in every-day language ; if a theory is adopted, the physical theory by preference should be chosen, and this should be expressed as plainly as the case will permit. Lastly, the treatment of the constructive details should be very practical. I have endeavoured to carry out these aims in the following pages, and I earnestly hope that the book may satisfy the expectations of the many kindly readers of my treatise on " Electric Light " who have expressed a desire to see a work by the same author on the Dynamo. The Introduction contains a condensed history of the subject; the salient features of dynamo-electric theory are touched upon in the first and second chapters ; and the remainder of the work is devoted to technical expositions of the " build " of various kinds of machines, including chapters descriptive of typical dynamos and motors. The illustrations, with one or two exceptions, are original, and have been engraved from photographs accurately taken for the purpose. May, 1891. CONTENTS. INTRODUCTION. PAGE DEFINITIONS A Magneto-Electric Machine An Electric Motor Evolution of the Dynamo Faraday's Experiments of 1831 Earliest Attempts to Devise Magneto Machines Faraday's Disc Machine Early Attempts to Construct Magneto-Electric Ma- chines Sturgeon's Armature Stohrer's Machine of 1836 Woolrich's Machine of 1841 Wheatstone andCooke's Improve- ments Suggestions of Soren Hjorth Brett's Improvements The "Alliance" Electric Light Magneto Machine Siemens- Shuttle Armature Wilde's Improvements Development of the Self-Energizing Principle in Dynamos The Term " Dynamo- Electric Machine " Non-Fluctuating Current Gramme Armature of 1870 The Alteneck Armature Further Improvements in the Dynamo The Return to Alternating Currents Sir William Thomson's Suggestions of 1881 Development of Constant Potential Working Improvement in Brush's Armature . . I CHAPTER I. ELEMENTS OF THE DYNAMO. CHIEF PARTS OF THE DYNAMO Simplest Conception of a Dynamo The Field Magnet The Simplest Armature The Collector or Commutator 20 CHAPTER II. NOTES CONCERNING THE ELEMENTARY PRINCIPLES. MAGNETIC FIELD Magnetic Field due to a Current -bearing Wire Curves of the Magnetic Lines Diffusion of the Lines Concen- tration of the Lines Magnetic "Leakage" Physical Signifi- cance of the Lines of Force Magnetic Reluctance A Magnetic Unit The Value of the Lines of Force Lines of Force and a viii CONTENTS. PAGE Conductor Lines of Force in the Field of a Dynamo Maximum Magnetization Motion of a Conductor in the Field The Mag- netic Field of a Dynamo The Armature The Commutator . 30 CHAPTER III. DYNAMO FIELD MAGNETS. SEPARATE EXCITATION Series Winding Shunt Winding Com- pound Winding . . . . . . f . . 41 CHAPTER IV. CALCULATIONS RESPECTING EXCITING COILS. MAGNETIZING POWER OF A CURRENT The Permeability of Iron to Magnetism Dr. Rowland's Researches A Curve of Mag- netization Electro-Magnet Formulae Modern Conception of a Magnetic Circuit Ohm's Law and the Magnetic Circuit Mag- netic Saturation Field Magnet Coils Trial Method of Deter- mining Magnet Winding Magneto-Motive Force . . -S3 CHAPTER V. DETAILS RESPECTING EXCITING COILS. TABLE OF CURRENT DENSITIES AND SECTIONAL AREAS OF DYNAMO WIRES Length of the Bobbins Field Magnet and Armature Insulated Wire Operation of Winding 70 CHAPTER VI. FORM OF THE FIELD MAGNET. SINGLE CIRCUIT MAGNETS Cast-iron Field Magnets Edges and Corners The Efficient Section of Core is undoubtedly a Circle Pole Pieces The Armature Chamber or Bore Consequent Pole Magnets Cast-iron Magnets Right and Left-handed Coil- ings Direction of the Helix Cross-Connections . . . .79 CHAPTER VII. THE ARMATURE. REVOLUTION OF IRON CORE NOT NECESSARY Means of Super- seding the Iron Core Commutator Continuous Current Armature c CONTENTS. IX CHAPTER VIII. THE ARMATURE CORE. PAGE LAMINATION OF THE IRON Foucault or Eddy Currents Heat of Core, or Eddy Currents in, Detrimental to Magnetic Induction The Laminations Lamination of Drum Armatures Lamination not without Disadvantages Lamination of Ring Armatures Gramme Armature Influence of the Pacinotti Projections Material of the Armature Cores The Core regarded as a Link in the Magnetic Circuit Cross Section of the Core Rules apper- taining to Armature Cores Classification of Armature Cores Drum Armatures Ring Armatures Spherical Armatures . .102 CHAPTER IX. ARMATURE WINDING. FORMULA OF ELECTROMOTIVE FORCE IN ARMATURE Determi- nation of the Current Proportion between Depth of Windings and Diameter of Core Measurement of Magnetic Lines through Armature . . . 118 CHAPTER X. RING ARMATURE WINDING. CONTINUOUS HELIX METHOD Insulation of the Core Rotation Mounting of the Core Coils of the Helix Breakdown of Insu- lation Operative Details of the Winding Causes of Sparking Collector for Symmetrically Wound Ring Collector Brushes for Ring Armature Typical Ring Armature Dynamo Dissected Winding Ring for a Multipolar Field Multipolar Windings Square Section Wire for Armature Winding Cylinder Ring Winding Fan Spokes of the Star Wheel Driving Horns Manipulation of Heavy Conductors Ring Armature with Open Coil Spherical Armature . . 125 CHAPTER XI. DRUM ARMATURE WINDING. DIAGRAMMATIC VIEWS OF CYLINDER OR DRUM WINDINGS Drum Windings in General Use Dividing the Coils Drum Armature with Frolich Windings Windings for High and Low Tension X CONTENTS. PAGE Testing for Short Circuits Various Devices for Neutralising Eddy Currents in Drum Armature Heating of the Pole Pieces Ventilation of the Armature Turns in Multiple Arc in Armature Cuirent Density in the Wires Depth of the Air Gap "Dead " and "Active" Wire on the Armature Circumferential Speed of Armature Lines of Force per Watt Cross Section of the Armature Conductor per Ampere Percentage of the Diameter of Armature Occupied by Windings Low Resistance Drum Armatures Circumferential Speed of Armatures Yards of Con- ductor per Volt of Electromotive Force Alternating- Current Armatures Iron-Cored Bobbins Coil, Ribbon, and Loop Alternating-Current Armatures The Coils Ferranti's Alter- nator Drum Alternator Armature Ring Alternator Armature Alternator Collectors Machine without Collectors or Com- mutatorsUnipolar Dynamo . . . . . . .152 CHAPTER XII. ECONOMIC DESIGN. THE MAGNETIC LINES Example I. Resistance Fall of Potential in Armature Percentage Loss of Power Kapp Lines in Arma- ture Core Dimensions of Field Magnet Core Dimensions of Armature Core Magnetic Reluctance of Field Magnet Mag- netic Reluctance of Air Space Magnetic Reluctance of Armature Proportioning of Ampere Turns 187 CHAPTER XIII. DYNAMO GOVERNING. REGULATION BY SHIFTING BRUSHES Governing by Speed Governing by Variable Resistance Variation of the Magnetic Field Regulation by Varying the Width of the Air Gap Hand Regulation Cases of Excitation Resistance Regulators Regu- lation of Series Dynamos Self-regulation by Shunt Winding Regulation by Compounding Regulation by a Composite Field Constant Current Regulation Impracticable .... 200 CHAPTER XIV. OUTPUT AND EFFICIENCY. THE ELECTROMOTIVE FORCE LOST INTERNALLY Power Absorbed Internally Horse-Power Transmitted to Dynamo . . .213 CONTENTS. xi CHAPTER XV. GRAPHICAL RECORDS. PAGE ORIGIN OF CHARACTERISTIC CURVES Setting Out Curves Squared Paper Hopkinson's Curve -Electromotive Force and Current Curves Horse-Power Curves Characteristic with H.-P. Lines Curve of External Electrical Activity Line Representing Internal Resistance Variable Speed Curve Graphic Record of Shunt Dynamo Characteristics from Shunt and Series Coils Characteristic from a Compound Dynamo . . . .219 CHAPTER XVI. DYNAMOS IN SERIES AND PARALLEL. SERIES WORKING OF Two DYNAMOS Shunt Wound Dynamos in Series Parallel Working of Two Dynamos Series Wound Dynamos in Parallel Shunt Wound Machines in Parallel Compound Dynamos in Parallel Interaction of the Dynamos Alternating- Current Dynamos in Parallel Series Running of Alternators Impracticable Interaction of Alternators Switch- ing in Parallel Synchronising of Two Alternators, or Alternators in Step 230 CHAPTER XVII. THE DYNAMO IN ELECTRIC LIGHTING. SEPARATE EXCITATION OF ALTERNATOR Compensation Exci- tation of Alternator Alternators Working Transformers Alter- nator and Exciter on One Shaft Compound Dynamo in Incan- descent Lighting The Shunt Machine in Electric Lighting The Series Dynamo in Arc Lighting Number of Arcs Lighted by One Machine 241 CHAPTER XVIII. OPERATIVE NOTES. ERECTION OF DYNAMOS Alignment of Bearings Handling of Armature Treatment of Collector or Commutator Connections of the Circuit Polarity of the Core Course of the Current Belting and Belt Joints Rope Driving Faults Ground Fault Testing for " Ground " Circuit Closer and Reverser for Test- ing Localisation of Faults Short Circuits and Dead Breaks Burnt-out Coils Short Circuiting of Shunt Dynamo Distri- buting Leakage Tests Failure of Dynamo to Excite or Start xii CONTENTS. PACK Ribbon Lead as Safety Fuse Failure of the Residual Magnetism Points of Best Collection Position of Brushes Worn Col- lector or Commutator Overloaded Dynamo .... 248 CHAPTER XIX. ELECTRO-DEPOSITING DYNAMOS. " INTENSITY " AND " QUANTITY " IN ELECTRO -PLATING Electro- motive Force Required in Plating Table of the Forces Current Density Required Table of the Currents Woolrich's Early Plating Dynamo Gramme's Electro -Depositing Dynamos Secondary Current of the Plating Vat Circuit Interrupter Baths or Vats in Series Electro Copper Ore Refining Siemens Dynamo in Electrolysis 262 CHAPTER XX. TYPICAL DYNAMOS. THE MACHINES CLASSIFIED Dynamos of the Gramme System Gramme's Type Superieur Dynamos of the Siemens System Sautter -Lemonnier Dynamo Rechniewski's Dynamo The Desroziers Dynamo Dynamo of the Societe Alsacienne de Con- structions Mechaniques Brush's Dynamo Edison's Dynnmo Elwell Parker Dynamo Kapp's Dynamos Kapp's Armatures Curves of Magnetization Kapp's Central Station Dynamo Curve of the Magnetization Kapp's Alternating-Current Dynamo Ferranti's Alternators The Dynamos of Deptford Four Views of these Dynamos Details of the Construction Firth's Method of Regulating E.M.F. of Dynamo Firth's Machine Width of the Air Gaps and the E.M.F. Single Coil Field Magnet Paterson and Cooper's Dynamo The Thomson-Houston Dynamo The Spherical Armature Dynamo Incandescent Light Dynamo Motor-type Dynamo Alternating Cuirent Thomson-Houston Dynamo Composite Winding The Westinghouse Alternator Westinghouse's Armature Safety Device of the Westinghouse System Tests of the Westinghouse Dynamo . . . .271 CHAPTER XXL THE DYNAMO AS A MOTOR. MAGNETIC PRINCIPLES OF THE ELECTRO-MOTOR Immisch's Motor Sprague's Motor Ayrton and Perry's Motor Crocker- Wheeler Motor The Electro-Motor in England . . . 330 LIST OF ILLUSTRATIONS. FIG. PAGE 1. Early Type of Magneto-Electric Machines . . 7 2. Circuit Interrupter 7 3. Early Form of the Commutator .... 7 4. The Induction Coils Combined with the Field Magnet ........ 9 5. Shuttle Armature, Longitudinal and Cross Section . n 6. ,, ,, Complete . . . . .11 7. in Field of Six Magnets . . 1 1 8. Cross Section in Field of Magnet 1 1 9. Magneto-Electric Machine with Shuttle Armature . 1 2 10. Short Shuttle Armature for Small Currents . . 12 11. Diagram Illustrating principle of Gramme's Ring Armature. . . . . . . .16 1 2. Diagram Illustrating the " Overtype " of Dynamo . 2 1 13. Section of the Collector Bars 26 14. The Collector and Brushes ... . . .26 15. Two Part Commutator 27 1 6. Overtype of Dynamo Depicting the Leading Fea- tures ........ 28 17. Electro Magnet of the 'Common Type ... 42 1 8. Rheostat or Regulator of Resistance ... 43 19. Diagram showing separate Excitation ... 44 20. of the Series Winding .... 45 21. ,, showing the Shunt Winding ... 47 22. of Compound Winding . . -5 23. Gramme Type of Field Magnets .... 87 24. Siemens Horizontal Type of Field Magnets . . 87 XIV LIST OF ILLUSTRATIONS. FIG. PAGE 25. Type of Alternating-Current Dynamo Field Mag- nets in General . . . . .87 26. Brush Type of Field Magnet 87 27. Thomson-Houston Type of Field Magnet . . 87 28. Mather and Platt Type (" Manchester" Dynamo) . 88 79. Alternator Field Magnets . . ... . 88 30. Single Coil Magnets, Kennedy's Dynamo . . 88 31. Morday Alternator Type Field Magnets . . 88 32. Course of a Current around Magnet . . . 89 33. Diagram of Single Loop Armature in a Magnetic Field . . . . ... . .92 34. Diagram of the Currents in Single Loop Armature . 92 35. Impulses due to One Loop in Armature . . 97 36- Two . . 97 37- ,, >, Four 97 38. Armature of Alternator . . . . .. .100 39. Disc from Ribbed Armature Core . '. . 106 40. Ribbed Armature Core . . .... .106 41. Ring Core of Gramme Armature .... 108 42. Cylinder or Elongated Ring Core . . . .109 43. Ring with Driving Spider . . - . .109 44. Ring Core with Pacinotti Projections . . . no 45. ,, Armature and Collector . . .- .124 46. ,, Connections . . . . .124 47. Complete Ring Armature . . . . .124 48. Collector Bar and its Insulation . . . .133 49. Details of the Single Brush Yoke or Rocker . . 136 50. Multiple Brush 137 51. Complete Cylinder Ring Armature . . .138 52. The Brush Rocker . . . . . .138 53. The Base, Bearings and Field Magnets . . .139 54. Cross Connection of Opposite Coils . . . 140 55. Windings of Multipolar Ring four Brushes . . 142 56. two Brushes . . 143 57. Section of Driving " Spider " .... 144 LIST OF ILLUSTRATIONS. XV IG. PAGE 58. Diagram of End of Drum Armature . . . 154 59. Edison Winding 155 60. Siemens (Alteneck) Winding . . . . .156 61. Diagram of various Drum Armature Windings . 156 62 of Weston's Windings . . . .156 63. Section Across Weston's Drum Armature . .158 64. Diagram of Dr. Frolich's Drum Winding . . 159 65. Course of the Conductor in a Drum Winding . 162 66. Right and Left-handed Arrangement of Alternator Coils 176 67. Coils in Series . . . . . . .179 68. Multiple Arc .... . 179 69. or Cells in Series . . . . .180 70. ,, Multiple . . . . .180 71. Intermediate Arrangement . . . . .180 72. Wilde's Commutator for Alternating . . .184 73. Characteristic Curve . . . . . .222 74. with H.P. Lines .... 224 75. Characteristics from a " Compound " Dynamo . 228 76. Characteristic of a Compound-wound Dynamo . 229 77 and 78. Two Forms of Circuit Closer for Testing Purposes 254 79. Current Reverser for Testing Purposes . . .254 80. Diagram of Gramme Dynamo (Type Superieur) . 272 81. Section of Gramme Dynamo ,, . 273 82. Sautter-Lemonnier Dynamo . . . . .275 83. Diagram of Brush's Dynamo . .... 279 84. The Edison-Hopkinson Dynamo (English Type) . 280 85. Elwell Parker (Overtype with Fly Wheel) . .282 86. Kapp's Overtype Dynamo (Longitudinal Section) . 283 87. ,, Dynamo (Transverse Section) . . . 284 88. Armature of Kapp Dynamo (Longitudinal Section) 285 89. Curves of Magnetisation ..... 286 90. Kapp's Overtype Dynamo (General View) . . 287 91. Central Station Multipolar Dynamo . . 288 XVI LIST OF ILLUSTRATIONS. FIG. PAGE 92. Characteristic from Kapp's Central Station Dynamo. 290 93. Kapp's Alternator (General view) . . .292 94. Ferranti Alternating-Current Dynamo . . . 295 95. Dynamo open for Examination . .296 96. with their Engines . . .297 97. Marine Type Driving Engines of Ferranti Dynamo. 298 98. Ferranti Dynamo Open, Showing Armature and Field Magnets ....... 299 99. Bobbin of Ferranti Armature .... 300 JOG. Details of the Bobbin Holder .... 300 TOI. Armature incomplete, showing Method of Mounting the Bobbins 301 102. Connections of the Coils 302 103. View of the Collectors and "Leading off" System. 303 104. Ferranti Dynamo (Longitudinal Section) . . 304 105. Firth's Dynamo with Separated Magnets and Slid- ing Regulating Gear . . : . . . 305 1 06. Diagram of Kennedy's Single Bobbin Dynamo . 308 107. Thomson-Houston Compound Wound Dynamo . 309 1 08. Overtype Bipolar Dynamo . 311 109. ,, Alternating Current Self-exciting Dynamo . . . . . . . * 314 no. Westinghouse Armature . . . ,. . 317 in. Armature Coil . . . . . . 318 112. Westinghouse Armature (Longitudinal Section) . 318 113. Diagram of the Tatham Dynamometer . . . 326 DYNAMO CONSTRUCTION. INTRODUCTION. Definitions. The word " Dynamo " has by the force of common usage become equivalent to the longer term Dynamo Electric Machine. But, as employed in connection with Electricity, the abbreviated form is not likely to cause confusion. In the light of the rapid improvements of the past five years it seems unfortunate, however, that so apt a term as Dynamo Electric Machine should have only a limited applica- tion to electric generative machines. Although it was originally proposed by Dr. Werner Siemens to distinguish an important development in the earlier form of power electrical machines, and served the purpose very well at that time, yet the progress of electrical invention exhibits at the pre- sent day greater differences between two " dynamos " than ever existed between the early magneto-machine and its self-energizing offspring. Any machine moved by mechanical means, and adapted to convert the power of motion into the energy of elec- tricity, may be called a dynamo. The older magneto- electric machines effected nothing less than this, yet, B 2 INTRODUCTION. A Magneto- Electric Machine an apparatus in which steel magnets are used to furnish the " mag- netic field" is not strictly, by common consent, regarded as a dynamo. A dynamo is really a magneto-electric machine in which the " field " is maintained by that form of iron magnet called electro, the electro-magnet being " electri- fied " or excited by the current of the machine itself. Magneto-electric machines are an almost obsolete type. Every year renders the distinction between them and dynamos less marked, and they are gradu- ally becoming recognised as merely an old-fashioned pattern of dynamo. The duty of the dynamo is the conversion of one form of energy into another form of energy. But it has been discovered that a dynamo is a reversible machine. When it is driven by a steam engine it returns a large proportion of the power expended upon it in the form of an electric current. When, on the contrary, the dynamo is " fed " with an electric current, it becomes itself a motor. An Electric Motor is merely a dynamo with its function reversed. While in the first sense it is dynamo-electric, in the second sense it becomes electro-dynamic. A dynamo may thus be regarded as a machine which is adapted either to convert mechanical energy into electricity, or electrical energy into mechanical power. Evolution of the Dynamo. The history of dynamic electricity may be said to date from the year 1831. In that year Dr. Faraday made public several new facts relating to the corre- EVOLUTION OF THE DYNAMO. 3 lation between electricity and the magnetism of soft iron.* In the published results now so well known, two important experiments, amongst others, are detailed bearing upon the principles of obtaining electricity from common magnets. Faraday believed that, as magnetism could be conferred upon soft iron by causing an electrical current to circulate around it, the converse of this must be true, and that currents could be obtained by means of magnets. Faraday's Experiments of 1831. The most striking experiment consisted in wrapping around a soft iron bar a considerable number of turns of insulated wire and connecting the extremities of the coil to a " gal vanometric multiplier," what is now known as a simple galvanometer or detector of current. When the free extremities of the iron bar were brought suddenly in contact with the poles of a common magnet, an electrical impulse flowed through the coil, causing a deflection of the galvanometer needle to one side. Again, when the bar was pulled away from the magnet, another electrical impulse occurred, but opposite in direction, as shown by the deflection of the needle to the opposite, side. It was unneces- sary to cause the bar to come into contact with the magnet ; motion of the bar to or from its poles only, resulted in currents being set up in the wire. Enhanced effects were obtained when an electro magnet was used in place of a steel " permanent " magnet. This was due simply to the superior mag- netic intensity of field set up by the electro magnet. Currents were also obtained by using the coil alone, * Phil. Tram, of the Royal Society, Nov., 1831. 4 INTRODUCTION. after withdrawal of the iron core. These currents were less marked. All the effects obtained were momentary, or lasted only while the motion was maintained. The famous iron ring experiment published at the same time, exhibited the same facts. In the first experiment, the iron bar and coil were magnetized by being brought in contiguity with the poles of a magnet. A current resulted from the increasing magnetization and a reverse current from its de- crease. The iron ring effected this merely in another way. Around opposite sides of an iron ring, several inches in diameter, and an inch in thickness, were coiled two separate lengths of insulated copper wire. The ends of one coil were connected with a galvano- meter, and the extremities of the other coil were connected with the poles of a voltaic battery. As soon as the battery current flowed in its coil, the opposite coil showed an electric impulse. Another impulse, opposite in direction, marked the stoppage or rupture of the battery current. Here we have the magnetization and demagnetization of iron causing currents in a circuit of wire surrounding it. Faraday showed that the iron ring might be dispensed with, and one coil merely wound over the other instead. The presence of a core of iron, however, intensified the effects. Earliest attempts to devise Magneto Machines. At- tempts were soon made, as we shall see, to construct upon this principle of the magnetization and de- magnetization of iron, machines in which the effects might be augmented in force, and rendered as nearly continuous as possible. The first dynamo-electric machine was constructed FARADAY'S DISC MACHINE. 5 upon a rather different principle by Faraday himself* He found that, while currents might be obtained by merely bringing a coil of wire under the influence of magnetism, this inductive effect might be rendered contimwus by some arrangement of a continuous conductor. Faraday's Disc Machine. From this conception was evolved the celebrated disc machine. It consisted merely of a copper disc, about a foot in diameter, capable of being made to rotate in a vertical plane, its edge passing between the poles of a powerful mag- net. In order to collect the current a wire was led from the axis, and another wire was pressed upon the periphery of the disc. These conductors were connected with a galvanometer, as before. Upon imparting brisk motion to the disc, a continuous current kept the galvanometer needle deflected, A reverse current marked the reversal of motion. Here, then, was demonstrated the practicability of two elementary types of electrical machine. The first foreshowed the ordinary dynamo machine, in which an iron core surrounded by a coil is either alternately magnetized and demagnetized, or in which the magnetism is continually changing its position. The second showed the method to be pur- sued in generating electricity continuously without the intervention of a core of iron. We cannot in this place follow Faraday further. Reference should be made by the student to the original papers. The elementary principles, as far as they affect the dynamo, are dealt with further on, but many of the interesting early experiments in electro-magnetic induction do not come within the * Experimental Researches, vol. i. INTRODUCTION. scope of the present pages. Excellent text books are not wanting in which the science of electro- magnetism is ably treated. Nor does it appear even necessary to enter upon such well known facts as those appertaining to the inductive influence of cur- rents upon neighbouring conductors, or to explain that an electro-magnet is composed of a bar of soft iron around which a current is sent circulating. These facts can be studied very fully in any modern treatise, dealing with the laws of electricity and magnetism. EARLY ATTEMPTS TO CONSTRUCT MAGNETO-ELECTRIC MACHINES. Scarcely a year passed after the publication of Dr. Farad ay's' researches, before several attempts were made, in different parts of Europe, to construct some form of generating machine. It must be remembered that at that time the " creation " of electricity, as it was considered, had made but little progress ; that the voltaic battery, which in later years became so perfect an instrument, was in a very rudimentary form, and that the desire for some mechanico-electric generative appliance was very intense. The first attempt of which there is published recoid, appears to have been that of the Abbe Salvatore Dal Negro, professor of Philosophy in the University of Padua. Dal Negro's Apparatus. A few months after the publication of Fara- day's discoveries various attempts were made to construct electrical gener- ating machines based upon his experiments. An apparatus said to have been devised in the year 1830, in which the moveablepart was subjected to a vibratory motion, was one of the first of these.* Pixh's Machine is generally regarded as the parent of magneto-electric apparatus in the form of machines for evolving currents. This device consisted of a steel permanent magnet, of horseshoe shape, mounted with its poles upwards, and so arranged upon an axis that it could be made to rotate. A similar horseshoe of iron, having coils of insulated wire upon its limbs, was fixed above, so that the poles passed each other in close contiguity. When the steel magnet was caused to revolve, currents were induced in the coils of wire. The currents were reversed in direction twice in each revolution, or when the poles passed the points of strongest attrac- tion. At the suggestion of Ampere, Pixii improved his machine by pro- viding it with a commutating device, intended to give the ever-changing currents a constant direction. f Improvements continued to be made in the machine, notably by Ritchie, J by Saxton, 1833 ; and by Clark. Saxton appears to have been the first to * See Philosophical Magazine, July, .1832. t See Ann. Chim. Phys., 1832. t Phil. Trans, of the Royal Society, 1833. Phil. Mag., p. 360. ,' TYPICAL EARLY MACHINE. make the steel inducing magnet a fixture, and to cause the wire coils to revolve instead. In Fig I, is depicted the general principle of construction embodied by all these early magneto-electric machines. N and S are the polar extremities of a per- manent magnet. In front is mounted upon an axis an electro magnet, consisting of a flat iron yoke piece, with projecting cores of the same metal, over which are slipped spools of insulated wire, connected as repre- sented. The electromotive force set up by such an apparatus depended upon (i) the intensity of the magnetic field, or, briefly, the strength of the mag- net; (2) the velocity of rota- Fig, i. Early Type of Magneto-Electric Machines. tion, and (3) the number of turns of wire wound upon the iron cores. The induced electromotive force of each impulse might be said to be proportional to these conditions. Saxton and other inventors employed four and more bobbins in place of a single pair. Both Saxton and Clark employed a sliding connection, bear- ing upon the axis of the revolving part, for the purpose of collecting the electrical impulses into conducting wires exterior to the machine. Clark's machine attracted a great deal of attention, inasmuch as its induction coils revolved not opposite to the polar ends of the magnet, but close to the Fig. 2 Circuit Interrupter. Fig. 3. Early Form of the Commutator. sides of the poles. The machine was also furnished with a "physiological commutator," for the purpose of administering sharp shocks for medical purposes. The model of this machine is still retained for those purposes.* In Figs. 2 and 3 are represented, diagramatically, one form of both the physiological and the commutating devices. In Fig. 2, the extremities of * See Phil. Mag., 1836, p. 262 ; 1837, p. 365, 455. 8 INTRODUCTION. the coils were taken to a pair of metallic rings, insulated from, but rotating with the spindle. Upon each of these a fixed spring was caused to press, so as to lead off the current. Only one of these, d, is depicted in the dia- gram. The contact ling under this spring was cut away at two opposite siJes as shown, so that contact or continuity was broken twice in each revolution. The effect of this arrangement in the medical machines is well known as an electrical shock. The constant interruption of the current caused the continuous numbing effect. If there should be provided two continuous contacts, there would still exist a strong physiological effect, due simply to the reversal of the currents, as already spoken of. The simplest device for " commuting " the currents to a continuous direction is depicted in Fig. 3. In this case the extremities of the coils are taken to a pair of half rings, c c' t insulated from and rotating with the shaft. Two collecting springs or " brushes, " d d', bear upon the lings. The position of the half rings upon the spindle, and the springs with respect to them, were so adjusted that at the instant the armature experienced a reversal of polarity (or current), the half rings would also exchange spring^. In this simple manner, spring d would always be positive, while d would be negative. Sturgeon's Armature. Various inventors continued to make improve- ments in the details of the machine, but the next important step appears to be due to Sturgeon, who constructed an entirely new kind of induction coil for such apparatus. It will be convenient to note that the iron-cored coils used in these machines become known as armatures, since, to a cer- tain extent, they served the purpose of the iron "keepers," or armatures universally employed to connect the poles of steel magnets. Sturgeon conceived the idea of concentrating the bulk of his armature, and to secure this end he gave it a shuttle shape. But while Sturgeon placed his coil longitudinally between the limbs of the magnet, the full value of this idei was not discovered until Siemens and Halske introduced their famous shuttle armature many years afterwards.* Sturgeon also effected im- provements in the commutating arrangements. f While, as we have observed, Faraday discovered that a metal disc, revolved between the poles of a magnet, yielded a current of electricity, Sturgeon showed that such a disc, when a current was passed from its periphery to its axis, be- came an electro motor, the disc continuing to revolve as long as the current is continued. Barlow observed the same effect. J Stohrer's Machine of 1836 consisted of several bobbins of wire, having iron cores, which were caused to pass successively in front of the two poles of a permanent magnet. It was soon found that a machine could be constructed in which, as in Fig. 4, the inducing magnet, n s, might be a fixture, and support upon its poles the soft iron cores and coils, while the armature, consisting simply of a bar of iron, might be caused to revolve. This "principle, although it has been carried into the construction of some modern machines, cannot, how- ever, be ?aid to be so successful for the production of electricity as those already mentioned. Ritchie showed that the iron cores were more effective if in the form of * Specification of patent, 2,017, of 1856. t See Annals of Electricity, 1838. % See Professor Barlow's treatise on Magnetic Attractions. WHEATSTONE AND COOKERS IMPROVEMENTS. g split tubes, and later experimenters have shown that the idea of division may be carried with advantage still further, until the core is formed of a bundle of iron wires. Indeed, the sub-division of the iron cores has be- Fig. 4. The Induction Coils combined with the Field Magnet. come an essential feature in modern dynamo machines for several reasons, to be further explained. Several patents were taken out for machines, based upon the principle already fully stated, between the years 1836 and 1840, but nothing of fresh interest appears to have been produced. Woolrich's Machine of 1841.* Mr. Woolrich, of Birmingham, con- stiucted a magneto-electric machine for electro-plating purposes, as early as 1841. It consisted of a number of bobbins of wire, having iron cores, fixed to a revolving disc, and passing close to the poles of a number of steel horseshoe magnets. The currents were commuted to a uniform direction. The machine was an extension of the principle of the smaller models already described. It was driven by a steam-engine, and for many years supplied the current required in the plating works of Messrs. Prime. The original machine was shown at the Electrical Exhibition held in Birmingham in 1889. This apparatus was doubtless one of the first, if not the very first, dynamo or magneto -electric machines made for practical purposes, and driven in a regular way by steam power. Wheatstone and Cookers Improvements. An important step towards the development of the dynamo machine was taken by Sir Chas. Wheatstone, who, in conjunction with Mr. Cooke, in the year 1845, patented f the substitution of an electro-magnet in place of a permanent magnet in magneto-electric machines. \ Prior to this date, Wheatstone and Cooke effected various improvements in detail in magneto-electric machines for telegraphic purposes. The chief of these is considered to be the employment of a number of armatures in one machine, with appropriate commutators, so that a large number of impulses or currents might be * Specification of patent, 9,431, of 1842. t Specification of patent, 10,655, f l %45' J An electro-magnet consists of a core of soft iron, generally in the form of a horseshoe, having coiled upon each of its limbs a quantity of insulated copper wire. Tne iron becomes powerfully magnetic, for the time being, when a current of electricity is passed through the coils. Electro-magnets are much more powerful than permanent magnets. 10 INTRODUCTION. obtained in one revolution, thereby practically producing a continuous current. Suggestion of Soren Hjorth. But a far more significant improvement was yet to be effected ; the germ of the true dynamo-electric principle as it is generally understood. The honour of first suggesting the idea of exciting the field magnet of the machine by the current evolved by the machine //to?//" appears to be due most clearly to Soren Hjorth, of Copenhagen, who published* his invention of the principle in the clearest way, giving drawings. The machine of Hjorth was chiefly remarkable in being fur- nished with an electro-field magnet, through which the current, when once started, was caused to circulate forming an apparatus doubtless adapted to work on the principle known as mutual accumulation up to the magnetic saturation of the iron. The only way in which the dynamo of Hjorth differed from most machines of the present day appears to lie in the provision within it, in addition to its iron field magnet, of a small steel magnet intended to give the initial current, after the manner of the older magneto machines. The originator of this remarkable improvement was probably not aware of the fact that, provided the iron of the electro- magnet were hard enough to retain a little of its magnetism residually and permanently, that alone would suffice to give the machine the required slight starting current, without having recourse to a permanent steel magnet at all. Brett's Improvements. A few weeks prior to the patent of Hjorth, Brett obtained a patent f for an improvement almost equally remarkable. In this machine, which was of the usual magneto-electric type, with steel magnets, the current from the machine itself, or a portion of it, was led around coils encircling the field magnet, so as to augment its force. It is remarkable that the publication of this vital principle did not appear to excite much curiosity amongst makers of large magneto-machines. On the contrary, it was allowed to lie neglected for a period of nearly twenty years. The "Alliance" Electric Light Magneto Machine. Inventors con- tinued, notwithstanding the invention of the dynamo-electric principle, to improve and enlarge the simple magneto-machine, and in the year 1850 Nollet, of Brussels, built a large magneto-machine with the view of decom- posing water for the production of oxygen and hydrogen for the lime light. Ultimately, this machine was improved by Van Maldren and Holmes with a view to adapt it for producing an electric light for lighthouse purposes. Several machines were made in Paris after the model adopted by Nollet and Holmes, and were used for many years in the French lighthouses. The construction of the machine exhibits merely an extension of the simple magneto apparatus already described. A large number of bobbins of wire, having iron cores, were attached in two rings, one upon each face of a large metal disc. This disc was caused to rotate by means of a horizontal axis or shaft, geared to a steam engine. The exciting steel magnets were ranged in two groups on either side of the wheel, and in close proximity to the moving bobbins. In the larger machines several such systems were combined. The alternating currents produced were led direct to the electric lamp. * Specification of patent, 12,295, of 1848. t Specification No. 12,054, of 1848. SIEMENS* EARLY ARMATURE. II Siemens' Shuttle Armature. The shuttle form of armature, previously mentioned, was re-invented by "Werner Siemens, of Berlin, and patented in England in 1856.* It was at first used mainly for telegraphic purpose?, in magneto machines of miniature dimensions, but later on by several makers in machines of the largest class. Fig-. 5. Shuttle Armature. Longitudinal and Cross Sections. This arrangement is represented in Fig. 5. A bar of soft iron, of the H-like section depicted at a a, was mounted longitudinally upon an axis. The wire enveloping it was also longitudinal in direction, as shown in the lengthwise section. The extremities of the wire coil were taken to a pair of collecting rings upon the spindle, as already explained. Or, in some cases, a commutator of the split-hoop form was employed. The complete Fig. 6. Shuttle Armature, complete. armature is shown in Fig. 6, where a, a, represents the enveloping coil ; , b, brass bands intended to keep it in position"; d, c, the axis and driving pinion ; and e, e, the commutator. The magnetic field was obtained by means n, TV TV TV rv a a a a a a TV s==sJ a a a a a a 5 S S S S S Fig. 7. Shuttle Armature in Field of Six Fig. 8. Shuttle Armature- Cross Sec- Magnets Telegraphic Machine. tion in Field of Magnet. of a number of steel magnets, arranged with their poles as in Fig. 7, n, s, &c. This is still more clearly depicted in Fig. 8, where it is to be seen that the polar extremities were hollowed out to receive, and partially embrace, the armature, n', s'. The whole constituted a very powerful arrangement. It has for many years been used in telegraph instruments. This form of miniature machine has also been employed for igniting powder in blasting, gunnery, &c., and for medical purposes. Fig. 9 represents one form of * Specification of patent, 2,017, of 1856. 12 INTRODUCTION. these apparatus, having a pile of magnets, a, furnished with soft iron extension pieces, n, s, the currents being collected by the brushes, d, d', while motion could be given to the armature by the hand-wheel h rotating upon the axis e. Still another form, in which the short shuttle armature is placed lengthwise within the limbs of a magnet, is represented in Fig. 10. This type has been largely used for furnishing the current for ringing bells, telegraphic signals, &c. A slight to and fro movement of the armature suffices to generate a current. Wilde s Improvements. Amongst others who experimented with the shuttle form of ai mature was Mr. Wilde, of Manchester, who, in 1863, produced a remarkable combination of a large machine, having an electro field magnet, with a small magneto (steel magnet) machine to provide the cuirtnt required to excite it.* This combination was by far the most powerful that had hitherto been produced. In a subsequent extension of the same principle, Wilde produced a machine in which a small magneto machine (diameter of armature, if inch) excited the shuttle armature of a second (diameter, 5 inches), which in turn provided the current to excite the field magnet of a still larger machine (diameter, 10 inches). The current from this machine or combination, as exhibited at the conversazione of the Royal Society, in 1867, was sufficiently powerful to fuse an iron rod 15 inches in length, and \ inch indiameter ; and an electric light of enormous power was produced between carbon rods \ inch square. Fig. 9. Magneto-electric Machine, with Shuttle Armature. Fig. io. Short Shuttle Armature for Small Currents. Mr. Wilde also produced machines of the disc type, in which a metallic disc, furnished with a horizontal shaft, carried a series of bobbins, with iron * Specifications of patents, 299, 858, 1,994, and 2 >997> of 1861 ; 516 and 3,006, of 1863; I,4i2and2,753, of 1865 ; 3,209, of 1886 ; and 824, of 1867. THE SELF-ENERGIZING PRINCIPLE. 13 co:es, upon either face. These were excited, during revolution, not by permanent magnets, as in the "Alliance " machine, but by electro-magnets energized by the current from a small auxiliary magneto-machine. Development of the Self -Energizing Principle in Dynamos. As men- tioned previously, although more than one inventor had published the self- exciting principle as early as 1848, no application of it had occurred in the machines used for electric light or electro metallurgy up to about the year 1867. In a remaikable specification of patent,* published in the year 1858, the significant words, " It is proposed to employ the electro-magnet in obtaining induced electricity, which supplies wholly or partially the electricity necessary for polarising the electro-magnets, which electricity would otherwise be required to be obtained from batteries or other known sources," occur. Mr. Murray throws out a suggestion early in i866,f calling attention to an expedient he had adopted in improving his magneto-machine. He coiled wires around the limbs of the steel field magnet, and led the current from the armature through them in such a direction as to intensify the field magnet, so materially increasing the power of the machine. The same piinciple again appears in Baker's patent of 1866,^ wherein it is suggested that " the currents from the revolving magnets [presumably armature] may be applied to magnetize the fixed magnets." The Mess-rs. Vailey, in December, 1866, filed a patent specification relating to a machine furnished with an electro field magnet, to be maintained in a magnetized condition by the current from the machine itself. It is specified, however, that the magnet required, at first starting, to be partially energized by the current from some other electric source, and it is not quite clear whether this refers to the mere initial " polarising" of the magnet, which in modern dynamos does not require repetition. Amongst other machines, Mr. S. A. Varley produced a remarkable arrangement, in 1876, in which the field magnet uas wound with two distinct wires, one of which was finer than the other, and the circuit of which was always kept closed, while the other was opened several times during the revolution of the armature. || This idea appears to be an early step in the development of the important principle now known as compound winding m dynamos. In continuation of our trace of the still more important self-exciting principle, we find that Dr. W. Siemens made a communication respecting it to the Academy of Science of Berlin, in January, 1867 ; and, a month later, Dr. C. W. Siemens communicated the principle to the Royal Society of London. On the same day, February I4th, Sir Chas. Wheat- stone made a communication, almost identical, to the Royal Society. "While the piinciple of Dr. Werner Siemens' self-exciting dynamo pro- vided that the field electro-magnet coils should be connected in continuation, or "series," with those of the armature, that proposed by Sir Chas. Wheatstone suggests that the electro-magnet should be con- * No. 2,670, of 1858. f See Engineer, of July 2Oth, 1866. % Specification 3,039, November, 1866. Specification No. 3,394, of [867. jj See Specification of patent, 4,905, of 1876. 14 INTRODUCTION. nected in a by-path, loop, or " shunt " circuit, as it is termed. In the first case, the whole of the current evolved by the armature would pass through the magnet coils. In the second instance, a certain proportion only, depending upon the relative resistances of the external and field magnet circuits, would pass by this path. The machine proposed by Siemens would now be called a "series" dynamo; that suggested by Wheatstone, a "shunt" dynamo. But the importance of these communications to the learned societies, although they doubtless served a good purpose in drawing attention to the development of dynamos was, after all, only secondary, in the light of the repeated publication of the dynamo-electric principle on several previous occasions already cited. The Term " Dynamo- Electric Machine." Dr. "Werner Siemens sug- gested that the machines in which the self-exciting principle was employed should be known as dynamo -electric machines, to distinguish them from the earlier form in which permanent magnets were used, and which still continued to be called magneto-electric machines. The principle of mutual accumulation, thus brought prominently for- ward, does not at first appear to be in accordance with the nature of soft iron, but it may be thus concisely stated : If the soft iron field magnet possesses the slightest magnetic polarity, in a residual form and all iron once magnetized may be said to possess and retain it the feeble magnetic field thus existing in the path of the armature suffices to generate in the coils of the latter a feeble current. This current, being caused to circulate around the field magnet, quickly energizes it so as to strengthen the field ; this again re-acts upon the armature, causing it to yield yet stronger currents, which in turn still further strengthen the field ; and so on, by mutual re-action, until the field magnet is said to be " saturated," and is thus incapable of being further strengthened. On imparting rotation to the armature of such a machine, on " short" circuit the resistance to motion increases rapidly, and in a few moments either the driving band begins to slip or the coils of the machine become highly heated, and may even be fused. The enormously greater power of dynamo-machines over magneto- machines, weight for weight, soon caused the abandonment of the steel magnet class, except for a few special purposes. Non- Fluctuating Current. Hitherto, the best forms of machine, both magneto- and dynamo-electric, were furnished with the improved armature of shuttle shape, first devised, as we have observed, by Sturgeon, and re- invented by Siemens. In the revolution of this armature in the magnetic field, two impulses or short currents were given off during each turn, and however great the velocity of the armature the resulting " current" partook of an intermittent character, or at least might be regarded as a current of rapidly recurring pulsations. Many attempts had been made to overcome this defect, and to produce an armature of such form that the current therefrom would resemble a fall of water. One of the most remarkable of these was Pacinotti's Ring Armature. The invention of this device is believed to date from 1860, but no published account of Pacinotti's machine has been discovered earlier than 1865.* The model in which the armature was first See the Italian journal // Nuovo Cimento, xix. p. 378, 1865. PACINOTTI' S MACHINE. 15 used was made for the Physical Cabinet of the University of Pisa, and was at first intended as an electromotor, but its suitability to act as a generator is alluded to by Professor Pacinotti in the clearest way. He says that " that which augments the value of this model is the facility which itjoffers of being able to transform this electro-magnetic machine into a magneto- electric machine with continuous currents. If, instead of the electro- magnet there was a permanent magnet, and if the transversal electro- magnet [i.e., the ring-like armature] were set turning, one would have made it into a magneto-electric machine which would give a continuous induced current directed always in the same sense." Without knowing it, Pacinotti had invented a self-exciting dynamo machine of a high order of merit, for, if instead of replacing the electro field magnet by a steel magnet, the current from the ring had been merely passed through the field magnet as it stood, the result would have been a series dynamo after the Gramme or Brush pattern. Professor Pacinotti had produced a machine of such form and design that, with the single exception alluded to above, it might even to-day form an efficient model for a dynamo of a superior order. It consists, first of a large electro-magnet, the limbs of which point upwards, and which is fixed rigidly to a base. A vertical shaft is supported midway between the limbs, by the aid of an overhanging cross-piece, clear above the magnet limbs, and upon this shaft is keyed the ring armature. This consists of a ring of iron furnished with sixteen wide tooth-like projections, providing sixteen deep gaps, in which an equal number of coils of insulated wire are wound. The finishing extremity of one coil is connected to the commence- ment of the next, and so on, the whole of the wire forming in effect a right-handed helix around the ring. From the juncture between each pair of coils a wire is led to one of sixteen segmental brass plates, fitted into a wooden cylinder rotating with the shaft. This part represents the commutator from which the currents are collected by two brass springs pressing upon opposite diameters. The springs or "brushes" touch the cylinder in a line at right angles to that joining the magnet poles. In order that the inductive effect of the electro-magnet may be distributed to more than one coil at a time, each pole carries a soft iron extension-piece, or horn, the interior of which embraces the iron ring closely without touching. The distinguishing merit of the ring' armature lies in the fact that it possesses a continuous core and a continuous coil. There is no break of continuity in either wire or core, {and the resulting current resembles a constant stream, inasmuch as it is free from impulses or fluctuations. A period of about ten years passed after Pacinotti's invention, during which this beautiful device appears to have been forgotten. Gramme's Armature of 1870. In the year 1870 M. Gramme, an electrician of the Alliance Company in Paris, independently invented a ring armature *similiar in many' respects to that of Pacinotti, but intended primarily for use in a dynamo-electric machine upon the self-energizing principle. This armature consisted of a smooth core of soft iron wire, Fig. ir, completely over-wound with an endless helix of insulated copper wire several layers deep. From a large number of segmental points in the helix connecting wires led to an equal number of commutator plates * Specifications of patent, j,668 of 1870, and 953 of 1878. i6 INTRODUCTION. Fig. ii. Diagram Illustrating Pinciple of Gramme's Ring Armature. fixed in grooves in a wooden axis a, the current being led away by the brushes a, b. This ring was monnted npon a horizontal shaft, in a vertical plane, and rotated between the polar extensions of a powerful electro- magnet. The introduction of Gramme's machine (details of which will be found in succeed- ing pages) gave a great impetus to electric lighting, and may in- deed be said to be the initial step towards the general utilisation of the arc light for street illumina- tion. The Alteneck Armature. The next important step towards the perfection of the dynamo machine occurred in 1873, when Von Hefner Alteneck, of the firm of Siemens & Halske, of Berlin, brought out* an improved form of the earlier Siemens shuttle ai mature. This consisted essentially in making the core in the form of an iron cylinder, and over-winding every portion of it, longitudinally, with equally spaced coils of insulated wire, several layers deep. The windings passed clear across the ends of the cylinder, and were not threaded through it. In this respect, it will be observed, tbere was an important difference between Alteneck's armature and that of Pacinotti or Gramme. The cylinder was mounted to rotale with a horizontal shalt, passed longitudinally through it. In another form of the armature the iron core was stationary and the wire envelope, attached to a German silver envelope, was caused to revolve over it. The advantage of this arrangement was found not to be of sufficient import- ance, while it necessitated a more costly structure, and such arma- tures have latterly been constructed to revolve bodily. The armature was mounted to rotate between the poles of a large, flat, double electro-magnet. The introduction of the Siemens machine was at once seen to mark an important forward step in dynamo design, and led to the electric light being furnished to several British lighthouses. Further Improvements in the Dynamo. Several inventors about this date endeavoured to design dynamos yielding a non-fluctuating or unbroken current. One of the most remarkable of these was the device of Lontin, who constructed several machines with armatures in the form of spokes radiating from a central drum.f Brush, in 1878, re-invented the Pacinotti armature J with this difference that the projections or *' teeth" (now generally known as " Pacinotti projections ") were upon either face of the ring instead of upon its periphery. The ring was also placed in a vertical plane, upon a horizontal shaft, and revolved in a very intense magnetic field, obtained from two double electro-magnets. The armature of Brush's dynamo had its coils so connected to a peculiar form of commutator that * Specifications of patents, 2,006 of 1873, and 3,134 of 1878. t See Specification of patent, 473 of 1875, 386 and 3,264 of 1876. % Specification of patent, 2,003 of 1878, EVOLUTION OF THE DYNAMO. 17 those that were for the moment inactive (i.e. out of the magnetic field) were cut out of the circuit, so reducing the total resistance and increasing the force of the current. This " open coil" method of winding was employed by others with equally good results. Brush is also generally accredited with the invention of that important method of exciting the field magnets for purposes of automatic regulation, known as " compound winding." This consisted of a combination of the series and shunt methods, and enabled the machine to instantly modify its current to suit the requirements of the external portion of the circuit. For example, if a Brush machine were feeding twenty lamp?, and ten of these were to be suddenly extinguished, the current evolved at the dynamo would instantly fall the required 50 per cent., or become again powerful if the lamps \vere re-lighted. This principle, and that of open coil winding, will be found more fully explained in subsequent pages. The Return to Alternating Currents. The introduction of the Edison and the Swan incandescent lamps, about the year 1880, led to a test of the comparative merits of continuous v, alternating currents for such lamps. In the result, inventors of dynamos arrived at the conclusion (whi h has Leen amply justified by subsequent experience) that alternating currents were quite as suitab'e for this purpose as continuous current^, provided the pulsations of alternations (now known as the " phase " were of a quickly recurring character (now called the " periodicity "). ' Sir WiLliam Thomson, in 1 88 1* suggested the employment for incan- descent lighting of a machine having a disc-like armature, furni-hed with numerous coils near its periphery. This armature was set upon a horizontal shaft, in a vertical plane, and revolved between two opposite rings of magnetic poles. The currents which had a high periodicity were alternating in direction, and were taken direct from the machine, without being commuted. As it is obvious that such a machine cannot excite its own field magnets (for which purpose continuous current is required), a small independent dynamo is reserved for this duty alone, so that all the carrent evolved by the machine is available for external purposes. Mr. Gordon^ brought this class of machine, by independent invention, to a high state of perfection, and Mr. Ferranti, in conjunction with Su. William Thomson, J developed the method of winding with copper strap, producing a machine having extraordinary powers in small space. The Ferranti machine of this type has no iron- in the armature, a circumstance tint tends to maintain it in a cool condition, even when evolving the gteatest currents. Some of the largest dynamos in existence have been erected after this model at the London Electric Supply Company's Station at Deptford. Engravings from photographs of thete are given in a subsequent chapter. Various improvements in conshuc'iicn were made about this period (1880-1883), Dv Lord Elphinstone and Mr. Vincent, by MorQ Q __ 33-5 amperes. Those who V I'Q are accustomed to handling dynamos will know that this is very much what we actually find, and it gives us confidence in the applications of theory. It is generally known that an external surface of coil of 223 square inches will continuously dissipate a watt (or volt ampere) of electrical energy when the temperature of the coil is i Fahr. above that of the surrounding air. The capacity of the surface for dis- sipating heat is directly proportional to the tempera- ture of the coil above that of the air. In other words, every square inch of coil surface would dissipate a watt of energy at a temperature of 223 Fahr. above that of the surrounding air. Or the rule may be formulated \V =; t S = "00476 t S. 223 In which w represents the watts lost in heating, t the temperature (Fahr.) above the surrounding air, and S the surface in square inches. CHAPTER V. DETAILS RESPECTING EXCITING COILS. IN Chap. IV. (pp. 64-66) will be found the necessary equations for finding the ampere-turns required for any given degree of magnetization. Having found the number of ampere-turns, the determination of the correct size of wire, and the space to be occupied by it, appears a comparatively simple matter. It is assumed that it is only necessary to find the size that will carry the required number of amperes without over-heating. Nevertheless, the finding of these values may present some difficulty. The first rule to remember is that a small current of one ampere, flowing one hundred times around the core of the field magnet, will have precisely the same magnetizing effect as a current of ten amperes flowing around it ten times only. Let us consider a simple case, which will settle the question whether the wire wastes energy when fine and economises it when thick. Suppose an exciting coil, having one hundred turns of wire, say of such a size as will carry sixteen amperes without becoming heated. This coil will have a certain magnetizing effect, it will consume a certain proportion of the energy, and it will have a certain number of ohms of resistance. Now, suppose that all of these values have been noted, and that the THE AMPERE TURNS. 71 magnet has been re-wound to the same dimensions of coil with a wire of one-half the former diameter. This coil will take four times as many turns (four hundred) to fill up the space. The wire will be four times as long, and it will have one- fourth the sectional area of the first wire. It will carry, therefore, a current of only four amperes (at the same current density as before). But as this current flows around the core four hundred times, the ampere-turns will be the same as before. Thus, multiplying the turns into the amperes gives in the first and second cases sixteen hundred ampere-turns. Now, the current density being the same, the waste upon resistance will be no greater in the second case than in the first. So long, then, as the ampere-turns are provided it is of no consequence in the final result whether the wire be fine or thick. But it is essential that an economical proportion be held between the section of the wire and the current it is intended to carry. And it must not be overlooked that, while the magnetizing power increases in direct proportion to the current, the heating effect increases as the square of the latter. Hence, to avoid waste, it is important to fix upon some economical current density. This is generally made as great as is practicable. There are certain conditions that may be said to control this. The most important condition is depth of coil in other words, the thickness of the ceilings. A winding of one or two layers only would be called a shallow coil ; a winding of many layers would form a deep coil. Now, the cooling effect of the air- radiation from the coil will be more effective in respect to the shallow coil than it would be in respect to the deep coil ; while the former would rapidly part 72 DETAILS RESPECTING EXCITING COILS. with its heat, the latter would retain it to a much greater extent. The same remarks apply to the insula- ting covering. Substances, as silk or wool, of low heat- conductivity, would retain the heat longer than the cotton which is generally used in covering dynamo- wire. In a machine for high tension working, the insulation of the coils will be thicker than in a dynamo for currents of low tension, and this also will have its effect. Now, dynamo builders are generally in agreement in allowing from 1,000 to 2,000 amperes per square inch sectional area of the conductor that is, the general practice is to allow from one-thousandth to two-thousandths of a square inch of conductor to each ampere flowing around the coil. The higher density is very commonly exceeded, but in coils of one layer only, as in the single-layer series coils commonly superimposed upon the shunt windings in a compound dynamo. The following table gives the current density in (or carrying capacity of) the various commonly used sizes of wires at both 1,000 and 2,000 amperes per square inch. TABLE OF CURRENT DENSITIES AND SECTIONAL AREAS OF DYNAMO WIRES. Standard Wire Gauge. Sectional Area, sq. inch. Diameter inch. Current at i,oooamps. per sq. in. Current at 2,000 amps, per sq. in. American Wire Gauges (Nearest). amps. amps. 7/0 200 500 2OO 400 ... 6/0 175 464 175 35 0000 5/o I 5 432 ISO 300 .... 4/0 I2 S 400 125 230 ooo 3/o TOO 372 100 200 00 2/0 OQO 348 90 1 80 1 080 324 80 1 60 I 070 300 70 I 4 .... 2 060 276 60 120 I 3 'OSS 252 55 1 10 2 4 0425 232 42-5 85 3 5 0375 212 37'5 75 TABLE OF THE WIRES. 73 TAB LE continued* Standard Wire Gauge. Sectional Area, sq. inch. Diamete inch. 6 0275 I 9 2 7 0250 I 7 6 8 O2OI 160 9 0163 144 10 0128 128 ii OIO5 166 12 0085 104 13 OO6O 092 14 0050 080 15 OO4O 072 16 0032 064 17 O024 056 18 00l8 048 19 0012 040 20 0010 036 Current at i, ooo amps. Current at American 2, coo amps. Wire Gauges per sq. in. per sq. in. (Nearest). amps. amps. 30 60 4 20 49 40 i 16-3 f-6 7 12-8 8 10-5 21 9 8'5 17 10 6-6 13-2 ii 5 10 12 4 8 13 6-2 H 2-4 4-8 15 1-8 36 16 1.26 2-52 18 I'O 2 19 In the ordinary coils used for exciting field magnets having only a moderate depth, the rise of temperature after one hour will not exceed an average of 50 Fahr. above the surrounding air at a density of i, ooo amperes to the square inch. But it is useless to cite rules (as is often done) in respect to this. The conditions vary, and a number of matters contribute to the result, which cannot easily be foreseen. In the specifications for dynamos it is usual to stipulate that the exciting coils shall not exceed, in full work, a temperature 100 Fahr. above the surrounding air, and this condition is easily complied with. When the conditions of supply respecting the dynamo are that it shall give a constant current (as in series machines for arc lighting), the larger the gauge of wire the less the waste in heat. On the other hand, when the conditions of supply are that the dynamo shall maintain a constant potential (as in a shunt machine for incandescent lighting), the longer the wire the less will be the energy wasted as heat. 74 DETAILS RESPECTING EXCITING COILS. Again, for series dynamos (constant-current working) the magnetizing power of the coil is not dependent upon the gauge of wire, but is controlled by its length. When the conditions of the machine are for constant potential (shunt dynamo) the magnetizing power of the coil is independent of its length, but is controlled entirely by the gauge. In other words, it is essential to employ a thick wire, in a small number of turns, when the whole output of the machine passes around the magnet, as in an ordinary series wound dynamo. On the same principle, both series and compound wound machines must be wound (the latter in the series coils only) with thick wire. The conditions are precisely analogous to the cases ol an amperemeter intended to measure current, and a voltmeter intended to indicate E.M.F. or volts. Length of the Bobbins. It has long been known that a magnet with a considerable length of core possessed a greater attractive strength than one with short limbs. But the superior effect is not due to the length of the core. It is due entirely to the fact that long magnets are furnished with longer magnetizing bobbins, containing a greater number of turns than short magnets. It is well known that field magnets cannot be made too short. The shorter they are the less their magnetic reluctance. But there is always a well-defined limit to this condition. It is impos- sible to get upon the limbs of an. exceedingly short magnet the turns of wire requisite to provide the magnetizing force needed to project the magnetic lines through the armature. In other words, we must have the proper number of ampere-turns upon the limbs, and these must be wound to a convenient depth, so as to provide for radiation of heat. In the INSULATED DYNAMO WIRE. 75 best dynamos the exciting coils seldom or never have a depth (from the surface of the core to the outside surface of the coil) exceeding one-half the diameter of the core (if round). There are many old time- honoured rules to be found in the text-books respect- ing the dimensions of electro-magnets, and amongst them several which lay the depth of bobbin windings at various values, from the full diameter of the core to one-fourth its diameter. These may be safely neglected, and attention given entirely to the con- venience of the case and the question of the emission of heat. It is, of course, advantageous to employ a high current density for many reasons already discussed. Hence dynamo builders, in many cases, design the depth and gauge of the wire to allow ot the highest safe temperature. Field Magnet and Armature Insulated Wire. Cotton- covered copper wire is almost invariably preferred for all common dynamo work. While cotton may be said to be a sufficiently good insulator, it conducts heat away quicker than silk. But the cost of the latter renders its employment prohibitive, except in special cases. It is important to use wire neatly covered. If the insulation is not uniform, irregularities will occur in the winding, which will increase with each layer coiled. Double cotton-covered is generally preferred, but this must not be too thick. Perfect covering is far more important than merely thick covering. The aim of the coverer should be to insure tight and perfect coating of the wire in the case of both windings of cotton. Several inventors have applied for patents for this process. The conductivity of the wire is a most important matter. It should in no case be under 95 per cent, of 76 DETAILS RESPECTING EXCITING COILS. that of absolutely pure copper, and is frequently higher. It should not be " hard drawn/' This makes it extremely stiff and resilient, and therefore very un- manageable in the case of winding an armature. It should be soft, round (if of that section), and smooth on the surface. The reputed gauge of the wire is frequently not the actual gauge, so that this point should be tested before making calculations. A very slight difference in size makes a very great difference in resistance or carrying capacity. Wire coverers deliver dynamo wire in quantities of several hundred-weights (usually i, 2, 4, and 6), wound upon wooden drums in continuous lengths for these weights. In special cases it is varnished in addition to the cotton covering, but this is generally left to the later stage of the work, so that the varnish is applied after winding. Paraffin wax, although one of the best insulators known, has too low a melting point to be applicable for general dynamo work. Rubber varnishes are, generally speaking, open to the same objection, although they are sometimes used. A good, hard, and quick-drying japan varnish, or, for cheaper work, bitumen varnish, is to be preferred. Operation of Winding. The first matter to be attended to in winding the bobbins is to ensure that there shall be no possibility of metallic contact between the wire and the iron of the magnet, or the metal of the reel or former. Reels are sometimes cast whole, flanges and body in one. It is difficult, however, to obtain castings sufficiently thin. Waste of space between the wire and the core is a great fault in a magnet. This fact leads many builders to wind direct upon the iron; but that can only be WINDING OF THE COILS. 77 effected if the form of the core admits of it ; and it is open to the objection that, in view of a possible future fault, it would be necessary to take the machine apart. The general practice is to wind the coils upon reels of the shape of the cores. The tube or body is preferably made in thin sheet brass, which must be slit up one side so that the reel shall not form a path for wasteful induced current under the variations of the field magnet current in shunt and other dynamos. The flanges or ends are usually cast in brass, and should be similarly slit, both slits corresponding in position in the finished bobbin. Non-metallic material is sometimes used in both body and flanges. Insulation of the core and reel is effected by var- nishing, and by a layer of Willesden paper, or thin vulcanised fibre, or sheet asbestos. Sometimes strong canvas is used. The interior of the flanges are similarly covered, but to three times the thickness. In winding cores of shunt machines, the wire being long and thin, the assistance of a winding machine is sometimes called in. This consists of the usual bobbin mandril and to-and-fro guide, the latter being moved either by a cam, as in the American machines, or by a screw. Hand-guiding is, however, the common practice in this country. The reel, or frame, or core, as the case may be, is put upon a mandril in a back-geared lathe, and a slow motion of rotation is thus imparted to it. In the commencement of the winding, if the extremity of the wire is to be taken out through the flange a very common plan the channel or hole should be lined with a porcelain or fibre tube. In winding on the wire it must be put into position under some tension. But the pull must not be greater than suffices to fully straighten the 78 DETAILS RESPECTING EXCITING COILS. wire. It may happen that, in imposing too much tension, the wire may be stretched, and thereby made thinner and longer than was intended. The tension arrangement generally consists of a grooved pulley, a foot or more in diameter, around which the wire takes one turn. Friction is put upon the pulley by means of a flat disc, pressed upon it by a large volute spring and screw. CHAPTER VI. FOR M OF THE FIELD MAGNET. FROM the foregoing considerations respecting the magnetic circuit, inasmuch as it affects the field magnet, it will be clear that a high figure of con- ductivity in this circuit is of equal importance with low resistance in the armature itself. The form of field magnet best fulfilling this requirement will have a short, thick core, few or no joints, and large pole- pieces. The material must, to secure a maximum conductivity in a minimum sectional area, be of the softest iron. The "grain/' o-r texture of the iron, must run parallel to the lines of force through the core. Single Circtiit Magnets* The course of the magnetic circuit in all the earlier forms of the dynamo was that due to a horseshoe, or similar shape. Here we have the lines of force flowing, as it were, from one pole, through the core, direct to the other pole, as through an arc. Wilde's early dynamos had this form. It has lately been adopted by Edison and many others. Its two most common shapes represent a horse-shoe, or U magnet; (i) with its poles down- wards, as in Wilde's and Edison's dynamos, and (2) with its poles upwards, as in Kapp's latest dynamos. The chief fault of the early field magnets lay in 80 FORM OF THE FIELD MAGNET. the false notions then entertained of the essential requirements of the core portion. The development of the theory of the magnetic circuit opened the eyes of electrical engineers to the defects of field-magnets. It made clear what was before an untranslated page, and removed the objectionable factor of empiricism from the rules of construction. The theory dictates that not only must the core be of the softest and purest iron, but that it be of the largest practicable cross-section, and form, as nearly as possible, a closed magnetic circuit. Formerly it was considered correct practice to make the circuit of a considerable length. The investigations of Drs. J. and E. Hopkinson, however, revealed the fact that not only was reluctance thereby increased, but that magnetic leakage occurred, to a great extent, from the long circuits. Practice and theory together now dic- tate that the circuit shall be as short as possible, consistent with allowing space for the exciting helices. There is one great fault in the inverted p| form employed by Wilde and Edison, and to which we have before alluded. We refer to the inevitable loss, by leakage, that results from attaching the polar- pieces to the necessary cast-iron bed-plate, even although there be interposed a deep footstep of zinc or other non-magnetic material. This consideration has led many of our best dynamo builders to abandon the earlier n construction, and to invert the magnet. The temptation to place the poles downwards is very strong. It refers, and is due, to mechanical con- siderations. The lower the bearings of the armature the less the vibration, and the machine becomes altogether more rigid. This fa^ct led Siemens and MAGNETIC "LEAKAGE." 8 1 Halske to place their well-known horizontal pattern dynamo with its magnet as close to the bed-plate as possible. But, with rigid frameworks, this objection to high armature bearings need not apply. It has, therefore, become the rule to place the magnet with its poles upward, and to make it from other con- siderations as short or stumpy as possible. The advocates of the Edison or Wilde style of magnet, however, contend that it is practicable to obviate appreciable magnetic leakage by improved methods of connection with the bed-plate. But their strongest argument appears to refer to the armature. It is well known that in many dynamos the " drag " of the magnetic field in such constructions as are under consideration, tends to pull the armature forcibly towards the yoke of the magnet. This is equivalent to saying that the field is not symmetrical, and that it is strongest across that region of the armature chamber nearest to the exciting coils. This fault has been combated by setting the armature out of circle, and practically placing it a trifle nearer to the extremities of the poles than before, with the intention of equalising the magnetic pull. In the case of a dynamo with a n magnet it is contended that this unequal pull supports the weight of the arma- ture, enabling it to run practically without heaviness upon its bearings. From an engineer's point of view this would be of considerable advantage. It is frequently said that a field-magnet has salient poles. This implies that the latter project merely, and it is generally used to distinguish this type of magnet from those having what has been termed consequent poles a term often used to denote field magnets of the earlier Siemens and Gramme patterns, G 82 FORM OF THE FIELD MAGNET. A perfect magnet core should have no joints. Me- chanical difficulties, however, render the accomplish- ment of this, in many cases, impracticable. Thus, instead of the Edison magnet being bent from one long bar, it has been found preferable to form it in substantially five sections. These are the two limbs, which are made of sufficient length to receive the exciting coils ; the yoke piece, which is of much larger sectional area than the limbs, and the two pole pieces, also made of greater section than the limbs. Ex- perience dictates that if there be joints they must be as perfect as possible. Contact, surface to surface, must be as good as planing and scraping can make them, otherwise there will be a good deal of loss by reduction of the sectional area at those points. The case is quite similar to that of an indifferent contact between an electric circuit wire and its bind- ing screw. Experience also points out the necessity for yokes in any form of magnet being of sufficient sectional area. Many of the early forms of field magnet were deficient in this respect. But it is far more important to observe that what- ever shape the field magnet assumes it is not divided. To work economically the ironwork should form one solid core, and not a series of bars. In relation to this the mind reverts to the horizontal pattern of the Siemens dynamo, in which the magnet was composed almost exclusively of iron bars, excited by a common helix a form of magnet now abandoned. The practice of the present time is strongly in favour of three conditions respecting the ironwork of dynamo field magnets. These are, a sufficient cross- section, a short circuit, and a pattern as simple as possible as nearly of the pattern of a simple horse- CAST-IRON FIELD MAGNETS. 83 shoe magnet as practicable. Complicated forms are, and have been, very common. These generally con- tain a number of joints. Each joint introduces an additional chance of waste and weakness ; and it can readily be supposed that in such dynamos as have thus a complex, built-up magnetic circuit, the cost of the magnetic field, in energy, is considerably greater than it should be. Cast-iron Field Magnets have been very common. The low magnetic permeability of cast-iron, as we have already seen, is a sufficient reason for its con- demnation for this purpose, except in exceptional circumstances. The temptation to use castings in lieu of forgings is, however, very great, and where weight and bulk are of no consequence a cast-iron field magnet may prove nearly as economical as one of wrought-iron, costing considerably more. There appears, however, to be one source of loss which the low permeability of cast-iron per square inch may compel dynamo builders to recognise. A bulky magnet requires a considerable length of wire to encircle it probably one-third more than that used for a wrought-iron magnet of similar power and it is conceivable that this, by introducing extra elec- trical resistance, may well prove a constant source of unnecessary expense. Edges and ^Corners are to be avoided in the iron- work. These frequently protrude sufficiently to act, to a certain extent, as poles, and cannot therefore be regarded but as a source of loss. This is especially the case when the useless corners protrude from the pole pieces. The Most Efficient Section of Core is undoubtedly a Circle. This, of all forms, includes the greatest pro- 84 FORM OF THE FIELD MAGNET. portional mass of iron to periphery. Hence, the circular form will require the least length of exciting wire. Owing, however, to structural reasons, cores and yokes of rectangular, or oblong section, with rounded corners, are very commonly employed. Pole Pieces are very generally of cast-iron ; and for this reason they are made of considerably greater cross-section than the core. Protruding edges, as before spoken of, must be particularly avoided in the polar terminations. The shape to be given to them must have for its object the concentration of the mag- netic lines upon the armature, and not their diffusion through the air. For this reason the flanks or " horns" of the pole pieces, where they come nearly together in embracing the armature, must be thinned off, so that the inductive loss, or leakage from pole to pole, will be reduced to a minimum. To produce a uniform field a good deal depends upon the exact shape given to the pole pieces. When the magnetic field is weak the maximum induction takes place, not uniformly over the surface, but at the edges of the pole, or at two points apart in the pole piece. A more intense field, with chamfered polar horns, ob- viates this defect. When the poles are properly formed it is advantageous to make them embrace almost four-fifths of the armature's periphery. In certain forms of dynamo, however, it is found advantageous to reduce this proportion. The Armature Chamber or Bore through the pole pieces should always be tooled out. It is usual to mount both polar blocks upon the face-plate of the lathe, separated to the required distance. The bore is then turned out quite true, a trifle larger than the circle described by the armature. If the pole-blocks CONSEQUENT POLES. 85 are to be fitted upon cylindrical cores the core-holes should be turned out similarly. The surface contact between the two should be as perfect as practicable. Consequent-Pole Magnets. Hitherto we have considered only the simple form of magnet, having two limbs salient. If we take an iron ring, without a break but with projections as pole pieces, it will be practicable, by means of ap- propriate windings, to concentrate therein, at two opposite points, magnetic poles. The ring really, then, consists of two electro-mag- nets, with their like poles together. This arrange- ment gives rise to what has been termed consequent poles. An electro-magnet, with consequent poles, was first applied to dynamos by Gramme, who embodied this construction in his constant-current machine as early as 1870. Consequent-pole field magnets were very com- monly used in dynamos until the investigations of Hopkinson and others revealed the fact that this construction generally involved considerable avoid- able loss of energy. As commonly carried out, the design embraces a considerable length of magnetic circuit, as it includes in the Gramme dynamo the end-frames of the machine. In addition to the exten- sion of the circuit this form of magnet commonly involves a considerable number of joints always a weakening feature in field magnets. Experience proves that although this combined form of field magnet presents many advantages from a construc- tive point of view, they are more than counter- balanced by the drawbacks already mentioned. An 6 FORM OF THE FIELD MAGNET. ideal field magnet would have the shortest possible circuit, the greatest possible sectional area, consist of the softest possible iron, and be entirely free from joints. The diagrams of the different combined magnets here given, in which N S represent the poles, Y the yoke, and a the armature space, with cross lines depicting the coils, show very clearly wherein the chief defects lie. Efficiency is sacrificed to con- structive considerations in many of them. Cast- iron is used where wrought iron should be em- ployed. Some of them meet the difficulty half way, and put wrought-iron cores to cast-iron yokes here joints are inevitable. But if cast-iron is to be em- ployed at all its only useful function is that of a yoke, or connecting piece, or as pole pieces. Cast-iron, owing to its low permeability, as we have already shown, is wrongly employed as a core. Cast-iron Magnets may be made as powerful as wrought-iron magnets, but not of equal size or weight. Since we may regard the cast magnet as one-third larger than the wrought magnet, there will be a pro- portionate difference in the resistance of the exciting coils required to encircle them. If cast-iron is to be used at all, and it is employed, say, as a yoke piece, its section must show at least the above proportion to that of the core. Cast-iron magnets may be considerably improved by being annealed. The annealing may, in some cases, be carried so far as to convert the metal into "cast- malleable," by which means the permeability may be increased considerably. Dr. Hopkinson found, in his experiments, that wrought-iron showed 18,250 lines per square centimetre, 12,408 lines in malleable TYPICAL FIELD MAGNETS. Fig. 23 Gramme Type. Fig. 24. Siemens Horizontal Type. Fig. 25. Type of Alternating 'Current Dynamo Field Magnets in General. S N N S Fig. 26. Brush Type. .Fig. 27. Thomson-Houston Type. OTH7IBS1T7 88 FORM OF THE FIELD MAGNET. Fig. 28. Mather and Platt Type ( " Manchester" Dynamo). Fig. 29. " Inward Projecting " Field Magnets of Alternating-Current and other Dynamos. Fig. 30 Single-Coil Magnet, Kennedy's Dynamo. D \!U Fig. ji. Mordey Alternator Type. RIGHT AND LEFT COILINGS. 89 cast-iron, 10,783 lines in grey cast-iron ("white metal"), and 10,546 lines in mottled (or common) cast-iron. Mitis iron is a material of recent intro- duction. It consists of wrought-iron, containing a small proportion of aluminium. It is easily cast, and is likely to be employed largely for the cheaper classes of dynamos. It is probably not superior to malleable cast-iron in permeability, but its actual value has not yet been determined. Right and Left-handed Ceilings. It appears scarcely necessary to state that the coil- ing, as such, has any influence in determining the sign of the poles. A north pole is not necessarily produced by either direction of coiling. The direction of the current is, of course, the determining cause. If a magnet be exhibiting the wrong poles, the coils need not be disturbed. It is only necessary to reverse the connections with the electric source. In some cases dynamos may, by accident, become re- versed. That is, the residual, or " permanent " mag- netism may not accord with the direction of rota- tion. The pole-signs may easily be found by pre- senting to them the needle of a small compass, and any fault may either be rectified by changing the connections of the coils, or by passing through them a strong enough current to reverse the polarity. The latter is the better expedient. Direction of the Helix Cross-Connections. No dif- ficulty need be experienced in determining the con- QO FORM OF THE FIELD MAGNET. nections of a complex form of field magnet. If we take a long bar, and coil it from end to end with a right-handed winding, this helix will always run right-handedly, whether we bend the bar into a horse- shoe shape or not. Such a magnet would commonly be excited by two deep windings upon the straight limbs, as it is not found particularly advantageous to continue them over the bend, or yoke. The connec- tion between the coils would cross from one link to the other in the form of the letter co, as depicted in Fig. 32. CHAPTER VII. THE ARMATURE. AN armature may be defined as a closed conducting circuit, capable of revolving in or cutting a magnetic field. But a much clearer apprehension of what an armature must be is obtained from the conception of a magnetic circuit. The field is merely part of this circuit. The armature is a link, nearly completing the circuit. A magnetic circuit, incomplete, is provided. The gap is called the magnetic field. It is a region across which lines of force are projected. Any metallic body set rotating so that it cuts these lines of force will have induced in it currents of electricity. The moving body may merely consist of a circle of any conductor having an axis set transversely to the lines of force. This is the simplest kind of armature, It is also the least effective. An arrangement of this kind is depicted in Fig. 33. It maybe regarded as the simplest form a dynamo can assume. It is only useful for purposes of illustration. In its revolution it cuts the lines of force twice, and the direction of the current is reversed twice. Two short impulsive currents are induced in it. The strength of these currents reaches a maximum at the moment when it is cutting the greatest number of 92 THE ARMATURE. magnetic lines. It is clear that as this occurs twice in a revolution there will be two points of maximum and Fiff- 33- Diagram of Single Loop Armature in a Magnetic Field. two points of minimum strength of current. It is at the minimum points that the reversal takes place. ig- 34- Biagram of the Currents in Single Loop Armature. This is represented diagrammatically in Fig. 34. There the dotted line is the neutral region, and from SIMPLE LOOP ARMATURE. 93 this, upon either side, the impulses spring, rising to a maximum electromotive force and again falling to the line of least action. The first and second half circles, marked in degrees from o to 180, show that at the points 90 and 270 the electromotive force induced is at a maximum. The currents produced by such simple arrangements have two drawbacks. They alternate in direction, and they are not continuous. The first fault may be rectified by collecting the currents from the surface of a two-part commutator ; the second drawback is in- separable from an armature of this kind. Without further elaborating our conception of the armature we may suppose the simple loop to form a single convolution around a mass of iron, revolving freely with it in the magnetic field. The effect of this would be to transform the simple loop with its core into an electro-magnet. The currents induced in it would remain of the same character. But they would be considerably augmented in force. We may inquire the reason of this. In the first case our magnetic field was an empty air-space, except when the loop cuts through it at each turn. In the second case it is occupied by a mass of iron. We have regarded the air-space as a gap, simply, in the magnetic circuit of the inducing magnet. To project lines of force through this gap consumes considerable energy; in other words, the magnetic field will be comparatively weak. The gap, then, offers great reluctance to the lines of force. If we desire to reduce this reluctance, the simplest expedient appears to be to partially bridge it across with a mass of iron, this being the substance best adapted for the conveyance of the lines of magnetic force. Tfce number of lines of force 94 THE ARMATURE. will now be considerably augmented ; the reluctance in the field will be chiefly composed of two narrow air gaps, or that necessary] " clearance" space between the armature and the polar faces. // is not necessary that the iron core should revolve. In our conception of a magnetic circuit it merely serves to reduce the magnetic reluctance of that circuit. It may be regarded as a partial continuation of the body or core of the magnet itself. It influences the result very little whether it moves around with the conductor or not. The iron core of an armature is thus a means of bringing the lines offeree in the field with increased power through the turns of the conductor. The iron core may be dispensed with by adopting other means of reducing the reluctance of the air gap. If the conductor, instead of forming a simple loop, having an axis transverse to the lines of force, be formed in a snail-like, flat spiral, the spiral may be moved bodily across the field, cutting it edge-wise. The air gap between the poles of the field magnet may thus be greatly diminished in breadth. It need only be wide enough to allow of the passage of the spiral. The width of this will be determined by the thickness of the conductor employed in forming it. A very intense magnetic field, having comparatively little reluctance, is thus possible. It is quite unnecessary, as practice has abundantly proved, to employ iron in any form in combination with an armature coil of this description. With regard to the use of iron as a core for an armature, it may be remembered that from the earliest history of the magnetic machine its presence was con- sidered practically indispensable. This arose from the description of armatures employed. They were all electro-magnets of some form. The first "keeper* COMMUTATOR. 95 or armature was merely a piece of iron employed to cross the poles of a magnet and so maintain the magnetic circuit by contact. The early experimental- ists showed that if this keeper had wound upon it a few turns of insulated wire, every removal and re- placement of it from the poles or every break and make of the magnetic circuit led to the inducement of a current in that wire. Before long steps were taken to give the keeper and its coil a motion, by mechanical means, across the poles of the magnet. Currents were induced as before, and from this germ has been evolved the iron-cored armature. The early experiments made with a view to obtain equal electrical effects from coils without iron cores were much less successful. We now understand the reason. It is clear that iron is not essential. But as every- thing depends upon the nature of the armature, and the disposition of the field, iron cores are neces- sarily largely used, and will probably always be employed for dynamos. As before stated, however, some of the most conspicuously successful dynamos have not a particle of iron in the armature. Commutator. The simplest armature consists, as we have seen, of a single conducting circuit cutting lines of force. The currents it yields are undulatory and alternating in direction. For many purposes the undulatory currents are unsuitable, especially if the rise and fall of the current- wave be slow. If, however, the waves occur with great rapidity, or many hundreds to the second of time, such an undulatory current may find many uses. The alternate direction of the current is a less serious 96 THE ARMATURE. objection. It may easily be commuted to a uniform direction. But alternating-direction currents of rapid recurrence are in common use for feeding incan- descent lamps. This class of current is, indeed, in high favour for that purpose. It is clear that, in order that the to-and-fro current shall not be observable in the light emitted by the lamp, its wave or " phase " shall be rapid. This " periodicity" is frequently as high as 200 alternations per second of time. Continuous currents are yielded by several descrip- tions of armature. But a large number give off alter- nating currents. It is generally required to commute these to take a constant direction with respect to the exterior (or useful) portion of the circuit. The most usual arrangement to meet this consists of a divided copper sleeve insulated from, but rotating with, the shaft or axis. The coils have their extremities con- nected to the several portions of this sleeve, and the currents are taken from the surface by two springs of copper or brass, bearing upon its opposite diameters. If the armature consist of two parts, or only one complete circle, as in our first example, the com- mutator will be in the form of a copper tube, split into two equal portions, longitudinally. (This form of commutator was illustrated and explained at p. 27.) These are insulated from the shaft and from each other. The collecting springs (or " brushes" as they are generally termed) are fixed in such a position that at the instant the current experiences a reversal the two half tubes shall exchange springs. It will thus be clear that one of the springs must always receive the positive current (as we may for the moment term it) while the other invariably receives the negative current. This simple device was one CONTINUOUS CURRENT ARMATURE. 97 of the earliest improvements made in this class of machines after their first invention. If the armature were to consist of two loops instead of one only, the commutator would then have four separate parts to receive the four extremities. But such commutators are only of the simplest kind, and are no longer used in dynamos. The connections of the wires and loops involve no problem. In many machines the arrangement of the wires forming the circuit of the armature are very complex, and we cannot at this early stage enter upon the details. Continuous Current Armature. We have already considered the faults of the simple single-loop armature. Its current consists of two fmprds&s due- to on& loop trv armatoxp& Fig- 35- Two loops in, armature Fig. 36. Four loop Fig. 37- sharp impulses. Only a very feeble effect can be pro- duced by this arrangement. If, however, two loops be arranged at right angles to each other, four impulses will be given in each revolution. While the first loop is passing through the weakest part of its circle g 8 THE ARMATURE. giving its minimum effect the second loop will occupy the maximum position. The object aimed at is to so arrange the loops that there is always a maximum current flowing. In Figs. 35, 36, and 37, the impulses due to a single loop, a double loop, and a four-part loop are depicted. In Fig. 37, the impulses combine to form a nearly continuous current. The letters a b c trace the positions of the impulses. It is plain that if a larger number of coils or loops be employed, they may be so disposed, at regular intervals in a circle, as to ensure that one or more of them occupies at any period of the revolution the point of maximum effect. This is the secret of the great success that has attended the introduction of the Pacinotti ring principle (Gramme's armature) and that of the Alteneck drum armature. Both of these famous armatures yielded absolutely continuous cur- rents. The same effects have of late attended the development of several other kinds of armatures. It is regarded as an essential condition in a well-designed dynamo. The circle being filled with active conductors, it becomes a study of the deepest interest how best to combine these among themselves, and how to deliver the effects to the collector or commutator. These considerations apply more particularly to the forms of armature in which loops or circles of con- ductor, having an axis through them transversely to the lines of force, are employed. The case respecting connections is somewhat different in what are called disc armatures and one or two others. We have already seen that a conductor wound up in the form of a flat spiral, or in any other flat ring shape, will have induced in it an electric current upon DISC ARMATURE. 99 passing bodily through a magnetic field. In the majority of disc armatures the coils are arranged at equal distances around the periphery of a disc or wheel. The principle of the disc armature is very old, but it has lately been revived in the construction of alternating dynamos. The disc is arranged upon an axis, and generally rotates in a vertical plane. In order to ensure the continuity of current in this class of armature the field magnets are constructed in an entirely different way from that already spoken of. While the loop or drum armature is usually mounted between the poles of a single massive electro-magnet, the disc armature is furnished with multiple magnetic field set up by a large number of small electro- magnets. These are arranged in two crowns or circles, concentric with the disc, and upon either side of it, as previously explained and illustrated (p. 87.) By the simple expedient of ensuring that there shall be a greater number of armature coils than field magnets, the essential condition of continuity is secured. The arrangement is such that two or more of the disc coils are at the maximum while others are at the minimum. In fact, as in a well designed loop armature, there is no perceptible undulation in the current. This arrangement is represented in Fig. 38. Where all the coils, c c, &c , are joined in series and their terminals taken to a pair of collector rings, r r, rotat- ing with, but insulated from the shaft, the coils are generally wound alternately right and left-handedly. In relation to the simple question of continuity of current, there remains to be mentioned that class of armatures generally known as ring armatures. This class has been the subject of a great deal of attention 100 THE ARMATURE, from writers on electricity. The questions involved in the action of a Gramme ring armature are, indeed, among the most fascinating in the whole science. We cannot dwell fully upon it here, and will, therefore, content ourselves with a sketch of the conditions. The ring armature (Gramme's pattern) is well known to consist of an iron core, of ring shape, sur- rounded with an endless helix of insulated wire. It is THE RING ARMATURE. 10 1 mounted upon an axis passing through its centre, and is caused to revolve in a vertical plane after the manner of a wheel between the two poles of a large field magnet, as already illustrated and described at p. 1 6. It may be considered, for our present purpose, that the currents are simply collected by two springs, pressing upon opposite diameters of the ring so as to make contact with the helix. The current evolved in this arrangement, in its revolution in the magnetic field, has not inaptly been likened to a fall of water, free from undulations and reversals. As the ring revolves, its iron core experiences a continuous magnetization at two opposite points. The core, indeed, forms two magnets with their similar poles connected as one.* Here, then, we have the case of a helix, in effect moving continuously over two con- sequent magnetic poles (for we may at once ignore the fact that the iron core itself moves, since we are dealing with the magnetic lines of force only), and at the same time cutting the lines of force projected from the field magnet. The effect of this is to cause an assumed flow of current towards two opposite diameters of the ring at points cut by a line drawn at right angles to the poles of induction. The collecting springs or brushes, touching these two points of flow, convey the current to the external work and com- plete the circuit.f * It should be remembered that a magnetic pole may be concentrated in any part of an iron circle, as well as at the extremity of a bar. The former is very generally spoken of as a " consequent " pole, the latter as " salient." f The reactions in the Gramme ring have given rise to a good deal of discussion, and diversified opinion exists as to the precise conditions of generation of current. Although the problem is full of interest, our space forbids a full consideration of the case in these pages. CHAPTER VIII. THE ARMATURE CORE. THE two classes of armatures in which iron cores are employed are mainly Drum Armatures, or those having a cylinder shape, and Ring Armatures, or those of annular form. The greater number of arma- tures belong to one or other of these two kinds. The Drum Armature has assumed the leading position in dynamos for constant current. The earliest attempt to form a drum armature appears to be that of Stur- geon (p. 8], who produced an iron shuttle, with the requisite windings of insulated wire. At a later period Siemens and Halske introduced their well known H girder armature (p. n), a device which gave a considerable impetus to the use of magneto machines at that time. This form has been so frequently described that (since it is now obsolete except for small machines) it need not further occupy our attention. At a later period followed the cylin- drical iron core of Alteneck, and the famous Ring of Gramme, which, however, had been anticipated by the toothed ring of Pacinotti (p. 14). This latter was unquestionably the first attempt to form an armature capable of either yielding a continuous current or of acting with a continuous mechanical effect as a motor. The core consisted of a ring or rim of iron LAMINATION OF THE IRON. 103 having sixteen tooth-like projections. These formed very wide teeth : the spaces between them wide "pockets/ 5 in which the induction coils were wound. Thus tooth and coil alternated sixteen of each. The coils were of insulated wire, and were, as a whole, carefully isolated from contact with the iron rim. The only difference between Pacinotti's core and the later celebrated armatures of Gramme and Brush lay in the fact that Gramme dispensed with the projecting teeth, and, in common with Brush, set his ring in a vertical plane (while Pacinotti adopted the horizontal position). Lamination of the Iron. If a solid core of iron be employed in any form of armature the result of its action wall be the evolution of great heat. In any armature generating large currents in the presence of a mass of iron it becomes a difficult matter to eliminate the heat. To dissipate the heat by currents of air, or by water circulation (as was tried in soma of Wilde's machines) is clearly a mistake. At best, it is but the dissipation of energy, and must necessarily be wasteful. Foucault or Eddy Currents. The researches of Dr. Frolich* first drew attention to the wasteful effects of heat in armatures, and to the true cause of this rise of temperature. He pointed out that much, if not most, of the unaccounted-for loss of energy in gene- rators was to be attributed to the generation of 'waste- ful eddy currents in the iron composing the core. The conception of these currents soon admitted of proof. It was shown that not only did they arise wastefully * Elektrotechnische Zeitschrift, vol. ii., p. 174, 1881, 104 THE ARMATURE CORE. in the mass of the core, but may even prove a draw- back in the conductors surrounding it. It has been shown that in armatures of extremely low resistances, where the conductors take the form of solid copper plates or bars, there may be a considerable loss from eddy currents in the conductors themselves, apart altogether from the loss incurred by non-lamination of the iron core. In the large armatures used for in- candescent lighting this defect caused a considerable waste of energy, and was otherwise troublesome. More recent researches of Dr. Frolich and others have indicated the existence of these currents, chiefly in the form of vortices. The case of eddy currents in the conductors around the armature has been most successfully met by a system of lamination. The solid copper bars of the earlier dynamos are usually superseded by strap or band copper, every layer of which is separately in- sulated. When conductors become large a distinct advantage is gained by this method, apart from the question of eddy currents. It is found that a smaller weight of copper will, when laminated, yield maxi- mum effects. Heat of Core or Eddy Currents in detrimental to Magnetic Induction. It is well known that magnetism in iron or steel is quickly and completely destroyed by heat. Obeying the same law in a relative degree, it is known that hot iron has a much lower magnetic susceptibility than cold iron. To magnetize a hot core, therefore, calls for a greater energy in the field, and this explains why a dynamo frequently falls off in performance after it has become heated. Apart from this, however, the effect of heat in the armature is the certain destruction of the insulation. The LAMINATION OF DRUM ARMATURE. 105 process may be gradual, but it is, nevertheless, certain. Under favourable conditions the heat may even quickly destroy the insulation. The Laminations. 'During the evolution of the common induction coil, or Rhumkorff's inductorium, several experimentalists pointed out that a consider- able gain could be secured by subdividing the iron core. A core slit in two, longitudinally, was found better than a solid bar, and a bundle of rods or wires was found to be a still greater improvement. This refers to bars or masses magnetized in the direction of their length, and not transversely. The distinction is important. The cores of armatures used in dynamos are seldom magnetized longitudinally. The transverse magneti- zation calls for a different arrangement of the laminae. The cores of all common forms of armatures should be laminated in planes parallel to the lines of force in the magnetic field, and never at right angles thereto. In most cases this is equivalent to sub-division in planes normal to the currents induced in the armature. The reason for this is to be found in the fact that the induction tends to cause eddy currents directed at right angles to the field. The sub-division must be arranged to obviate this, and to render impossible any current directed at right angles to the lines of force in the field. Lamination of Drum Armatures is very satisfactorily effected by building up the required cylinder from a large number of thin washers or discs of iron. The softest charcoal iron should be used for this purpose. In order that the discs may become magnetically dis- continuous it is usual to separate each pair with a paper washer, or a washer of mica. In inferior io6 THE ARMATURE CORE. dynamos the discs are simply varnished. It is pos- sible that the latter method, if it can be carried out without distortion of the washers, might become a sufficient protection in itself. Drum armatures are frequently constructed after the manner of Pacinotti's ring, with projections. In this case the washers are stamped out in the required form, and clamped together, so that the projections and interspaces form ridges and channels for the recep- tion of the coils. This method is more frequently followed in the for- mation of ring armatures of the deep-cylinder type. It is depicted in Figs. 39 and 40. Fig. 39 repre- sents one of the washers, which, in addition to the slotted central shaft-hole, is pierced with four ventilating apertures, for the purpose of cooling the armature by the admission of air. These Fig- 39. Disc from Ribbed Armature Core. Fig. 40. Ribbed Armature Core. discs are usually built into a solid cylinder (d d, fig. 40), between two flanges of gun-metal, also fur- nished with projections, or ribs. The whole arrange- ment shows a compact cylinder, with longitudinal ribs, r r, and ventilating apertures, v v. To a certain extent these ribs may be regarded as Pacinotti's pro- LAMINATION INDISPENSABLE. 107 jections. They are usually as deep as the windings. They serve admirably as divisions, forming regularly- spaced channels for the reception of the coils. Edison or Siemens armature cores are built in the same way, except that the washers are not furnished with teeth. The end flanges, however, are provided with equally- spaced ribs, to facilitate the winding. In Edison's armature (drum type) the plain washers are threaded upon the shaft, against a suitable end- flange, and when the pile is completed the whole is compressed from the opposite end by a pair of lock- nuts, turning upon threads cut upon the shaft. This is the general method of construction. Many modi- fications of it have failed to show that it can be materially improved upon. If longitudinal bolts be used to compress the discs apart from the shaft, care must be taken to insulate them from each other, and from the discs themselves. If this precaution be neglected, induced currents will circulate in the system of bolts, giving rise to as much heat and waste as the lamination is intended to obviate. Experience points to the plan first given as the better of the two. Lamination not without Disadvantages. The mag- netic discontinuity of iron cores may, from another standpoint, be regarded as a disadvantage. Although its observance in the case of armature cores, or in any part of a dynamo subject to changes of magnetic strength is indispensable, it introduces an increase of magnetic reluctance or resistance. It decreases the effective cross section of the armature. In many forms of armature it is difficult to adhere rigidly to the rule that the planes or lines of lamination shall be parallel to the lines of the inducing field. For this io8 THE ARMATURE CORE. reason wires are seldom employed for purposes of sub- division. The direction of magnetization must always determine the plane of subdivision. When an arma- ture revolves this will, in most cases, be normal to the axis. Subdivision that violates these principles may be considered of doubtful advantage. Lamination of Ring Armatures. Gramme's arma- ture core consists, as already stated, of iron wire, wound upon a suitable former, until a flat, annular core is built up. The wire being varnished before being wound may be regarded as a fairly complete protection against eddy currents. But this method is not regarded as entirely satisfactory. Theory dictates that the core should be built up from a large number of thin iron rings to the required breadth. Each ring should be separated by paper or mica from its neighbour. This latter method is preferable as reducing the magnetic reluctance of the ring. Either of these methods of subdivision is adapted to a core to be magnetized across its diameter. This method of mounting the Gramme ring, it will be seen, forms the ring virtually into two magnets with two consequent or combined poles. Gramme armatures are built in two leading forms. These are the ring armature simply, having a core of the form depicted in Fig. 41, and the cylinder ring armature, in which the core assumes more or less the form Fig. 41. King Core of Gramme Armature. o f a cylinder or drum. The core of this design takes the shape shown in Fig. 42. As a rule the sharp edges of these ring cores are carefully chamfered or rounded off not CYLINDER RING CORES. 109 shown in the diagrams and channels are milled or planed out of the interior, at the required intervals, to receive the arms of the driving arrangement centred Fig. 42. C} r linder or Elongated Ring Core. Fig. 43. Cylinder Ring with Driving Spider. upon the shaft. This, in the improved and later dynamos, usually consists of a " spider " of bronze, as represented in Fig. 43, having arms as thin as may be permissible, in order to obviate the taking up of space required for the enveloping coils. Ring cores of the Brush type are magnetized in a very different way. Here the lamination is most ad- vantageously disposed parallel to the axis of the ring. In the early Brush machines the armature core con- sisted of a ring of cast iron. The double side projec- tions, or teeth (known as Pacinotti projections) were carefully slit, and the body of the ring itself was partially slotted in a plane parallel to the driving shaft. This form of ring heats considerably. Fig. 44 represents a Brush's ring, with twelve Paci- notti projections, p p, without windings or axial ar- rangements. The pockets into which the coils are no THE ARMATURE CORE. Fig. 44. Ring Core with Pacinotti Projections. wound are formed with parallel sides, so that the " teeth/' p p y are of a somewhat tapering form. This kind of core has been very extensively used. The magnetization in Brush's dynamo is paral- lel to the line p p. In a later improvement of this armature the lami- nation is effected as fol- lows : A strong foundation- ring is taken of a size exteriorly to form the interior diameter of the active ring. A ribbon of soft iron, having a thick- ness of i *5 millimetres, is secured parallel to its surface. This ribbon is wound upon the foundation to the size of ring required, 45 convolutions being employed. But as the Brush ring has two sets of Pacinotti projections, one from either side, those are formed by inserting, at suitable intervals, H shaped pieces of iron. These project from either side to the required distance. They are so disposed as to leave "pockets," or in- dents, for the coils, having parallel sides. This plan was adopted so that the coils might be of parallel shape. Insulated radial bolts are passed through both ring and projections, securing the whole into a compact body. The details of construction, however, vary with the particular forms of ring to be laminated. This ribbon method of building up ring armature cores intended to be magnetized parallel to their axis is likely to have extended application. These examples will suffice to show the devices that MATERIAL OF THE CORES. Ill experience has proved effective in the elimination of eddy currents and the heating of armatures. That the lamination of the core is of considerable advan- tage beyond the mere stoppage of the wasteful currents is shown strikingly in the case of Brush's dynamo. A machine of the old type, built to supply sixteen arc lamps, is found, when fitted with the lami- nated armature, to be powerful enough to feed twenty- five lamps. Influence of the Pacinotti Projections. Considerable discussion has been evoked in various publications bearing upon the utility, or otherwise, of the pro- jecting teeth first applied to a ring armature by Pacinotti, and more lately modified and elaborated by several experimentalists. The researches of Prof. Thompson, Mr. Crompton, and Mr. Esson all tend to emphasise the general opinion that the toothed ring is superior to the smooth core. The advantage is doubtless attributable to the influence of the projec- tions in reducing the magnetic resistance, in affording direct paths for the lines of force across the field. It has also been pointed out that the projections tend to cool the core by carrying the heat from its interior. Material of the Armature Cores. From the considerations already discussed, it is evident that soft iron is the only admissible metallic core for an armature. By the word "core " is under- stood the central mass of the armature intended to play a part in its action. A core of wood, or brass, might be employed ; and even the latter might not prove detrimental to the performance of the armature if it were suitably laminated. But such non-mag- 112 THE ARMATURE CORE. netic cores would be without effect in the resultant electrical currents. They would act as mere formers, or bobbins, to receive the conductors composing the armature. The material must be iron, because that metal offers least resistance to the transference of the lines of force across the field. In other words, it has least magnetic reluctance ; it is easily and rapidly mag- netized and demagnetized. The iron must be soft or ductile under the hammer, because a fine quality of Swedish or charcoal iron possesses much less mag- netic reluctance than harder varieties. It thereby re- duces the magnetic resistance, so to speak, of the whole armature. If a hard quality of iron or steel were employed a certain damming-back of the lines of force across the field or gap would result. It would acquire a certain degree of permanent magneti- zation ; it would, as a whole, fail to perform with that degree of mobility throughout its mass which is a characteristic of the best kind of armatures. If the core be composed of any of those metals or alloys called non-magnetic, such as brass or copper, the magnetic reluctance would be practically infinite, and it would entirely fail as a core acting by magnetic induction. The Core regarded as a Link in the Magnetic Circuit. A very clear conception of what an armature core must be is to be obtained from a correct discernment of the lately-developed theory of the magnetic circuit, as applied to the dynamo. A partially complete magnetic circuit exists there is a gap as yet. This FUNCTIONS OF THE CORE. 113 is the field magnet ; the gap the magnetic field itself. Across its space are projected lines of force. The magnetic resistance of this air gap is very great. Within the gap, nearly filling it, but still free to revolve, is placed a metallic body of peculiar con- struction. From one point of view its function is to complete the magnetic circuit. It is possible, although there yet exist two air spaces, to impel the lines of force across the air gaps : they are simply to be regarded as resistances to the lines of magnetism. The wider the armature gap the greater its resist- ance, and the less intense the field therein. When it is wide, the magnetic continuity across can be most easily ensured by filling it with the most permeable magnetic conducting substance. As this implies the substance having the least known magnetic resist- ance, soft iron is chosen. It will now be plain that the magnetic field gap or armature gap must not be too wide to ensure a maximum intensity. It must be extremely narrow, if nothing is to be used to reduce its resistance. If the armature-conductors are not to be coiled upon a core of soft iron they must form a thin body a flat ring or a disc. This rule applies with much force to all dynamos in which iron-cored armatures are dispensed with.* But when the armature assumes the form of a cylinder a narrow field gap is impracticable. A much larger proportion of the whole magnetic circuit must then be cut out. As far as is practicable the circuit must be again completed. This is accom- plished by the insertion of the largest practicable, and * In some of the largest of the famous Ferranti dynamos, the distance between the opposing magnetic poles, the width of the field, is scarcely over half an inch. 114 THE ARMATURE CORE. least resisting body of iron. This iron core carries upon its surface certain coils of conductors. The air gaps across which the lines offeree have to be driven are, in width, equal to the distance of the iron core from the electro-magnet faces. Hence the narrower this air space is made the better. It is made as narrow as possible, but the practicability of this is limited by two considerations, (i) The enveloping induction wires must be arranged in number sufficient to yield the electromotive force required from the dynamo " number " is equivalent to depth of wind- ings. (2) The induction wires must be as thick as possible, so as to offer the least possible electrical resistance to the currents they carry. Cross Section of the Core. The particular form of armature will always deter- mine several points, (i) Whether it is to be iron- cored or not ; (2) if iron-cored, the disposition and planes of the lamination. But there is one observa- tion that appears common to all kinds of iron-cored armatures : it refers to the cross-section of iron em- ployed. The cross-section should be as great as possible, for reasons discussed in the preceding paragraph. This is a condition which modern practice has proved to be of the greatest importance. It has been fre- quently violated in many otherwise well- designed dynamos. In some of the earlier Siemens machines, for example, the iron core merely consisted of a thin iron cylinder, overspun with iron wire, providing but a small area or cross-section to carry on the important work of maintaining the continuity of the magnetic circuit. RULES APPERTAINING TO CORES. 115 If the armature be cylindrical, it can be cored and laminated with a considerable cross-section by the use of the iron discs previously spoken of.* No better kind of core for this class of armature has ever been devised. A tube of iron would prove a very objec- tionable kind of core. Iron wire laid parallel to the axis is still worse, since its plane would be across the lines of force, tending" to cut them up. Iron wire wound upon a wooden foundation has frequently been used, and answers fairly well, if of sufficient depth ; but it is open to the objection that the continuity it offers to the lines of force is imperfect. Moreover, unless the wire be of square section it will occupy useless space, and thereby not comply with the above rule. For the same reason iron wire is not so suitable for a ring armature, such as Gramme's, as a core built up of thin discs. Armatures consisting of wheels, carry- ing near the edge a series of bobbins of wire, present a difficult case. If iron cores are to be employed they must not be solid. Split tubes are too light. Bundles of wires are the most suitable, but are, for manufac- turing purposes, troublesome. These objections are the chief causes of the decline of this class of dynamo. Siemens was the first to dispense with the iron alto- gether, and narrow the bobbins down to mere discs of wire. Rules Appertaining to Armature Cores. To sum up briefly the lines of best construction of an armature core, it must fulfil the following con- ditions : * In the Edison -Hopkinson dynamo, 1,000 of these discs is employed for one armature. Il6 THE ARMATURE CORE. 1. It must consist of the softest Swedish or charcoal iron. 2. The iron must be laminated, and the laminae separated by a non-magnetic substance, in planes normal to the axis, and parallel to the lines of mag- netic force in the field. 3. Its cross-section must be as great as is practic- able there must be plenty of iron in the core. 4. The parts composing the core must be very securely attached to each other and to the shaft, to resist the powerful tangential drag exercised by the field. 5. Means of ventilation are advisable, although this is seldom requisite if the metal be suitably sub- divided. It is frequently objectionable as diminishing the cross-section of the active iron. Classification of Armature Cores. Iron-cored armatures represent by far the most important class. For practical purposes they may be divided into two main branches : Drum Armatures, iron-cored, had their rise in the semi-drum shuttle armature of Siemens. Modern examples are to be found in the Siemens drum-arma- ture dynamo ; in Weston's dynamo (the first in which projecting teeth were employed) ; in Edison's ma- chine ; in Crompton's drum machine ; in Immisch's dynamo ; in Paris and Scott's machine, and in numerous others. Ring Armatures, iron-cored, had their origin in Pacinotti's machine. It was followed by Gramme's ring dynamo, and by that of Brush. One of the earliest was the cylinder ring dynamo of Maxim. CLASSIFICATION OF CORES. 117 Some of the best known are the Biirgin cylinder ring dynamo now called the Burgin-Crompton machine ; in Kapp's dynamo (cylinder ring) ; in Paterson and Cooper's machine (cylinder ring) ; in Schuckert's (flat ring) machine ; in Gulcher's dynamo (flat ring), and in those of many other makers. Spherical Armatures , iron-cored, are extremely rare. The chief representative of this type is the famous machine of Thomson and Houston. The armature is strictly spheroidal in form. CHAPTER IX. ARMATURE WINDING. IN Chap. VII. et seq. are discussed the effects of revolv- ing a single circuit of conductor within and across the lines of force in a magnetic field. Further, it was shown that, in order to obtain a continuous current, instead of two impulses during each revolution, the number of coils had to be increased. Thus an armature might be built up of circles of conductor, each one of which would deliver an impulse into the external portion of the circuit, so that the resultant current would be practically continuous. Now, the electromotive force developed in a wire cutting lines of magnetism depends upon the number of lines it cuts per second. In other words, it depends upon the intensity of the magnetism and the rate or velocity of its revolution. Whatever this electromotive force may be, it can be very easily multiplied by multiplying the number of wires or loops. The force then can be doubled by having two wires in one loop, both passing through practically the same part of the field at the same time. We may thus indefinitely increase the electromotive force by employing multiple loops or oblong coils of wire in the place of single conductors. We may also deter- mine the electromotive force by the speed, and by the strength of the magnetic field, ARMATURE WINDING. 119 It must be understood that the word "coil" implies a wire taking several turns, and having only two extremities. These are attached to the collector or commutator as if the wire described one turn only. From these considerations we may express the procedure in the case of determining the electromotive force in the following way : 1. To obtain a minimum electromotive force (it required under given conditions of speed and magnetic field) use loops, or coils, of a single turn. This enables us to utilise the space by making these loops of very thick wire, thus diminishing to a minimum the electrical resistance of the armature. 2. Augmentation of the electromotive force is got (under given conditions as before) by increasing the number of turns in each loop or coil. The electromotive force is approximately proportional to the number of turns. But this increase of number of wires neces- sitates a diminution in the size of the wire to allow, in a reasonable space and depth, the number of turns in each coil, and also the number of coils required around the armature to yield a continuous current. The necessity to diminish the cross section of the wire results in a corresponding increase in the resistance of that wire. Hence : Armatures of low electromotive force are usually of insignificant resistance. Armatures of high electromotive force are usually of considerable resistance. In the early days of the magneto-electric machine, Mr. Wilde used to have for his large machine (as exhibited to the Royal Society in the year 1867) two armatures. One of these was wound with copper plate or band, and had few turns, and a low resistance. 120 ARMATURE WINDING. It was called the " quantity " armature. The other was wound with many turns of insulated wire, and was of high resistance. It was termed the "intensity" armature. At the present time these armatures would be regarded as low and high resistance armatures, their performance as armatures of corresponding electromotive forces being understood.* Without entering upon a consideration of the nature of the electric current, and the laws that define the relationship between electromotive force and resistance, it may be remarked that a dynamo is not necessarily giving a weak current, or a weak electrical effect, when working at a low potential (electromotive force). Nor must it be supposed that a dynamo yielding a very high potential is necessarily giving rise to powerful electrical effect. On the other hand, the output of the dynamo is measured in watts, which at once expresses its power ; and two dynamos may be doing precisely equal electrical work, although evincing very different electromotive forces. Hence it is not necessarily a disadvantage to arrange an armature for low potential. Formula of Electromotive Force in Armature. The following rule is sufficiently accurate for deter- mining, in absolute units (C.G.S. system), the electro- motive force that will be induced in the armature of a continuous current machine : If M be the magnetization (effective) through the armature, in other words the number of lines of * * The student must not, however, fall into the error of supposing that an armature of either low or high ^resistance will necessarily yield corre- sponding electromotive force, DETERMINATION OF ELECTROMOTIVE FORCE. 121 magnetic force (measured by unit pole) impelled through the armature by the field magnet ; and T the turns described by the armature wire making each coil, in other words the number of turns in circuit or series at once, counted from one collector bar to the other, or from brush to brush, and at the number N of revolutions per minute ' j- = revolutions per second; then, E.M.F. standing for electromotive force, E.M.F. = M x T x ~. 60 This gives the E.M.F. in absolute units. For practical purposes these are reduced to volts by division by the number io 8 . Again, let V represent volts evolved by armature, - M X T X N 60 x io 8 ' This applies to dynamos of the closed coil descrip- tion, or those in which half the coils in the armature (approximately), as in Gramme's ring, are in circuit upon each side at once. A few dynamos, however, intended to give continuous currents, as Brush's machine, are wound upon the principle of throwing out of circuit the coils that are not for the moment active. In such cases it is necessary to count con- volutions actually in circuit only. Determination of the Current. The power of a dynamo is known in terms of its electromotive force (volts) and its current (amperes). The current will depend upon three matters : i . The electromotive force at its poles (volts). 122 ARMATURE WINDING. 2. The electrical resistance of the whole circuit in which the energy is expended. This includes the dynamo's own (" internal ") resistance, made up of armature turns in series and field magnet coils, and the external work, as leading wires and lamps. 3. In certain cases, counter electromotive force, as the back pressure of accumulators being charged, or back E.M.F. from any other cause. Let c stand for current in the external portion of the circuit ; E for the electromotive force of the machine. E<; for any counter electromotive force (in incan- descent lighting this quantity may be omitted). Rj, internal resistance of dynamo. R e , external resistance, leads, lamps, &c. Then : C (amperes) = j^- ; It is useless to occupy space by following a very general practice in books of giving several pages of ready-prepared " examples " of the application of Ohm's law of the circuit. Supposititious cases are always a questionable basis for such work. The case of alternating-current machines is rather more complex, and will be treated later. But it may here be remarked that the rule relating to the E.M.F. being proportional to the number of turns in the coil (under given conditions of speed, &c.), is the same practically for the two machines. The armatures of alternators (of the multipolar type) are frequently, however, made of extremely low resistance by the expedient of employing only one circuit. But this circuit consists practically of many induction turns, as in Ferranti's dynamo. The field, when measure- DETERMINATION OF THE CURRENT. 123 ments are to depend upon the lines of force, is to be regarded as the region between any two opposing magnets, or the magnetic lines that pass between any north pole and any south pole across the plane of the armature. These considerations are, however, more fully treated in Chap. II. Proportion between depth of Windings and Diameter of Core. In determining the number of turns in a coil upon the surface of any armature core it is important to remember that the size of the wire, that is, its sec- tional area, will limit the current it can carry in safety. To prevent overheating, the current may be as great as 2,000 amperes per square inch of sectional area. Many armature builders, however, exceed this considerably. The safe current will depend greatly upon the nature of the insulation, and the provision made for ventilation. In relation to this point it is necessary to remember that in loop armatures, such as those of the drum and ring type, where the extremities of the coil are really connected to two opposite collector plates -or brushes, only half the current passes by the wire. This will be evident when we remember the disposition of the coil upon the surface of the core. From these considerations (regarding the number of coils as having been deter- mined upon beforehand) the weight of copper that can be arranged upon the core can easily be settled. With regard to the radial depth of the coils, measurements made upon a number of the best working constant-current dynamos show an average of depth to radial depth of core of rather over one- 124 ARMATURE WINDING. sixth. This proportion is further useful in deter- mining the cross section of the core itself. These considerations apply chiefly to drum armatures of the types already spoken of. Relation of the parts to each other. In order to fix in the reader's mind the relative positions of the parts of the ring armature, it may prove useful to represent COLLECTOR Fiff- 45- Ring Core with three Coils, showing connections. them diagrammatically, as in Fig. 45, the three coils, c y having connections at z, and through con- ductors s (shown of abnormal length for the sake of Fig. 46. Diagram of Coils in Fig. 47. View of a completed (narrow a Ring Armature. Core) Ring Armature. clearness) to the collector lugs. Fig. 46 represents the coils and connections of one half of the ring, while in Fig. 47 is depicted a complete armature of the narrow or ring-core form. CHAPTER X. RING ARMATURE WINDING. HAVING already considered the reactions between the field and an armature of the ring type (p. 100), it now remains to discuss the methods adopted in practice in the winding of the ring. The Continuous Helix Method was first practised by Gramme, and is the best known. The core, as we have already seen (p. 108), consists of a flat ring, composed of soft iron wire or washers. Insulation of the Core. The iron ring is heated and placed in a vessel of melted bitumen, until the latter has sunk into all the intricacies of the coilings. It is then removed, and the superfluous bitumen turned off. A long strip of linen, two or three inches in width, is closely wound upon the core to a depth of two thicknesses. This is finally saturated with shellac varnish, and allowed to harden. In some cases, in armatures intended for high tensions, the core is covered with indiarubber, which is finally vulcanised in position a very excellent kind of protection. Rotation Mounting of the Core. The old French method was to leave the mounting until the ring had been wound, and to force it over a wooden drum, keyed upon the shaft. The objections to this plan are that, under the heating of the ring, the wood is 126 RING ARMATURE WINDING. apt to shrink, and finally to lose its grip upon the ring. Also, the insulation of the coils is apt to be injured by the pressure necessary in forcing the hub into position. American dynamo builders who have adopted the Gramme armature have effected a great improvement in the rotation mounting. This consists in substituting for the old wooden drum a gun-metal " spider," having four or six spokes radiating from a central sleeve-hub, keyed to the shaft. The arms of the spider are broad and flat in the axial plane, and are made thin enough to occupy but a small space between two adjacent ceilings, as already illustrated and explained at p. 109. Two methods of attaching the spider to the core are in use. The older consists in fitting the ring closely over the arms, and fixing them in position upon it by U-pieces or gun-metal staples screwed from the periphery. The later method consists in winding the core direct upon the spider, the arms of which are shaped to receive the coilings in the required form. The circular shape is preserved by the insertion of segmental pieces, which are after- wards removed from between the arms of the spider. In either case the winding of the induction coils is conducted as follows : The Coils of the Helix. We have already seen that the coiling of a ring armature does not consist of a single-wire helix. In order to gain electromotive force the helix really consists of several layers of wire. In order that the several sections of the coil as they cut the field may throw their accumulated force upon the collector at the right instant, the helix must be wound on in separate sections, each complete in itself. This is accomplished by arranging upon the ring a series of segmental coils, but each connected RING ARMATURE WINDING. 127 to its neighbour, so as to form a circle of bobbins in series. The winding is done by hand. In order to facilitate the formation of the coils and their symmetrical arrangement, the ring core is accurately divided into the required number of sections by marking. The latter is so arranged that the arms of the spider fall between two coils. It is of some importance that this division of the circle shall be accurate, for if any one coil be larger than the others it will upset the electrical balance of the ring, and prove a source of trouble by sparking at the commutator. A pair of " winding clamps " are employed to define the width and shape of the coil section. The ring core is fixed in a wooden clamp in a vertical plane at the height of the operator's elbow. The winding clamps are fixed in position. A wire of the length required to form one coil is taken. If it be long and thin (when the dynamo is intended to yield high E.M.F.) it is wound first upon two shuttles as follows : One end of the wire is taken and fastened in a notch in a wooden shuttle. One-half the wire is then wound upon this shuttle. Another shuttle is taken. The remaining end of the wire is fixed to it and wound up as before. One of the shuttles is then passed through the ring, and the operator proceeds to form exactly one-half of the coil by passing one of his shuttles the required number of turns through the ring. The other half of the coil is wound in the same way by winding off the remaining shuttle. By these means both extremities of the wire are gradually worked to the outside of the coil. There is con- siderable objection to winding the coil from one end, thereby leaving the inner extremity to be brought out 128 RING ARMATURE WINDING. between two coils. During the process of winding 1 , the operator takes care to place his wires as closely as possible in the segmental chamber. After each layer is wound, a coating of quick-drying varnish is applied: When the coil is finished it is sufficiently firm to stand by itself as a segment upon the core. Both ends of the wire are brought out at the side where it is intended to place the collector. One of the clamps is now moved forward to another division of the ring, and another coil is wound in the same way. Care is necessary to exactly divide the wire, to ensure that all the coil-lengths shall be the same, and that the turns exactly complete the allotted space. When every section is completed, the exterior is varnished. In order to prevent displacement of the coilings by the rapid motion of the ring, " binding coils " are placed over the segments. These consist of several turns of fine brass or steel wire wound tightly in three or more separate bands upon the periphery. These wire bands are finally soldered to obviate flying asunder. It should be noted that this binding wire must be as fine as is likely to effect the desired purpose. In order to preserve throughout the required circular outline, and the concentricity of the segments, it will readily be supposed that .particular care must be observed in so disposing of the wire that there shall be no difference between any two of the coils. The operator soon learns to fill all the space at his disposal, and this is the main condition. Space fillers of vulcanised fibre are generally placed between those coils from which the spider arms are absent, so equalising the positions. Breakdown of Insulation. Sparking may possibly OPERATIVE DETAILS OF WINDING. 129 Occur between adjacent ceilings if the E.M.F. developed by the machine be high. This is obviated by inserting divisions of thin varnished millboard, or sheets of vulcanised fibre, between the sectional windings. But the chance of a breakdown of the insulation is much greater through the core itself. Coils at opposite diameters will have potential differences as great as that of the machine. Sparking from coil to core, and from the latter to the diame- trically opposite coil, may therefore occur. This can only be obviated by proper insulation of the ring prior to winding the coils. There is probably nothing better for this purpose (other than vulcanised rubber) than several layers of varnished tape, each layer being wound and varnished, and allowed to become dry separately. Operative Details of the Winding The number of coils should be as great as possible. This will depend greatly upon the size of the core, the thickness of the wire, and other considerations. In the section of this work treating of typical dynamos, details used in leading Gramme machines may be found. These form a very good basis in calculating the numbers of a new armature. It will be found that, as the interior of the core is smaller than the periphery, a winding of two layers deep upon the latter will, if it be closely arranged, necessitate a winding three layers deep upon the interior of the core. This introduces some irregularity in the arrangement of the wires passing over the ends of the core, and a good deal of judgment is necessary in disposing of the turns to the best advantage. In order to ensure a smooth and regular exterior, some makers cover over all irregularities by interposing a layer of vul- K 130 RING ARMAIURE WINDING. canised fibre between the final layer and that under it. An odd number of layers will be found preferable to an even number, because, if the winding be con- ducted from the middle of the wire as suggested, this brings the finishing extremities to the two ends of the coils ready for connection to the next coil on either side, and to the respective collector bars. The plan of working both ends simultaneously to the outside ensures that short circuiting in the coil will be almost impossible, and facilitates repairs. Some winders prefer to wind in parallel coil spaces, by the insertion of wedges of V-shape in the interior of the core, between the coils. This, however, wastes a good deal of space, and does not appear to offer corre- sponding advantages. The wooden winding clamps are made in several patterns. The simplest form a guide from the ends over the periphery only. Double clamps form a guide on the interior of the core also. In the early dynamos it was the practice to twist together, and solder, adjacent coil ends. In improved forms the ends are kept separate, and are screwed into separate holes, with set screws, in the extension arms from the collector bars. The final binding wires or " bands " are preferably made of hard brass wire. Before they are applied, there should be wound on bands of mica, suitably connected by cement. Silk ribbon is frequently used for this purpose, but a harder protection appears advisable. Vulcanised rubber or fibre appears to be suitable. It must be particularly noted that, unless the insulation between these bands and the coils be sufficient, short circuiting from one half of the armature to the other will take place. In the winding of coils of thick wire, good judgment is necessary in " placing " the latter. CAUSES OF SPARKING. 131 Wooden wedges, with grooves or channels cut length- wise of their face, will be found useful as beaters, to be used with a hammer, in forcing the wire into position. Compact winding, having no interspaces and a neat finish, are all very desirable. Causes of Sparking. In most of the systems of winding of armatures two adjacent collecting cylinder strips represent respec- tively the two extremities of one induction coil. When the junction or insulation line of these two strips comes exactly under a brush, the latter touches both of them at once, and short circuits that coil. A momentarily strong current is thus set up in it. When, therefore, the brush leaves one of the strips, the short circuit is opened, and the extra current, due to self-induction, as well as the current normally due to its motion in the field, rushes across the breach, expending its force in a spark. If, on the other hand, the brush were to be so con- structed that it touched only one collector slip, it would then break contact with one slip before making contact with the next. This would have the effect simply of breaking the whole circuit momentarily, and would give rise to very destructive sparking. It appears essential, therefore, that the brushes shall bridge over, or short circuit, two slips or segments of the collector at once. From these considerations it is evident that the remedy for sparking lies very greatly in the practica- bility of reducing the self-induction of the coils so short-circuited. It is necessary, in short, to provide that the short-circuited coils shall be as far out of the 1$2 RING ARMATURE WINDING. region of magnetic activity as possible at that instant* This implies that they shall not be actively cutting 1 lines of force. The more idle the coil at the instant of short circuiting the better. In order that the idle coils may be out of the field, or nearly so, at the in- stant of contact, or short circuiting, the space between the extremities of the embracing horns of the field magnet must be carefully studied. If it be arranged that the coil be fairly within this space, and does not cut any of the magnetic lines, although they may thread through it, sparking will be reduced to a minimum. Self-induction, on the other hand, is best combatted by making each coil as short as possible, or, in other words, building the armature with the greatest possible number of coils and commutator strips. Collector* for Symmetrically Wound Ring. The collector consists of a number of segmental pieces of copper, insulated from each other, and rotating with the shaft. In the most improved forms the segments assume a narrow V-form, as illustrated and described at p. 26. There are as many segments as there are coils upon the ring. The segments are arranged so as to form a cylinder, and many ingenious devices have been introduced by different makers for the purpose of binding them together in that form. Be- tween each pair of segments an insulating space is provided. In the earlier dynamos this space was filled with asbestos millboard. In later machines mica of good quality has been found preferable. The insulating space is very narrow it is only essential that the seg- * It is incorrect to call the collector of a Gramme or Siemens machine a commutator. The latter is an arrangement intended to change the direc- tion of currents, and the term is not correctly applied otherwise. CONSTRUCTION OF COLLECTOR. 133 ments be separated. A thickness of mica of -^nd of an inch is generally considered sufficient, but it depends largely upon the electromotive force of the machine. There is little tendency to sparking be- tween coils adjacent in a ring unless the E.M.F. be very high. A considerable depth of segment is desirable, be- cause a collecting cylinder is constantly wearing down when in work, and it becomes necessary at intervals to turn off the roughened surface in the lathe. A collector of considerable depth, carefully built, will thus serve for several years' wear. The segments are BAR S.b. WITE Fig. 48. Collector Bar and its Insulation. made with outward projecting edges at either end. When in position these projections are engaged by a collar or flange of hard rubber or wood upon the shaft, having in its inner face a y groove to receive the seg- ments. The other end of the collector is similarly held by a screwed insulating flange, made secure from turning by a lock-nut. Considerable care is requisite in fitting the mica. It must not only be of uniform thickness for all the divisions, but it must completely fill the space. Between the segments and the shaft is interposed a sleeve of some insulating material, as ebonite or vulcanised fibre or wood. Hence, every 134 RING ARMATURE WINDING. section is completely insulated from its neighbours, and from the shaft. Fig. 48 is a sectional diagram of the positions of the collector, the insulating sleeve of vulcanised fibre or ebonite, and the insulation at the ends of the bar, when the latter is clamped tightly down to the sleeve and shaft. The connector or collector" lug" is shown fitted into a groove or slot turned in the bars. It is some- times soldered there, or attached by a screw. But each maker may be said to have his own particular method of connection. S b is a section of the bar. These collector bars, since they form, when as- sembled, a complete cylinder, are frequently made by casting a copper or bronze cylinder, and afterwards cutting it up in the milling-machine into the required number of segments. Later practice, however, has shown the superior wearing capacity of compressed drawn bronze or phosphor bronze. It is, therefore, becoming common to build collectors from " drawn bar" of perfect and uniform section, and of great tensile strength. Several different methods of fasten- ing the bars are shown in the Chapters on Typical Dynamos. The connections to the armature coils are generally effected as follows : To each segment is secured a radial arm or lug of brass. The arms are of sufficient length to reach to the inner diameter of the ring. The upper ends of the arms carry connecting screws to receive the two wires the finishing end of one coil, and the commencement of the next. Soldering was formerly resorted to for all these connections, but is now discarded in favour of screws. Collector Brushes for Ring Armature. The arma- ture, shaft and collector form one body, rotating in its COLLECTOR BRUSHES. 135 bearings. The currents evolved by the armature are taken off the revolving collecting drum by means of springs of copper or brass. These are usually called brushes. A line drawn through the armature axis, almost at right angles to another line parallel to the magnetic field centrally, gives the " line of collection," or the points of contact of the brushes. These two points are respectively those at which the potentials are theoretically highest and lowest. Slightly in front of this (in the direction of motion) the position of least sparking generally occurs. At that point the brushes are always placed. In some dynamos the " line of least sparking " and maximum electromotive force is parallel to the lines of the magnetic field. In most machines with ring and drum armatures it is at right angles nearly. The distance between the theo- retical line and that of best collection is often spoken of as the " angular lead " of the brushes. This posi- tion is generally found by trial when the machine is running. Whatever position the brushes may be required to hold with respect to the collector or armature, they must invariably (for the type of armature under con- sideration) be fixed in relation to each other upon a line passing through the axis at right angles. Hence, the points of contact must be exactly opposite each other. But as it is necessary to determine by experi- ment the point of best collection, a certain movement of the brush yoke around the axis is essential. This is effected by forming the yoke upon a large metallic ring moving round upon a concentric hub. This ring is generally provided with a set-screw for the purpose of locking it at any desired point. A pair of arms, partly of insulating material, project from 1 3 6 RING ARMATURE WINDING. the ring to receive the brushes. These latter slide in grooves cut in the arms, and can be set by a screw therein. Each maker has his own particular device for this purpose, and for giving spring contact to the brushes. All that is essential is that the brushes shall touch the collector exactly opposite each other, and that they have the requisite elasticity, and are in- sulated from each other. The brushes themselves usually consist of a number of hard-drawn copper wires, or a bundle of copper strips. The object of subdividing the points of contact is to distribute the destructive sparking over a con- siderable area, and to ensure that this area is in contact with the collecting brush. Fig. 49 depicts the whole arrangement generally called a brush rocker or yoke, m represents a portion of the main casting around a turned hub of which the split collar, r, upon which are cast the arms or handles h h, moves. By slackening a set-screw these arms may be set in any de- rig .49-Detail. of the Single Slred Potion COHCentric with Brush Yoke or Rocker. the shaft. The arms carry angle spindles, ^ s, forming brush holders, through which the brushes, b b, slide, and are set by screws. The cylindrical lined body, c, is the collector itself. The brush yokes, s s, are really swivelled upon their axis, and are provided with a small " hold-on " spring, the function of which is to keep the brush against the collector. In the most improved forms of brush rocker the same spring, by BRUSH ROCKERS. 137 means of a well-known "knuckle" movement, is made to act also as a "hold-off" spring. Thus, when it is desired to keep the brush away from the collector, it is pulled away forcibly until the knuckle is thrown over by the spring. In the case of large dynamos a single pair of brushes is never de- pended upon. The col- lecting cylinder is made of considerable length, and two or more sets of brushes are used. Any pair or one of these may be removed or held off separately. In this way it is unnecessary to stop the dynamo to trim a brush, or smooth a rough collector. The multiple system has other advantages, which need not occupy us further here. Referring to Fig. 50, which repre- sents a "three-pair" yoke, a is the end of the armature, / / the brush-set or tension screws, // the lever, and b a butterfly-nut used in tightening the collar. Typical Ring-Armature Dynamo dissected. Hav- ing now described the nature of the Gramme method of winding-ring armatures, it may prove useful to present a typical example of an armature completed and ready for running. This is depicted in Fig. 51, which represents a rather elongated or cylindrical ring, a.s distinguished from Fig. 47 (p. 124), which Fig-. 50. Details of the Multip'e Brush Yoke, or Rocker. RING ARMATURE WINDING. represented a shallow ring. The core is composed of iron washers separated by paper, a method of building now almost universal. It will be observed, on refer- ence to the former figure, that the connection lugs between the termini of the coils and the collecting cylinder are of considerable length, and that the col- lecting cylinder is situated as close as possible to the Fig. 51. Complete Cylinder- Ring Armature. plane of the ring itself. This latter condition allows of a very short shaft being used, with the advantage of its being correspondingly stiff. The armature is secured with several bands of steel or brass wire (the latter is deemed the better, but both are freely used by builders). Fig. 52 represents the brush rocker, removed from its boss on the main casting. It is fitted with hold-on-and- oif spring, by means of which the pressure of the brush upon the collecting surface may be maintained or the brush thrown back, and there retained by means of the second spring, Fig. 52. The Brush Rocker. WINDING FOR MULTIPOLAR FIELD. 159 In Fig. 53 is shown the frame or base, field magnet and shaft bearings of the dynamo. This particular type will be seen to consist of two magnets with their poles combined, forming consequent poles, as in Gramme's original machine, but not excited by hori- zontal divided coils as in that pattern. The particular form here shown is also used by Mather and Platt - 53- The Base, Bearings, and Field Magnet. in their smaller machines, with the exception that in their case the cores and coils are cylindrical. As here depicted the cores and coils are rectangular, with rounded corners, the substance of the cores being wrought ircn and that of the pole pieces cast iron. Winding Ring for a Multipolar Field. In the ordinary Gramme ring all the bobbins are connected J40 RING ARMATURE WINDING. together, forming practically an endless helix. Con- nection is then made between each pair of coils and each bar of the collector, This method of connecting is only adapted to the case in which the ring is set in an ordinary two-pole field. Of late there has been a tendency to bring the principle of the ring armature into the construction of multipolar machines for alternating and continuous current dynamos, and this construction entails different systems of connecting the coiis. The coils of the ring are arranged as before, but connections are established between those coils that arrive simultaneously at equal potential. Suppose that, in- stead of two poles, the magnets take the form of four poles, distributed equally in the circle, those coils that happen to be 1 80 apart will at the same instant arrive at equal poten- tial, and those two coils must be connected together, as in Fig. 54, when the terminals a a' would be connected to diame- Fig< 54 o~pposit s e^o n ns e . ction f trically opposite collector bars, and so on throughout the cir- cuit. The connections from the 'tween-coil junctions to the collector-plates are maintained as before. The brushes bear upon the collector at a distance 90 apart. This method is due to Mr. Mordey, who devised it for the improved Schuckert machine with four poles. It is especially adapted for dynamos intended to yield moderate potential. For armatures of higher poten- tial Professor Perry devised a method of cross-con- necting applicable to rings having an odd number of coils only. In this case the sectional coils are not WINDINGS. 141 Connected in series, as in the Gramme armature. Each section is connected as follows : Its commenc- ing end is connected to the collector-bar nearest to it. Its finishing end is connected across to the com- mencing end of the diametrically opposite coil, or to that coil which happens to be most nearly in that position. The same end of the latter coil is con- nected as before to the collector-bar nearest to it, and so on around the circle. As the armature is intended for a four-pole field, the collector brushes bear at points 90 apart as in the former case. This arrange- ment by cross-connection is similar to Gramme's, inasmuch as it yields the E.M.F. of half the coils at the brushes. Multipolar Windings. Multipolar dynamos are coming into extensive use, especially for central sta- tion lighting. They have many advantages to offer. While they are only generally adapted for compara- tively low tension working and large currents, they maybe driven at a slow speed, and have other advan- tages. The ring windings appear to be most in favour for these dynamos. The core is generally of the cylinder-ring shape, and the coils are frequently arranged alternately with Pacinotti projections. But armatures somewhat of the Brush pattern, or even more disc-like, are in considerable favour. Fig. 55 is a diagram of a four-pole cylinder armature as used in central station machines. It has four brushes, opposite brushes being of the same sign. The oppo- site brushes are in parallel. The coils c c take various forms. They are joined in series and again in multiple to the segment, as at a a. A somewhat similar winding has been used in the Gulcher machines. 142 RING ARMATURE WINDING. Fig. 56 is similar to the above, with coils coupled in four parallels Opposite coils of the same poten- tial are, however, coupled together, so that only two brushes are necessary. This method has been used in the Victoria machines. Several other methods of cross-connection have been devised ; they all aim at reducing the number of brushes. Square Section Wire for Armature Winding. In N N Fig. 55. Windings of Multipolar Ring Four Brushes. order to economise space, it is a very general prac- tice to wind rings and drums with wire of square section. By this means the space can be more fully occupied, and the distance between the core and field magnet faces diminished without a corresponding loss in copper conductivity. The use of square wire is therefore on the increase for this purpose. Cylinder Ring Winding. When the ring core is of MULTIPOLAR WINDINGS. 143 extra depth it assumes the cylindrical form, and the term " cylinder ring " has been reserved for it in order to distinguish such armatures from drum armatures. These latter they closely resemble, except in the winding, which is quite different. Many electricians object to this form of the ring, urging, as they do, and not without reason, that the interior portion of the winding is to a certain extent idle, and adds only N Fig. 56. Windings of Multipolar Ring Two Brushes. to the resistance. With a powerful magnetic field, this need not be the case. It is possible to bring the core up to such a condition of saturation over 16,000 lines per square centimetre that the interior wind- ings play an important part in the total output. Cylinder- ring cores (Fig. 42, p. 109) are now almost invariably built up of thin iron discs. These are separated by paper in the usual way, and bound 144 RING ARMATURE WINDING. together in the required depth with insulated bolts* The fitting of such cores to run truly balanced is always a somewhat difficult matter. The centre of the disc is stamped out to a sufficient diameter to provide space for the shaft and windings. Radial arms, or what is more usual, a gun-metal star- wheel, keyed upon the shaft, engages in slots cut in the interior of the ring. A sectional view form of one of these driv- ing appliances is given in Fig. 57. In all cases before winding the core is care- fully balanced and turned true. Fan Spokes of the Star-wheel. In some of the re- cently designed dynamos an excellent device has been adopted. It consists in forming the spokes or arms of the " spider " or driving-wheel, with a twist. This is so arranged as to draw air through the centre of the core continuously, while the armature is in motion. It is thus possible to allow an armature so furnished to evolve greater heat and show a greater current, with safety, than one wholly enclosed, or not cooled by an air current. As in the case of wire cores, the cylinder is coated with bitumen or japan. It is insulated further with wrappings of linen, varnished. The winding is greatly facilitated by the insertion of box- wood wedges in the core, marking the divisions for the sections. Slots are cut for these at either end at regular distances apart. It is, however, becoming more common to employ extra heavy end-plates of iron or brass with divisions cast on them. The wire generally employed in winding cylinder rings is not round. It is more frequently of nearly DRIVING HORNS OF ARMATURE. 145 rectangular section, being slightly of V form. This section is of great advantage in packing the wire in the interior of the ring. It will be clear that if it be required to wind the conductor closely covering the exterior of the ring in a single layer, the interior, being of smaller diameter, will probably be covered by two layers, and so on in proportion. Some makers employ thick conductors for the exterior windings, and thinner wire for the interior. This involves jointing, which is always objectionable. A good deal of skill is requisite in arranging the conductor to the best advantage, especially in maintaining its proper position in the interior. Driving Horns, &c. When the ring is very deep, cylindrically, a considerable length of wire lies with- out support along its length, exteriorly. It is usual in this case to provide wooden plugs or stops between the coils at regular intervals. These, in conjunction with the final circular binding wires, arranged in three or more bands, suffice to give the requisite stiff- ness to the exterior ceilings. In some of the later dynamos the wooden wedges formerly employed at the ends of the core have been dispensed with, and radial teeth or gaps cut in the core plates instead. But this idea has been carried much further, and the whole length of the core has been scored up by longi- tudinal slots, wide enough to receive the conductors. Still more lately Mr. Crompton adopted the plan of threading the conductors through longitudinal holes running near the surface around the periphery. The effect of this is to bring the conductor within the core, and it is possible by these means to run the armature extremely close to the field-magnet faces. This has the effect of greatly reducing the resistance of the air 146 RING ARMATURE WINDING. gap, and a possible saving of the energy of magnetic excitation is effected. In cylinder-ring machines intended for incandes- cent lighting direct, the electromotive force required need seldom be higher than no volts. It is found that at a moderate speed this E.M.F. can be deve- loped by even a single layer of conductors upon the armature. For example, in an armature of one of Crompton's incandescent lighting dynamos the wind- ings consist of 120 turns, every third turn being brought down and connected to a collector having 40 segments, The wire lies one deep upon the ex- terior and two deep upon the interior. The three turns constitute sectional coils with three turns in series. The conductor employed in the armature mentioned is of nearly rectangular sections, cotton covered, and further insulated by the insertion of strips of vulcanised fibre between the coils. Ventilation of the cores is not always necessary. But cooling gaps are frequently provided in cylinder ring cores, by the insertion of divisions of narrow width at intervals of two or three inches. The divi- sions consist usually of radial pieces. In Crompton's armature they are J-inch wide and occur every two inches of the length. Manipulation of Heavy Conductors. Conductors for cylinder-ring armatures are frequently of large sec- tion and low resistance (for dynamos of 100 volts and under). One method of manipulating these so as to reduce the jointing to a minimum is to bend the re- quisite turn-lengths in the form of a long, narrow H>, and to afterwards connect them in pairs or threes at the open end. In order to gain space the wire is sometimes drawn of oblong section, and the OPEN-COIL RING ARMATURE. 147 interior half of the loop is twisted at right angles to the exterior half, thus providing a narrower but deeper conductor on the interior than on the exterior. In one of Mr. Crompton's machines with grooved arma- ture core, the completed armature was 28 inches in length and 12 inches in diameter, radial depth of core discs 23 inches, windings, 69 turns of copper ribbon, oblong section, cores of field-magnets, 3 feet 6 inches in length, 24 inches wide, 43 inches thick, with about 24,000 ampere turns magnetizing coils. At a speed of 440 revolutions per minute, the current was 229 amperes at no volts at terminals. In this armature there was one turn on each coil, therefore each turn was connected direct to each collector sec- tion. But the turns as a whole formed an endless coil, the section of copper being rather over a square centimetre. The necessity to provide an adequate magnetic field for cylinder-ring dynamos has given rise to several devices for interior magnetic poles as well as exterior poles. It does not appear, however, that any one of these has proved itself a success. It will at once be discerned that as soon as we depart from the peri- pheral (Gramme) or face (Brush) excitation of a ring, and seek to complicate matters by additional poles, the armature becomes of a different character. It must be of larger diameter ; the magnetic circuit is of much greater length (regarded from the old stand- point) and the windings must necessarily be modified to suit the new conditions. Ring Armature with Open Coil. In one or two special forms of machine, intended for high E.M.F. and arc lighting, a different arrangement of the coils is adopted. Mr. Brush appears to have been the first 148 RING ARMATURE WINDING. to employ the method of open coil working. As we have seen in the ordinary ring, the series of coils formed a closed circuit, but with outlets at the col- lector between each pair. The disadvantage of this arrangement is that the coils not actually feeding the circuit i.e., the inactive coils still carry through them the whole work of the armature. The concep- tion of open coil winding consists in the cutting out of these coils, leaving only in the circuit those coils actually contributing to the resulting current. This result can be obtained in any ring armature by a system of cross connection and by providing collect- ing slips for each complete circuit or pair of coils. Thus in Brush's open coil armature the inner end of each sectional coil is soldered to the inner end of that diametrically opposite. But there is no connection between adjacent coils. In this respect the open coil arrangement is differ- ent from all other methods of winding-rings. The free extremities of the two opposite coils are then carried to two diametrically opposite plates of the collector or commutator. Each pair of coils may be said to have its own collector, consisting of two parts. In a machine having eight coils wound upon the ring, there are four pairs of coils. The collector con- sists of two divided cylinders, each forming four separate insulated parts. Every pair of divisions is connected to a pair of coils. As there are two separate collectors, each consisting of four plates, two sets of brushes one to each collector are required. The eifect of this arrangement is that the pairs of coils are only admitted into the working circuit during their period of lest action. As soon as they cease to evolve a current, or in other words, pass out of the field, they THE BRUSH WINDING. 1 49 are cut out of the working circuit, but at the instant that one pair is cut out the succeeding pair is cut in. Obviously a collector composed of four pairs, or right sections, and of the ordinary shape would not meet the requirements of this case. The period of contact, for instance, between brush and segment would only be the eighth part of a circle i.e., 45 and there are other considerations to be met in the working of the particular armature under discussion. The peculiar form of the Brush collector has, however, been so fully described by other writers that we cannot here enter upon a more detailed examination. We are chiefly concerned with the method of connecting in the ring itself, and as this merely consists in putting the diametrically opposite coils in series with one another, instead of establishing a series arrangement all round the circle, no difficulty is likely to be met in mentally working out the result. The Brush armature coils are wound in "pockets," or double recessions of the ring. The core (Fig. 44, p. no) is thus not wholly overwound with turns as in most ring armatures. The coils are of consider- able size and breadth, and only eight of them are wound upon the ordinary Brush armature. The larger armatures, intended for sixty lights (arcs), have twelve of these coils. In the smaller machine the ring is 20 inches in diameter. The " pockets " before winding, are care- fully covered with shellaced linen. The bobbins are necessarily wound by hand. The wire is in the first instance arranged upon a shuttle. Each bobbin consists of 900 feet of cotton-covered copper wire of a gauge of wire closely approximating to No. 14 stan- dard wire gauge (diameter -092 inches, sectional area, i5 RING ARMATURE WINDING. square inches '0050 ; square mm. 3*242). The wind- ing is carried out as compactly as possible with fre- quent divisions of varnished linen between the layers. All the coils are wound in a right-handed direction. They are coupled in opposite pairs as before ex- plained. Spherical Armature. One more instance of open coil winding deserves mention. The spherical arma- ture of the Thomson-Houston machine is absolutely unique both in its design and in its winding. The core has already been spoken of (Chap. VIII.) The coils are three in number, but they are so curiously combined that they may be regarded as forming one coil. Into the surface of the core are driven wooden pegs to facilitate the winding. The core is then carefully covered by an insulator. Three wires are taken, and their extremities connected together, and the whole carefully insulated. Commencing near the axis of the core, the winding of the three wires is taken in turns by sections. Half of the first wire is wound around the core. This is carried out in the form of a wide, flat coil. Half of the second coil is wound in the same way at an angle of 120 with the first. The third coil is then wound at a still further angle of 120. Then the remainder of the second wire is wound on, and finally the latter half of the first coil. All the ends finish off near the axis upon the side of the core opposite to the commencement. The free extremities are insulated and carried through a hole drilled longitudinally through the shaft, and so carried out to the collector. The object of this curious winding is to give the three coils equal distances from the iron core, and their arrangement SPHERICAL ARMATURE WINDINGS. 151 at angles of 120 is intended to distribute the turns all over the effective area of the core. The windings are secured by bands of steel wire, as in other arma- tures. The collector consists of three parts only, to which the three-coil extremities are connected. Two pairs of brushes are employed, the individual brushes of each pair being about 90 apart ; but the pairs are situated as usual diametrically opposite. We cannot in this chapter follow the reactions, but the effect of this arrangement is to cut out the sections of the coil that are idle, and to admit those that are active, as in Brush's armature. The field-magnet poles intended to receive the spherical armature are of cup form, and embrace between them two-thirds of its entire surface, as depicted in Fig. 27, p. 87. In the ordinary sized dynamo the armature complete is 23^ inches in diameter, and the gauge of wire used in winding, 08 1 inches. The armature resistance is 10*5 ohms. CHAPTER XI. DRUM ARMATURE WINDING. THE cylindrical armatures over-wound in the direction of their axis are generally known in England as drum armatures. There is this essential difference between them and the cylinder-ring armatures that, while the ring cylinder remains a ring and is wound with coils encircling the sides of the ring, the drum armature core may be regarded as a solid cylinder, the coils being formed by passing the conductor completely around it axially. As we have already observed (p. 105), the drum core may either consist of a laminated solid cylinder, or it may take the form of a hollow cylinder or tube. The former plan is adopted by Edison and many others ; the latter was first introduced by Alteneck in the famous Siemens drum armature. There is one point of similarity between drum armatures and the ring armatures already considered : drum winding usually takes the form of a closed coil, and generally forming a complete circuit from end to end. The varieties in winding refer chiefly to the connections that are established with the collector, and to cross connections between the coils. All the varieties of drum armature have sprung from the original shuttle armature of Siemens (1856, THE DRUM ARMATURE. 153 p. n). The great objection to this form was that it evolved not a continuous current but a series of impulses. This was due to the fact that the winding consisted of a single coil or " loop " (p. 93), and that the sides of this passed alternately into and out of the magnetic field. The current therefore consisted (if not commuted) of a series of waves, alternately nega- tive and positive. The waves were not rectified by commutation, although determined by one sign. The improvements that have been effected consist simply in increasing the number of loops, and in so distributing these around the core that one loop at least is to be found at any instant of the revolution in the position of maximum effect, while some other loop occupies the zero position. By these means the waves are so " overlapped " or combined that they form practically a continuous current. Drum armature cores have already been spoken of (p. 105). The same principle, that of effecting con- tinuity in the conductor, has been observed in the core. While the original core consisted of an elongated electro-magnet, with poles that might have been regarded as salient, the modern core is a continuous cylinder. Its magnetization involves no reversals, or discontinuity of the magnetism. On the other hand there is a continuous displacement of the polarity ; and if the core magnetically shows little " reluctance," the displacement, even under a high rate of revolution, is practically determined upon a line parallel to the lines of force crossing the field. It is convenient, in speaking of drum armature windings, to regard the individual coils as loops, the two sides of each of which occupy diametrically opposite positions, or nearly so, upon the cylindrical 154 DRUM ARMATURE WINDING. core. Nine-tenths of the best drum armatures are wound upon this plan. Again, by far the larger proportion have their coils so connected together that they form from end to end a continuous elongated bobbin in this respect there is a strong similarity between drum winding and ordinary closed coil ring winding. Two methods of winding were tried upon the Siemens armatures. The first (invented by Alteneck) was unsym metrical, and, to some extent, disadvan- tageous. It was abandoned in favour of a symmetrical winding known as the new Siemens winding, which, in turn, has to a great extent been superseded by a symmetrical method suggested by Dr. Frolich. Diagrammatic Views of Cylinder or Drum Windings. Since it has been found practically impossible to repre- sent the course of the windings in a drum armature by an intelligible pic- ture in perspective, the method of ex- hibiting it diagram- matically has been adopted by most writers. This has many advantages, but it leaves a good deal to the imagi- nation. If, however, the reader takes the pains to follow the simple explanation given below, he will have no difficulty in discovering the advantages of Fig. 58. Diagram of end of Drum Armature. DRUM WINDINGS. 155 the diagrammatic method. Fig. 58 represents the collector end of the armature, c c c being the bars ; h h are driving horns enclosing spaces in which two or more half- coils are wound ; d d are divisions be- tween each pair of half-coils. In all the diagrams here given the observer is supposed to be looking at that end of the drum armature at which the collector (commutator) is situated. Therefore, the length of the armature lying out of view may be neglected, and it serves the purpose to imagine the windings to be ar- ranged simply upon a disc. Thus a bold line upon the face of the diagram, and its continuation as a dotted line, is in- tended to represent the visible wire and its invisible contin- uation across the far Fig. 59. Edison Winding. ; (or pulley) end of the armature. Thus in Fig. 59, which is of Edison's method of winding, the course of the wires from the commutator bars along the armature core and across the far end is very easily discerned. Drum Windings in General Use. All the windings in use are modifications of the Alteneck winding, Fig. 60. They may be regarded as including every practicable method, and are known by the names of their inventors. The Frolich is a symmetrical alter- 156 DRUM ARMATURE WINDING. Fig. 60. Siemens (Alteneck) Winding. nate winding. The Edison is the Alteneck winding applied to an odd number of coils. The Weston is the Alteneck winding with the coils split up and distributed sym- metrically. The Breguet is a rather irregular Alteneck wind- ing. The Hering is the split-coil method applied to the Frolich winding. Referring to Fig. 6 1, if the end of a coil be fastened to a col- lector bar and the wire wound over the drum in the direction of a, and back over the far end and lower side, as shown by the dotted line, to s, the winding will be the Siemens or Alteneck. If the winding take the course a f the winding will be the Frolich. If it take the course a b it will be the Breguet winding. Fie:. 61. Diagram of various Drum Armature Windings. DIVIDING THE COILS. 157 In any one of these cases the coil is completed by bringing its finishing end back to the second collector plate, as represented. Dividing the Coils. Owing to the fact that each turn of the wire wound upon the drum occupies two lines upon its surface at diametrically opposite posi- tions, it is clear that if the core be closely over-wound while it is gradually being turned, it will be found completely covered by wire while it has described but half a revolution. Thus, if there be eight coil spaces or divisions and sixteen collector bars, if the coiling proceed closely, and a connection taken to the col- lector at each coil space, the drum will be completely covered by wire, and only eight collector divisions will be allotted to coils. This is the general Siemens or Alteneck system. Another set of coils is then wound upon the top of the first, by which the eight remaining collector bars are appropriated. This plan has the disadvantage that the under coils have both less surface velocity and length of circuit in the field than the upper coils, so that the armature may be regarded as out of balance electrically, the upper coils, occupying half the collector diametrically, having distinctly the advantage. The difficulty has in many cases been overcome by winding the coils in alternate sections, leaving blank sections for the remaining eight coils. This ensures that the coils shall have an equal mean radius and equal surface velocity. The method has been used in the winding of such Siemens machines as are provided with a moderate number of sections. When the number of sections (and collector bars) is great, some difficulties of winding are met with in carrying out the above method. Weston's method (windings shown in Fig, 158 DRUM ARMATURE WINDING. 62) undoubtedly meets all those difficulties in a practical way. The Weston armature is wound in channels formed in the core, as shown in Fig. 40 (p. 1 06). These channels are made to contain two coils (or two halves of opposite coils), but they are not superim- posed. They are di- vided ingeniously, as represented in Fig. 63, where the white circles denote the wires of one half and the dark circles the wires of the other half. Fig. 62. Diagram of Western's Winding. Their mean radius will thus be equal. Fig. 64 is a diagram of the Frolich winding, h h represent the driving horns, and the light and dark sections the going and returning halves of the eight coils. In winding an armature in this system it is necessary to ob- serve that the "returning" wire falls into the proper chan- nel, as there are always two . ---- v. paths open to it. Reference ( f N \ to Fig. 6 1 (p. 156) will make t hi s c i earj and will serve to explain why it is so easy to fall into either the Alteneck or Breguet winding. Weston's winding, with divided coils, is depicted in Fig. 62. It is rather more complicated to carry out than either of the others, as two coils have to be Fig. ea. THE FROLICH WINDING. 159 manipulated at the same time, as already explained. It appears to be specially suitable to any method of double winding. Drum Armature with Frolich Wind- ings. As an example of one of the latest improved armatures of this description, we may profitably describe the particu- lar arrangement of the Frolich method of grouping. The core consists, as al- ready described, of a large number of soft iron discs compressed into a cylindrical form between two brass flanges. These flanges have, cast upon their periphery, a series of regularly spaced oblong pins. These pins mark the divisions between the sectional windings. They are sufficiently high to stand to the level of the windings when complete, and serve also as driving horns for the coils. When the armature is very long a corresponding set of driving pins is inserted in the middle of the core. These are preferably projections from a malleable cast disc. Care is taken to round off every sharp corner in the course of the windings. The preliminary insulation is commenced by coating every part of the core and flanges with japan varnish. When this is dry the whole surface of the drum, including the driving pins (which are insulated separately), is Fig. 64. Diagram of Dr. Frolich's Drum Winding. 160 DRUM ARMATURE WINDING. covered with a layer of stout linen, varnished with shellac; or the excellent method described at p. 125 is employed. This is done as smoothly as possible, so as to economise space. The windings are arranged in two layers, in four, eight, sixteen, or thirty-two sections. There are as many sections as there are collector bars. Sixteen sections is a very common number. Siemens' first machines had either eight or sixteen. It is to be particularly noted that the windings pass entirely over the drum in a lengthwise direction. They pass up and down over the ends, and in this way form oblong loops of a certain number of turns each. In describing the winding it is convenient to suppose the collector cylinder in position upon the shaft, and to speak of the windings numerically, as one, two, three, &c. The wire is generally (in the most improved armatures) of a rectangular section. It is usually double cotton-covered, and this insulation is often strengthened by running the wire through a bath of shellac or other varnish as it is wound into position. Strips of vulcanised fibre (" fibrate ") or of Willesden paper are made of a three-sided rectangular shape, and these are placed between each pair of driving pins in order to separate the wire from them sufficiently. Let us suppose the length of wire for one loop or coil to be taken. Its commencing end is connected to No. i bar of the collector. It is then wound upon the drum (in four, eight, or sixteen turns, according to the size of the latter, and the E.M.F. required), entirely filling the space between the first two lines of driving pins. In coiling the wire over a drum armature it should be noticed that as the shaft, DRUM ARMATURE WINDING. l6l passing lengthwise through it, is necessarily in the direct path of the ceilings, these latter must be divided into two portions, one half of the coil taking the right hand and the other half the left. Let us suppose that the first coil has been completed, forming a single layer of wire of, say, eight turns around the core. Its finishing extremity will be connected to the second bar of the collector. From the second bar also will commence the second section of coiling But the winding of the second section does not in practice succeed that of the first section. On the contrary, in order to equalise the potentials, and preserve the insulation, the next coil to be wound is that diametrically opposite (i.e. No. 9). This section commences by being connected to No. 9 collector bar, and it is coiled compactly on the top of that already wound, the drum being given half a revolution prior to commencing this coil. Between the two sections or layers a band of vulcanised fibre is interposed. The finishing extremity of the No. 9 section is con- nected to No. 10 collector bar. Section No. 2 is now started by connection to No. 2 collector bar, or which is the same thing the finishing end of No. i section. This is coiled in the channel between the first section and the third row of driving pins, and its finishing end is connected to No. 3 collector bar. Then follows insulation, and the overwinding of No. 10 section, the commencement of which is con- nected to No. 10 collector bar (or to the finishing end of No. 9 section). The course of the wire in respect to its path upon the core will be rendered clearer by an inspection of Fig 65, in which, however, only two portions of coils at right angles to each other are shown. The col- M I 62 DRUM ARMATURE WINDING. lector, c y is also depicted as separated by some distance from the core, in order to render the arrange- ment clearer. In practice the collector is kept as close to the core, d, as circumstances permit. The connectors, s s, are attached as already explained.* Insulation must be very particularly looked after at those points at the ends of the armature where the wires of different sections cross. Some armature winders adopt the precaution of interposing a disc of vulcanised fibre between each two sections at either end. Others adopt the plan of winding an additional covering of varnished tape upon the wire where it Fig. 65. Course of the Conductor in a Drum Winding. crosses the ends. When the sections are composed of fine wire in a large number of turns the equivalent of high electromotive force special care is requisite in thoroughly insulating every part of the windings. But a great deal of useful space may be needlessly sacrificed in this way if the separations are not intelligently effected. It is only necessary to insert extra insulation between those sections that simul- taneously arrive at great differences of potential. Although we have supposed, for the sake of illustra- tion, that in winding the drum armature the collector * An excellent isoraetrical diagram of the ordinary drum conductors was given by Mr. Weymouth in the Electrician, vol xxiv., p. 274. HIGH TENSION WINDING. 163 is required, yet in practice this is dispensed with. The termination of each section is practically made one with the beginning of the next, and the junction is connected as one to the collector lug. In the best constructed dynamos the radial arms, extending from the collector plates to the periphery of the armature, are composed of thick bars of gun metal. They are screwed by means of projecting foot-pieces to the bars, and their free extremities are pierced with apertures and fitted with set screws for receiving the coil terminations. In the early dynamos the whole of this work was effected by soldering. Apart from its inferior stability the latter method presented the disadvantage that in the event of repairs being required the parts were not readily separated. Windings for High and Low Tension. The electro- motive force is nearly proportional to the number of turns in each section. The number of convolutions that can be wound in a given space will depend upon the section of the wire. The finest possible wire would thus yield the highest possible electromotive force, and conversely, the minimum electromotive force would result if only one turn of the thickest possible con- ductor were employed in each section. Between these two extremes there is a wide field for ingenious com- binations of windings to meet the requirements of different cases. Thus, a dynamo intended to run arc lamps in series the most economical plan must evolve volts in proportion to the number of lamps, and as a single lamp requires not less than 30 or 40 volts, the resistance of a number calls for a very high electromotive force. In this case the section must consist of a large number of turns. If the machine be intended for incandescent lighting, a "voltage" of 1 64 DRUM ARMATURE WINDING. about 100 will be sufficient. The section in this case would consist of a moderate number of turns only, and those of a much thicker wire. Further, if a very low " voltage " combined with a large current, as is required for electro-plating, be aimed at, the section might consist of one or two turns only. These remarks are not, however, intended as a guide to this impor- tant question. Many other things must be known, as the force of the magnetic field and the peripheral speed of the armature, together with the circuit resist- ance, before any one of these conditions could be even approximately determined. Testing for Short Circuits. During the progress ot winding drum armatures, it is essential to keep a watch upon the insulation of the wires. This be- comes of still greater importance if the wire be fine in many turns. After each section is wound it should be tested for the following possible faults : (1) Short circuit to core of armature. (2) Short circuit, or leakage, to any other section. (3) Short circuit within itself. The testing apparatus generally employed consists of a few cells of accumulators, or a bichromate battery to furnish the testing current, and a galvanometer for detecting purposes. To ascertain short circuit to core, connect battery, galvanometer and core in series, and make contact (with a wire from the remaining pole of the battery) to the ends of the section it is desired to test. The smallest deflection of the galvanometer will indicate a leakage. Short circuit, or leakage between section and sec- tion, is much more apt to occur. Before testing for this fault disconnect all sections from each other. NEUTRALISATION OF EDDIES. 165 Connect, as before, the various sections, each in turn, in series with the battery and galvanometer, and make contact with each remaining one of the sections. A deflection will indicate the sections that touch metal- lically in crossing In order to obviate the incon- veniences of unwinding several sections in case of a fault, this method of testing should be in constant requisition during the whole operation of winding the armature. In this way an incipient fault is located before other sections have covered it up. The third fault can only be detected by measuring the resistance of the section ; any diminution of this would, of course, indicate a cross between some two of its turns. Various Devices for Neutralising Eddy Currents in Drum Armatures. In the armature windings of dynamos intended for the production of large cur- rents various devices are resorted to for the purpose of preventing the waste of eddy currents. Siemens, in some of the larger dynamos, employs varnished stranded cable, forced by drawing or compression into the required rectangular cross section. More frequently the rectangular bar, required for one half-coil of the armature, is composed, in that shape, of wires. It is then taken and twisted through 1 80 at the middle. This has the effect of causing any current passing along one side to follow the twist and flow on the opposite side along the remaining half of the bar. Any eddy currents, therefore, coursing along the first half of the bar will meet opposing currents in the other half, after passing the twist. These two currents will, therefore, neutralise each other. After giving the bar the half-twist, it is again compressed by hydraulic power to the uniform rectangular section. Still another way is to form the bar of ribbon cop- 1 66 DRUM ARMATURE WINDING. per, varnished. The ends are all soldered together. But this is not entirely satisfactory, because the con- nection at the extremities opens up a path for the current up one side of the bar and down the other. This may, however, be obviated by imparting a half- twist to the bar at the middle as before, and finally compressing it to the required form. A considerable number of such devices have been patented. The aim in all of them is to find a method of perfectly neutralising eddies while preserving the essentially simple character of the plain bar. Dr. Hopkinson resorts to the device of giving greater clearance between the horns of the field magnet and the armature, than obtains at the central line parallel to the lines of force in the field. It simply consists in turning the armature bore-hole in the field magnet a little too large, and in bringing the magnet faces as closely as possible to the arma- ture's periphery. This forms a slightly elliptical chamber for the armature, and results in there being a greater space (or clearance) between armature and field magnet at the horns than elsewhere. But it is found that the eddies, in as far as they refer to the magnet, occur in greatest strength at the trailing or rear horns in the direction of motion, and a slight additional clearance there has the effect of rendering the field more symmetrical in respect to the armature chamber. Heating of the Pole Pieces. In the running of dynamos the effects of the eddy currents can easily be traced. They principally go to heat the field magnet. While the magnet's horns at the entering side (in the direction of motion) are generally com- paratively cool, the following horns are sometimes VENTILATION OF ARMATURE. 167 sufficiently heated to melt a stick of sealing-wax put in contact with them. The armature revolving, as it does, in air, is kept comparatively cool, but consider- able loss can, nevertheless, be traced to faulty construc- tion in the direction of non-lamination of the bars. Laminated armature bars are generally insulated by a close wrapping of varnished tape. But it is quite practicable to employ such bars quite bare. In some of the best dynamos this method is followed. It then becomes comparatively easy to keep such bars cool. Bare conductors are generally socketed in snugs of insulative material projecting from the body of the armature. The external wrappings of steel wire around the whole of the armature are wound upon a sufficiently thick band of mica, so effectually separating the wire and the bars. Ventilation of the Armature. Coupled with the question of the disposal of wasteful eddies is that of ventilation, so that the heat due simply to normal resistance may be got rid of by the cooling effects of air. A great deal of trouble was experienced in this direction by early builders. Given a well-laminated conductor, and a current- density not too high, a moderate number of openings for the passage of air through the armature suffices. It does not appear, however, that in any dynamo yet built, and working at full load, its designer has been able to afford to dispense altogether with ventilating apertures. Turns in Multiple Arc in Armature. Armatures intended for low resistance work, as for incandescent lighting or for electro-metallurgy, are usually con- structed so that their own resistance is inappreciable. This is effected by making each section essentially in the form of a copper bar, the area of which occupies 1 68 DRUM ARMATURE WINDING. the whole of the space available for each section. But the substitution of solid copper conductors of large cross section has been found to present, in practice, certain disadvantages (already alluded to under the head of "Eddy Currents," p. 103). The practice of lamination must, in short, be carried even into the conductors themselves. They consist, there- fore, of a number of copper ribbons, slightly insulated from each other. In many cases the strap copper is merely varnished. In the larger dynamos it is covered with a single layer of cotton. In addition to the electrical advantages of lamina- tion, there are certain mechanical advantages. It is more easy to manipulate conductors subdivided, and to wind or bend them to the required form. But armatures that are wire-wound in many turns, may be converted into low resistance armatures, by the simple method of connecting the turns in multiple arc. Suppose a section having eight turns of wire. If it be desired to halve its resistance, that may be accomplished if the wires are connected across in four pairs. The resistance might be again halved by again cross-connecting the four pairs, having two turns only. To illustrate what is meant, suppose, in the first case, we were to solder a wire or short junction across the first two turns, these two would act as one turn only. Similarly, with the next two turns, and so on. If a wire were soldered across, touching all the wires, bringing them electrically together, the whole of the turns would act as one turn only. Any junctions made in this way, in practice must be very substantial, and the bridging wire must be of large cross-section. Many low- resistance armatures are cross-connected (wound in DEPTH OF THE AIR GAP, 169 multiple arc), but it may be pointed out that the practice of dynamo builders is decidedly in favour of economising space by using, when possible, lightly separated copper strap. The desired end is thus secured without the waste of space inseparable from the employment of ordinary round insulated wire. In any case round wire is not so effective in a given space as square wire a greater cross-section of the latter is easily obtained. 2 Current Density in the Wires. It will be seen that the foregoing practical considerations bear strongly upon the question of sectional area and current. As the former is increased so may the latter be aug- mented. If we assume 2,000 amperes per square inch of sectional area to be a safe working current in a particular coil, we may maintain this density throughout any changes effected by connecting in multiple arc. In accordance with the law of Ohm, if a current of 50 amperes be safe in an armature section of eight turns, it may be augmented to 100 amperes if the wires be cross-connected so as to take but four turns. If the turns be again divided, and brought down to two, the current may with safety be 200 amperes, and so on. . Depth of the A ir Gap. The air gap through which the magnetic lines act consists of the distance between pole faces (of the field magnet) and peri- pheral surface of armature. The depth of wire upon the armature core is, therefore, a direct addition to the resistance of the air gap. It will thus be dis- covered that, in order to keep down the width of the air gap, the thinnest possible conductor and the least possible insulation should be employed. But other conditions must be considered. We must first have 170 DRUM ARMATURE WINDING. turns sufficient to develop the electromotive force required. Sectional area (which means thickness) must then be allowed to carry the current safely. But it is obvious that a mistake may well be made in providing too great a sectional area in the con- ductors. To a certain extent this would return us a certain percentage of advantage by reason of diminished armature resistance, but the loss due to increasing the air gap resistance needlessly, would more than counterbalance this, and a loss would result from having the conductors larger (deeper) than necessary. The precautions regarding current density refer, of course, to heat in the wires. If the armature be wound with only one layer, and ample ventilation is allowed, 2,000 amperes is a small current density. Many armatures are pushed far beyond this. There is, of course, a certain loss by reason of this heat ; energy is being dissipated. But it is assumed that there is a greater gain than loss in reducing the depth of the conductors to a minimum for reasons stated above. On the other hand, however, when there are necessarily several layers, heat is not easily dissipated, and the current density must be kept as low as possible. "Dead" and "Active" Wire on the Armature. A certain proportion of the length of wire wound upon a drum armature is always inactive. It does not come within the influence of the field and generates no electromotive force. This dead wire occurs at the ends of the cylinder. It is a necessary evil in every dynamo. Some means must be provided to carry the current across the diameter of the core. The most ready method is to simply carry the conductor itself across, and this is done in all armatures wound DEAD AND ACTIVE WIRE. 171 with wires or flexible cable. But in the case of larger armatures, when the conductors assume a more solid and less flexible form, this is impracti- cable. Half-circle segments, discs, and other devices are therefore employed, as exemplified in the con- struction of several dynamos described in these pages. Since the cross-diameter connections cannot be dis- pensed with, the builder's object must be to make them of as low a resistance as possible, so that very little energy is consumed in that direction. The active wire is that upon the sides of the core. In this position it moves well within the influence of the field. Every inch of the active wire is, therefore, to be calculated upon in estimating the electromotive force per foot of the conductor. The percentage of active conductor to the total varies generally from 30 to 60 per cent. In many cases it may be shown that portions of the cross wires, usually considered in- active, participate in the production of electromotive force, but the effect is generally so small, being due to oblique or " leakage " magnetic lines from pole to pole, that it may be safely neglected. The electromotive force in volts per yard of active conductor, varies with the intensity of the field and the speed. In some of the best dynamos yet built the mean intensity of the field in lines of force per square inch varies from 16,000 to 25,000. In the recent exhaustive tests of dynamos by the Franklin Institute, it was found that in an Edison dynamo, in which the field had a mean intensity of 25,000, the mean induction in volts per foot of conductor was 1733 an extremely high induction. Reduced to a speed of one foot per second, it was '0373 volt per foot. In low speed dynamos, with a moderately 172 DRUM ARMATURE WINDING. intense field, i volt per foot may be regarded as high, while from i to i'5 volt per foot is not uncommon in high tension arc lighting dynamos. With a circum- ferential velocity of 3,000 feet per minute, some tests of dynamos in this country, showed that with a moderate intensity of field the Edison-Hopkinson machine had -510 yard of conductor per volt evolved ; the Crompton showed *86o ; Kapp, -970 ; and Thom- son-Houston, 3*550. Circumferential Speed of Armature. The maximum peripheral velocity observed by good makers, may be taken as 3,000 feet per minute. This is very high ; 1,500 feet per minute is much more common. In the recent Franklin Institute tests, the mean velocity of the Edison (large) machine was 46*5 feet per second ; in the Weston (large) machine it was 37-4 feet per second. Lines of Force per Watt. The number of lines of force in the field per volt-ampere of output varies greatly. This may be regarded as the relative efficiency of the field. It may be said to vary from 5,000 in common dynamos to 10,000 in machines with wrought-iron magnets. Cross section of the Armature Conductor per Ampere. This is most usefully expressed in square mils. It varies greatly in different armatures. In those adapted for the rapid dissipation of heat only 400 square mils are generally allowed per ampere of current evolved. In closely wound armatures, where heat is apt to prove injurious, from 600 to 800 square mils per ampere are usually allowed. Percentage of the Diameter of Armature occupied by Windings. In the case of drum armatures this varies in different machines, from 8 to 1 2 per cent. LOW RESISTANCE ARMATURES. 173 Low Resistance Drum Armatures. Although we have seen that the resistance of an armature may be reduced to any required extent by the simple device of connecting its turns in multiple, yet that method has not found much favour in the building of very large machines. The construction of low- resistance armatures presents no difficulty in reference to that particular quality, per se, but other questions arise when large currents are to be carried by conductors of considerable cross-section in an armature. In the early Edison machines, the first of their kind devised for low tension electric lighting, solid bars of copper were used. Many other dynamo builders also con- structed armatures having heavy square bars as conductors, and at that time the method was con- sidered excellent. The discovery, however, that it was nearly impossible to keep such armatures cool, and that the chief cause of this was the generation of eddy currents in the bars, has changed the course of progress in that direction. There was not only the difficulty of heat to be dealt with that was trouble- some in frequently breaking down the insulation. It was soon discovered that this heat meant waste, and that the old-fashioned dynamos exhibited, under test, a very low efficiency. The method of winding adopted by Edison in his incandescent lighting armatures is described by means of a diagram in the patent specification. This shows a symmetrical arrangement, as in the Alteneck method, but the number being an odd one it is difficult to understand that it could be worked in connection with brushes bearing upon the collector at diametral positions. In the earlier dynamos a multiple of seven was generally taken as the number of paths or sec- 174 DRUM ARMATURE WINDING. tions of the armatures, up to forty-nine in the large machines used for street lighting in London. In those machines the conductors consisted of thick copper bars, except for the cross-connections at the ends. These were effected through a series of copper discs. Each disc had two projecting lugs, for purposes of connection to the bars and to the collector segments. The discs were carefully insulated from each other, and from the shaft. Since the introduction of suitable insulated ribbon copper the solid bars have fallen, to a large extent, into disuse. Strap copper is more easily manipu- lated than bars, and it is unnecessary to adopt the expedient of disc cross connections at the ends of the core. Mr. Edison's aim in inventing the disc device appears to have been, according to the specification, the reducing of the resistance of that portion of the windings necessarily idle, and passing across the ends. It may be pointed out, in reference to low resist- ance armatures, that their chief advantage in electric lighting by incandescence lies in the self-governing power they give the dynamo. Since the resistance of the armature is but a mere fraction of that of the external portion of the circuit (in many cases it is merely nominal) any increase or decrease in the ex- ternal resistance will have but a nominal influence upon the armature. This is especially so if the latter be run in a field of great intensity. The latter should be so powerful that any self-induction of the armature is easily overcome. Such machines are generally shunt wound ; and so perfect are they that in many cases it is unnecessary to employ compound winding ol the magnets, or any regulating device exterior to the machine. ALTERNATING CURRENT ARMATURES. 175 Circumferential Speed of Drum Armatures. The maximum circumferential speed of drum armatures may betaken as approximately 3,000 feet per minute. Yards of Conductor per Volt of Electromotive Force. The length of electric conductor wound upon arma- tures for each volt in the total potential difference varies greatly. Mr. Kapp gives the following figures to exemplify this : Edison-Hopkinson (Drum) -510 yards. Crompton (Cylinder Ring) -860 Kapp (Drum) '97O Thomson-Houston (Sphere) 3-55O 5 > Alternating Current Armatures. The most important class of this type appears to be the disc dynamo. Many excellent machines have, however, been constructed for alternating currents having drum armatures. We may consider the disc armature first. There is one leading feature in most of the machines of this kind a multipolar field. This is essential in view of the necessary rapidity of the alternations. Since the currents are required to recur some hun- dreds of times in a second this can only be accom- plished by increasing the number of poles between which the coils pass during one revolution. There are in many of these disc machines from twenty to fifty magnetic fields. When a single coil or section passes once around the circle it cuts the lines of force a proportionate number of times, and thus, by a com- paratively slow period of revolution, a disc armature may give rise to a high rate of alternations. The sectional windings of a disc armature generally 176 DRUM ARMATURE WINDING. assume the form of wire whirls, or snail-like spirals, or of narrow, disc-like coils. The course of the con- ductor in these disc coils almost invariably occurs in alternate directions in a series of coils, as represented Fig. 66. Right and Left-handed Arrangement of Alternator Coils. in Fig. 66. This is essential in view of the fact that the magnetic field is also of an alternating nature. But in armatures of very low resistance the coil sec- tion is dispensed with altogether, the conductors merely forming radial bars or loops. The multipolar field is common to all of these. Iron-cored Bobbins, mounted near the edge of a disc, belong to an early period of the history of the dynamo. They are at the present time superseded. But it may be of interest to inquire into the chief cause of their abandonment. Both in the alternating dynamos of Wilde and Siemens (the early experimental ma- chines of the latter) iron proved troublesome on account of heat. In other words, the rapid or sudden reversals of polarity gave rise to a great deal of waste in the form of eddy currents. Even the device of lamination, although successful enough in cases where the magnetic changes were slower, was unsuccessful. But if we regard the magnetic field as a space across ALTERNATING ARMATURES. 177 which lines of force are projected, and if we look upon the iron-cored form of armature as a means of filling the field with a body capable of conducting the lines of force across from one pole to the other, it is an easy transition of thought to the narrow magnetic field of Faraday's famous disc dynamo, and the abandonment of iron altogether. Faraday rotated a copper disc between two closely-approaching poles. We can obtain stronger effects by doing the same thing with a series of narrow coils. Siemens' dynamo, built upon these lines, had no iron in the armature. The bobbins were attached to the arms of a " spider " of gun metal, rotating with the shaft. The coils were as narrow disc-like as possible. The magnetic field from pole to pole was as thin as practicable. This dynamo proved that by concentrating the field, and by narrowing our con- ductors to the required form, it was not only practic- able, but advantageous to dispense with the inductive assistance of iron. The construction of alternating armatures greatly simplifies the dynamo. The mere fact that iron is dispensed with means a great deal more than the bare fact implies. We have to deal only with conductors cutting a magnetic field : and, in our calculations, we have to deal only with the magnetic permeability of air and copper. Coil, Ribbon, and Loop Alternating Armatures. We are not dealing here with the construction of the dynamo as a whole ; but it appears advisable to revert, for a moment, to the multipolar field of alter- nators. It consists, in nine machines out of ten, of two opposing crowns of poles, as already illustrated and explained (p. 87). Siemens* and Wilde's field N 178 DRUM ARMATURE WINDING. consisted of two circular cast iron frames, set in a vertical plane. Projecting from the adjacent faces of these were two circles of iron cores, carrying exciting bobbins. The frames were set so close that only a narrow space separated the opposing poles. The latter were so connected that alternate polarities were presented, and in each it faced a S pole. Hitherto we have spoken of the field magnets as fixed, while motion was given to the armature. But an opposite arrange- ment is not unknown. Mr. Mordey, in his famous alternator, has shown that an inverse arrangement is not only practicable, but, as embodied in his machine, a considerable advantage. If we take a coil wound in a particular direction, and pass it between the poles of a magnet a current in a certain direction will circulate in it. If we now reverse the polarity of the magnet, so that the pole that was N becomes S, and again pass the coil, an opposite current will be exhibited. Hence, in a mul- tipolar field, with alternate poles the armature coils must be connected or wound in alternate directions, otherwise the current in the first coil will nullify that in the second, and so on. As the kind of alternating armature under discus- sion consists of a disc or its equivalent, carrying coils, it will be obvious that that arrangement presents peculiar facilities for working at either high or low electromotive force, and for varying the resistance to correspond. 1. If all the coils be of the finest wire, and if they be connectedin series, as represented diagrammatically in Fig. 67, the E.M.F. will be the highest possible. 2. If the coils consist each of but one turn, and hat of the thickest conductor, and they are connected ALTERNATING ARMATURES. 179 in multiple arc, they will act as one coil, and the E.M.F. will be a minimum, while the resistance Fig. 67. Coils in Series also be the lowest possible, or, as in Fig. 68, when each coil consists of several turns. Fig. 68. -Coils in Multiple Arc. 3. If an intermediate arrangement is desired, it can be got by connecting either type of armature partly in multiple and partly in series. i8o DRUM ARMATURE WINDING. The conditions under which the electromotive force can be varied are exactly similar to those appertain- ing to the arrangement or grouping of voltaic cells. Fig. 69. Coils or Cells in Series. If, as in the diagram (Fig. 69) we connect the ten cells in series, we obtain the tension due to that Fig. 70. Coils or Cells in Multiple. number (i.e., if the electromotive force of one cell be one volt it will, under the above conditions, be in- creased to ten volts for the combination). If, on the other hand, we desire only the elec- tromotive force of one cell, but the current often, the grouping must be as in Fig. 70. If, for example, a voltage of 3 be desired, with the current of four elements, they must be grouped as in Fig. 71. Coil grouping is effected in the same way, each coil being re- garded as having a given elec- tromotive force. The Coils. Siemens' coils consisted of ordinary in- sulated wire of round section wound upon wooden Fig. 71. Intermediate Arrange- ment. ALTERNATING ARMATURES. l8l bobbins. The sides of the bobbins were pierced for ventilation. For arc lighting, by alternating currents, the whole armature was connected in series. The field was excited by a separate continuous current machine. For low resistance working the same machine is either connected partly in series and partly in multiple, or is wound with thick copper ribbon, and connected in series. Ferranti's alternator, at the suggestion of Sir Wm. Thomson, was at first furnished with an armature composed of a thick copper bar, bent into eight loops, radial from the centre. It has been likened to a flower of eight petals. Here we have no coils, but we have conductors cutting lines of magnetic force, which amounts to the same thing a kind of divided Fara- day disc. In this dynamo the poles of the field are elongated pear-shaped in the radial direction, so as to influence as great a radial depth of the conductor as possible. The patent specification shows the eight loops as connected in a single circuit. Later on the solar conductor was found to give trouble from heat- ing due to eddy currents. Lamination was resorted to with much success. As now constructed the arma- ture is composed of copper strap, wound in thirty layers, all carefully insulated. But these compose three complete circuits of ten strips each. The circuits are connected in multiple. The insulation is so perfect that with copper strap J inch in width the total width is only f inch. The magnetic field is therefore rather less than f inch in width. The armature windings are carried by a gun-metal star keyed to the shaft. The arms of the star are in two sets, between which the armature is mounted by the aid of cross-bolts. The ends of the armature con- 1 82 DRUM ARMATURE WINDING. ductor are led away to a pair of insulated gun-metal collecting rings, rotating with the shaft. Dynamos having armatures of this type, and with zig-zag con- ductors, are now comparatively common. Mordey, as stated above, finding that an armature of this description had certain faults, took a heroic step, and reversed the arrangement. When an arma- ture of the Ferranti type is running at a high rate of speed (the one under consideration was 30 inches in diameter, and moved at the rate of 1,400 revolutions per minute) certain axial undulations are very apt to show themselves. This is especially the case if there be not absolute uniformity in the tangential drag of the field. It is difficult to impart rigidity to a loop armature. Any wavy tendency in the axial line would necessitate greater clearance between armature and poles, and this implies a greater than propor- tionate loss of effect. Mr. Mordey conceived the idea of making this type of armature a fixture. To effect that purpose necessitated a different arrangement of the coils, and it implied the revolution of the mag- netic field. With the latter we are not at present concerned (see p. 88), but the coiling claims particular attention. The armature consists of a rigid ring of gun-metal, to the interior of which are attached the coils. These are eighteen in number, of the form of a V> with a rounded point. The coils com- pose a circle. They consist of copper strap, wound upon porcelain cores of the required form. In this case the conductors are in the form of individual coils, which are connected together in series or multiple, as may be required. Being laminated, there is little tendency to heating. Drum Alternator Armature. The coils in this case ALTERNATOR COLLECTORS. 183 consist of conductors wound usually in the form of a long, narrow link, and laid upon the surface of an iron core in the form of a drum. The link-like coils are made as long" as the drum, and are laid side by side, either upon insulating cores, or bound by clamps at the ends. In either case the radial depth of the hanks is made as small as possible in order to diminish the width of the air-and-copper gap. The field magnets are of an elongated type, having a length equal to that of the drum. The drum alter- nator takes several forms, which we cannot discuss here ; but the dynamo lately brought out by the West- inghouse Company is a good example of this class of machine. Ring Alternator Armature. This type is too im- portant to be passed over, although few examples of it are to be found. If a Gramme ring be so connected that its sections lead the current in opposite directions throughout, such a ring may be mounted in a multi- polar field. The connections to the external circuit must, however, not resemble those in an ordinary ring. The sections may all be connected in series, and the terminals taken to a simple pair of collector rings rotating with the shaft, or they may be put in multiple in any arrangement that will develop the required E.M.F. Alternator Collectors. There are one or two ma- chines in which the field magnets are excited by the current from the armature, but the application of this principle is becoming more and more rare. Mr. Wilde employed this device in his machine by diverting the currents from two or three of the armature bobbins to a separate commutator, the function of which was to impart to them a uniform direction. The currents 1 84 DRUM ARMATURE WINDING. from the remaining bobbins were passed direct to either a commutator or a simple collector, as the case might require, and utilised for external purposes. But most alternating current dynamos are separately excited. A small continuous current dynamo is used for that purpose. It is sometimes attached to the shaft of the larger machine direct, and runs at the same rate of speed as in Mordey's alternator. Since Fig. 72. Wilde's Commutator for Alternating Currents. the intensity of the magnetic field does not depend upon the work thrown upon the armature these machines are almost self-regulating, and are easily controlled. The collectors used for taking the current from the alternating armature consist simply of a pair of copper, gun-metal or phosphor-bronze rings. These are insulated from the shaft and from each other, They revolve with the shaft. The terminals of the MACHINES WITHOUT COLLECTORS. 185 external portion of the circuit consist of the usual pair of flexible metallic brushes. Wilde's commutator, intended to give the whole or any part of the alternating currents a uniform direc- tion, consisted of two cylinders of copper, cut in the form of crown wheels, the teeth of one cylinder fitted between the teeth of the other. They were insulated from each other, and from the shaft. There were an equal number of teeth and coils. A pair of brushes were used to collect the currents, one in advance of the other, the width of a tooth. It will be clear that upon the revolution of the commutator the brushes would press upon alternate teeth, or cylinders. The change from tooth to tooth took place at the instant of change of current direction in the coils. In this way the current in the brushes was determined in one direction. This arrangement is represented in Fig. 72. Another form of the alter- nating commutator consisted of an ordinary collecting cylinder, as used for continuous current dynamos. Every alternate bar was connected to one extremity of the armature coils, while the intervening set of bars were in like manner connected to the other extremity. In this way the brushes would exchange terminals as often as the currents in the coils were reversed. Machines without Collectors or Commutators. The collecting ring, or the commutator, is only required because the armature revolves. If the latter becomes a fixture, as in Mordey's machine, no collector is required in taking off the armature current, But in that case it is plain that as the field magnet revolves instead of the armature a pair of ring contacts will be required to pass the exciting current through the field magnet. 1 86 DRUM ARMATURE WINDING. Unipolar Dynamo. The name " unipolar" has been applied to that class of experimental machines designed to work upon the principle of Faraday's disc. Few, if any, of this class of dynamo have proved successful. The neces- sity for collecting the currents from the periphery of the armature is one of the practical objections to this type. The very low electromotive force seldom exceeding five volts is another objection. The de- velopment of the "unipolar" dynamo has been so slow, and the results, so far, so unsatisfactory, that it cannot be regarded as having passed through the experimental stage. CHAPTER XII. ECONOMIC DESIGN. BEFORE the scheme of a new dynamo can be laid out, certain conditions must be known. (1) The speed or number of revolutions of the arma- ture per minute. This will depend upon the nature of the proposed machine. If the dynamo be intended for ordinary purposes on land, a high rate of speed is permissible. The speed has a great deal to do with the size and the cost of the machine. The higher the speed the smaller the dynamo. But there is a prac- tical limit to the number of revolutions per minute. It is determined, first, by the nature of the motor to be used in driving, and secondly, by the require- ments of the armature shaft and commutator. Speed- ing above 1,500 revolutions per minute is uncommon; so is speeding below 500 revolutions per minute. A very usual rate is 1,000 for a land dynamo and 800 or even less for a machine to be used aboard ship. Let us suppose that a dynamo is required to be run at 1,000 revolutions. (2) The electromotive force required must be known that is, the E.M.F. required for useful purposes. This will depend upon the work to be done. For arc lighting it may have to be very high, and for 1 88 ECONOMIC DESIGN. incandescent lighting very low. For the latter it will depend upon the voltage of the lamps. These may be roughly regarded as taking an E.M.F. of either 50 or 100 volts. Dynamos yielding the latter E.M.F. are very commonly used for electric lighting. Over and above this pressure, allowance must be made for two causes of loss, or drop of pressure. These are (a\ the internal resistance of the machine itself, and (b) the resistance external to the machine, in the form of leading wires. The former will de- pend upon the kind of machine, but an allowance ot 10 per cent, is frequently made for it. The latter can to a certain extent be arranged to suit the dynamo, but an allowance of 10 per cent, is commonly made in respect of it. Working upon these lines the dy- namo would have to develop 120 volts, no of which would be available at the terminals for external purposes. For use aboard ship 50 to 80 volt slow speed dynamos are very commonly used. Current, as we have seen, will depend, according to Ohm's law, upon (i) the electromotive force, and (2) the resistance of the whole circuit. The number of amperes can therefore be got in the ordinary way. The resistance must be such that at least half an ampere is available for each 100 volt lamp, and about one ampere for each 50 volt lamp. The total electromotive force of the machine de- pends upon (i) the number of magnetic lines that flow from pole to pole of the field magnet, through the armature, (2) the number of turns of the armature wires in series at one time, and (3) the peripheral speed of the armature. If we represent the total E.M.F., or that actually generated by the armature, by the letters E a , DYNAMO DESIGN. 1 89 And the proportion of it available for external useful purposes at the terminals of the machine by e , The internal resistance of the dynamo armature and field magnets by R t -, The external resistance, or that due to leading wires and lamps by R^, The current in the armature by C a , And the external current (or proportion of the in- ternal) passing through the lamp circuits by C e , C a = ? = Total current, Ri + R, p And C e = - the external current. R e In the scheme of a new dynamo the magnetic cir- cuit is the most important consideration. This should be composed of the softest iron, and it should be as short as possible. Its permeability to magnetism, as we have already seen (p. 54), should be as great as possible this implies the greatest thickness of iron. If cast iron be used a much larger section, in accord- ance with its permeability, must be employed. The magnetic circuit may be taken as a line passing through the length of the field magnet and across the armature. Professor Jamieson* proposed the following method of dealing with the magnetic circuit, and its relations. The mean length of the magnetic circuit is indicated by the letters L m . The air spaces (between armature periphery and magnet poles), are marked L a8 . The path of the divided magnetic circuit through the armature is called L a . * Paper read before the Institution of Engineers in Scotland. ECONOMIC DESIGN. The magnetic circuit L w has a magnetic reluct- ance.* where 2 = Kapp's coefficient for the initial specific magnetic reluctance of soft wrought iron. The num- ber 3 to be used if the core be of cast iron. L OT = the mean length of field magnet circuit in inches. S m = sectional area in square inches (at right angles to L, w of magnet core). Reluctance of the A ir Spaces. These L fl8 , L s , have a reluctance where the number 1440 = Kapp's coefficient for the specific reluctance of air and copper ; when wrought- iron magnets are used (1800 to be used with cast-iron magnet cores and pole pieces, and 1500 with wrought- iron cores and cast-iron pole pieces). ~L as = depth of each air space in inches (and since there are two spaces, 2 L as is inserted in the formula). s as = sectional area of air space or surface area of each pole piece in square inches. Reluctance of Armature Core. The armature core circuits, L a ,' L a , have a magnetic resistance where L a = mean average length of armature core magnetic circuit in inches (if there was but one path instead of two we should have to multiply by the co- efficient 2, but 2-t^- = Lj. * " Resistance " in the original paper. ECONOMIC DESIGN. igi S a = cross sectional area of armature core in square inches, == twice the radial depth x length of armature core. Total Magnetic Reluctance. The total magnetic reluctance of the complete magnetic circuit is therefore I440 The Magnetic Lines* The total number of Kapp lines, K L , of magnetic force which pass through the magnet and air space can therefore be calculated by dividing the ampere-turns (A x T Mto ) on the mag- net windings by the total magnetic reluctance in the magnetic circuit, AX T WW) , K L = A X 1440 2 -^-* a - Electromotive Force in Armature. The E.M.F. de- veloped internally in the armature winding is E a = K Ln X T alc X N^. X 10 6 , where E a = E.M.F., developed in armature in volts, * Kapp lines. To give the magnetic line a convenient magnitude, Mr. Gisbert Kapp proposes a line = 6,000 C g s magnetic lines. The number 6,coo is made up of two terms, viz., 60, which enables revolutions to be counted per minute instead of second ; and 100 to bring down the measurement of the magnetic lines to reasonable numbers, or C g s lines c g s lines ^>o X IO ~~ 6,000 Then, I Kapp line 6,000 c g s lines. Since there are 6-4514 square centimetres in a square inch, I Kapp line per sq. in. = >O zz: 930 C g s lines per sq. centimetre. 6-4514 I Q2 ECONOMIC DESIGN. K Lfl = Kapp lines which only pass through arma- ture or the useful field, T aw = turns of armature wires in series, counted all round core. N ar = number of armature revolutions per minute. Example I. Let us now apply the foregoing formulae to the design of a single field compound dynamo. Let the dynamo be furnished with a long shunt, and be of 6,400 watts (external power pj, when driven at 1,000 revolutions per minute. First, let us determine the resistance, current, fall of potential in armature and magnets, and percentage loss of power in the armature, shunt, and main field magnet coils, using the same symbols as before. Given E e = 100 volts C e = 64 amperes. Resistance. Then R e = - = -' = 1-55 ohm. Suppose we agree to a loss of about 10 percent. of the total power in the dynamo, or say The electrical efficiency of the dynamo = 90 p. c. . . 90 per cent. : 100 per cent. :: 6,400 P w : x 9 .-. total power = x = 7,100 p w . Let R= .= Let R s = R a x 1,000 = -077 x 1,000 = 77 w. Let R OT = 75 % R a = | x -077 = -058 w. Now the external current = current in armature field and magnet main coils less the current in shunt. Currents, or c e = c' a C 8 . E 100 v. -D . But .-. 64 a = C a 1-3 a, KAPP LINES IN ARMATURE. 193 C fl =:64 + I'3, = 65*3 amperes. Fall of Potential in Armature. C rt R = 65-3 x 077, = 5*02 volts. Fall of Potential in Magnet Main Coils, = C, M ' R m = 65-3 X 0-58 = 378 volts. Total fall of potential in armature and magnet series coils. = C a or c w (R fl X R J, = 65-3 (-077 + -058) = 8-8 v; .-. E a = 8-8 -f E e = 1 08-8 volts. Percentage loss of power. In armature = C a 2 R a = 65*32 X "077 = 330 p w ::ioo:x rt x a = 4-63 per cent. In shunt coils r= c s 2 * R s = 1*3 # 2 x 77 ze; = J 32 P W ; .-. 7100 P W : 132 p w :: 100 :x^ x s = r86 per cent. In main coils = C w 2 R M = 65-3 2 x -058 x / = 3 '5 per cent. Totalling the different percentage losses we have : In armature . X = 4*63 per cent. In shunt coils, x, = i 86 In main coils . x w = 3-5 9-99 p. c. or, say, 10 p. c. Kapp Lines in Armature Core. Before substituting the above data in Kapp's formula we must agree upon the turns of wire upon the armature at the under- O IQ4 ECONOMIC DESIGN. stood 1,000 revolutions per minute. Let there be 36 commutator bars of 36 sections of wire in arma- ture, which has been found sufficient to give a current of practically uniform E.M.F. The number of turns of wire in each section of the armature depends upon whether we use double or single winding, and upon the current and the resistance of the armature wire. As we shall see further on, from our trial drawing and calculations, we can get in six turns of wire to each section. * T a? 36 X 6 = 216 turns of armature wire. Let N ar = i ,000 revolutions per minute ; now E a = K L x T aw x N ar x io 6 . K = Efl T aw X N ar X IO 6 - 108-8 v. _ " 216 X 1,000 x 1 06 ~~ 5 3 7 ' say = 50 Kapp lines in Armature Core. To obtain a certain number of Kapp lines or mag- netic induction in an armature core, it is necessary to give a greater magnetic intensity to the field magnet core, owing to the unavoidable leakage of magnetic lines which do not pass through the armature core. Dimensions of Field Magnet Core. In ordinary practice it is usual to assume that only about 80 per cent, of the field magnet lines pass through the armature core. Therefore the Kapp lines \^\ field magnets are 80 per cent. : 100 per cent. : : 500 : x = 625. We must now ascertain the dimensions of the field magnet core to carry the 625 Kapp lines. Suppose we consider the case of field magnet to be cast iron throughout (poles and core). DIMENSIONS OF ARMATURE CORE. 195 A safe working density is 9 Kapp lines per square inch. .-. s m 69-4 square inches. 9 =. 9-4 inches diameter (if round). In practice it is found that a dynamo magnet bobbin should be in length about i-J- times its diameter to give the necessary space for winding or ampere turns. .*. 9'4X 1*25 = 1175 inches long. Dimensions of Armature Core. It has been found advisable in designing the dimensions of the arma- ture core of a dynamo having a field magnet of the form we are now considering, to make the diameter of its core slightly larger, and its length slightly less than the diameter of the field magnet core. Therefore, calling the diameter of the Gramme armature core 10 inches, its length 9 inches, and allowing a density of 20 Kapp lines per square inch of core section, since it is made of the best permeable wrought iron, We have - = 25 square inches total cross section of armature. .. s a =: 25 square inches. Allowing 20 per cent, of total space for insulation between laminated plates in armature core we have 80 per cent. : 100 per cent. :: 25 \x = 31-5 square inches. .'. I = 1575 square inches in each half. " n == x '75 inch radial depth of core. Magnetic Reluctance of Field Magnet. Now, 196 ECONOMIC DESIGN. drawing armature and field magnets to scale, and al- lowing 2\ inches for depth of winding on field magnet bobbin and clearance for armature, we find the mean length of field magnet core L m = 44 inches, and remembering that in a formula for the magnetic reluctance of this part of the circuit we have to use a co-efficient of 3 instead of 2, seeing that the core is of cast iron, We have _ 3 _44__ I9< 3 69-4 Magnetic Reluctance of A ir Space. With two layers of insulated conductors having a cross section of '08 inch deep, by *2 inch broad, including the covering, we find the total depth of air space on one side between pole pieces and armature core (allowing -14 inch mechanical clearance equal to *3 of an inch. Consequently, 2 L as = 2 x *3 = *6 inch. The bore of pole piece will be equal to the diameter of the armature core + 2 ~L as = 10 inches -}- -6 inch = 10-6 inches. It is good practice to allow the corners of pole pieces to form an angle of 30 with centre of arma- ture. The angle embraced by each pole piece will therefore be 180 30 = 150, which gives us a circumferential length of say 14 inches for each pole. And since our armature core is 9 inches long, and it is unusual to make the pole pieces broader than this length, we have S ag = 14 inches x 9 inches = 126 square inches. Hence R= 1800 2L * RELUCTANCE OF ARMATURE. 197 = 1800 2 X 126 Magnetic Reluctance of Armature. Referring to scale or full sized sections, we find by measurement that L fl = 15 inches. We have already determined s fl to be 25 square inches. Consequently R a - S a =-11 =-6. 25 - R, 4- R + R = i'9 + 8'5 + '6 = 1 1 Kapp units of magnetic reluctance. Ampere Turns. From formula for cast iron, K - = - A " = 625 (gross Kapp .-. A X T mw = K L (R M + R as + Rj 625 X II, = 6,875 total ampere turns in shunt and main field magnet coils. Proportioning of Ampere Turns between Shunt and Alain Coils. The total ampere turns have now to be divided in proper proportion between the series coils and the shunt coils of the field magnet windings. In order to do this so as to give the desired form of characteristic curve, we must have recourse to actual experiment. The following method is carried out by many dynamo builders : i . A workshop bobbin or experimental coil, with a known number of turns of wire is kept for every size of dynamo machine made. This bobbin is put on to the magnet core in circuit with an amperemeter, and is separately excited by another dynamo or by stor- age cells. The dynamo to be wound is run at the igS ECONOMIC DESIGN. normal speed with the external circuit R e , equal to that of shunt, viz., 77 w., and with the voltmeter placed between the terminals. The exciting current through the experimental bobbin is now gradually increased until the required number of volts is ob- served on the voltmeter ; e.g., suppose the experimen- tal bobbin to have 500 turns, and the amperemeter reads 8^25 amperes when the normal voltage of 100 volts is reached, then the ampere turns of shunt wire A x T^ = 500 x 8-25 = 4,125 ampere turns. 2. Connect up the armature of the dynamo being constructed to a resistance equal to the joint resist- ance of the shunt and the normal lamp circuit through an amperemeter, and run the dynamo at the normal speed. Now increase the exciting current in the experimental bobbin until the normal voltage of 100 volts and normal armature current of 65*3 amperes are both obtained. At the same time observe the exciting current. But the total required ampere turns = 6,875, and from experiment we found that 4,125 ampere turns produced the requisite E.M.F. * 6,875 4,125 = 2,750 ampere turns left for series coils. 3. The normal current at full load required to pass through the series coils was found to be 65*3 amperes. Consequently the number of turns required in the series coils > = 42 about. 65-3 4. From experiment i we found that 4,125 ampere turns give us the required excitation to produce the PROPORTIONS OF THE CONDUCTORS. 199 normal E.M.F., and from our former calculation we found that the current in shunt .-. 4*1^^3,! 73 turns. * o C g = 1*3 ampere. But the series coils are also carrying the i -3 ampere required for the shunt when dynamo free. ' 3,i73 (42 turns x 1-3 a) 3,173 54 = 3,119 turns on shunt coils. 5. All we now have to do is to so proportion the size of our series and shunt coil conductors that they shall carry the necessary currents required in each case at the rate of not exceeding 1,000 amperes per sectional area square inch. For armatures this may be, and is in practice increased to even 3,000 am- peres per square inch without undue overheating, owing to the cooling effect of the air carrying off the heat generated in the revolving armature. Mere radiation only acts on the field-magnet coils : there- fore the sectional area is of necessity much greater. CHAPTER XIII. DYNAMO GOVERNING. ONE of the earliest discoveries in the evolution of the dynamo was that the position of the brushes upon the collector or commutator might be made to determine the output of electricity therefrom. When the brushes were set exactly upon the neutral line, the current was found to be at its strongest. When they were moved to one side or the other the current fell off in strength. But although this plan was often resorted to in the early machines, it was not always satisfac- tory. Such a method may probably be left to control the current, but it is not sufficient to maintain a fairly constant electromotive force. Regulation by Shifting Brushes. Hence, regulation by means of shifting brushes was soon found better adapted to the case of running arc lamps in series than to that of glow lamps in parallel. In the former case a fairly constant current is very desirable, and the E.M.F. may be allowed to vary somewhat. In the latter case unvarying potential is of the greatest importance, aud this cannot be secured by merely shifting the brushes. Many attempts have been made to utilise the brush- shifting method for lighting purposes. A great dif- BRUSH-SHIFTING GOVERNOR. 2OI ficulty had, however, to be overcome. The real effect of shifting the brushes is to upset the electrical balance of the armature. Since its two halves are connected in multiple (in most armatures), each half yields an equal share in the potential and current. This occurs when the brushes occupy the neutral, or " line of best collection." When, however, they are moved away, the current in certain of the coils upon one side begin to oppose the current in equal coils upon the other side, the result being neutralization of the output of those coils. But those coils are still active. The result of moving the brushes is to rup- ture their circuit before the proper time, and a great increase in the sparking is the result. Normally, with the brushes upon the neutral line, one at least of these coils on each side will be short circuited by the brush ; to shift the latter is to give these "dead" coils life, which is discharged in a shower of sparks. This destructive sparking soon deterred inventors from introducing the method of shifting brushes, even for arc lighting. But the designers of the Thomson- Houston machine saw a way out of the difficulty, which was at least applicable to their dynamo. The chief objection to the sparking was its destructive effect upon both brushes and collector segments. This could, however, be obviated by blowing out the sparks by means of an air-blast, and to this automatic device alone is due the success of the Thomson- Houston dynamo in its feature of self-regulation. It is probably the only form of machine in which brush shifting has proved a success. In this dynamo the automatic moving of the brushes is performed by means of a regulating magnet in effect somewhat 202 DYNAMO GOVERNING. similar to the arrangement employed by Maxim in America, and by Statter and others in this country.* Governing by Speed. The output of a dynamo may be controlled to some extent by changing or varying the speed. This fact has led several inventors to devise gear the function of which is to control the speed by governing the steam engine. This method has not, however, come into general use, and it has many defects. Governing by Variable Resistance. Scarcely less satisfactory is the old method of maintaining a cer- tain resistance in the circuit, and varying this to meet the exigencies of the work. This method in- volves waste of energy in proportion to the other- wise useless resistance included in the circuit, and is generally so crude that it is seldom resorted to. Variation of the Magnetic Field. It may be said generally that the most successful method of regulat- ing the output of a dynamo consists in varying the density of the lines of magnetism in the field. This has a direct result upon the electromotive force evolved by the armature. It may be done in several ways. The most obvious method is, of course, to vary the "strength" of the field magnet by controlling its excitation. This opens up a wide field of inquiry, as it is possible to effect the required object by different methods, as separate excitation, shunt winding, com- pound winding, and the later composite windings. All of these we shall briefly describe, although some of them have already been spoken of (p. 44). Before, however, entering upon a consideration of the methods based upon varying the exciting current, it will be of * A detailed description of the Thomson-Houston regulator was given by Mr. Kapp in the Engineer for August 28, 1885. HAND REGULATION. 203 interest to mention at least one ingenious means of varying the density of the lines of magnetism with- out in any way altering the exciting current. We refer to the method proposed and carried out by Mr. O. Firth. Regulation by varying the Width of the A ir Gap. Firth's method consists, briefly, in so arranging the two halves of the field magnet upon suitable slides that they may be separated or brought together, so varying the distance between the pole faces and the armature. The separation is effected by means of a screw gear, composed of a single shaft, upon the two halves of which are cut right and left-handed threads. These work in nuts attached to the magnet cores. The arrangement is extremely simple. From experi- ments made with a dynamo of this kind, it is shown that when the field magnet is closed up, and the machine is yielding its full output, as shown upon the voltmeter, a considerable separation of the two halves can be made before an appreciable effect is shown upon the E.M.F. Hand Regulation. Governing by hand consists in varying a resistance placed in the field magnet cir- cuit by that means. It usually refers to separately excited dynamos. Since the exciting current is never very great, the loss involved in controlling it by wasting the surplus in the resistance coils in the form of heat is more than counterbalanced by the advantages gained. This may be effected automatic- ally, although it does not appear that automatic regulation carried out in this way has met with general approval. Governing by hand may be ap- plied to shunt-wound machines. This is Edison's device. The magnets being shunt-wound have a 204 DYNAMO GOVERNING. certain power of self-regulation. But in order to meet extreme demands for E.M.F., a set of resistance coils are kept in the shunt circuit. These are switched out as the potential of the dynamo begins to fall (by reason of the switching in of lamps). This method, like every other depending upon resistance, is to a certain extent wasteful. Edison has also operated this device by means of an automatic governor. In cases of Separate Excitation the usual practice is to vary the resistance of the exciting machine's mag- net windings. Separate excitation is becoming very common in the running of large dynamos. A small continuous current dynamo is reserved for the pur- pose. The method of governing the output of the main dynamo by controlling the exciting current of the exciter, is considered one of the best. Resistance coils are employed for this purpose. Since the cur- rent exciting the small dynamo is but a fraction of the whole to be controlled, the loss in resistance is sufficiently small to be of little moment. This con- trol is generally exercised by hand. But it is a very common practice to arrange matters so that one con- tinuous current dynamo shall furnish the current required for exciting the field magnets of several dynamos. It will be obvious, therefore, that the above method will not always be applicable to such a case as this. For any variation in the current given by the exciter will react impartially upon all the dynamos fed by it. This may be desirable or not, according to the nature of the case. It may answer if all the dynamos are feeding into a common circuit, and call for an augmentation or decrease of mag- netism simultaneously. But if they are feeding into independent circuits such a method cannot be other RESISTANCE REGULATORS. 2O5 than confusing. In the latter case, therefore, the control must obviously apply to each working dy- namo separately. Hence, variable resistances are placed in their field-magnet circuits for this purpose. Resistance Regulators. These variable resistances consist in most cases of coils of iron wire, arranged as before explained and illustrated (p. 43, Fig. 18). The wire is sufficiently thick to prevent over-heating. (Nos. 8 to 1 6 of the standard wire gauge are gener- ally used.) It is coiled upon some incombustible substance, with the turns well separated. One of the most usual methods is to coil the wire upon iron gas tubing, a layer of abestos millboard being interposed between them to prevent short circuiting. The coils may vary from a fourth of an ohm up to several ohms, rising by fourths. A series of studs with a contact lever working from a centre are then arranged so that any resistance from zero to the full effect may be switched into the circuit. The coils will heat. Care is therefore to be taken that (i) they are arranged upon an incombustible base, preferably slate ; and (2) that they are so wound and separated that the heat may pass off into the surrounding air. Soldered joints are to be avoided in such apparatus. It should be so constructed that danger from fire is impossible, even if the coils should by accident be fused. Such arrangements are known as rheostats, or resistance frames, according to the forms they assume. In many cases ribbon iron is used instead of round wire. This form of conductor presents more surface to the cooling effects of the air than round wire. The rib- bon is generally arranged in a zig-zag or corrugated form, so that a considerable length of it may be in- cluded between the sides of the "frame," the con- 206 DYNAMO GOVERNING. ductors being arranged in a number of parallel lengths across a square or oblong framework. In such forms of rheostat, contact plugs are generally used to throw in and out of the circuit the lengths of ribbon. This form of rheostat is now not so gener- ally used as formerly. In some special cases German silver is employed instead of iron to form the con- ductors. Series Dynamos may be said to be regulated by one of two methods. The first of these, that of shifting the brushes, has been already spoken of. The second is the more generally practicable. It consists in establishing a shunt wire across the magnets. That is, a variable resistance is connected across from the terminal where the main current flows into, to the terminal from which the main current leaves the magnet's circuit. This constitutes a short circuit, but it must present sufficient resistance to obviate the cutting off of too large a proportion of the current. When the dynamo is required to work at its full capacity, the resistance of the shunt would be equal to infinity, or no current would pass through it. When the dynamo is required to work at a small proportion of its capacity, the resistance of the shunt would be very much less, and a considerable pro- portion of the main current would flow through it. This method of governing a series dynamo is pre- ferable to the old plan of varying the resistance ot the main circuit, but it is distinctly inferior to the device of winding the magnets themselves with wire so fine that it may in itself constitute a shunt. This is, in fact,* * Series winding has already been spoken of at p. 45, and again at p. 197. SHUNT WINDING REGULATION. 207 Shunt Winding, and it is intended to act as a self- regulator of the potential. The effects of shunt winding have already been briefly considered (p. 46). The magnets of the machine are wound with coils of wire so fine that the resistance of this circuit is frequently 1,000 times that of the armature. The result is that very little current flows in the shunt when the work portion of the circuit presents com- paratively little resistance. Hence, if the dynamo is feeding one arc lamp, the resistance of this compared to that of the shunt being small, leads away the greater portion of the current generated, and very little flows around the magnets. If another lamp be switched into the work circuit, the resistance of that portion will be increased ; less current will flow in it, but more current will flow across the shunt, and so strengthen the magnet. The dynamo will thus begin to evolve a stronger current. If another lamp be switched in, a still greater proportion of the current will flow in the shunt, and the dynamo will evolve a still greater current. In this way a shunt dynamo may be said to regulate perfectly with regard to current (although, for other reasons, a constant- current dynamo has not yet been invented). Similarly, if the dynamo be feeding glow lamps connected in multiple across the mains, its electromotive force will be fairly maintained, even within wide limits of load. But it is impossible in such a machine to prevent the electromotive force from falling slightly. As more and more lamps are switched across the mains, the resistance external continues to fall, and the current to increase. Now, increased current in the mains implies diminished current in the magnet's circuit, and the result is, of course, a slight drop in the 208 DYNAMO GOVERNING. electromotive force evolved. This is shown by the " characteristic " of such a dynamo having a falling tendency. But this slight falling off in the power of the machine may be very easily regulated by inserting a variable resistance in the shunt cimiit. This is operated, as before, by hand. When a small load is on the dynamo the whole of this resistance is in circuit. As the load increases, the lamps will begin to dim. It may here be mentioned that a drop of 5 per cent, in the potential will show greatly upon the lamps. The variable resistance is then diminished, allowing a greater proportion of the current to flow in the magnet's circuit, and so restoring the balance. A very little variation of the shunt resistance will suffice to regulate a shunt dynamo. This is especially the case if the armature's resistance is small. If the latter presented no resistance there would be, theo- retically, no drop in the potential. Although a shunt dynamo regulates so well under varying conditions of load, it is found to perform badly under variable conditions of driving. If the steam-engine be unsteady, a shunt machine will be less satisfactory than a series machine in feeding arc lamps. This is due to the great self-induction of the shunt coils, wound as they are upon iron cores. It takes time to effect a change in such a circuit. While an increase or diminution of speed will instantly disturb the lamps, it will not so quickly affect the current in the shunt. Hence the lamp circuit is much more sensitive to the variations of the speed than the magnet's circuit. If the changes were slow, the shunt would presently recover its balance and meet the exigencies of the moment ; but, as it performs but sluggishly, it fails to meet momentary variations. REGULATION BY COMPOUNDING. 20Q Shunt dynamos are, therefore, unsuited generally for feeding arc lamps, especially when the driving speed is apt to vary. On the other hand, a shunt machine performs excellently when the only changes involved are those of current and electromotive force. The arrangements of shunt winding have already been spoken of at p. 46. Regulation by Compounding. It has been said that the slight drooping tendency of the characteristic by a shunt machine may be obviated by employing a variable resistance in the shunt circuit. Many attempts have been made to render this part auto- matic, and with the greatest success. But a still better method of regulation has been obtained by combining the attributes of the series dynamo with those of the shunt. The series dynamo has the merit that it is almost free from the evils, due to self-induction, mentioned above. The storing-up tendency of the long shunt coil is absent, or nearly so, in the short, thick series windings. The effect is that the self-induction of lamp circuit and magnets are more nearly equal. This allows of considerable variations in the driving or speed, without their being apparent in the lights. In other words, the magnet part of the circuit responds to a change of speed as quickly as the lamp part of the circuit, and both feel it equally. When a dynamo is "compounded" by furnishing its magnets with a few turns of series winding in addition to the shunt coils, it immediately partakes of the character of the series dynamo in respect of non-sensitiveness to inequalities in driving. The real effect and function of the series turns is to compensate for the slight tendency to lose electromotive force P 210 DYNAMO GOVERNING. when there is an increased demand for current in the lamp circuit. If a shunt dynamo could be provided with an armature having no resistance, it would yield a constant electromotive force, whether the exterior resistance was small or great. This condition is, however, impossible, although dynamos have been constructed having conductors so thick in the arma- ture that the resistance of this part is merely nominal. Nevertheless, these machines will lose some of their electromotive force when the external current becomes a maximum, because the volts in the working portion of the circuit are but a proportion of the whole, and not the whole. This fault can, however, be overcome by sending the main current round the magnet so as to reinforce the field as soon as the current in the working part of the circuit becomes large enough to cause a drop in the electromotive force. It has been said that the falling off is due to the increased current. This increase of current, if it be sent round the magnet, however, reinforces the magnetization, and in this way it is possible to make a compound wound dynamo increase in power faster than the load can be switched on, pro- vided we are dealing with glow-lamp lighting in parallel, and that the load is gradually increased. The " characteristic " of a compound machine would show a perfectly straight line ; that is, the volts would be maintained the same while the amperes of current varied from light to full load. It is, indeed, comparatively easy to give the characteristic any desired shape. But most makers prefer to give the electromotive force a slight rise at full load. A well- designed compound machine will, therefore, show a COMPOSITE FIELD REGULATION. 211 slightly upward-sloping characteristic, as depicted in Chap. XV (p. 229). The arrangement of compound winding has been already spoken of at p. 49, and again at p. 65. "Composite" Field Dynamo. This method of gov- erning a dynamo was first suggested by Deprez. It appears to have had a more extended application in America than elsewhere. It consists in taking an ordinary series wound machine, and adding thereto additional exciting coils fed by an independent source. It is, indeed, a combination of series and separate excitation. One of the most interesting examples of the com- posite field method applied as it has been to an alternating- current dynamo occurs in the new " composite " field machine of the Thomson-Houston system. The armature of the dynamo is wound for alternating currents, and it revolves in a multipolar field for that purpose. These currents pass direct to the lamp circuit. But below the alternating-current windings (sometimes, however, side by side with them), and directly placed upon the core of the armature, occur a few turns of conductor forming an independent winding. The (necessarily alternating) currents from these turns are passed to a commutator upon the shaft. The function of this is to commute them to a continuous direction. They then pass into the exciting coils of the field, and constitute a self- excitation. The field magnets are, however, pro- vided with two sets of coils. The second set is reserved for the current from a separate exciting machine. The self-exciting current may be regarded as a shunted portion of the main current. The machine may be regarded as a " compounded " 212 DYNAMO GOVERNING. alternating-current dynamo, of which we do not appear to have any examples in this country. In another form of the machine the self-exciting coils are wound upon all the armature cores except two. These are situated directly opposite to each other. They are excited by the current from the separate exciting dynamo. The main object in all such com- binations is to secure an initial and independent field, which, being independent of the variations in the main current, affords every facility to render the dynamo self-regulating. Constant Current Regulation Impracticable. It will be observed that most of the methods of governing here described have for their object the maintenance of a constant potential, and are therefore adapted more especially for incandescent lighting. But many attempts have been made to regulate for constant current. So far these endeavours have not been attended with success. Electromotive force is the attribute of the dynamo, and can be predetermined. Current, on the other hand, depends entirely upon the total resistance in the circuit. The nearest method we have to constant current governing con- sists in the combination of a shunt machine with a separate source of excitation, acting in independent coils. CHAPTER XIV. OUTPUT AND EFFICIENCY. THE electrical activity of a dynamo, or, as it is some- times called, its electrical horse-power, can be readily determined, provided two matters are known. These are, first, the " terminal voltage," or the volts of electromotive force indicated by a voltmeter placed across the terminals ; second, the " amperage," or the number of amperes, or volume of the current indicated by an amperemeter put in the circuit. In the case of a series, compound, or separately excited dynamo, the voltmeter may be simply connected across from one terminal to the other, so preventing the armature from generating a current. In the case of a series dynamo it must either be temporarily separately excited, or the resistance of any leading wires used allowed for. This would be called running the dynamo upon open circuit. It is assumed that the fractional current set up through the voltmeter coil may be neglected. The product of the volts into the amperes gives the rate of working, or the power of the machine. Power, or electrical activity, is usually expressed in terms of the unit of power the watt. A watt is a volt-ampere. The product of volts into amperes, therefore, gives the electrical effect in watts ; 746 watts = i electrical horse-power. If we compare 214 OUTPUT AND EFFICIENCY. the electrical activity (expressed in this way) with the mechanical power expended in moving the dynamo we have a determination of the "efficiency" of the dynamo. If a machine absorbs 100 horse-power from the engine, and returns an electrical activity of 90 electrical horse-power, its commercial efficiency is, of course, 90 per cent. The actual electrical efficiency of the machine will be greater than this, because it has to overcome the resistances of its armature and field magnet. A certain portion of its efficiency of con- version is, therefore, expended (and wasted as heat) in the machine itself. The total electrical effect includes this waste, and is generally known as the electrical efficiency. The useful, or external electrical effect is spoken of as the commercial efficiency. The volt-ampere or watt is a convenient unit in terms of which to express the capacity of a dynamo. Machines may be specified as so many watt machines. A dynamo yielding 10 volts and 100 amperes may be called a thousand watt machine. Similarly, a dynamo giving 100 volts and 10 amperes would be a thousand watt machine. It would still remain a thousand watt machine if its E.M.F. were raised to 1,000 volts and its current diminished to i ampere. The proposal, by the Board of Trade, to form a unit of electric lighting, having a magnitude of 1,000 watts or volt-amperes (also called, according to the decimal system, a kilowatt) has led many makers of dynamos to designate their machines as so many Board of Trade unit machines. Thus, a 10 unit dynamo would mean a machine capable of furnishing 1 0,000 watts. But dynamos are still in some instances designated by the makers' numbers or letters. It is still more misleading to speak of a dynamo as a so- OHM'S LAW. 215 many-lamp machine. A thousand lamp dynamo might possibly imply that the output was a thousand amperes at 50 volts, or it might imply something very different. Incandescent lamps take so many watts per candle-power. The consumption varies greatly, from about 3*5 to 5 watts per candle, and no two lamps, even by the same maker, can be absolutely equal in their consumption, save by accident. Arc lighting dynamos are very frequently spoken of as so many lamp machines. In this case the candle-power, effective, of the lamps should be known, but this varies with carbons, length of arc, and so on. Hence, the only practicable method of designating a machine's output is to give both its volts and amperes, or its watts. In dealing with the output of dynamos through certain resistances, Ohm's law gives the necessary formulae. C is generally used as the symbol of current (or amperes) ; E of electromotive force (or volts), and R of resistance (expressed in ohms). The law may be variously stated : C = ? ; R = - ; and E = R X C R C Or, in other words : Amperfes = ^ ; Ohms = Yol * s ohms amperes ; Volts = ohms x amperes. The electrical activity or rate of doing work varies, in a circuit, as the square of the volts. If a volt be applied in a circuit whose resistance is an ohm, the current will be an ampere, and the work will be a volt-ampere or watt. If the electromotive force be doubled, or two volts, the current will also be doubled, so that the electrical activity will be four volt-amperes 2l6 OUTPUT AND EFFICIENCY. or watts. The electrical activity varies, as amperes x volts, and, therefore watts (or power) = amperes x volts. The electrical activity or power also varies as the square of the current, for if the current in any given resistance is doubled, the electromotive force will also be doubled, and the power will thus be fourfold, or watts = c 2 R. Electrical activity varies directly as resistance. If a resistance be doubled, with a current to be pre- served constant, the electromotive force must be similarly doubled, or volts = amperes x ohms. Electrical activity varies inversely as the resistance when the electromotive force is constant. If a circuit of a resistance of 10 ohms has in it an E.M.F. of 10 volts, there will be a current of 10 amperes, or 100 watts, of electrical work. But if the resistance be halved, or 5 ohms, the amperes will rise to 20, the volts remaining the same as before, so that the power will be increased to 200 watts. The Electromotive Force lost internally. As already stated, the electrical activity yielded by the machine for useful (or external) purposes is not the whole of the converted energy. A proportion is wasted in maintaining the current throughout the internal circuits of the machine itself. It is convenient to distinguish between the sources of loss. These are, usually, the armature (which always presents a cer- tain resistance) and the field magnet coils, which generally offer considerable resistance. Experience dictates that certain proportions should be observed between these resistances. Armature resistance should be kept down to at least -5-V tn f tnat f tne external (or interpolar working) resistance. This applies to most cases of POWER ABSORBED INTERNALLY. 217 ordinary working, and gives the proportion between armature and lamp circuits. In compound and series machines the resistance of the series coils should never exceed that of the arma- ture. In the best machines it is considerably less. In shunt-wound machines the resistance of the shunt should be at least 400 times as great as that of the armature. In well designed machines it is frequently as great as 1,000 times. This applies equally to the shunt coils of compound dynamos. Hence, the current that can be set up round the shunt coils will seldom exceed 5 per cent, of that passing in the external or useful portion of the circuit. Series machines are subject to the same law as the voltaic battery. The electrical effect is at a maximum when the current in the armature and in the external portion of the circuit are equal. Po?ver absorbed internally. In a well designed com- pound dynamo the watts lost in the armature, shunt coil and series turns, seldom exceeds 10 per cent, of the total. It is distributed somewhat as follows : armature, 4 per cent. ; shunt, 4 per cent. ; series coil, 2 per cent. Horse-power transmitted to Dynamo. This is measured usually by a transmission dynamometer, applied to the belt. The horse-power absorbed by the machine must be ascertained before attempting to determine its rate of conversion. This is generally effected by means of a dynamometer of the Hefner Alteneck type, as used by Dr. J. Hopkinson* in his tests of the efficiency of the Edison-Hopkinson See Phil. Trans, of the Royal Society, p. 347, 1886. 2l8 OUTPUT AND EFFICIENCY. machine, or by indicator diagram taken from the engine in the usual way. It may be useful to remark that although designers of dynamos endeavour to attain a high rate of con- version and commercial efficiency, a useful output as high as 90 per cent, of the energy absorbed in driving them is not a common occurrence. In Dr. Hopkinson's tests of the above-mentioned machine, 93 per cent, was shown, the remainder being lost as follows : power lost in armature, 3-17 per cent. ; lost in magnet windings, r66 per cent. ; lost in core, 1-94 per cent. These figures show that as far as efficiency is concerned, there is little further to be gained in the future development of dynamos. CHAPTER XV. GRAPHICAL RECORDS. MECHANICAL engineers are in the habit of exhibiting the working of a steam engine by means of a curved line. This is well known as an indicator diagram. The application of the same principle to the dynamo machine is due to Deprez, and to Dr. Hopkinson, who first pointed out its advantages in a paper read before the Institution of Mechanical Engineers in April, 1879. This paper contained several results deduced from tests made in this way upon a Siemens series dynamo. But while, in its application to the case of the steam- engine, the curve is usually obtained automatically by means of a pencil, moved under the control of a diagram indicator, in the case of a dynamo it has to be plotted out from certain values obtained under different conditions, as of speed and load. Since the publication of this paper the graphic method of re- cording experiments with dynamos has come into general favour. It is doubtless to be preferred, in most instances, to an algebraic method, over which it has many advantages. It shows, at a glance, the performance of a machine. It indicates unmistakably not only its excellences and faults, but can be made to exhibit the electrical horse-power it evolves, and its relation to the most economical speed. The dia- 220 GRAPHICAL RECORDS. gram shows the relation subsisting between the magnetism, the armature, and the windings. There is scarcely a question of importance that cannot be elucidated by means of a curve. The graphical method has doubtless commended itself to practical men because of its intrinsic advantage of being very easily understood. It forms a line-picture of the working easily read by persons unversed in even the symbols of algebra. In 1 88 1 M. Deprez, who had developed the method, and applied it to many useful purposes, suggested the term characteristic curve, a proposal which has met with general adoption. Hence it is common to refer to a particular curve as the " characteristic " of the dynamo. A graphic record is intended to show the result of a series of experiments. It may prove useful to de- scribe the method followed in obtaining the curve. The paper upon which the line is to be drawn is to be divided into small squares, by means of straight lines drawn at right angles to each other. This paper is to be obtained commercially, already lined, with con- siderable accuracy, under the name of squared paper. In one of the most useful forms of the curve two sets of values are obtained by experiment upon the machine. These are plotted as dots, as represented in the diagram (Fig. 73, p. 2 2 2), according to their position in relation to two scales laid off at right angles to each other, vertically and horizontally. Hopkinson's curve was obtained from observations in which the abscissae, measured horizontally, represent the number of amperes of current, and the ordinates, shown vertically, the corresponding values of the electromotive force. CHARACTERISTIC CURVE. 221 In the drawing of these curves a sufficient number of points, or results, are first obtained. These are denoted at their exact corresponding positions in the squares, according to the scales, and a curved line is carefully drawn, so as to pass through, if possible, all the points. This is most easily done by means of the aid of an elastic steel ribbon, so bent as to pass through the points, and a line run through them with pencil or pen. The divisions of the paper may be taken to represent single amperes or volts ; or, if the values are likely to be large and the scale limited in size, tens of each may be supposed to be included in each division. But it will be obvious that if the squares are only small size it will be a difficult matter to subdivide them into ten parts in endeavouring to find the exact point for any obtained value between one and ten, and so on. Hence, squared paper upon which curves are to be drawn should be large. Each division should be of a good size, and, if practicable a division should be taken to represent a single ampere or a volt, as the case may be. We have before (p. 54) referred to the use of these curves by both Rowland and Hopkinson in recording their experiments on the magnetic permeability of iron, and it will be obvious from this that any two sets of results may be scaled upon the horizontal and vertical lines, as intensity of magnetism and mag- netizing current, permeability and magnetic induc- tion, and so on. Attempts have been made to apply an automatic indicator to the dynamo, but the instru- ment has not yet come into general use. In Dr. Hopkinson's curve (Fig. 73) the speed was kept constant. The electromotive force depends upon the speed, the turns of the armature wire, and 222 GRAPHICAL RECORDS. the intensity of the magnetic field. Since the speed and the turns of the armature wire did not vary, the steep part of the curve, showing a rapid rise in the electromotive force, can only be attributed to the increasing intensity of the field. This is shown to bear a very significant relationship to the total, or 90 80 TO CO 50 40 30 10 \to > 1 Q ^-~~~ -#r- +S ,*<* j / / / / / / / I Q 1C 1O 30 4O 50 GO 7 Amperes. Fig- 73- Characteristic Curve. magnetizing, current. The curve fulfils its purpose in exhibiting graphically the relationship between the current and the electromotive force under those con- ditions. Keeping the speed constant, the current was varied simply by inserting resistances in the circuit that is, inserting a high resistance, and gradually diminishing it as in the following columns figures HORSE POWER CURVES. 223 which correspond with the points plotted in the diagram. It must be remembered that the volts and amperes must be drawn to the same scale in forming the curve. VALUES RELATING TO GRAPHICAL RECORD IN FIG. 73. Resistance in Ohms. E.M.F. in Volts. Current in Amperes. 8-3 3'95 0-48 5'33 7'73 i-45 4-07 68-4 16-8 3-88 70-6 18-2 3-205 79-5 24-8 3-025 81-1 26-8 2-62 84-4 32-2 2'43 83-8 34-5 2-28 84-6 37" 1 2-08 87-4 42-0 Horse-power Curves. But the curve is sufficient to afford still further information. If drawn to a scale it can be made to show the horse-power evolved. If we multiply the amperes by the volts the product represents the electrical activity in watts. In the electrical horse-power there are 746 watts. Hence it is practicable to calculate the horse-power relating to any given point of the curve, because that point indicates at once both values required. But the values may exchange names, and the rule still holds good. If we, taking the first case, find that we can set off horse-power points at the intersection of the two values which, multiplied together as above explained, give the required 746 watts, it will be evident that there will also be a point where the smaller value may be exchanged for the greater, and that this will give us a line of horse-power. For example, horse-power lines will pass through all those points in the diagram where volts into amperes 224 GRAPHICAL RECORDS. will give 746, or multiples of 746. Either 37-3 volts and 20 amperes, or 20 volts and 373 amperes, will correspond to one horse-power. It is usual to plot out these electrical horse-power lines, so that a separate curve can be given for each horse-power, as represented in Fig. 75. Thus the graphic record, 10O\ \ \ \ \ \ 10 10 30 4C 50 60 10 Amperes. Fig. 74. Characteristic with H.-P. Lines. so far, affords a great deal of information relating to the dynamo of which it is a characteristic. But the work-picture thus drawn can be still further elabo- rated. The curves just spoken of are known as the horse-power characteristic. Curve of External Electrical Activity. The main VARIABLE SPEED CURVE. 225 curve first plotted out gives obviously the total electro- motive force of the dynamo. The available E.M.F., or that at its terminals, is somewhat smaller than this. If the E.M.F. required to overcome the resist- ance of the armature and that of the field magnets be deducted from the total, another curve is obtained considerably within the main curve. This is marked external to distinguish it from the total electrical activity. Hence, in calculations from a diagram it is the external curve that is to be considered if these considerations are to apply only to the activity in the exterior or useful portion of the circuit. This curve is known as the external characteristic. Line representing Internal Resistance. By deduct- ing the electromotive force required to overcome the resistance of armature and field magnet coils for different values, a line corresponding to the internal resistance can be drawn. The points cut by this line show at a glance the volts lost corresponding to dif- ferent strengths of current. Dr. Hopkinson plotted out the internal line by multiplying the resistance of the armature by the current which represented the electro- motive force required for overcoming it, and by deduct- ing this from the total. Hence, loss due to internal resistance can be represented by either the curve of external activity or by the line of internal resistance. Variable Speed Curve. If the speed be varied, as was done by M. Deprez, a series of curves is obtained, exhibiting the relation of speed to electromotive force. Up to a certain point, critical for each dynamo, the E.M.F. is, generally speaking, proportional to speed. In the case, however, of a series dynamo the critical speed may be said to vary somewhat with the resistances in circuit. 226 GRAPHICAL RECORDS. Graphic Record of Shunt Dynamo. In a series machine, as the external resistance is diminished, the current is increased, and the E.M.F. rises rapidly, until the magnets are saturated. The E.M.F. then falls off for any further diminution of the external resistance, showing a drop in the continua- tion of the curve. Hence for considerable variations of external resistance the current is maintained fairly constant. Thus in the characteristic just given the current only rises to the extent of 20 amperes, while the E.M.F. increases from o to 70^6 volts, and while the resistance, as shown in the table (p. 223) varied from 8*3 ohms down to 3*88 ohms, the better the proportions of the series machine the less the varia- tion in the current, the steeper the slope of the curve. If we now consider the case of a shunt dynamo running on open circuit, its initial interpolar E.M.F., if intended for incandescent lighting, might be as high as no volts. As current is drawn from the external circuit by gradually diminishing the inter- polar resistance, or in other words by switching in lamps, the amperes should rise in proportion ; but the resulting diagram, if the figure be plotted, would not show a practically straight line. There would be a downward tendency, due to a falling off in the E.M.F. ; and this, in turn, would be due to the in- creased current. In a shunt machine having an excessively small armature resistance, and a magnetic circuit of the softest iron, the line would be practically straight, since under these conditions there would be little or no drop in the E.M.F. at full load, The defect of ordinary shunt machines, when tried in in- candescent lighting, is that the E.M.F. is not main- CURVE DUE TO A SHUNT. 227 tained constant. But the slight drop may be compen- sated for by a few turns of the main circuit around the magnets, constituting a compound of series and shunt winding. If a shunt machine diagram be plotted out, com- mencing with the machine on short circuit, working through a short, thick wire, and gradually increasing the resistance, a rapidly ascending curve is obtained, in which volts and amperes equally participate. This slope may be regarded as corresponding to magnet saturation. As the external resistance is still further increased, the volts continue to increase, but there is no increase in the current. As the resistance is carried still further the current falls off, as is usually shown by the curve bending back to the scale of ordinates, since the lost volts or drop of potential at full load is due simply to the fact that the armature plays an appreciable part in the total resistance, it may be shown that this corresponds to the angle formed by the drooping line, or is proportional to the vertical ordinates so enclosed. A compound dynamo, as we have already seen, can be made to give constant potential, so that a diagram plotted from it would show, first, a rise of the line to the critical speed (or condition of full excitation), and then a sharp curve to the right, continuing thence as a straight line along the scale of abscissae up to the full number of amperes the armature would safely evolve. The proportion between the shunt and series windings can be set forth in a graphic record. As we have already seen in Chap. IV., the series or main coils should have a resistance rather more than 300 times (400 times is better) that of the arma- ture. The effect of the series windings must be such 228 GRAPHICAL RECORDS. as will result in such a diagram as is shown in Fig. 75, in which ohms of resistance are the abscissae and volts the ordinates. This shows the relation between the E.M.F. at the terminals and the inter- polar resistance of a compound wound machine. The shunt curve begins at o, and rises finally to 1 10 volts. no ICC 90 80 70 eo 50 4V 30 20 \ 01 2345675 Fig. 75. Characteristics from a " Compound" Dynamo, The series curve begins at no volts and falls to o. If the series and shunt coils are properly proportioned they will each give, at the same speed of armature, a curve crossing a certain point. In this case it is 55 volts. Their curves will cross at that value, and at 50 volts such a dynamo would give constant COMPOUND DYNAMO CHARACTERISTIC. 229 E.M.F. If a diagram be plotted, as in Fig. 76, in which the current is taken as ordinates, and the volts as abscissae, the horizontal part of the line should have no tendency to droop even at full current. If it falls its curve represents lost volts, and shows that the series coils are insufficient. If it rise slightly at full load that circumstance will, in practice, be found advantageous rather than otherwise. It is indeed the present practice to rather over-compensate, CO 10 20 30 40 50 GO 7O 80 90 100 110 120 Ampere* or Icunps. Fig. 76. Characteristic of a Compound- wound Di'namo. so as to give such a curve. But if the line should rise considerably, say, so as to show an increase of ten per cent, in the E.M.F., it shows that the series coils are over-sufficient. It should, however, be pointed out that any change effected in the series windings is apt to upset the relation previously subsisting between them at a certain critical speed, and that the true compounding may be still further departed from, unless that relationship, shown in Fig. 75, be re- established. At pp. 286 290 are given two curves of magnetiza- tion, exhibiting the relationship between ampere turns and lines of force in the field of Kapp's dynamos. CHAPTER XVI. DYNAMOS IN SERIES AND PARALLEL. To combine the outputs of two or more machines in a common circuit effectively, calls for some consider- ation. It may be required to produce in a circuit an electromotive force of 100 volts. The machine power available may consist of two 50 volt dynamos, neither of which can do the work by itself. If, however, the machines can be run upon one circuit, similarly to two cells of a battery, their joint E.M.F. will be double that of one alone. This is series working. On the other hand a current of 100 amperes may be required, at an E.M.F. as low as that of one ma- chine only. Two machines are then to be coupled in multiple, which will have the effect of doubling the amperes while maintaining the volts equal to that of one machine. This is known as parallel or multiple working. Series Working. Let us consider the case of series running first, and that with series wound machines. Given the case of two dynamos of equal power, it would only be necessary to connect the -f terminal of the first machine with the terminal of the second. The SHUNT DYNAMOS IN SERIES. 231 combined E.M.F. of both will then feed into the common circuit. This arrangement only works well when the dynamos are of approximately equal power. It must not be forgotten that this is a severe test of the insulation of both machines. If a dynamo be built and insulated to withstand its own E.M.F. of say, 50 volts, the 100 volts that would result from the combination with another machine might break down that insulation, leaving the covering of the wires pierced in numerous points, where the potential difference happened to be greatest. Strictly speak- ing, series running is thus only applicable, first, to well insulated dynamos, and secondly, to machines not differing greatly in their volts. Shunt-wound Dynamos in Series. Shunt machines will not work well in series unless the two shunts be first put in series with one another. The two shunts are then to be treated as one long shunt. The same precautions with respect to insulation have to be observed as in the case of series machines. For reasons already mentioned, the running of dynamos in series is very seldom resorted to. But in some cases of arc lighting, where the build and insulation of the armature and coils are particularly well adapted for high potentials (as in Brush's dynamos) arc lighting is successfully carried out on this plan. At best, however, it cannot be regarded by engineers as anything better than a makeshift, in which a temporary use of two dynamos has to be substituted for one machine of the requisite E.M.F. Parallel Working. By the use of two dynamos in parallel circuit a gain of as much as 20 per cent, is frequently obtained. 232 DYNAMOS IN SERIES AND PARALLEL. That is, the combined current is stronger than the two currents, flowing in separate circuits, added together. Series-wound Dynamos in Parallel. A good deal of difficulty is experienced if it be attempted to connect machines simply in parallel ; that is, both + poles to one lead, and both poles to the other lead. Indeed, as thus simply arranged they cannot work to advan- tage unless they are of exactly equal voltage and continue to run at the same rate of speed. If one of the machines should have a lower E.M.F. than the other, the stronger machine will force part of its current through the weaker, thereby finding a partial short-circuit, and will ultimately reverse and drive it as a motor. For many years this difficulty stood in the way of parallel working with series machines, until M. Gramme pointed out that as it is impossible to maintain perfect uniformity of electromotive force in both machines, a path can be opened to take the excess from either, without interfering with the weaker dynamo. Gramme pointed out that if both the -f poles be joined to one leading wire (and both the poles to the other), the + brushes form practi- cally neutral points between the two dynamos except when there is an excess of E.M.F. on one side. Hence, if the two + brushes be connected across with a wire, the excess may find a short circuit by that path, instead of flowing through the weaker dynamo. This cross connection of the brushes may be applied to either the positive or negative side. It will be evi- dent that as the preponderating E.M.F. is short circuited, it will scarcely prove economical to run series dynamos not approximately equal in power and moving at the same speed in parallel. SHUNT DYNAMOS IN PARALLEL. 233 Series dynamos may be run without any difficulty by the simple expedient of causing one to excite the other's field magnet, and vice versa. This method has the additional advantage of acting as a constant current equaliser. Shunt-ivound Dynamos in Parallel. On the other hand, the running of shunt machines is very easily effected. It was first introduced on a large scale by Edison, who showed the principle as applied to in- candescent lighting, first in this country at the Holborn Viaduct lighting station. The nature of the circuits in this case is such that a reversal can only take place when the disproportion between the two machines is very great. For example, suppose one of the machines to cease giving current, the current from the other machine would flow through its arma- ture and convert it into a motor. But this never takes place under ordinary conditions. The require- ments of incandescent lighting are such that a pair of mains may, up to a certain hour, be supplied amply by one dynamo. The demand for current may then increase, necessitating the application of greater dynamo power upon the same circuit. The need for a fresh machine is indicated by the amperemeter denoting that the single dynamo is working up to its full capacity. Any further demand would, then, over- heat this dynamo. But it is impracticable to merely switch on a fresh dynamo without preparing it. If this were done the result would be disastrous to thq lamps, and might bring the whole arrangement to a standstill. The fresh dynamo is invariably "built up " before switching in. That is, the machine is set in motion and its circuit closed in a group ot lamps, or a rheostat. The resistance of this is varied 234 DYNAMOS IN SERIES AND PARALLEL. until the machine's amperes and volts agree with those of the first machine. At this point it is switched on to the mains, and immediately takes half the load. The temporary bank of lamps or rheostat is switched out at the same time. Compound-wound Dynamos in Parallel. It is prac- ticable to run two similar compound machines in parallel by merely adopting the above plan of causing each to excite the other's series exciting coils only. This is frequently done, but it is doubtful whether the device is applicable to the exigencies of an electric-lighting station. It has the disadvantage that, without loss, dynamos of different capacities cannot be worked together. If compound dynamos are simply connected in parallel, without resorting to the above device, they tend to overpower each other ; in other words, if one of the machines happens to gain the ascendency, it not only maintains it but begins to force or dam back the current of the other. Gramme's short circuiting method is, however, equally applicable to compound machines, and is now largely used in lighting stations, proving its perfect adaptation to the exacting requirements of such work. The device consists merely of a cross connection between the two + brushes of the machines. In lighting-station work, this connecting wire is provided with a switch. There is also a switch in each of the shunt windings, where they leave the brush. Another switch upon each machine is interposed between the main lead and the brush. These switches are required in " switching in " the fresh machine at the moment when the load upon the other has attained a maxi- mum. Let us suppose such a case. The switches ALTERNATORS IN PARALLEL. 235 of the working dynamo will, of course, be closed. The operation observed in throwing in the fresh machine is very simple. The machine is set in motion at the normal speed. Its shunt wire switch is then to be closed, thus exciting its field magnet. The switch on the cross connecting, or Gramme wire, is next closed, and finally its terminal with the main lead. If this is done in the order given, the lamps in circuit will evince no sign of any disturbance in the circuit. When it is required to cut out the auxiliary machine, the order of switching is to be the reverse of the above. Either shunt or compound dynamos tend to pull each other into uniform working. If one of the machines happens to slow down, its output will diminish in proportion, and it will demand from the engine less power. There will immediately be a tendency in this dynamo to race, while the temporary failure in its output throws more work upon the remaining machine, which will, in turn, tend to move more slowly. Thus, there is between the two dynamos a continual self or mutual adjustment, each pulling the other into work as required. It is evident that this tendency can be taken advantage of to run dynamos of different capacities in parallel, and this, indeed, is frequently done in incandescent light- ing. Difficulties, however, are more likely to arise in working very dissimilar dynamos together. Unless the " compensation turns " of the two machines bear a certain fixed ratio to their output, the machines may regulate very badly. The resistance of these turns should be inversely proportional to the respective capacities. Alternating-current Dynamos in Parallel. The usual 236 DYNAMOS IN SERIES AND PARALLEL. alternating current consists of waves or impulses. A wave, starting from zero, is impelled through the circuit, it reaches a maximum and curves downward to zero. Let us call this a positive wave. It is fol- lowed by a similar wave, again starting from zero, attaining its maximum and falling to zero ; but inas- much as this second wave is determined in the oppo- site direction to that of the first, we call it a negative wave. The period of time taken to begin and com- plete the back and forth waves, determined the phase of the dynamo ; the phase then, being practically the periodicity of the machine, is determined by the speed of the armature. This varies in different machines. But the number of armature and field-magnet poles also varies, so that one dynamo, having, say, twenty of each, would, at a given speed, have a periodicity twice as high as that of a machine with ten poles of each only. In order that these to-and-fro waves may be used to illuminate incandescent lamps, without there being apparent in the latter any sign of rise and fall of current strength, or reversal, the perio- dicity must be high. The symbol oj is generally used to denote perio- dicity or phase. Thus, it is said that an alternator gives 100 per second, meaning that there are fifty positive and fifty negative waves in that period of time. This periodicity occurs in different machines at rates varying from about 80 up to 300 (\> per second. The principles underlying the practicable working of alternating dynamos in parallel, were first published by Mr. Wilde, deduced from experiments with his alternating machine.* The theory has subsequently * Phi!. Mag. i. 1869. ALTERNATORS IN SERIES. 237 been elaborated by Dr. John Hopkinson and others, and a very full investigation of the subject is given in Hopkinson's paper.* When alternators were first put in parallel across the mains of an incandescent lighting circuit, it was believed that only machines having exactly equal periodicity could be yoked together. Subsequent experience, however, has shown that a dynamo having a period or phase recurring at some multiple generally a small multiple of that of another dynamo may be worked together with it. Alter- nators of the same periodicity are in practice gene- rally employed, because (it is to be presumed) there is less risk of confusion in switching in the fresh machine. Series Running impracticable. It is theoretically possible to work two alternators in series. But con- siderable difficulty will necessarily be found in main- taining the respective phases exactly the same. The difficulty of realising it in practice would be insuper- able for the following reason : there are, say, fifty periods of positive maximum and an equal number of periods of negative maximum, occurring in a second of time. If we suppose the two dynamos to arrive at positive maximum at the same instant, they will work perfectly so long as this holds good. But if one of the machines were to quicken its period, from any cause, to the extent of half of a phase or, in other words, become accelerated in speed the hundredth part of a second that dynamo would then be arriving at its negative maximum, while its fellow would attain positive maximum. Now, since two opposite and equal electrical currents neutralise each * Proc. Inst. Civil Eng. 1883. 238 DYNAMOS IN SERIES AND PARALLEL. other, there would be no current from either of the machines in the mains. We have supposed the extreme case of the dynamo becoming accelerated in speed, or its fellow lagging behind, to the full extent of half a wave, but in practice this would not be likely to occur all at once. But if from any cause one of the machines altered its phase in the minutest degree, the action of the other machine would be, not to pull it back into phase, but to throw it further and further out of phase, because more work would be required of the slow machine, which would tend to still further slow it. This is very clearly shown by Dr. Hopkinson, by graphic and other proofs. On the other hand, parallel working shows a state of things exactly the reverse of this. Alternating dynamos, in fact, tend to pull one another into phase or agreement. Switching in Parallel. The conditions under which alternators are used, are generally as follow : For feeding a system of incandescent lamps, the mains may have a capacity for the output of several dyna- mos. During the early hours of the evening only a small proportion of the lamps upon the mains may be alight. As darkness sets in, lamps are turned on and the output of, say, the single alternator, may have to be increased from time to time (either auto- matically or by hand government), until its load is as great as the dynamo is known to be capable of main- taining without overheating. It now becomes neces- sary to switch on another alternator. This obviously would not be done until the speed of the fresh machine had attained a maximum. But if the fresh alternator happened to be at exactly the same phase, and by a rare chance the same period of phase as the SYNCHRONISING OF TWO ALTERNATORS. 239 first machine, it would take half the load without in the least disturbing the brightness of the lamps, and once yoked together the two would work in perfect unison. Only, however, by chance would the tresh machine arrive at this exact condition or fall into step y and such a rare contingency is never relied upon. If switched in when not " in phase/' the fresh machine would, it is true, be quickly pulled into unison, but meantime the lamps would be certain to suffer very severely. Several rapid extinctions and relightings might take place, and in addition to the obvious disadvantages of this in public lighting, the machines would probably suffer injury to their insulation. Accordingly a plan for bringing the new machine into perfect unison with the working machine is essential, and the method adopted is aptly termed the Synchronising of Two Alternators. Various devices and methods have been employed in order to ensure that the two machines are working in perfect unison. Alternators are almost invariably separately excited. The first step, then, is to bring the armature up to full speed. Then to switch on a small exciting current and to gradually increase this until the ampere and volt- meters in the machine's circuit show volts and amperes agreeing with those of the working dynamo. In addition to these precautions, and sometimes indeed independent of them, a single lamp is used, through which only the fresh machine is put in parallel with the working machine. When this lamp is fully lighted up, and thus perfectly steady, the main switch is shut, bringing the two machines upon the same mains. If this is carefully done, even with 240 DYNAMOS IN SERIES AND PARALLEL. the aid of a lamp alone, no disturbance of the main lighting will ensue. These precautions are taken when dynamos are driven by belts, either from one or two engines. But alternators are frequently driven by direct gearing with the engine shaft, and the fresh dynamo is merely clutched on. If the clutch is positive, allow- ing of no slips, very little appears to be left to be done beyond so regulating the field magnet current that the armature shall develop the required electro- motive force. But in the case of a friction or flexible clutch, where slip may possibly occur, the machine should be treated as a dynamo driven by belting from an independent source. CHAPTER XVII. THE DYNAMO IN ELECTRIC LIGHTING. WHEN an alternating current dynamo is used, the two carbons in the arc lamp waste equally. It is therefore a simple matter to make such a lamp focus- sing, or capable of keeping its arc at one point. When dynamo currents were first used for practical arc lighting in lighthouses it was the alternating current that was employed. When this current is employed for incandescent lighting there is said to be a similar equalization of the waste inevitable in the carbon fila- ment. When a continuous current is employed there is a perceptible thinning away of the filament at one of the poles (the positive). The advantages to be derived in this way, however, from the use of an alternator dynamo are not sufficiently marked to warrant the exclusive use of alternating currents for glow lamps. In the early days of the Alliance machine the mag- netic field was obtained from permanent magnets. Later dynamos bear a certain similarity to the Alli- ance inasmuch as that they are almost invariably separately excited. There is this obvious advantage in the latter arrangement, that it affords an excellent means of controlling the electromotive force of the machine. Whereas the intensity of the field in a R 242 THE DYNAMO IN ELECTRIC LIGHTING. magneto machine was fixed, and depended upon the strength of the steel magnets, electro magnets are easily controlled, and the E.M.F. of the dynamo thereby raised or lowered by merely varying the ex- citing current. A device, having for its object the controlling of the magnetic intensity was formerly employed in the case of magneto machines. It con- sisted in placing a " divertor," composed of soft iron partially across the limbs of the magnet, so as to magnetically shunt off part of the lines of force, or in other words to magnetically short-circuit the magnet. The electromotive force of the alternating current dynamo can be altered by varying the speed of the armature, as well as by varying the exciting current, and both methods are in use in large distributing stations. Compensation Excitation of Alternator. But alter- nators are frequently excited by a portion of their own current. In this case a pair or more coils of the armature are put in circuit with the field coils, through a commutator upon the shaft. This method allows of the exciting current being varied by the insertion or withdrawal of resistances generally by hand. A com- pensated alternator is similarly but partially excited, the remainder of the exciting current being obtained from a small transformer in the main circuit of the machine, the alternating impulses of which are con- nected to a continuous current by means of a commu- tator upon the shaft, as before. The object of this recently introduced plan of partial excitation is to make the dynamo self governing. When properly arranged such a machine may be made to yield con- stant electromotive force. This is essential for the running of incandescent lamps. The fall of potential ALTERNATORS AND TRANSFORMERS. 243 when fresh lamps are switched in is very small, hence a weak compensating current suffices to maintain the potential. Compensated machines of the alternator type being only of recent intro- duction have not been extensively used. Alternators and Transformers. Alternating-current machines are now almost invariably (when used in large distributing stations) employed to feed trans- formers. The function of the transformer is to convert currents of high E.M.F. into currents of low E.M.F., or the reverse. Small currents under high E.M.F. are more easily carried to great distances than large currents under low E.M.F. That is to say, a small or thin conductor may be used to convey current under high pressure, whereas the same amount of electrical power conveyed under low pressure would necessitate a large or thick conductor. Thus, an alter- nator develops an alternating current of i, coo volts. This is conveyed in a thin conductor to the trans- former, when it (or a portion of it) is converted or reduced to a pressure of 100 volts, which is used to feed the lamps direct. The principle of the trans- former is almost identical with that of the ordinary induction coil. Ordinary transformers cannot be used with constant-direction current. Hence there is considerable advantage in the use of alternating currents for public electric lighting. So great indeed has been the success of the Ferranti, the Westing- house, and the Mordey transformer systems that this method of distribution appears likely to supersede most of the continuous-current systems. The alternating-current dynamos for working trans formers are generally excited, as before mentioned, by a small continuous-current dynamo Mr Mordev 244 THE DYNAMO IN ELECTRIC LIGHTING. attaches this " exciter " direct to the large machine's shaft. This plan (although very convenient) may possibly have some disadvantages, as it does not allow of the speed of the exciter being varied. In the circuit of the exciting machine, or in its own field- magnet circuit, is placed a rheostat, by means of which the whole of the current can be varied. By these means the output of the alternator is to a cer- tain extent under control. The alternator gives only alternating currents, collected off two plain rings revolving with the shaft (p. 99). Compound Dynamo in Incandescent Lighting. We have seen (p. 209) that a compound dynamo consists of a shunt machine to which a few turns of series winding has been added in order to compensate for the slight fall of potential due to the switching in of additional lamps. It is clear that if the number of lamps was always the same, a shunt-wound machine would prove all that could be desired for incandescent lighting, but such cases are extremely rare. Con- tinuous current compound machines have proved themselves perfectly adapted for installation working, where all the lamps can be worked off one dynamo, as in ship lighting. They call for no regulation. A well designed compound machine, in which the mag- netic circuit has low reluctance (and is therefore of wrought iron) should be capable of withstanding the following test. With one hundred lamps across the mains, all fully lighted up, any number of the lamps may be switched off without in any way affecting the remainder. Or, ninety-nine of them may be cut out without the change being visible in the hundredth. The same process may be reversed : one lamp may be burning across the mains, and ninety-nine more SHUNT DYNAMOS IN ELECTRIC LIGHTING. 245 may be switched in at once without the change being appreciably apparent in the single lamp. Another method of controlling the E.M.F. of a compound-wound dynamo is frequently employed for special purposes. The machine itself works as a shunt dynamo, the series winding being in the circuit of a separate smaller dynamo. This current is regu- lated either by hand or by some automatic device. There are still other methods and combinations, but they belong more to experimental regulation than to everyday practice. The Shunt Machine in Electric Lighting. In incan- descent lighting on a large scale, when continuous currents are used, as in Edison's system, the shunt method is preferred, and it is controlled chiefly by hand regulation, which has hitherto been found more trustworthy than any automatic device. Edison in- cludes a rheostat in the shunt circuit, the resistance of which can thus be varied to suit the requirements of the work upon the mains. But shunt dynamos in incandescent lighting have a considerable range of self regulation, and in many cases where the load does not vary considerably they are used with perfect success. Where, however, a large number of fresh lamps are switched in, there is a call for current; this is at once supplied, because the act of switching in fresh lamps in parallel is to reduce the external resistance, and a larger proportion of current flows in that division of the circuit. But this increased flow causes a drop in the E.M.F., which is not easily recovered by the dynamo at a constant speed. If, however, there be means of varying the resistance of the shunt the exciting current may be slightly in- creased. In cases where the shunt machine is found 246 THE DYNAMO IN ELECTRIC LIGHTING. to regulate itself within wide limits it will always be found that the armature resistance is extremely small. A shunt machine with a considerable resistance of armature is always a failure in point of self regulation on parallel circuit working. Shunt machines, having considerable self induction in the long magnet coils are very sensitive to inequalities of driving, and call for a constant speed. The Series Dynamo in Arc Lighting. The running of arc lamps in parallel has not proved practically economical, and in point of expense of energy cannot be compared with series running. While in the parallel systems of incandescent lighting the potential has to be kept constant within very narrow limits, in series arc lighting the potential will vary according to the number of lamps, but the current (usually of ten amperes) must be as nearly constant as possible. Numerous attempts have been made to render dynamo machines self regulating for constant current, but so far without success, unless we include the admir- able exterior device of 'shifting the brushes used by Professors Thomson and Houston, and by Maxim, and a few other regulators of the same nature. But this is a different thing from self regulation by means of exciting coils, as in a compound machine. What is required in series arc lighting is such arrangement of the windings as will enable the machine to give the same number of amperes, whether there be one or many lamps in circuit. Series wound dynamos are preferred for arc light- ing. They are less sensitive to inequalities of driving than shunt machines. The first experiments in street lighting by means of continuous currents were made with series machines, and it was then thought im- SERIES DYNAMO IN ARC LIGHTING. 247 practicable to work more than one lamp from one dynamo. If, however, means are employed to main- tain the current constant, it has been shown by Brush and Professors Thomson and Houston that a large number (sometimes exceeding fifty) can be success- fully run in a single circuit. Street lighting by arc lamps is generally worked in this way. CHAPTER XVIII. OPERATIVE NOTES. In Erecting large dynamos the magnetic joints must be made as perfect as practicable. The surfaces must be clean and " fairly " bolted, so as to come into general contact. Dowel-pins are generally furnished in such joints, and also in the basis of the bearings, so as to ensure proper alignment. Warping of cast- ings may occur by reason of unequal foundations. This is a very bad fault. Warping may, however, be caused by the bolting down of other parts than the base. In erecting it is best to observe the rule that no two portions of the ironwork are to be forced into contact by means of bolts or nuts. Joints should lie perfectly " fair " prior to bolting. Foundation-rails, or belt - tightening rails, must be very carefully levelled, and free from warping throughout their length. Alignment of Bearings. Bearings of axis, if not dowelled into alignment, must be so set that the periphery of the armature occupies an exactly central position in the armature chamber. On no account must the armature be allowed to touch either of the pole pieces. The shaft should not only turn quite freely by hand, when the boxes are bolted down, but should be allowed an end-play of at least one-fourth of HANDLING THE ARMATURE. 249 an inch. This assists in distributing the oil. As the armature shaft becomes heated in working it must not be fitted quite full into the boxes, otherwise the expansion will cause binding. The boxes should have spiral oil-distributing channels cut in them, or at the least one longitudinal channel in connection with the lubricator. Handling of Armature. Armatures admit only of the most careful handling. They should be lifted by means of the shaft, and in no case rolled over a floor. Brush brackets must be properly bolted together in the order generally indicated by figures stamped upon them, care being taken that the insulating sleeves, washers, or thimbles are put in their proper places, Brushes should be trimmed square, so as to bear equally upon the collector drum. They must be free from twist, which might cause them to bear upon the bars with one corner only. The touch must be flexible, and not too heavy. One of the most frequent causes of the destruction of commutators and collectors is the too heavy touch of the brushes. Collector bars are now generally made from lengths of copper or phosphor-bronze, hard drawn to section. Such bars will withstand a heavier touch than those of soft cast copper. When in work a new collector should be frequently wiped free from copper dust, and lightly touched with vaseline, or a mineral lubricant, until it acquires the hard, burnished surface which practically eliminates the chance of further wear. The best compound dyna- mos are now made so perfect that there is no sparking at the brushes, so that mechanical wear is the only matter to be looked after. Attrition, or dry cutting, is always due to a heavy touch of the brushes, and to 250 OPERATIVE NOTES. allowing copper dust or grit to accumulate beneath the point of contact, and to the want of lubrication. " Connectmg-up." Connecting of the coils and brushes and terminals will depend entirely upon the nature of the machine. A series dynamo is very easily connected. Shunt and compound machines have their connections arranged as in the diagrams on pp. 47 and 50. Polarity of Core. When a dynamo is first started a strong current is passed through its field-magnet coils, in order to impart to the core a certain polarity, and leave therein a certain residual magnetism. It is upon this feeble magnetism that the machine begins to excite (p. 13); and because it is feeble it is easily destroyed by knocks, or it may be reversed by acci- dental contact with other magnets. In such a case the dynamo will either fail to excite or will give a current in the wrong direction in relation to the terminals, which are usually marked + and , or indicated by the screw being blackened. Com- plete failure of the residual magnetism is rare, but in such a case a sufficient current must be passed from some other source. A few accumulator cells, or the current of another dynamo, may be employed for this purpose ; but failing both of these, as in the case of the faulty dynamo being situated away from power- ful sources of electricity, a few large cells of the ordinary bichromate battery should be used. The massive cast-iron pole pieces of dynamos or the cast- iron yoke of the field magnet may generally be relied upon to retain sufficient magnetization. In " connecting up/' as it is termed, some difficulty is frequently experienced by beginners in determining the proper course of the current, so that it shall corre- DIRECTION OF THE CURRENT. 251 spond with the direction of rotation and the marked direction of current from the terminals. In such case it is best to ascertain, first, the polarity of the field. This can be done with a pocket compass, or a very small bar magnet, for a N. pole will repel a similar pole, according to the law of magnets. Many rules are to be found in text books for finding the relative direction of the polarity and the current. If, however, we pick up an ordinary screw-bolt and look at it, end on, that extremity will be a S. pole, if we suppose the current flowing from us, in the direction of the screw. The course of the windings upon the magnet are easily traced, and the connections made accord- ingly. The best dynamo builders take care to mark all the terminals with letters or figures, so that A and A would be connected together, and similarly with B and B, or i and i or 2 and 2, and so forth. In making connections a good contact must be ensured, and the set screws made sufficiently tight. Con- nectors are not generally insulated, so that they must be kept \vell away from field coils or any of the metallic work. In alternators there is no + and , so that it is not of any consequence to which of the tv/o collector rings the beginning or end of the coils is attached. The field magnets in these being separately excited, do not require residual magnetism for starting, and it is generally of no consequence in which way the current flows around them. The " direction " of the current from any dynamo can be readily ascertained by means of a pocket compass. The operator (facing north), standing with his back to the machine, places his com- pass under the leading wire. If the current is flow- ing from the dynamo in that wire the N. pole of the 252 OPERATIVE NOTES. compass will turn to his /, through a filter A. These dynamos yield an electromotive force of 6,000 volts of pressure, but are adapted for still higher FIRTH'S METHOD OF REGULATING. 305 tension. This pressure is afterwards augmented, for purposes of transmission in the mains, to 20,000 volts, by means of transformers of the Ferranti pattern. They are driven by marine-type engines of the latest improved pattern, each of 2,500 horse-power. Firth's Method of Regulating E.M.F. of Dynamo, Firth's dynamo, represented in Fig 105, is chiefly remarkable in its governing arrangement. The field Fig. 105. Firth's Dynamo with separated Magnets and Sliding Regulating Gear. magnet is of peculiar construction. It forms essen- tially two magnets with consequent poles, but the two halves are separated in a plane passing through the axis of the armature. The " consequent " poles are thus divided, as represented, into four pieces. Each magnet has its base arranged so that it can be moved in a slide. This slide is planed out of the upper face of the base or main casting. The magnets 3,re thus free to be moved laterally, transversely to X 306 TYPICAL DYNAMOS. the axis, but are quite rigid otherwise. Projecting downwards through a slot cast in the base, each magnet carries a nutpiece, threaded out to receive a right and left-handed screw shaft. This shaft is set in bearings in the main casting. A handwheel, shown in the figure, is provided upon one end of the shaft. Any motion of this wheel is thus transmitted to the magnets, which can be made to advance towards or recede from the armature simultaneously and equally. The object of the arrangement is to allow of the separation of the magnets, and their consequent withdrawal from the armature when it is required to reduce the electromotive force of the machine. Such separation is equivalent to diminish- ing the number of the lines of force projected through the armature. It may be said to be practically equivalent to increasing the reluctance of the air gaps. Width of the. A ir Gaps and the Electromotive Force. A very interesting series of experiments were made by Mr. Firth, at our suggestion, to determine the effect, in the above construction of dynamos, of gradually increasing the separation of the magnets, and noting the corresponding E.M.F. In a shunt dynamo having a normal E.M.F. of 52 volts on open circuit, the results obtained were as follows, the measurements being between pole faces and peri- phery of armature : Speed. Distance. Volts. 2,000 normal 52 1% inch 48 A , 46 A 40 36 31 20 But a still more remarkable series of experiments SINGLE COIL FIELD MAGNET. 307 were made with a small series-wound dynamo, with armature 5^ inches diameter by 6 inches long, built for an output of 15 amperes at 100 volts. It will be observed that the proportional fall of the volts exhibits values contrary to general expectation, and the figures altogether strikingly emphasise a growing opinion amongst electrical engineers that the greatest pos- sible nearness of pole pieces and armature is not necessarily a corresponding advantage. As in the former case, the measurements were taken between pole faces and the periphery of the armature : Speed. 2000 Distance. normal \ inch Volts. 100 94 68 5 4| 36 30 20 Single Coil Field Magnet Dynamo. A diagram of this form of dynamo is shown in Fig. 106. It is a type of machine which, while it has been produced by several builders, has received most attention at the hands of Mr. Kennedy. Its chief merit lies in its simplicity. There are only two parts, or at most three, in the field magnet. These are the base or foundation, with which is cast the lower pole piece ; the core of the magnet, which is preferably made from wrought iron, but may be of cast iron and pro- duced at once with the foundation ; and the cap or upper pole piece. In a machine of this kind built by 308 TYPICAL DYNAMOS. Mr. Kennedy, the core of the magnet is of hammered scrap iron and measures 10 inches in diameter and 14 inches in length. The pole pieces are of hematite iron. The armature is of the Gramme type and is built of charcoal-iron discs turned true outside and inside. It is mounted on a spoked wheel keyed to the shaft. The core is 1 2 inches in length, the ring Fig. 106. Diagram of Kennedy's Single Bobbin Dynamo. being of the cylinder type. Its external diameter is 10 inches, and its internal diameter 6 inches. It is wound with flat wire 5 mm. by 37 mm. in one layer outside. The current allowed in the armature is 90 amperes. The commutator is composed of solid drawn copper sections insulated with mica. Resistance of armature, "04 ohm; resistance of shunt coil, 20 ohms; resistance of series turns, '03 ohm ; speed, 620 revolu- tions ; E.M.F. at terminals, open circuit 100 volts, PATERSON AND COOPER'S DYNAMO. 309 Pater son and Cooper's "Phoenix* Dynamo. The armature of this remarkable machine is built up from a large number of toothed iron discs. In the 42,000 310 TYPICAL DYNAMOS. watt machine the core is 22 J in. in external diameter and 9 in. in length, with a radial depth of 4J in. The notches form 42 long grooves, each containing two coils side by side. It is wound with fifty 48 mils, diameter wires in the form of a cable. Square wire has been used in some of the later dynamos. The field magnet is of the bipolar upright type. Thomson-Houston Dynamos. The name Thomson-Houston is more particularly associated with the famous spherical armature arc- lighting dynamo than with the incandescent system, but this company have lately perfected a distinct plant for glow lighting, the features of which call for particular description. The Sphere-armature Dynamo is too well-known, even in England, to demand more than brief mention. Its leading features are a ball-like armature, over- wound with three distinct coils already spoken of (p. 150). This revolves in the field of a large bipolar magnet, having cup-like pole pieces, embracing the armature. Another peculiar invention embodied in the design is the automatic regulator, based upon the principle of varying the lead of the brushes. By this means the Thomson-Houston may justly be claimed to be one of the best generators yet invented for furnishing constant current an essential condition in arc lighting. The general appearance of the dynamo is very similar to that of the compound- wound dynamo for incandescent lighting depicted in Fig. 107. The Direct Current Incandescent Light Dynamo is built upon the same general lines as the older arc dynamo. It has the same form of armature (a sphere) THOMSON-HOUSTON DYNAMOS. 311 and this is caused to revolve in the cup-like recesses of a similar field magnet. The armature winding is, however, different, consisting as it does of numerous coils connected to a commutator of a large number of sections, The output of this dynamo has the features of the low tension direct system, a low TYPICAL DYNAMOS. electromotive force (under 200 volts), and a large current. The field magnets are shunt wound. But the most remarkable point in the machine is the disposition of the series coils, for the dynamo is com- pound wound. In ordinary dynamos the series turns are placed in one of three positions: (i) under the shunt coils ; (2) over the shunt coils ; (3) at one side or the other of the shunt coils. The inventors of this dynamo, however, have departed from the beaten track. Recognising the fact that the real function of the series windings is to magnetize the armature, they abandon the ordinary position and place the coils around the armature, or at either " end " of it axially. The position of these coils will be observed in the figure. They have no reference to the field magnet, but they have a powerful influence upon the field itself. The conductors forming them are of a flat rectangular shape, overwound with tape. These carry, as in other compound dynamos, the whole of the current, and are, therefore, of considerable cross sectional area. The short distance lighting incan- descent dynamo is intended to work direct into circuits having a radius of about 2,000 feet, without connectors. It is furnished with very perfect collect- ing brushes, arranged in four independent sets upon either side ; and, like all recent dynamos of the first order, it is furnished with slides and belt-tightening gear. It is built in the following sizes, the figures comparing weight and output with speed, being of especial interest. Class. No. of 60 Weight, watt Lamps. Ibs. Revs, per Minute. Floor space, ins. Diam, Pulle B 50 700 1, 600 31 X 221 7 C 100 1,200 1,550 37i X 28 9 E 200 2,250 1,250 4 X 35i 12 H 400 4,400 te\ X 43i J 5 THOMSON-HOUSTON DYNAMOS. 313 Thomson- Houston "Motor-type" Dynamo. As will be observed by reference to Fig. 108, which gives a general view of the machine, this dynamo belongs to the class known in England as the "bipolar over- type/' It is built chiefly for the lighting of isolated installations, but as this work is largely done by the class previously described, the "motor-type" has been chiefly utilised as exciters for alternating current dynamos and as motors or generators for the trans- mission of power. The armature is of the usual drum type, and is wound for a low tension output and large current. The chief peculiarity, however, consists in the dispositions of the series windings, when the dynamo is compound wound. These are arranged, as represented in the figure, at either extremity of the armature and close to the edges of the pole pieces. The other details of the dynamo are of the usual kind, the brush rocker being of excellent design. This class is built in several sizes, but the following data of five of them will serve to show the relationship between weight, output, speed, power as a motor and so forth : No. of 60 watt Lamps. Diam. of Volts. H.P. as a Weight, Revs, per Floor space, Pulley, Class. J 25 80 Motor. Ibs. Minute. j ins. ins. I 35 45 3 480 2,OCO 29 X 16 5 3 IOO 125 1\ 1,080 1, 600 37 X 21 8 6 200 250 15 J >943 1,400 44 X 27 10 20 600 800 60 1,020 81 X 4 17 25 800 1050 75 10,000 900 88 X 46 19 Alternating Current Thomson-Houston Dynamo. For electric lighting on the incandescent system, at distances over 6,000 feet radius, the use of alternating currents of high tension is becoming common. In Fig. 109 is depicted the leading features of the alter- nator, built for the system under consideration. The TYPICAL DYNAMOS. main framework is of cast iron. The field magnet circle is built in two halves. The lower half is cast as one with the base. The upper half is bolted to it. By these means it is a simple matter to separate them, THOMSON -HOUSTON DYNAMOS. 315 and to lift out the armature. Each half circle carries, projecting radially inwards, a series of magnet poles, forming the half of the whole number alternately N and S. The number of these in the smallest machine is eight. In the large machines there are as many as twenty-two. The armature is composed of a drum core of iron discs, pierced for ventilation, separated by insulating substance, and bound together in the usual way to form a solid body in the cylindrical form. The coils are in the form of flat hanks. They are laid upon the surface of the drum, and secured in position. The wire used in forming the hanks is of square cross section. There are an equal number of coils on the armature and poles forming the mag- netic field. When the dynamo is intended to be self- exciting, as in the particular machine represented by the engraving, these coils are formed with a central open space. This space is then filled with the coils whose function it is to generate current for exciting the field magnets. The whole is bound with brass wire bands. In the smaller machines the lighting coils are connected up in one series with the external work. In the larger dynamos there are two series, connected in parallel. There are several different methods of exciting the field. The simplest is the employment of a separate exciting dynamo of small size. This is generally of the overtype already de- scribed. Again, the dynamo may be entirely self- excited as in the case under review. Further, it may be " composite wound." The self-exciting winding consists of a few turns of the alternate coiling, as applied to drum armatures. These turns alternate with, and fill, the interspaces between the lighting coils of the armature. Since the 3l6 TYPICAL DYNAMOS. currents so obtained are necessarily alternating, the terminals of these coils are carried out (through the shaft) to a commutator on the end of the shaft, specially reserved for this purpose. The function of this part is to give these currents a continuous direc- tion. This commutator is somewhat of the Wilde pattern already fully described, and the number of its sequents correspond with the number of pole pieces in the field magnet. This arrangement forms, in effect, a continuous current winding below an alter- nating current winding. The Composite Winding. This is intended to regu- late the machine for constant electromotive force. In one form of the machine the field magnets are excited by two separate windings. One of these sets is supplied with current by the machine itself in the manner already explained. This may be regarded as a shunting of a portion of the main current. Indeed, in some cases the main current is so shunted, a commutator being employed as before. The second set of coils is supplied with current by a separate exciting machine. In another machine all the magnet poles but two are excited by the separate machine. The two remaining poles (diametrically opposed) are excited by the current from the machine itself. These machines may be regarded as compound alternating current dynamos a class of which we have no ex- amples built in this country. The Westinghouse A Iternator. Conspicuous among the many successful dynamos produced in America is the famous alternator of the Westinghouse Electric Company. It has from time to time been improved, so that at present it is considered as occupying the first rank among alternators. In the WESTINGHOUSE'S ALTERNATOR. 317 central station dynamo, which is in appearance very similar to Fig. 109, p. 314, the armature is composed of iron discs, pierced for ventilation, and having recessed projections, forming " heads/ 5 as represented in the cross-section, Fig. no. It will be observed, in respect to this peculiarity, that the coils are wound in those neck-like recesses, the heads projecting over the coils, in the manner of the top of a mushroom-headed Fig. no. Westinghouse Alternating Current Armature. End View. One coil in cross section. screw, as shown in the coil to the right, shown in cross section. The spaces between the coils and the heads are filled with wooden sections, shown darker. When the iron discs are built together to form the core the recessed portions form longitudinal channels, partially shrouded by the heads. The coils are not actually wound in these recesses. One of the coils is shown in Fig. in. It is wound by machine. When slipped into position parallel to the axis of the TYPICAL DYNAMOS. armature, so that its two sides embrace the " necked " channel, as represented in the preceding figure in section, it is compressed by a special appliance, so as to fit the channel closely. Since the winding is virtually back and forth, the connections between the coils are between alter- nate coils at either end of the armature, as shown in Fig. no. ARMATURE COIL. ^ e arrangement is FiO OO in O ^- i ^- coaNrhb b N ro vo oo O\ rO Tt- rfO rJ-vO iii O OO O 00 un r b j^ M ob b " O ONONOO OOO ,2.3 O e C l-si ON t- fO o LOVO -^ 10 co rl- i- ON ob rovb N CO ro oi^.b to -t- b HH _' _ N op t^sO rh N 1-1 ON ro > O vb CO M ro OO irj w a d c a rt rt rt rt 12 .2 .2 .12 o o" a HQQQ Q . " >-, >% Q p WESTINGHOUSE' s MACHINE TESTS. 325 While the continuous direction current dynamo has received a good deal of attention in order to afford means of investigating the causes of its performance under varying conditions, and the determination of its efficiency, very little has been done in this way in the case of the alternating-current machine. Some ex- periments have lately, however, been carried out at the Franklin Institute by Dr. Duncan and Mr. Hasson upon a Westinghouse alternator, working in conjunc- tion with converters of the same system. The apparatus consisted of a Westinghouse 750- light No. i dynamo, excited by a small continuous current machine, and an outfit of 4o-light converters. The driving plant consisted of a 75-h.p. Armington and Sims engine, driving the dynamo and exciter through a Tatham transmission dynamometer. En- gine, dynamometer, and dynamos were firmly secured to heavy parallel timbers, which served as a founda- tion. The converters were banked on a wooden framework at a distance of some thirty yards from the dynamo, and their primaries were permanently secured to the dynamo circuit, a switch in the latter serving to cut them off when desired. The ammeter belong- ing to the plant was put in this circuit, and was read when efficiency measurements were being taken. The secondaries of the converters were conveyed to a switch board, and then to incandescent lamps mounted on racks. The first experiments had re- ference to Power Measurements. The Armington and Sims engine supplying the power worked regularly and satisfactorily, and the governor could be adjusted to give the speed required at the dynamo. The Tatham dynamometer was the one used for power measure- 326 TYPICAL DYNAMOS. ments at the Electrical Exhibition held at Phila- delphia in 1884, when its accuracy was checked by making with it a determination of the mechanical equivalent of heat. The result obtained in the latter measurement was 772-8 foot pounds per degree Fahr., and shows that the dynamometer is practically accurate. Since this form of dynamometer is likely to be largely used in future tests of power electrical apparatus, it may prove useful to briefly describe its construction by the aid of a diagram. In Fig. 113 is shown an endless belt, passing over the driven pulley S to the shaft to which the engine is belted, round the pulleys S and B to the driving pulley A, and back over E l and Sj to S again. The bearings of the pulleys B and B! are in cradles pivoted on knife edges, C, at their outer ends, and at the inner ends are con- nected by links at equal Yi s- 3. distances on the two sides of a knife edge which sup- ports the scale beam W. The outer side of the belt passes through the line of the knife edges, C, and therefore has no effect on the scale beam, but the tensions of the inner parts of the belt act directly on the scale beam, and as they are on opposite sides of the fulcrum, they act against one another. The beam is so graduated that this difference of tension is read off directly in pounds, and this quantity the dif- ference of tension of the belt on the two sides of A WESTINGHOUSE DYNAMO TESTS. 327 multiplied by its circumference and speed gives the horse-power delivered. A weight travels on the beam, w, and readings can be taken with great accuracy. Electrical Measurements. The energy in the second- ary circuit was measured by means of a Cardew volt- meter and a Thomson ampere balance. As it is not the custom to put a number of secondaries in parallel each converter had its separate lamp circuit. Before making an efficiency test the electromotive force in the primary was regulated there being a Cardew voltmeter in that circuit and a separate measure- ment of the electromotive force and current in each secondary circuit was made. When the test was actually in progress the voltmeter and ampere balance were used in one of the circuits, and the currents and electromotive forces in the others were calculated from the readings in this circuit, together with the previous measurements. Both the voltmeter and ampere balance were accurately calibrated, the former being checked after each test, while the latter had its constant determined with both continuous and alter- nating currents. The electromotive force at the terminals of a non-inductive German silver resistance in circuit in the balance was observed when a con- tinuous current was flowing, and also with an alternating current of the same periodicity as that employed in the test. The current in each case was calculated from the resistance and electromotive force, and the results gave no appreciable difference in the constant for continuous and alternating circuits. The tests were carried out as in the following tables : 328 TYPICAL DYNAMOS. HORSE-POWER ABSORBED AND VARYING ELECTROMOTIVE FORCES. E.M.F. H.P. Dynamo. Exciter. Horse-Power for Exciter, Field not made , ,, Field made , ,, Dynamo alone , ,, Dynamo and Exciter o 1376 1168 1099 1040 1216 1171 1107 1048 1 10 107 124 104 105 105 105 104 104 104 '34 75 273 3-04 3-5i 12-5 IO'I 9-60 9-0 12-0 n-8 II'I2 10-64 , Primaries of Converters on . > > > > > > TABLE OF EFFICIENCY AT VARYING LOADS. i EXCITER. DYNAMO PRIMARY. CONVERTERS. a . 81 "gg B 1 8 i- 3 sfi si N < E.M.F. Cur- rent. E.M.F. Cur- rent. E.M.F. Cur- rent. i ft el < w^ n 51 1 |i IB W , 105 9-4 1,107 10 49'5 153-9 10-21 21-83 11-62 46-8 $ 104 10-5 1,107 18-9 49-6 33 8> 4 22-50 34'4 11-90 65-4 * 101 ir-o I,I3 28'6 50-0 520-7 3V9 48-0 13-1 727 Full 112 "'5 1,123 3'i 5'9 739'S j S'48 64-44 13-96 7'3 In connection with this subject it maybe instructive to give the results of the experiments made with the converters worked in conjunction with the dynamo. No. of Lamps. 4 O EFFICIENCY OF CONVERTERS. FORTY-LIGHT CONVERTER. Watts in Volts. ' . Secondary. 50-0 2,001 50-9 o Loss in Watts. 109 Loss in Iron. Efficiency, 94-8 WESTINGHOUSE CONVERTER TESTS. 329 TWENTY-LIGHT CONVERTER. No. of Watts in I Loss in Watts Loss in Efficiency Lamps. Volts. Secondary. in Secondary. Iron, Watts. per cent. 20 48-8 952 106 95'2 9O-O 15 52-2 817 114-8 108-9 87-6 10 5'3 506 101-7 99-2 83-3 5 5i-44 264 109-4 108-7 70-7 52-3 1105 110-5 The efficiency of the converters was measured by placing them in a metal calorimeter, between the double walls of which water was allowed to flow. The temperature of exit and entrance was observed, as well as the weight of water which passed through ; at the same time the current and electromotive force in the secondary circuit of the converter were mea- sured. A separate observation gave the radiation, which was of course allowed for, although it was made as small as possible. Examining these figures, we are struck by two things : the very large amount of power absorbed in the core of the armature and the very small loss in the converters on open circuit. The dynamo losses due to reversals of magnetism and eddy currents at the electromotive force used in the test are no less than 6 horse power, while the energy due to reversal of magnetism and eddy currents in the converters is only i *6 horse power. Another rather striking thing is the almost constant ratio of primary and secondary currents over a considerable range. The maximum efficiency is about 78 per cent. CHAPTER XXI. THE DYNAMO AS A MOTOR. IF the terminals of a dynamo in motion be connected with the terminals of a dynamo standing idle, the current from the active dynamo will traverse the circuit of the idle machine and cause its armature to revolve. The first machine acts as a generator ; the second machine becomes a motor. The conductors employed to convey the current from the generator to the motor exemplify the principle of the electrical transference of energy. Since the efficiency of such a system' is very high, the transmission and distribu- tion of motive power by means of electricity is being rapidly utilised for various purposes, among which the Electrical Railway is likely to occupy the first place. Magnetic Principles of the Motor. If a straight wire be placed in a magnetic field with its length perpendicular to the lines of magnetic force, and a current passed through it, it will ex- perience a force tending to move it perpendicularly to itself and to the lines of the field. Provided the wire be free to act under the influence of this moving force, it will tend to cut the magnetic field, and a counter, or opposite, current is induced in it. Hence, DYNAMOS AS MOTORS. 331 while the wire (or armature) is impelled to move across the magnetic lines, it acts to a certain extent also as a generator. The counter electromotive force induced in it greatly diminishes, or dams back, the moving current. The more rapid the motion of the armature the greater does this counter current become. Its strength is also dependent upon the strength of the magnetic field. This magnetic reaction of the armature of a motor is a matter of the greatest importance in the electrical transference of power. The current in the coils of an iron-cored generator armature tends to make that core become a magnet, having poles opposed to those creating the magnetic field. This is well known as the reaction of the armature. In cases where the field magnet is weak it becomes a serious source of loss and other drawbacks. In dynamos, however, it is the builder's aim to set up so powerful a field relatively to the possible counter action of the arma- ture core that the latter is entirely overpowered. Let us now consider the case of a dynamo becoming a motor. Let a current be passed into it so that the polarity of the field is the same as when the machine acts as a dynamo. It will be found that the current in the armature is in a direction the reverse of that induced in it as a generator. The polarity of the armature will also be reversed that is, it will exhibit poles the reverse of those of the field. These poles will mutually attract or strengthen one another. Hence, the reaction of the armature's magnetism in a motor is contrary to what it is as a generator. But as in the case of a generator this is not an advantage, but on the whole the reverse, and it is the aim 332 THE DYNAMO AS A MOTOR. of the motor builder to employ so powerful a field magnet that the armature's magnetic reaction may be left almost out of account. As in the case of a generator the reaction tends to distort the direction of the lines of force in the field, and this distortion is the main cause of the necessity for " lead " in the brushes as employed in the case of generators. Hence, it is important to remember, that, in a per- fect motor the twist (torque) communicated to the armature shaft is due not to the magnetism of the iron-core but to the currents in the coils enveloping it. Mechanically considered, therefore, the means of attaching the latter through the core to the shaft demands considerable attention, otherwise the coils are apt to be pulled backwards from their proper position upon the core. Such faults were of constant occurrence in both the earlier dynamos and motors. Efficiency of Electrical Transmission. The electrical transference of motive power has been found to be more efficient than transmission by ropes, water, or compressed air. This fact alone has sufficed to bring electro-motors into use, in many cases to the displacement of every other workable system. The whole of the power supplied electrically to the motor is not, however, converted into mechanical effect. There are various unavoidable sources of loss. There is, first, the resistance of the connecting wires. This may be regarded as the loss due to transmission. There is, in the second place, a certain loss due to resistance, which appears as heat in the ELECTRICAL TRANSMISSION OF POWER. 333 motor. Thirdly, there is the loss due to friction, mechanically considered, of the motor. There is, also, the invariable magnetic friction giving rise to eddy currents in the motor, but this is frequently so small in the best types that it may be left out of account. The electrical power put into the motor is most conveniently expressed in watts. If c be the current, expressed in amperes, which actually flows in the circuit of the motor, and E be the electromotive force, expressed in volts, at the terminals of the motor, then the electrical power (per second) in watts, p, is found by multiplying together the amperes and volts, and dividing by 746 to obtain the electrical horse power. E C Electrical Horse Power = r* Since only a proportion of the electrical power supplied to the motor (owing to causes already men- tioned), is returned as mechanical effect at its pulley, it is convenient to express the efficiency of the motor as follows. If C is the current (in amperes) that flows through the motor, and E the electromotive force (in volts) the watts, P, of mechanical effect is P = E C. The counter electromotive force of the armature varies with different motors. In the best types it is from five to ten per cent, less than the E.M F. measured at the terminals of the motor. Conditions of Electrical Transmission of Power. The simplest case is that in which a dynamo at one place is connected in circuit with a dynamo (motor) at another place. The conductors between the ma- chines must be insulated in the usual way. That is, 334 THE DYNAMO AS A MOTOR. if they are of naked copper they must be suspended above the ground and attached to insulators. If they are of the nature of heavily protected cable, they may either be laid along the ground or buried beneath it. In many cases they are laid in water, as across streams. In the case of simply running a dynamo and a motor in this way the machines should be adapted to the work to be done. In most cases the generating dynamo is moved at a constant speed. In that case both the generator and the motor should be series-wound machines. When the generator is run at a constant speed the motor will also maintain an approximately constant speed under all conditions ot load. The speed in this case depends entirely upon the E.M.F. The torque depends, on the other hand, entirely upon the current. This is known as simple series transmission. But in the case of motors being run off circuits used also for lighting, where, instead of constant current constant potential is required, as on an incandescent light circuit, series motors are found to be unsuitable ; they will not maintain a constant speed under vary- ing loads. But any shunt wound or compounded motor will do this under the above conditions, be- cause the current through the shunt does not vary, and there is less variation of the strength of the field. Shunt-wound motors, if they are to maintain a con- stant speed upon a constant potential circuit must be furnished with armatures of low resistance. The field magnet must be relatively very powerful. If a shunt motor, on the other hand, be put upon a constant current circuit (such as that running arc lamps) its speed will increase with its load, and will always fall off as the load is diminished. GENERATORS AS MOTORS. 335 Generators as Motors. There is this distinction to be remembered in the cases of setting dynamos to work as motors, or motors as dynamos. Taking the case of an ordinary series machine with brushes set (and having forward " lead " ) it will, when worked as a motor, run in the wrong direction, or against its brushes. It is usual in this case to reverse the direc- tion of the current in the field magnet, by changing the connections, or, leaving the field magnet, to re- verse the connections of the armature. The machine will then run with its brushes. If these connections be left standing the brushes must be reversed and set with the lead in the other direction. Shunt Dynamo as Motor. Shunt dynamos, however, are not subject to the same rule, for it is evident that while the current in the armature is in the same direction as before, that in the shunt will necessarily be in the reverse direction, and the machine will run as a motor without further change. Compound Dynamo as Motor. The case of a com* pound machine is somewhat different. It depends upon the relative magnetising effects of the shunt and series coils whether it will behave as a series or as a shunt dynamo in the direction of its motion. If the shunt, as is usually the case, have a greater magnetising effect than the series turns, the machine will act as a shunt dynamo, inasmuch as it will run as a motor in the same direction as it does as a generator. If, however, as is sometimes the case, the series coils preponderate in determining the mag- netic polarity of the field, the machine will run against its brushes, and it must be reversed by altering the connections, as in the case of a series motor. Since the compound dynamo has the polarity 336 THE DYNAMO AS A MOTOR. of its field determined by the combined effects of both shunt and series coils, it is evident that when used as a motor the current in the shunt will oppose that in the series coils. Hence, the difference between the magnetising powers of the two coils will determine the polarity and strength of the magnetic field. Such a machine is known as a differentially -wound motor. " Lead" of the Brushes of Motors. The self induc- tion due to the armature of a generator chiefly deter- mines the lead of the brushes. If it is great, and the field is weak, the lead will be considerable. If it is small, and the field be powerful, the lead will be small also. But in the case of a motor exactly the reverse is the case. Here the self induction, being in the reverse sense, tends to diminish the lead. When a motor is desired to run in a particular direction the lead must be determined to give, in that direction, the strongest mechanical effect. It the brushes be set with no lead the armature will be apt to run in either Direction, as it may happen to be started, but with- out exerting its maximum effect. In cases where the motor is required to reverse its direction of running, by reversing the current (as is frequently done) the brushes must not be given any lead. There is, how- ever, an element of uncertainty (in many cases) that the motor shall reverse its direction of turning upon a reversal of the current. It is immaterial whether (in the case of a series motor) the current is reversed in the armature or in the field magnet. Although almost any type of continuous current dynamo may be used as a motor, yet makers usually produce specially built machines for this purpose. As a rule motors, especially if used for propelling vehicles, must be more heavily built than dynamos. ELECTRO MOTOR GOVERNING. 337 They are subject to greater strains, and the mechani- cal arrangement of the induction coils, the core and the shaft of the armature must be as solidly con- structed as possible. This is especially true of the connections between the coils and the core. The wires are preferably sunk permanently, with hard insulation, in channels in the core, as in the Weston and the Westinghouse armatures. The core, if built of plates, must be properly keyed or "feathered " upon the shaft. Many attempts have been made to render the arma- tures of motors waterproof. Lieut. Sprague, in the con- struction of his famous motor, has produced machines so perfect in this respect that they may, it is stated, be washed with a hose and water after the day's run under the street cars upon which they are em- ployed. This implies that the whole of the elec- trical work is similarly waterproof. Electro Motor Governing. Government or regulation by differential winding appears to be the most suitable method adapted to the case of motors. It has the great advantage that no breaks in the circuit are required. A great num- ber of ingenious regulators have been invented in which the current is admitted to the circuit of the motor during a proportion only of the time of each revolution. The chief drawback of this system lies in the fact that break and make of circuit are necessary, involving a great deal of destructive sparking at the points of rupture. The proportions between the shunt and series wind- ings of the field magnets vary in different motors, but those expressed in Ayrton and Perry's formula have z 338 THE DYNAMO AS A MOTOR. produced motors almost perfectly self-regulating. Let S stand for the number of turns of the series coils, z for those of the shunt coil, R^ for the resistance of the shunt, R fl for the resistance of the armature, and R s for that of the series turns (expressed in ohms) then : z R, S R w + R 8 . The Sprague motors, that have been so successfully used in America, are wound according to this rule. A method of governing applicable to the case of a motor with more than one pair of poles has been proposed by Professor S. P. Thompson. He uses as field magnets a double set of poles set at different angles with respect of the brushes of the motor. One pair of magnetic poles, having a certain lead, is actuated by series coils; the other pair, having a different lead, by shunt coils. When both shunt and series are working there will be a resultant pole having some intermediate lead. If the load of the motor is diminished, it will tend to run faster, in- creasing the current in the shunt part,* decreasing it in the series part, and therefore altering the effective lead and preventing the increase of speed. Inferior Efficiencies of the Compound- Wound Motor. It can easily be shown, however, that in point of efficiency a differentially wound motor must be in- ferior to a motor either plain series or shunt wound. This shortcoming is due to the fact that the energy required to magnetize the field magnet is greater in the case of employing two opposing coils, as when * This effect is due, as previously explained, to the increased counter electromotive force of the armature coils, increasing as it does with the velocity it may, therefore, be regarded as equivalent to an increased resistance of those coils. NON-STARTING OF SHUNT MOTOR. 339 the series and shunt machines are combined in one. The great advantages, however, of the differential method of winding in motors, combined with the fact that the loss due to the opposing coils is always relatively small, will probably lead to the almost universal adoption of compound motors for regular running. The energy consumed in magnetizing the field is always a small proportion of that supplied at the terminals, series or shunt, of the motor, and even if the opposing coils in a compound motor con- sume fifty per cent, more it is still advantageous to employ this method of regulation. Non-starting of a Shunt Motor. A shunt motor, without any auxiliary starting arrangement, may refuse to begin to rotate of itself if standing idle when the current is switched on. This defect is due to the fact that the current, finding a path of con- paratively low resistance through the armature as compared with the shunt windings, flows almost entirely in that path. Only a small proportion of the current, therefore, flows in the shunt. The lower the armature's resistance the less current will flow in the shunt, and there will be little or no magnetism in the field. When, however, the motor is started, the revolution of the armature immediately sets up in its coils an opposing or counter electromotive force, as before explained. This being, in the case in point, equivalent to increasing the resistance of the arma- ture, a proportionately larger current will at once flow in the shunt, and the field magnet will become energised. As the speed increases more and more current will be diverted round the shunt, because the counter current of the armature is nearly pro- portional to the speed. The greatest effect will 340 THE DYNAMO AS A MOTOR. therefore be exerted by the motor when the magnets are magnetized to saturation. Typical Motors. The first dynamos used in this country as motors were series-wound Gramme and Siemens machines. These types are still to a considerable extent em- ployed for motive power purposes. Immisch's Motors. These motors attracted a great deal of attention at the recent Exhibitions, chiefly on account of their high efficiency. They are built with both ring and drum armatures. The ring type appears to be reserved for small motors, under two- horse power. The field magnet of the larger type is of the Siemens horizontal pattern, with four coils, but, unlike it, is not divided into parallel bars. The pole pieces are solid. The drum armature is built upon a core of iron discs with asbestos insulation. At intervals along the length of the core occur thick discs having driving horns. These form longitudinal channels for the reception of the ceilings. The commutator bars are arranged alternately in two groups, side by side. By the contact of a pair of brushes, or a single broad brush, the coil that reaches the neutral point or that connecting the front bar to the back bar is cut out of circuit. The inventor states that this is equivalent to employing an ordi- nary winding and collector and a pair (connected as one) of brushes on each side, the brushes of each pair being set apart the width of a bar. This arrange- ment is said to obviate changing the lead of the brushes and to diminish cross magnetizing. This motor has already been used extensively in the pro- pulsion of street cars. They have also been em- SPRAGUE'S MOTOR. 341 ployed for hoists, but their most important application appears to be to the case of pumping in mines. In many instances the Immisch motors have displaced the best system of compressed air power transmission for that purpose. Ayr ton & Perry's Motor. This motor is remark- able in being of an extremely compact construction. It is of great power in proportion to its dimensions and weight. Further it is remarkable inasmuch that the field magnet rotates while the armature remains a fixture. The armature is made in the form of an elongated Pacinotti ring. It is built up from toothed discs, so that the teeth form longitudinal channels along the length of the core, into which the coils are wound. This part is a fixture and forms the outer casing of the machine. The field magnet is constructed in the form of a shuttle armature, with extending polar shoes. While the rings through which the current is passed to the armature are fixed, the brushes leading it into the rings rotate with the shaft and the field magnet. These motors have been used for various purposes. Sprague's Motors. The application of the Sprague motor in America to the propulsion of vehicles is considerable. The machines assume various forms to adapt them to the particular class of work to be done. One of the best is that generally used for stationary purposes. It is in the form of a bipolar dynamo. The field magnet is in the main similar to that of the Sautter-Lemonnier dynamo (Fig. 82, p. 275), with this difference that in the Sprague motor the magnet cores are cylindrical. The centre of gravity of the rotating portion is thus kept well down, and the bearings being in consequence low 342 THE DYNAMO AS A MOTOR. the whole is adapted for steadiness in running at high velocities. The armature is of the drum type. These motors are usually differentially wound, and are therefore adapted for automatic regulation. They run at a constant speed upon constant potential cir- cuits. In the case of arc lighting circuits simple series-wound motors are preferred. Crocker - Wheeler Motor. This type has become very popular in the United States, and it is used in this country for various purposes. Its construction is of a high order of merit. The field magnet is of the bipolar type as in the Kapp dynamo (Fig. 90, p. 287), but with cylindrical cores. The mounting of the armature is also of the overtype. The collecting cylinder is long and gives sufficient space to shift the brushes to fresh positions of contact. There are two pairs of brushes, or one pair in duplicate, so that any one brush may be removed and trimmed without interrupting the current. " C and C " Motor. The application of this famous motor has been very extensive, especially in America. It consists of a field magnet similar in design to Fig. 82 (p. 275), but having the coil portion of the core curved inwards to the arc of a circle. The armature is of the ring type and is mounted as near the base as practicable. These motors are built either series wound for use on arc circuits or differentially wound for running upon constant potential circuits. They are made in sizes from Jth horse-power to 30 horse- power. Motors in England. Most of the applications of electromotors in England have been in connection with the heavier branches of engineering. These have been, hitherto, electric traction, as railways and MOTORS IN ENGLAND. 343 tram cars, and hauling and pumping in collieries. With the exception of the Immisch motor, which is specially built for transforming electric current into motive power, few firms build machines specially for motor work. On the other hand, the ordinary dyna- mos of English manufacture form the most efficient motors, and many of them have been applied to the conversion of electricity into power with but little alteration. The Crompton, the Edison-Hopkinson, the Elwell Parker, the Kapp, and numerous other English built dynamos may be used either as gener- ators or motors, and there is this advantage in that feature that at any time a motor may be turned into a dynamo, since there are no special fittings render- ing it unfit for that work. The best example of the electrical railway in this country (the City and Southwark Subway, London, is run by motors con- sisting of Edison-Hopkinson dynamos. The spread of networks of electric mains in the larger towns will doubtless, as has been the case in America, lead to the extensive utilisation of electromotors for many minor purposes requiring an expenditure of energy under five horse-power. Both coal and gas are, how- ever, so inexpensive in this country, and gas motors have attained to such a pitch of perfection, that the introduction of the electromotor will no doubt be thereby materially retarded. INDEX. DAL NEGRO'S ma- chine, 6 Activity, external, curves of, 224 Air spaces, resistance of, I 95 gaps, width of and the E.M.F., 306 Alignment of bearings in dynamo, 248 Alliance dynamo, the, 10 Alteneck's armature, 16 Alternator, Siemens', 274 in parallel, 235 periodicity of, 236 phase of, 236 synchronizing of, in parallel, 239 " in step," 239 compensation, excitation of, 242 and transformers, 243 Kapp's, 291 Ferranti's, 293 Thomson -Houston, 313 Ampere turns in exciting coils, 71 determination of, 198 Apparatus, Dal Negro's, 6 Armature, Sturgeon's, 8 shuttle, n shuttle, Siemens', n Pacinotti's, 14 Gramme's, 15 Alteneck's, 16 the simplest, 24 Armature, nature of the, 36 wire, insulated, 75 fall of potential in, 193 core, Kapp lines in, 193 dimensions of, 193 reluctance of, 197 handling, 249 Kapp's multipolar, 284, 289 Westinghouse's, 317 Arc lighting, series dynamos in, 246 Asbestos insulation of collector, 257 Attrition of collector cylinder, 249 Ayiton & Perry's motors, 341 TDATHS or vats in series, 268 Bearings, alignment of, in dynamo, 248 Bell ringing, magneto machine for, 12 Belting of dynamos, 252 Best collection, point of, 259 Bipolar dynamo, Siemens', 274 Board of Trade unit, 214 Brett's improvements of 1848, IO Brushes, nature of the, 26 Brush-shifting regulation, 200 effects of 201 position of, 259 Brush's " teazer" winding, 267 dynamo, 278 Burnt coils, 256 INDEX. 345 CALCULATION of exciting ^ coils, 53 Capacity of the main and shunt coils, 199 Characteristic curves, 219 " Characteristics," method of draw- ing, 221 horse power, 223 Characteristics of shunt dynamo, 226 compound ditto, 227 magnetization, 229 Chief pai ts of the dynamo, 20 Circuit interrupter, 7 closers for testing, 254 opener for plating dynamo, 267 Clark's machine, 6 Crocker-Wheeler motors, 342 Coils, induction, combined with magnet, 9 exciting, calculation of, 53 details of, 70 depth of, 71 short circuited, 256 Collector, nature of the, 25 brushes, nature of, 26 or commutator for drum arma- ture, 26 re-turning of, 260 worn, 260 bars, short circuiting of, 257 Commercial efficiency of dynamo, 214 Common form of electro-magnet, 42 Commutator, earliest form of, 7 nature of the, 25 or collector for drum armature, 26,37 treatment of, 249 attrition of, 249 worn, 260 re-turning, 260 Compensation excitation of alter- nator, 242 Composite field, regulation by, 211 wound dynamo, 313 winding, Thomson -Houston, 316 Compound winding, early concep- tion of, 13, 49 diagram of, 50 Compounding, regulation by, 209 Compound dynamo, 217 in glow lighting, 244 in parallel, 234 Conditions of working, essential, 37 Conductivity of insulated wire, 75 Connecting up new dynamo, 250 Continuous current dynamo, the earlies f , 5 Constant potential working, deve- lopment of, 1 8 current, regulating, 212 Counter-direction current from plat- ing vat, 266 Course of the current in the dynamo, 250 Current, non-fluctuating, 14 causing magnetic field, 31 density in magnetic coils, 72 course of the, in dynamo, 250 revcrser for testing, 254 in electro-plating, 263 Cut-outs at dynamo, 258 Curves of magnetic lines, 31 magnetization, 55 characteristic, 219 method of drawing, 220 horse-power, 223 of external electrical activity, 224 representing internal resistance, 225 variable speed, 225 from compound dynamo, 227 magnetization, 286 from Kapp's dynamo, 290 346 INDEX. T)AL NEGRO'S apparatus, 6 Dead break fault, 255 Definition of the word " dynamo," I Depth of exciting coils, 71 Deptford, dynamos at, 294 Density of current in magnet coils, 72 electro-plating, 264 Desroziers' dynamo, the, 276 Determination of the exciting cur- rent, 198 Details respecting exciting coils, 70 Development of the self-energizing principle, 13 of constant potential working, 18 Diagram of Gramme ring armature, 16 separate excitation, 44 shunt winding, 47 series winding, 45 Diffusion of the magnetic lines, 32 Dimensions of field magnet core, 194 armature core, 195 Direct-current dynamo for ligh;ing, Thomson-Houston, 310 Disc dynamo, Faraday's, 5 Dissimilar dynamos yoked together, 235 Divertor, magnetic, 242 Drawing curves, 221 Diiving by rope gear, 252 Drum armature, collector or com- mutator for, 26 Dynamo, definition of the word, I a motor, 2 evolution of the, 2 Dynamic electricity, early history of, 2 Dynamo, the first, 4 earliest attempts to construct, 4 continuous current, 5 Woolrich's early, 9 Dynamo, Brett's, of 1848, 10 the Alliance, 10 development of the self-ener- gizing principle in, 13 compound, early invention of, 13 shunt, early invention of, 14 electric machine, origin of the term, 14 Pacinotti's, 15 improvements in the, 16 in, by Sir William Thom- son, 17 in, by Gordon, 17 elements of the, 20 chief parts of the, 20 .supplementary parts of the, 21 simplest conception of a, 23 " overtype" of, 28 lines of force in, 35 magnetic field in, 36 field magnets, 41 separate exciter of, 44 series, winding, of, 45 shunt, winding of, 46 compound winding of, 49 in series and parallel, 230 in electric lighting, 241 and exciter on one shaft, 243 compound, in incandescent lighting, 245 shunt- wound, in incandescent lighting, 245 series, in arc lighting, 246 connections of, 250 starting and belting, 252 overloaded, 261 for electro deposition, 262 typical, 271 Siemens', 274 Sautter-Lemonnier, 274 Rechniewski's, 276 the Desroziers, 276 INDEX. 347 Dynamo of the Societe alsacienne de Constructions Mcchani- ques, 277 Brush's, 278 Edison's, 279 Edison-Hopkinson, 279 Elwell Parker, the, 281 Kapp's, 283 alternating current, 291 Ferranti's, 293 at Deptford, the, 294 Firth's, 305 Kennedy's, 307 Paterson & Cooper's, 309 the sphere armature, 310 Thomson-Houston alternating current, 313 composite wound, 316 Westinghouse's, 316 "J7ARLIEST magneto machines, Early type of magneto machine, 7 commutator, 7 Edison's dynamo, 279 Efficiency and output, 213 of dynamo, commercial, 214 electrical, 214 Electro motor, nature of, 2 magnet, common form of, 42 formulae, 56 Electrical efficiency, 214 effect of dynamo, total, 214 activity, variation of, 216 Electric lighting, dynamos in, 241 Electro - plating, " intensity and quantity" in, 262 depositing dynamos, 262 Electro-plating dynamos, 262 E.M.F. required in, 263 current required in, 263 Electro copper ore refining, 269 Electrolysis and copper ore, 269 Electro motor, magnetic principles of the, 330 Elements of the dynamo, 20 Elementary principles, the, 30 Elwell Parker dynamo, 218 E.M.F. lost internally, 216 in electro-plating, 263 Essential conditions of working, 37 Evolution of the dynamo, 2 Excitation, separate, 44 Exciting coils, calculation of, 53 details respecting, 70 ampere-turns of, 71 depth of, 7 1 current, determination of, 198 Excitation, compensation of alters nator, 242 Exciter and dynamo upon one axis, 243 Excite, failure to, 257 Experiment, Faraday's iron ring, 4 with Firth's dynamos, 306 External electrical activity, curve- of, 224 "P ALLURE to excite, 257 of residual magnetism, 255 Fall of potential in armature, 193 Faraday's iron bar experiment, 3 experiments of 1831, 3 disc dynamo, 5 Faults of field magnets, 80 Faults, testing for, 252 in dynamo, 252 localization of, 255 Faulty cut-outs, 258 Ferranti's alternators, 293 dynamos, 293 alternator in working order, 295 open, 296 bobbins of,?3oo armature, 301 348 INDEX. Ferranti's alternator, sectional view of, 304 Field magnet, junction of the, 23 nature of the, 24 the magnetic, 30 magnets of dynamos, 41 magnet coils, calculation of, 53 magnet coils, 61 magnet, details respecting, 70 magnet, forms of, 79 magnets, faults of, 80 magnet core, dimensions of, 194 magnet, reluctance of, 195 Firth's method of regulating, 203 dynamo, 305 experiments with, 306 First dynamo, 4 Formulae of electro-magnets, 56 Forms of field magnets, 79 Function of the field magnet, 23 shunt winding, 48 Fusible plugs, faulty, 258 at dynamo, 258 lighting, compound dy- namos in, 244 Gordon's improvements in dynamos, 17 Governing by variation of the mag- netism, 202 variable resistance, 202 speed, 202 of series dynamo, 206 of shunt dynamo, 207 by composite field, 211 Gramme's armature, 15 Gramme connection between dy- namos, 232 Gramme's dynamos in electio de- position, 265 typical, 272 Type superieur dynamo, 273 dimensions and output of, 273 Graphical records, 219 of shunt dynamo, 226 of magnetization, 286 Ground faults, 252 TLJAND regulation, 203 Handling armatures, 249 Heat in magnet windings, calcula- tion of, 87 Heating of the coils, experiments respecting, 68 Heaviside and magnetic resistance, 33 Hering's formula for magnet wind- ing, 64 Hjorth's dynamo of 1848, 10 Hopkinson's curve, 221 Horse-power curves, 223 transmitted to dynamo, 217 JMPROVEMENTS, Wheatstone and Cooke's, 9 by Wilde, : 2 in dynamos, 16 by Sir William Thomson, 17 by Gordon, 17 in Brush's armature, 18 Immisch's motors, 340 Incandescent lighting, compound dynamo in, 244 Induction coils combined with mag- net, 9 Insulated wire, 75 conductivity of, 75 Insulation of dynamo foundation 1 ?, 253 Intensity of the magnetic field, 34 and quantity in electro-plating, 262 Internal losses in dynamo, 193, 216 resistance, line of, 225 Interrupter, circuit, 7 INDEX. Iron ring experiment, Faraday's, 4 Iron, permeability of, not constant, r/i 349 54 lines in armature core, 193 Kapp's dynamo, 283 armature, 284 multipolar armature, 289 alternator, 291 central station dynamo, 288 Kennedy's dynamo, 307 Kilowatt, the, 214 T AMP test for leakage, in ex- ternal circuit, 256 Large current dynamos, 265 Lead ribbon fuses, 258 Leakage, magnetic, 32 tests for, 256 Length of the magnetic bobbin, 74 Lines of magnetization, physical significance of, 32 magnetism, diffusion of the, 32 force and a conductor, 34 force, value of the, 34 in dynamo, 35 Localization of faults, 255 Losses in dynamo, internal, 193 A/f ACHINE, Faraday's disc, 5 Dal Negro's, 6 Ritchie's, 6 Clark's, 6 Saxton's, 6 magneto, early type of, 7 Stohrer's, 8 Woolrich's, of 1841, 9 Brett's, of 1848, 10 Hjorth's, of 1848, 1C the Alliance, 10 Pacinotti's, 15 Machine winding, 77 Magneto-electric, meaning of, 2 Magneto-electric machines, earliest, 4 early type of, 7 the Alliance, 10 Siemens' telegraph, 1 1 for bell ringing, 12 Magnetic field, the, 30 of current, 31 Magnetic lines, curves of, 31 diffusion of the, 32 Magnetic leakage, 32 lines, physical significance o r , 32 unit, the, 33 reluctance, 33 field, intensity of the, 34 Magnetization, maximum, 35 Magnetic field of dynamo, 36 researches of Rowlands, 54 Magnetization, cuive of, 55 Magnetic circuit, Ohm's law and the, 58 saturation, 60 Magnet coils, 6 1 winding, trial method of deter- mining, 6 1 Hering's formula for, 64 relationship of the coils, 65 calculations respecting, 66 Magneto motive force, 66 Magnet wires, table of, 73 Magnet bobbin, length of, 74 insulated wire, 75 Magnet, vaiious forms of, 79 Magnets, single circuit, 79 Magnetic circuit in the core, 80 reluctance of air spaces, 195 Magnetization, " characteristic," 229 curves of, 286 Magnetic diverter, 242 Main and shunt coils, proportion between, 197 Maximum magnetization, 53 350 INDEX. Mica insulation of collector, 257 Momentary short circuiting of dy- namo, 258 Modern view of the magnetic cir- cuit, 56 Mordey's alternating current dy- namo, 18 Motion of a conductor in a field, 36 Multipolar drum dynamo, Kapp's, 288 Motor, electric, nature of, 2 NJEGATIVE and positive ter- minals of dynamo, 251 Non-fluctuating current, 14 Notes, operative, 248 law and the magnetic circuit, 58 and the dynamo, 215 Open coil armature, early applica- tion of, 17 Operation of winding, 76 Operative notes, 248 Overloaded dynamo, 261 Overtype dynamo, 28 Gramme dynamo, 272 dynamo, Kapp's, 283 Elwell Parker dynamo, 281 Output and efficiency, 213 pACINOTTI'S ring armature, 14 machine, 15 Parallel working, 231 and series, dynamo in, 232 running of compound dynamos, 234 of alternators, 235 working of two alternators, 235 Parts of the dynamo, 20 Paterson & Cooper's dynamo, 309 Percentages of loss in dynamo coils, 193 Permeability of iron not constant, 54 Phoenix dynamo, 309 Physical significance of the lines of magnetism, 32 Pixii's machine, 6 Plating vat, secondary current from, 266 Polarity of the field magnet in ex- citing, 250 Positive and negative terminals of alternators, 251 Position of brushes, 259 Potential, fall of, in armature, 193 Principle, the self-energizing, 13 Principles, the elementary, 30 Proportions of main and shunt coil-;, 197 J^ECHNIEWSKTS dynamo, 276 Records, graphical, 219 Regulation by shifting brushes, 200 by hand, 203 by varying the reluctance, 203 Firth's method of, 203 through separate excitation, 204 resistance, 205 of series dynamo, 206 of shunt dynamo, 207 by compounding, 209 by composite field, 2 1 1 for constant current, 212 of E.M.F., Firth's method, 305 Relationship of the field magnet coils, 65 Reluctance, magnetic, 33 of field magnet, 195 of air spaces, 196 of armature, 197 variation of, and governing, 203 Reputed gauge of wire not reliable, 76 INDEX. 351 Residual magnetism, failure of, 259 Resistance regulator, 43, 205 internal, line of, 225 Re-turning of collector, 260 Reverser of current for testing, 254 Rheostat or resistance regulator, 43 Ribbon lead fuses, 258 Ring armature, Pacinotti's, 14 Gramme's, 15 Ritchie's maclrne, 6 Rowland's researches, 54 Rope driving of dynamo, 252 gATURATJON, magnetic, 60 Sautter-Lemonnier dynamo, 274 dimensions of, 275 Saxton's machine, 6 Secondary current of plating vat, 266 Self-energizing principles, develop- ment of, 13 Separate excitation, 44 regulation by, 204 Series winding, 45 and shunt coils, carrying capa- city of, 199 curves compared, 228 Series working, 230 and parallel running, 230 Series-wound dynamos in parallel, 232 Series-running of two alternators, 237 Series dynamos in arc lighting, 246 regulation of, 206 Series arrangement of vats, 268 Shifting of brushes and regulation, 200 effects of, 20 1 Short circuit faults, 255 circuiting by collector bars, 257 Shunt dynamo, early invention of, Shunt winding, 46 function of the, 48 Shunt and main coils, proportion between, 197 carrying capacity of, 199 Shunt dynamo, regulation of, 207 and series coils, proportion between, 217 Shunt dynamos, characteristics, 226 and series curves compared, 228 Shunt dynamos in series, 231 in parallel, 233 in incandescent lighting, 245 and short circuiting, 250 Shuttle armature, Sturgeon's, 8 Siemens', I r short, 12 Siemens' shuttle armature, 1 1 dynamo in electrolysis, 269, 274 bipolar, 274 Simplest conception of the dynamo, 23 armature, 24 Single circuit magnets, 79 coil field magnet dynamo, 307 Sir William Thomson's improve- ments in dynamos, 17 Soren Hjorth's dynamo, 10 Speed, governing by, 202 variable, curve of, 225 Spherical armature dynamo, the, 3 10 Squared paper for curves, 220 Sprague's motors, 341 Stohrer's machine, 8 Stretching wire in winding, 78 Sturgeon's armature, 8 Suggestions of Hjorth, 10 Supplementary parts of the dynamo, 21 Switching alternators into parallel, 238 Synchronizing of two alternators, 239 352 INDEX. ''FABLE of magnet-wires, 72 values relating to charac- teristics, 223 of E.M.F. required in electro- plating, 263 of current density in electro- plating, 264 " Teazer winding" brushes, 267 Telegraphic magneto machine, 1 1 Testing for faults, 252 for leakage, 256 The ampere-turns in exciting coils, 71 The Watt unit of power, 214 Thomson-Houston dynamos, the, 310 Transformers and alternators, 243 Treatment of new collector, 249 Trial, method of determining the magnet winding, 6 1 Two-part commutator, 27 Typical dynamos, 271 T JNIT, magnetic, 33 the Board of Trade, 214 \T ALUE of the lines of force, 34 Variable speed curves, 225 resistance, governing by, 202 Variation of the magnetism, regu- lating by, 202 Vats or baths in series, 268 Volts lost internally, 216 Volt-ampere, the, 2 [4 "\XTATT, unit of power, 214 Westinghouse's alternator, 316 armature, 317 safety device, 320 dynamos, tests of, 323 converters, tests of, 328 Wheatstone & Cook's early im- provements, 9 Width of the air gaps and the E.M.F., 306 Wilde's improvements, 12 Winding, compound, early concep- tion of, 13 shunt, early invention of, 14 series, 45 shunt, 46 compound, 49 of magnets, calculations re- specting, 66 calculation of the heating of, 67 operation of, 76 machine, 77 composite, 316 Wires, table of magnet, 72 insulated, 75 reputed gauge of, 76 Woolrich's machine of 1841, 9 dynamo, of 1841, 264 Worn commutator, 260 PRINTED BY J. 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"To such of our readers as are interested in the subject of fires and fire apparatus, we can most heartily commend this book." Engineering. " It displays much evidence of careful research ; and Mr. Young has put his facts neatly together. It is evident enough that his acquaintance with the practical details of the construction of steam fire engines Is accurate and full." Ettg-imer. Estimating for Engineering Wor7t, tractors for many important engineering works." Engineer. HUMBER'S RECORD OF MODERN ENGINEERING. SECOND SERIES. Imp. 410, with 36 Double Plates, Photographic Portrait of Robert Stephenson, C.E., M.P., F.R.S., &c., and copious descriptive Letterpress > Specifications, &c., 3 3$. half-morocco. List of the Plates and Diagrams. and Abergavenny Railway; Ebbw Viaduct, Merthyr, Tredegar, and Abergavenny Rail- way ; College Wood Viaduct, Cornwall Rail- way; Dublin Winter Palace Roof (3 plates); Bridge over the Thames, L. C. & D. Railway (6 plates) ; Albert Harbour, Greenock (4 platesf. Birkenhead Docks, Low Water Basin (15 plates); Charing Cross Station Roof, C. C. R.flway (3 plates) ; Digswell Viaduct, Great Northern Railway ; Robbery Wood Viaduct, Great Northern Railway ; Iron Permanent Way; Clydach Viaduct, Merthyr, Tredegar, " Mr. Humber has done tha profession good and true service, by the fine collection of examples he has here brought before the profession and the public." Practical Mechanic's Journal. HUMBER'S RECORD OF MODERN ENGINEERING. THIRD SERIES. Imp. 4to, with 40 Double Plates, Photographic Portrait of J. R. M'Clean, late Pres. Inst. C.E., and copious descriptive Letterpress, Speci- fications, &c., 3 3$. half-morocco. List of the Plates and Diagrams. MAIN DRAINAGE, METROPOLIS. North SitU. Map showing Interception of Sewers j Middle Level Sewer (* plates) ; Outfall Sewer, Bridge over River Lea (3 plates) ; Outfall Sewer, Bridge over Marsh Lane, North Woolwich Railway, and Bow and Barking Railway Junc- tion ; Outfall Sewer, Bridge over Bow and Barking Railway (3 plate*); Outfall Sewer. Bridge over East London Waterworks' Feeder Sewer, Reservoir and Outlet (4 plates) ; Outfall Sewer, Filth Hoist; Sections of Sewers (North and South Sides). THAMES EMBANKMENT. Section of River Wall ; Steamboat Pier, Westminster (2 plates); Landing Stairs between Charing Cross and Waterloo Bridges ; York Gate (2 plates) ; Over- flow and Outlet at Savoy Street Sewer (3 plates) ; Steamboat Pier, Waterloo Bridge (3 plates) ; J_unction _ of Sewers, Plans and Sections ; Gullies, Plans and Sections; Rolling Stock; Granite and Iron Forts. (i plates) ; Outfall Sewer, Reservoir (2 plates) ; Outfall Sewer, Tumbling Bay and Outlet ; Out- fall Sewer, Penstocks. South Stdt. Outfall Sewer, Bermondsey Branch (2 plates) ; Outfall " The drawings have a constantly increasing ralue, and whoever desire* to possess clear repre- sentations of the two great works carried out by our Metropolitan Board will obtain Mr. Humber's volume." Engineer. HUMBER'S RECORD OF MODERN ENGINEERING. FOURTH SERIES. Imp. 410, with 36 Double Plates, Photographic Portrait of John Fowler, late Pres. Inst. C.E., and copious descriptive Letterpress, Speci- fications, &c., 3 35. half-morocco. List of the Plates and Diagrams. Abbey Mills Pumping Station, Main Drain- age, Metropolis (4 plates); Barrow Docks (5 pktes) ; Manquis Viaduct, Santiago and Val- paraiso Railway (2 plates) ; Adam's Locomo- ay (2 plates) ; Sharing Cross Mesopotamia ; Viaduct over the River Wye, Midland Railway (3 plates) ; St. Germans Via- duct, Cornwall Railway (2 plates); Wrought- Iron Cylinder for Diving Bell ; Millwall Docks (6 plates) ; Milroy's Patent Excavator ; Metro- politan District Railway (6 plates); Harbours, Ports, and Breakwaters (3 plates). live, St. Helen's Canal Rail Cannon Street Station Roof, C Railway (3 plates) ; Road Bridge over the River Moka (2 plates) ; Telegraphic Apparatus for "We fladly welcome another year's issue of this valuable publication from the able pen ot Mr. Humber. The accuracy and general excellence of this work are well known, while its useful- iv-* in giving the measurements and details ot' some of the latest examples of engineering , ts carried out by the most eminent men in the profession, cannot be too highly prized." Artisan. CIVIL ENGINEERING, SURVEYING, etc. 9 MR. HUMBER'S ENGINEERING BOOKS continued. Strains, Calculation of. A HANDY BOOK FOR THE CALCULATION OF STRAINS IN GIRDERS AND SIMILAR STRUCTURES, AND THEIR STRENGTH. Consisting of Formulae and Corresponding Diagrams, with numerous details for Practical Application, &c. By WILLIAU HUMBER, A-M.Inst.C.E., &c. Fourth Edition. Crown 8vo, nearly 100 Woodcuts and 3 Plates, 75. 6d. cloth. " The formulae are neatly expressed, and the diagrams good." Athenaum. " We heartily commend this really handy book to our engineer and architect readers." Ettf lish Mechanic. Barlow's Strength of Materials, enlarged byHumber A TREATISE ON THE STRENGTH OF MATERIALS; with Rules for Application in Architecture, the Construction of Suspension Bridges, Railways, &c. By PETER BARLOW, F.R.S. A New Edition, revised by his Sons, P. W. BARLOW, F.R.S., and W. H. BARLOW, F.R.S. ; to which a-e added, Experiments by HODGKINSON, FAIRBAIRN, and KIRKALDY; and Formulas for Calculating Girders, &c. Arranged and Edited by W. HUMBER, A-M.Inst.C.E. Demy 8vo, 400 pp., with 19 large Plates and numerous Wood- cuts, i8s. cloth. " Valuable alike to the student, tyro, and th experienced practitioner, It will always rank in future, as it has hitherto done, as the standard treatise on that particular subject." Engineer. " There is no greater authority than Barlow." Building News. " As a scientific work of the first class, it deserves a foremost place on the bookshelves of every civil engineer and practical mechanic." English Mechanic. Trigonometrical Surveying. AN OUTLINE OF THE METHOD OF CONDUCTING A TRIGONOMETRICAL SURVEY, for the Formation of Geographical and Topographical Maps and Plans , Military Reconnaissance, Levelling, &c., with Useful Problems, Formulae, and Tables. By Lieut.-General FROMB, R.E. Fourth Edition, Revised and partly Re- written by Major General Sir CHARLES WARREN, G.C.M.G., R.E. With 19 Plates and 115 Woodcuts, royal 8vo, i6s. cloth. "The simple fact that a fourth edition has been called for Is the b*t testimony to Its merits. No words of praise from us can strengthen the position so well and so steadily maintained by this work. Sir Charles Warren has revised the entire work, and made such additions as were necessary to bring every portion of the contents up to the present date." Broad Arrow. Field Fortification. A TREATISE ON FIELD FORTIFICATION, THE ATTACK OF FORTRESSES, MILITARY MINING, AND RECONNOITRING. By Colonel I. S. MACAULAY, late Professor of Fortification in the R.M.A., Wool- wich. Sixth Edition, crown 8vo, cloth, with separate Atlas of 12 Plates, 125. Oblique Bridges. A PR A CTICA LAND THEORETICA L ESS A Y ON OBLIQ UE BRIDGES. With 13 large Plates. By the late GEORGE WATSON BUCK, M.I.C.E. Third Edition, revised by his Son, J. H. WATSON BUCK, M.I.C.E. ; and with the addition of Description to Diagrams for Facilitating the Con- struction of Oblique Bridges, by W. H. BARLOW, M.I.C.E. Royal 8vo, izs. cloth. " The standard text-book for all engineers regarding skew arches Is Mr. Buck's treatise, and it would be impossible to consult a better. ' Engineer. "Mr. Buck's treatise is recognised as a standard text-book, and his treatment has divested the subject of many of the intricacies supposed to belong to it. As a guide to the engineer and archi- tect, on a confessedly difficult subject, Mr. Buck's work is unsurpassed." Building News. Water Storage, Conveyance and Utilisation. WA TER ENGINEERING : A Practical Treatise on the Measure- ment, 'Storage, Conveyance and Utilisation of Water for the Supply of Towns, for Mill Power, and for other Purposes. By CHARLES SLAGG, Water and Drainage Engineer, A.M.Inst.C.E., Author of " Sanitary Work in the Smaller Towns, and in Villages," &c. With numerous Illusts. Cr. 8vo. 75. 6d. cloth. " As a small practical treatise on the water supply of towns, and on some applications of water-power, the work is in many respects excellent." Engineering: " The author has collated the results deduced from the experiments of the most eminent authorities, and has presented them in a compact and practical form, accompanied by very clear and detailed explanations. . . . The application of water as a motive power is treated very carefully and exhaustively." Builder. "For anyone who desires to begin the study of hydraulics with a consideration of the practical . applications of the science there is no better guide." Architect. ro CROSBY LOCK WOOD & SON'S CATALOGUE. Statics, Graphic and Analytic. GRAPHIC AND ANALYTIC STATICS, in their Practical Appli. cation to the Treatment of Stresses in Roofs, Selid Girders, Lattice, Bowstring and Suspension Bridges, Braced Iron Arches and Piers, and other Frameworks. By R. HUDSON GRAHAM, C.E. Containing Diagrams and Plates to Scale. With numerous Examples, many taken from existing Structures. Specially arranged for Class- work in Colleges and Universities. Second Edition, Re- vised and Enlarged. 8vo, i6s. cloth. "Mr. Graham's book will find a place wherever graphic and analytic statics are used or studied." Engineer. " The work is excellent from a practical point of view, and has evidently been prepared with much care. The directions for working are ample, and are illustrated by an abundance of well- selected examples. It is an excellent text-book for the practical draughtsman." Athtnceum. Student's Text-Book on Surveying. PRACTICAL SURVEYING: A Text-Book for Students pre- paring for Examination or for Survey-work in the Colonies. By GEORGE W. USILL, A.M.I.C.E., Author of "The Statistics of the Water Supply of Great Britain." With Four Lithographic Plates and upwards of 330 Illustra- tions. Second Edition, Revised. Crown 8vo, 75. 6d. cloth. ' The best forms of instruments are described as to their construction, uses and modes of employment, and there are innumerable hints on work and equipment such as the author, in his experience as surveyor, draughtsman and teacher, has found necessary, and which the student in his inexperience will find most serviceable." Engineer. " The latest treatise in the English language on surveying, and we have no hesitation in say- ing that the student wi,ll find it a better guide than any of its predecessors .... Deserves to b recognised as the first book which should be put in the nands of a pupil of Civil Engineering, and every gentleman of education who sets out for th Colonies would find it well to have a copy." Architect. " A very useful, practical handbook on field practice. Clear, accurate and not too con- densed." Journal of Education. Survey Practice. A.M.I.C.E., Author of " Hydraulic Manual," "Modern Metrology,' Second Edition, Enlarged. Large crown 8vo, I2S. 6d. cloth. "Mr. Jackson has produced a valuable vade-mecum for the surveyor. We can recommend this book as containing an admirable supplement to the teaching of the accomplished surveyor." Athtnaum. " As a text-book we should advise all surveyors to place It In their libraries, and study well the matured instructions afforded in its pages." Colliery Guardian. " The author brings to his work a fortunate union of theory and practical experience which, aided by a dear and lucid style of writing, renders the book a very useful one." Builder. Surveying, Land and Marine. LAND AND MARINE SUR V EYING, in Reference to the Pre- paration of Plans for Roads and Railways ; Canals, Rivers, Towns' Water Supplies ; Docks and Harbours. With Description and Use of Surveying Instruments. By W. D. HASKOLL, C.E., Author of " Bridge and Viaduct Con- struction,'' &c. Second Edition, Revised, with Additions. Large cr. 8vo, gs. ci. " This book must prove of great value to the student. We have no hesitation in r SON'S CATALOGUE. DELAMOTTE'S WORKS ON ILLUMINATION AND ALPHABETS, A PRIMER OF THE ART OF ILLUMINATION, for the Use of Beginners : with a Rudimentary Treatise on the Art, Practical Directions for its exercise, and Examples taken from Illuminated MSS. .printed in Gold and Colours. By F. DELAMOTTE. New and Cheaper Edition. Small 4to, 6s. orna- mental boards. "The examples of ancient MSS. recommended to the student, which, with much good sense, the author chooses from collections accessible to all, are selected with judgment and Knowledge, as well as taste." Athenaum. ORNAMENTAL ALPHABETS, Ancient and Medieval, from the Eighth Century, with Numerals; including Gothic, Church-Text, large and small, German, Italian, Arabesque, Initials for Illumination, Monograms, Crosses, &c. &c., for the use of Architectural and Engineering Draughtsmen, Missal Painters, Masons, Decorative Painters, Lithographers, Engravers, Carvers, &c. &c. Collected and Engraved by F. DELAMOTTE, and printed in Colours. New and Cheaper Edition. Royal 8vo, oblong, as. 6d. ornamental boards. "For those who Insert enamelled sentences round gilded chalices, who blazon shop legends over shop-doors, who letter church walls with pithy sentences from the Decalogue, this book will be use- fuL Athenentm. EXAMPLES OF MODERN ALPHABETS, Plain and Ornamental; including German, Old English, Saxon, Italic, Perspective, Greek, Hebrew, Court Hand, Engrossing, Tuscan, Riband, Gothic, Rustic, and Arabesque ; with several Original Designs, and an Analysis of the Roman and Old English Alphabets, large and small, and Numerals, for the use of Draughtsmen, Sur- veyors, Masons, Decorative Painters, Lithographers, Engravers, Carvers, &c. Collected and Engraved by F. DELAMOTTE, and printed in Colours. New and Cheaper Edition. Royal 8vo, oblong, as. 6d. ornamental boards. "There is comprised In it ev*ry possible shape into which the letters of the alphabet and numerals can be formed, and the talent which has been expended in the conception of the various plain and ornamental letters is wonderful." Standard. MEDIEVAL ALPHABETS AND INITIALS FOR ILLUMI- NA TORS. By F. G. DELAMOTTE. Containing 21 Plates and Illuminated Title, printed in Gold and Colours. With an Introduction by T. WILLIS BROOKS. Fourth and Cheaper Edition. Small 4to, 45. ornamental boards. " A volume in which the letters of the alphabet come forth glorified in gilding andall the colours of the prism interwoven and intertwined and intermingled." Sun. THE EMBROIDERER'S BOOK OF DESIGN. Containing Initials, Emblems, Cyphers, Monograms, Ornamental Borders, Ecclesiastical Devices, Mediaeval and Modern Alphabets, and National Emblems. Col- lected by F. DELAMOTTE, and printed in Colours. Oblong royal 8vo, is. 6d. ornamental wrapper. "The book will be of great assistance to ladies and young children who are endowed with the art of plying the needle in this most ornamental and useful pretty work." East Anglian Times. Wood Carving. INSTRUCTIONS IN WOOD-CARVING, for Amateurs; with Hints on Design. By A LADY. With Ten Plates. New and Cheaper Edition. Crown 8vo, as. in emblematic wrapper. "The handicraft of the wood-carver, so well as a book can impart it, may be learnt from ' A Lady's ' publication." Athenaum. " The directions given are plain and easily understood. English Mechanic, Glass Painting. GLASS STAINING AND THE ART OF PAINTING ON GLASS. From the German of Dr. GESSERT and EMANUEL OTTO FROMBERG. With an Appendix on THE ART OF ENAMELLING. iamo, as. 6d. cloth limp, Letter fainting. THE ART OF LETTER PAINTING MADE EASY. By JAMES GREIG BADENOCH. With ia full-page Engravings of Examples, is. 6d. cloth limp. " The system is a simple one, but quite original, and well worth the careful attention of letter painters. It can be easily mastered and remembered." Building News, CARPENTRY, TIMBER, etc. 19 CARPENTRY, TIMBER, etc. Tredgold's Carpentry, Revised & Enlarged by Tarn. THE ELEMENTARY PRINCIPLES OF CARPENTRY. A Treatise on the Pressure and Equilibrium of Timber Framing, the Resist- ance of Timber, and the Construction of Floors, Arches, Bridges, Roofs, Uniting Iron and Stone with Timber, &c. To which is added an Essay on the Nature and Properties of Timber, &c., with Descriptions of the kinds of Wood used in Building ; also numerous Tables of the Scantlings of Tim- ber for different purposes, the Specific Gravities of Materials, &c. By THOMAS TREDGOLD, C.E. With an Appendix of Specimens of Various Roofs of Iron and Stone, Illustrated. Seventh Edition, thoroughly revised and considerably enlarged by E. WYNDHAM TARN, M.A., Author of "The Science of 'Build- ing," &c. With 61 Plates, Portrait of the Author, and several Woodcuts. In one large vol., 4to, price i 5$. cloth. "Ought to be in every architect's and every builder's library. " Builder. " A work whose monumental excellence must commend it wherever skilful carpentry Is con- cerned. The author's principles are rather confirmed than impaired by time. The additional plates are of great intrinsic value." Building News. Woodworking Machinery. WOODWORKING MACHINERY: Its Rise, Progress, and Construction. With Hints on the Management of Saw Mills and the Economi- cal Conversion of Timber. IllustratedjWith Examples ot Recent Designs by leading English, French, and American Engineers. By M. Powis BALE, A.M.Inst.C.E., M.I.M.E. Large crown 8vo, 125. 6d. cloth. " Mr. Bale is evidently an expert on the subject and he has collected so much information that his book is all-sufficient for builders and others engaged in the conversion of timber." AyJtiiect. "The most comprehensive compendium of wood- working machinery we have seen. The author is a thorough master of his subject." Building Nevis. " The appearance of this book at the present time will, we should think, give a considerable Impetus to the onward march of the machinist engaged in the designing and manufacture of wood-working machines. It should be in the office of every wood-working factory." English Mechanic. Saw Mills. SA W MILLS : Their Arrangement and Management, and the Economical Conversion of Timber. (A Companion Volume to " Woodwork- ing Machinery.") By M. Powis BALE. With numerous Illustrations. Crown 8vo, IDS. 6d. cloth. " The administration of a large sawing establishment is discussed, and the subject examined rom a financial standpoint. We could not desire a more complete or practical treatise." Builder. "We highly recommend Mr. Bale's work to the attention and perusal of all those who are en- gaged in the art of wood conversion, or who are about building or remodelling saw-mills on im- proved principles." Building Ne-wi. Carpentering. THE CARPENTER'S NEW GUIDE ; or, Book of Lines for Car- penters ; comprising all the Elementary Principles essential for acquiring a knowledge of Carpentry. Founded on the late PETER NICHOLSON'S Standard Work. A New Edition, Revised by ARTHUR ASHPITEL, F.S.A. Together with Practical Rules on Drawing, by GEORGE PYNK. With 74 Plates, 4to, i is. cloth. Handrailinff and Stairbuildinff. A PRACTICAL TREATISE ON HANDRAILING : Showing New and Simple Methods for Finding the Pitch of the Plank, Drawing the Moulds, Bevelling, Jointing-up, and Squaring the Wreath. By GEORGE COLLINGS. Second Edition, Revised and Enlarged, to which is added A TREATISE ON STAIRBUILDING. With Plates and Diagrams, izmo, 2s. 6d. cloth limp. ' ' Will be found of practical utility in the execution of this difficult branch of joinery." Suilaer. " Almost every difficult phase of this somewhat intricate branch of joinery is elucidated by the aid of plates and explanatory letterpress." Furniture Gazette. Circular Work. CIRCULAR WORK IN CARPENTRY AND JOINERY: A Practical Treatise on Circular Work of Single and Double Curvature. By GEORGE COLLINGS, Author of " A Practical Treatise on Handrailing." Illus- trated with numerous Diagrams. Second Edition. I2mo, 2s. 6d. cloth lioip. " An excellent example of what a book of this kind should be. Cheap in price, clear In defini- tion and practical in the examples selected." liuiuter. 20 CROSBY LOCK WOOD & SON 'S CATALOGUE. Umber Merchant's Companion. THE TIMBER MERCHANT'S AND BUILDER'S COM- PANION. Containing New and Copious Tables of the Reduced Weight and Measurement of Deals and Battens, of all sizes, from One to a Thousand Pieces, and the relative Price that each size bears per Lineal Foot to any given Price per Petersburg Standard Hundred ; the Price per Cube Foot of Square Timber to any given Price per Load of 50 Feet ; the proportionate Value of Deals and Battens by the Standard, to Square Timber by the Load of 50 Feet ; the readiest mode of ascertaining the Price of Scantling per Lineal Foot of any size, to any given Figure per Cube Foot, &c. &c. By WILLIAM DOWSING. Fourth Edition, Revised and Corrected. Cr. 8vo, 35. cl. " We are glad to see a fourth edition of these admirable tables, which for correctness and simplicity of arrangement leave nothing- to be desired." Timber Trades "Journal. "An exceedingly well-arranged, clear, and concise manual of tables for the use of all who buy or sell timber." Journal qf Forestry. ^Practical Timber MercTiant. THE PRACTICAL TIMBER MERCHANT. Being a Guide for the use of Building Contractors, Surveyors, Builders, &c., comprising useful Tables for all purposes connected with the Timber Trade, Marks of Wood, Essay on the Strength of Timber, Remarks on the Growth of Timber, &c. By W. RICHARDSON. Fcap. 8vo, 35. 6d. cloth. " This handy manual contains much valuable information for the use of timber merchant?, builders, foresters, and all others connected with the growth, sale, and manufacture of timber. ' Jownml of Forestry. Timber Freight Book. THE TIMBER MERCHANTS, SAW MILLER'S. AND IMPORTER'S FREIGHT BOOK AND ASSISTANT. Comprising Rules, Tables, and Memoranda relating to the Timber Trade. By WILLIAM RICHARDSON, Timber Broker; together with a Chapter on " SPEEDS OF SAW MILL MACHINERY," by M. Powis BALE, M.I.M.E., &c. i2mo, 35. 6d. cl. boards. " A very useful manual of rules, tables, and memoranda relating to the timber trade. We re- commend it as a compendium of calculation to all timber measurers and merchants, and as supply- Ing a real want In the trade." Building News. Packing-Case Makers, Tables for. PACKING-CASE TABLES ; showing the number of Super- ficial Feet in Boxes or Packing-Cases, from six inches square and upwards. By W. RICHARDSON, Timber Broker. Third Edition. Oblong 4to, 3$. 6d. cJ. " Invaluable labour-saving tables." Ironmonger. "Will save much labour acd calculation." Grocer. Superficial Measurement. THE TRADESMAN'S GUIDE TO SUPERFICIAL MEA- SUREMENT. Tables calculated from i to 200 inches in length, by i to 108 inches in breadth. For the use of Architects, Surveyors, Engineers, Timber Merchants, Builders, &c. By JAMES HAWKINGS. Third Edition, Fcap., 35. 6d. cloth. " A useful collection of tables to facilitate rapid calculation of surfaces. The exact area of any s-irface of which the limits have been ascertained can be instantly determined. The book will be found of the greatest utility to all engaged in building operations." Scotsman. " These tables will be found of great assistance to all who require to make calculations in super- ficial measurement." English Mechanic. Forestry. THE ELEMENTS OF FORESTRY. Designed to afford In- formation concerning the Planting and Care of Forest Trees for Ornament or Profit, with Suggestions upon the Creation and Care of Woodlands. By F. B. HOUGH. Large crown 8vo, tos. cloth. Timber Importer's Guide. THE TIMBER IMPORTER'S, TIMBER MERCHANT'S AND BUILDER'S STANDARD GUIDE. By RICHARD E. GRANDY. Compris- ing an Analysis of Deal Standards, Home and Foreign, with Comparative Values and Tabular Arrangements for fixing Nett Landed Cost on Baltic and North American Deals, including all intermediate Expenses, Freight, Insurance, &c. &c. Together with copious Information for the Retailer and Builder. Third Edition, Revised, ismo, as. cloth limp. " Everything- it pretends to be : built up gradually, it leads one from a forest to a treenail, and throws in, as 2 makeweight, a host of material concerning bricks, columns, cisterns, &c." English Mxhanic. MARINE ENGINEERING, NAVIGATION, etc. MARINE ENGINEERING, NAVIGATION, etc. Chain Cables. CHAIN CABLES AND CHAINS. Comprising Sizes and Curves of Links, Studs, &c., Iron for Cables and Chains, Chain Cable and Chain Making, Forming and Welding Links, Strength of Cables and Chains, Certificates for Cables, Marking Cables, Prices of Chain Cables and Chains, Historical Notes, Acts of Parliament, Statutory Tests, Charges for Testing, List of Manufacturers of Cables, &c. &c. By THOMAS W. TRAILL, F.E.R.N., M. Inst. C.E., Engineer Surveyor in Chief, Board of Trade, Inspector of Chain Cable and Anchor Proving Establishments, and General Superin- tendent, Lloyd's Committee on Proving Establishments. With numerous Tables, Illustrations and Lithographic Drawings. Folio, 2 25. cloth, bevelled boards. "It contains a vast amount of valuable information. Nothing 1 seems to be wanting to make it a complete and standard work of reference on the subject." Nautical Mag azint. Marine Engineering. MARINE ENGINES AND STEAM VESSELS (A Treatise on). By ROBERT MURRAY, C.E. Eighth Edition, thoroughly Revised, with considerable Additions by the Author and by GEORGE CARLISLE, C.E., Senior Surveyor to the Board of Trade at Liverpool. 12010, 5$, cloth boards. " Well adapted to give the young steamship engineer or marine engine and boiler maker a general Introduction into his practical work." Mechanical World. " We feel sure that this thoroughly revised edition will continue to be as popular in the future as it has been in the past, as, for its size, it contains more useful information than any similar t realise. ' ' Industries. The information given is both sound and sensible, and well qualified tD direct young sea- going hands on the straight road to the extra chief's c-rtificate. Most useful to survejors, inspectors, draughtsmen, and all young engineers who take an interest in their profession." Glasgow Herald. "An indispensable manual for the student of marine engineering." Liverpool Mercury. Focket-BooJe for Naval Architects and Shipbuilders. THE NAVAL ARCHITECT'S AND SHIPBUILDER'S POCKE T-BOOK of Formula:, Rules, and Tables, and MA RINE ENGINEER'S AND SURVEYOR'S Handy Book of Reference. By CLEMENT MACKROW, Member of the Institution of Naval Architects, Naval Draughtsman. Fourth Edition, Revised. With numerous Diagrams, &c. Fcap., 125. 6d. strongly bound in leather. " >VU1 oe found to contain the most useful tables and formulae required by shipbuilders, carefully -collected from the best authorities, and put together in a popular and simple form." Engineer. " The professional shipbuilder has now, in a convenient and accessible form, reliable data for solving many of the numerous problems that present themselves in the course of his work." Iron. "There is scarcely a subject on which a naval architect or shipbuilder can require to refresh his memory which will not be found within the covers of Mr. Mackrow'sbook." English Mechanic. rocket-Book for Marine Engineers. A POCKET-BOOK OF USEFUL TABLES AND FOF- UULM FOR MARINE ENGINEERS. By FRANK PROCTOR, A.I.N.A, Third Edition. Royal same, leather, gilt edges, with strap, 45. "We recommend it to our readers as going far to supply a long-felt want." Naval Scitnce. "A most useful companion to all marine engineers." United Service Gazette. Introduction to Marine Engineering. ELEMENTARY ENGINEERING : A Manual for Young Marine Engineers and Apprentices. In the Form of Questions and Answers on Metals, Alloys, Strength of Materials, Construction and Management of Marine Engines and Boilers, Geometry, &c. &c. With an Appendix of Useful Tables. By JOHN SHERREN BREWER, Government Marine Surveyor, Hong- kong. Small crown 8vo, 2s. cloth. " Contains much valuable information for the class for whnm it is intended, especially in the chapters on the management of boilers and eng nes." Nautical Magazine. ' A useful introduction to the more elaborate text books." Scotsman. " To a student who has the requisite desire and resolve to attai.i a thorough knowledge, Mr. Brewer offers decidedly useful help.'' Atftenaum. Navigation, PRACTICAL NAVIGATION. Consisting of THE SAILOR'S SEA-BOOK, by JAMES GREENWOOD and W. H. ROSSER ; together with the requisite Mathematical and Nautical Tables for the Working of the Problems, by HENRY LAW, C.E., and Professor J. R. YOUNG. Illustrated, ijino, 7$. strongly halt-bound. 22 CROSBY LOCK WOOD & SON'S CATALOGUE. MINING AND METALLURGY. Metalliferous Mining in the United Kingdom. BRITISH MINING : A Treatise on the History, Discovery .Practical Development, and Future Prospects of Metalliferous Mines in the United King- dom. By ROBERT HUNT, F.R.S., Keeper of Mining Records; Editor of " Ure's Dictionary of Arts, Manufactures, and Mines, &c. Upwards of 950 pp., with 230 Illustrations. Second Edition, Revised, Super-royal 8vo, 2 2*. cloth. "One of the most valuable works of reference of modem times. Mr. Hunt, as keeper of mining records of the United Kingdom, has had opportunities for such a task not enjoyed by anyone else, and has evidently made the most of them. . . . The language and style adopted are good, and the treatment of the various subjects laborious, conscientious, and scientific." Engineering: "The book is, in fact, a treasure-house of statistical information on mining: subjects, and we know of no other work embodying so great a mass of matter of this kind. Were this the only merit f Mr. Hunt's volume, it would be sufficient to render it indispensable in this library of everyone interested in the development of the mining and metallurgical industries of this country." Athenaum. "A mass of information not elsewhere available, and of the greatest value to those who may b interested in our great mineral industries." Engineer. " A sound, business-like collection of interesting facts. . . . The amount of Information Mr. Hunt has brought together is enormous. . . . The volume appears likely to convey more Instruction upon the subject than any work hitherto published." Mining yournal. Colliery Management. THE COLLIERY MANAGER'S HANDBOOK; A Compre- hensive Treatise on the Laying-out and Working of Collieries, Designed as a Book of Reference for Colliery Managers, and for the Use of Coal-Mining Students preparing for First-class Certificates. By CALEB PAMELY, Mining Engineer and Surveyor; Member of the North of England Institute of Mining and Mechanical Engineers ; and Member of the South Wales Insti- tute of Mining Engineers. With nearly 500 Plans, Diagrams, and other Illustrations. Medium 8vo, about Coo pages. Price fi *s. strongly bound. [just published. Coal and Iron. THE COAL AND IRON INDUSTRIES OF THE UNITED KINGDOM. Comprising a Description of the Coal Fields, and of the Principal Seams of Coal, with Returns of their Produce and its Distribu- tion, and Analyses of Special Varieties. Also an Account of the occurrence of Iron Ores in Veins or Seams ; Analyses of each Variety ; and a History ot the Rise and Progress of Pig Iron Manufacture. By RICHARD MEADE, Assistant Keeper of Mining Records. With Maps. 8vo, i 8s. cloth. " The book is one which must find a place on the shelves of all Interested In coal and iroa production, and in the iron, steel, and other metallurgical industries." Engineer, " Of this book we may unreservedly say that it is the best of its class which we have ever met. . . A book of reference which no one engaged in the iron or coal trades should omit from his brary." Iron, and Coal Trades Review. Prospecting for Gold and other Metals. THE PROSPECTOR'S HANDBOOK: A Guide for the Pro- spector and Traveller in Search of Metal-Bearing or other Valuable Minerals. By J. W. ANDERSON, M.A. (Camb.), F.R.G.S., Author of "Fiji and New Caledonia." Fifth Edition, thoroughly Revised and Enlarged. Small crown 8vo, 3$. 6d. cloth. "Will supply a much felt want, especially among Colonists, in whose way are so often thrown many mineral ogical specimens the value of which it is difficult to determine." Rnginttr. "How to find commercial minerals, and how to identify them when they are round, are the leading points to which attention is directed. The author has managed to pack as much practical detail into his pages as would supply material for a book three times its size." Mining Journal. Mining Notes and Formulce. NOTES AND FORMULAE FOR MINING STUDENTS. By JOHN HERMAN MERIVALE, M.A., Certificated Colliery Manager, Professor of Mining in the Durham College of Science, Newcastle-upon-Tyne. Third Edition, Revised and Enlarged. Small crown 8vo,2S. 6d. cloth. " Invaluable to anyone who is working up for an examination on mining subjects." Coal and Iron Trades Review. " The author has done his work in an exceedingly creditable manner, and has produced a book that will be of service to students, and those who are practically engaged in mining operations. 1 ' Engineer. " A vast amount of technical matter of the utmost value to mining engineers, and of consider- able interest to students." Schoolmaster. MINING AND METALLURGY. 23 Explosives. A HANDBOOK ON MODERN EXPLOSIVES. Being a Practical Treatise on the Manufacture and Application of Dynamite, Gun- Cotton, Nitro-Glycerine and other Explosive Compounds. Including the Manufacture of Collodion-Cotton. By M. EISSLER, Mining Engineer and Metallurgical Chemist, Author of " The Metallurgy of Gold," &c. With about too Illustrations. Crown 8vo, IDS. 6d. cloth. " Useful not only to the miner, but also to officers of both services to whom blasting and the use of explosives generally may at any time become a necessary auxiliary." Nature. "A veritable mine of information on the subject of explosives employed for military, mining and blasting: purposes." Army and Navy Gaeette. " The book is clearly written. Taken as a whole, we consider it an excellent little book and one that should be found of great service to miners and others who are engaged in work requiring the use of explosives." Athencenm. Gold, Metallurgy of. THE METALLURGY OF GOLD : A Practical Treatise on the Metallurgical Treatment of Gold-bearing Ores. Including the Processt s ot Concentration and Chlorination, and the Assaying, Melting and Refining of Gold. By M. EISSLER, Mining Engineer and Metallurgical Chemist, formerly Assistant Assayer of the U. S. Mint, San Francisco. Third Edition, Revised and greatly Enlarged. With 187 Illustrations. Crown 8vo, izs. 6d. cloth. "This book thoroughly deserves its title of a ' Practical Treatise.' The whole process of gold milling, from the breaking of the quartz to the assay of the bullion, is described in clear and orderly narrative and with much, but not too much, fulness of detail." Saturday Review. " The work is a storehouse of information and valuable data, and we strongly recommend it to all professional men engaged in the gold-mining industry." Mining Journal Silver, Metallurgy of. THE METALLURGY OF SILVER : A Practical Treatise on the Amalgamation, Roasting and Lixiviation of Silver Ores, Including the Assaying, Melting and Refining of Silver Bullion. By M. EISSLER, Author of "The Metallurgy of Gold ' Second Edition, Enlarged. With 150 Illus- trations. Crown 8vo, IDS. 6d. cloth. [Just published. " A practical treatise, and a technical work which we are convinced will supply a long felt want amongst practical men, and at the same time be of value to students and others indhectly connected with tne industries." Mining Journal. " From first to last the book is thoroughly sound and reliable." Colliery Guardian. " For chemists, practical miners, assayers and investors alike, we do not know of any work on the subject so handy and yet so comprehensive." Glasgow Herald. Silver-Lead, Metallurgy of. THE METALLURGY OF ARGENTIFEROUS LEAD: A Practical Treatise on the Smelting of Silver-Lead Ores and the Refining of Lead Bullion. Including Reports on various Smelting Establishments and Descriptions of Modern Furnaces and Plants in Europe and America. By M. EISSLER, M.E., Author of "The Metallurgy of Gold," &c. Crown 8vo. 400 pp., with numerous Illustrations, izs. 6d. cloth. [Just published. Metalliferous Minerals and Mining. TREATISE ON METALLIFEROUS MINERALS AND ilflNING. By D. C. DAVIES, F.G.S., Mining Engineer, &c., Author of "A Treatise on Slate and Slate Quarrying." Illustrated with numerous Wood Engravings. Fourth Edition, carefully Revised. Crown 8vo, ias. 6d. cloth. " Neither the practical miner nor the general reader Interested in mines can have a better book for his companion and his guide." Mining Journal. \_Mining World. " We are doing our readers a service in calling their attention to this valuable work." "As a history of the present state of mining throughout Uie world this book has a real value, and it supplies an actual want." Athenceum. . Earthy Minerals and Mining. A TREATISE ON EARTHY 6- OTHER MINERALS AND MINING. By D. C. DAVIES, F.G.S. Uniform with, and forming a Com- panion Volume to, the same Author's " Metalliferous Minerals and Mining." With 76 Wood Engravings. Second Edition. Crown 8vo, izs. 6d. cloth. " We do not remember to have met with any English work on mining matters that contains the same amount of information packed in equally convenient form." Academy. " We should be inclined to rank it as among the very best of the handy technical and trades manuals which have recently appeared." British Quarterly Review. 24 CROSBY LOCK WOOD 6- SON'S CATALOGUE. Mineral Surveying and Valuing. THE MINERAL SURVEYOR AND VALUER'S COMPLETE GUIDE, comprising a Treatise on Improved Mining Surveying and the Valua- tion of Mining Properties, with New Traverse Tables. By WM. LINTERN, Mining and Civil Engineer. Third Edition, with an Appendix on "Magnetic and Angular Surveying," with Records of the Peculiarities of Needle Dis- turbances. With Four Plates of Diagrams, Plans, &c. i2mo, 45. cloth. " Mr. Lintern's book forms a valuable and thorouglily trustworthy guide." Iron and Coal Trades Review. " This new edition must be of the highest value to colliery surveyors, proprietors and mana- gers." Colliery Guardian. Asbestos and Us Uses. ASBESTOS: Its Properties, Occurrence and Uses. With some Account of the Mines of Italy and Canada. By ROBERT H. JONES. With Eight Collotype Plates and other Illustrations. Crown 8vo, I2S. Cd. cloth. " An interesting- and invaluable work." Collitrv Guardian. " We counsel our readers to get this exceedingly interesting work for themselves ; they will find in it much that is suggestive, and a great deal that is of immediate and practical usefulness." Builder. " A valuable addition to the architect's and engineer's library." Building News. Underground Pumping Machinery. MINE DRAINAGE. Being a Complete and Practical Treatise on Direct-Acting Underground Steam Pumping Machinery, with a Descrip- tion of a large number of the best known Engines, their General Utility and the Special Sphere of their Action, the Mode of their Application, and their merits compared with other forms of Pumping Machinery. By STEPHEN MICHELL. 8vo, 155. cloth. "Will be highly esteemed by colliery owners and lessees, mining engineers, and students generally who require to be acquainted with the best means of securing the drainage of mines. It Is a most valuable work, and stands almost alone in the literature of steam pumping machinery.'' Colliery Guardian. " Much valuable information is given, so that the book is thoroughly worthy of an extensive circulation amongst practical men and purchasers of machinery." Mining Journal. Mining Tools. A MANUAL OF MINING TOOLS. For the Use of Mine Managers, Agents, Students, &c. By WILLIAM MORGANS, Lecturer on Prac- tical Mining at the Bristol School of Mines. i2mo, zs. 6d. cloth limp. ATLAS OF ENGRAVINGS to Illustrate the above, contain- ing 235 Illustrations of Mining Tools, drawn to scale. 4to, 45. 6d. cloth. " Students in the science of mining, and overmen, captains, managers, and viewers may gain practical knowledge and useful hints by the study of Mr. Morgans' manual." Colliery Guardian. " A valuable work, which will tend materially to improve our mining literature." Mining Journal. Coal Mining. COAL AND COAL MINING: A Rudimentary Treatise on. By the late Sir WARINGTON W. SMYTH, M.A., F.R.S., &c., Chief Inspector of the Mines of the Crown. Seventh Edition, Revised and Enlarged. With numerous Illustrations. I2mo, 45. cloth boards. "As an outline is given of every known coal-field in this and other countries, as well as of the principal methods of working, the book will doubtless interest a very large number of readers." Mintnf Journal. Subterraneous Surveying. SUBTERRANEOUS SURVEYING, Elementary and Practical Treatise on, -with and without the Magnetic Needle. ByTHOMAS FENWICK, Surveyor of Mines, and THOMAS BAKER, C.E. Illust. i2ino, 35. cloth boards. Granite Quarrying. GRANITES AND OUR GRANITE INDUSTRIES. By GEORGE F. HARRIS, F.G.S., Membre de la Societe Beige de Geologic, Lec- turer on Economic Geology at the Birkbeck Institution, &c. With Illustra- tions. Crown 8vo, zs. 6d. cloth. " A clearly and well-written manual for persons engaged or interested in the granite industry. ' Scotsman. "^An interesting work, whirh will be deservedly estef med." Colliery Guardian. " An exceedingly interesting and valuable monograph on a subject which has hitherto received unaccountably little attention in the shape of systematic littrary treatment." Scottish Leader. ELECTRICITY, ELECTRICAL ENGINEERING, etc. 25 ELECTRICITY, ELECTRICAL ENGINEERING, etc. Electrical Engineering. THE ELECTRICAL ENGINEER'S POCKET-BOOK OF MODERN RULES, FORMULAE, TABLES AND DATA. By H. R. KEMPE, M.Inst.E.E., A.M.Inst C.E., Technical Officer Postal Telegraphs, Author of "A Handbook of Electrical Testing," &c. With numerous Illus- trations, royal 321110, oblong, 55. leather. L7 MS * Published. " There is very little in the shape of formulae or data which the electrician is likely to want In a hutry which cannot be found in its pages." Practical Engineer. "A very useful book of reference for daily use in practical electrical engineering and its various applications to the industries of the present day." Iron. " It is the best book of its kind." Electrical Engineer. "The Electrical Engineer's Pocket-Book is a good on." Electrieian. "Strongly recommended to thos engaged in tn various electrical industries." Electrical Review. Electric Lighting. ELECTRIC LIGHT FITTING: A Handbook for Working Electrical Engineers, embodying Practical Notes on Installation Manage- ment. By JOHN W. URQUHART, Electrician, Author of " Electric Light," &c. With numerous Illustrations, crown 8vo, 55. cloth. [Just published. "This volume deals with what may be termed the mechanici of electric lighting, and is addressed to rmn who are already engaged in the work or are training for it. The work traverses a grreat deal of ground, and may be read as a sequel to the same author's useful work on ' Electric Light.' "Electrician. " This is an attempt to state in the simplest language the precautions which should be adopted in instal ing the electric light, and to g ; ve information, for the guidance of those who have to run the plant when installed. The book is well worth the perusal of the workmen for whom it is written." Electrical Review. ' Eminently practical and useful. . . . Ought to be in the hands of everyone in charge of an electric light plant." Electrical Engineer. " A really capital book, which we hav no hesitation in recommending to the notice of working electricians and electrical engineers." Mechanical h-'orld. Electric Light. ELECTRIC LIGHT : Its Production and Use. Embodying Plain Directions for the Treatment of Dynamo-Electric Machines, Batteries, Accumulators, and Electric Lamps. By J. W. URQUHART, C.E., Author of " Electric Light Fitting," &c. Fourth Edition, Revised, with Large Additions and 145 Illustrations. Crown 8vo, 75. 6^. cloth. [Just published. 'The book is by far the best that we have yet met with on the subject." Atfienaum. " It is the only work at present available which gives, in language intelligible for the most part to the ordinary reader, a general but concise history of the means which have been adopted up to the present time in producing the electric light." Metropolitan. The book contains a general account of the means adopted in producing the electric light, not only as obtained from voltaic or galvanic batteries, but treats at length of the dynamo-electric machine in several of its forms." Colliery Guardian. Construction of Dynamos. DYNAMO CONSTRUCTION : A Practical Handbook for the Use of Engineer Constructors and Electricians in Charge. With Examples of leading English, American and Continental Dynamos and Motors. By J. W. URQUHART, Author of " Electric Light," &c. Crown 8vo, 75. 6d. cloth. [Just published. " The author has producd a book for which a demand has long existed. Thesubjeit treated in a thoroughly practical manner." Mechanical ll'orld. Dynamic Electricity and Magnetism. THE ELEMENTS OF DYNAMIC ELECTRICITY AND MAGNETISM. By PHILIP ATKINSON, A.M., Ph.D. Crown 8vo. 400 pp. Wah 120 Illustrations, ics. 6d. cloth. [just publish, d. Tea t Book of Electricity. THE STUDENT'S TEXT-BOOK OF ELECTRICITY. By HENRY M. NOAD, Ph.D., F.R.S., F.C.S. New Edition, carefully Revised. With an Introduction and Additional Chapters, by W. H. PREECE, M.I.C.E., Vice- President of tl e Society of Telegraph Engineers, &c. With 470 Illustra- tions. Crown 8vo, 12 . 6d. cloth. "We can recommend Dr. Noad's book for clear style, great range of subject, a good index, and a plethora of woodcuts. Such collections as the present are indispensable. ' Atheiiccum. " An admirable text book for every student beginner or advanced of electricity." 26 CROSBY LOCK WOOD & SON'S CATALOGUE. Electric Lighting. THE ELEMENTARY PRINCIPLES OF ELECTRIC LIGHT- ING. By ALAN A. CAMPBELL SWINTON, Associate I.E.E. Second Edition, Enlarged and Revised. With 16 Illustrations. Crown 8vo, is. 6d. cloth. "Anyone who desires a short and thoroughly clear exposition of the elementary principles of electric-lighting cannot do better than read this little work." Bradford Observer. Electricity. A MANUAL OF ELECTRICITY: Including Galvanism, Mag. netism, Dia-Magnetism, Electro- Dynamics, Magno-Electricity, and the Electric Telegraph. By HENRY M. NOAD, Ph.D., F.R.S., F.C.S. Fourth Edition. With 500 Woodcuts. 8vo, i 45. cloth. "It is worthy of a place in the library of every public institution." Mining Journal. Dynamo Construction. HO W TO MAKE A D YNA MO : A Practical Treatise for A mateurs. Containing numerous Illustrations and Detailed Instructions for Construct- ing a Small Dynamo, to Produce the Electric Light. By ALFRED CROFTS. Third Edition, Revised and Enlarged. Crown 8vo, 25. cloth. "The instructions given in this unpretentious little book are sufficiently clear and explicit to enable any amateur mechanic possess-d of arerage skill and the usual tools to be found in an amateur's workshop, to build a practical dynamo machine." Electrician. NATURAL SCIENCE, etc. Pneumatics and Acoustics. PNEUMATICS : including Acoustics and the Phenomena of Wind Currents, for the Use of Beginners. By CHARLES TOMLINSON, F.R.S. F.C.S. , &c. Fourth Edition, Enlarged. lamo, is. 6d. cloth. " Beginners in the study of this Important application of science could not have a better manual. " Scotsman. " A valuable and suitable text-book for students of Acoustics and the Pheno- mena of Wind Currents." Schoolmaster. Conchology. A MANUAL OF THE MOLLUSC A : Being a Treatise on Recent and Fossil Shells. By S. P. WOODWARD, A.L.S., F.G.S., late Assistant Palaeontologist in the British Museum. With an Appendix on Recent and Fossil Conchological Discoveries, by RALPH TATE, A.L.S., F.G.S. Illustrated by A. N. WATERHOUSE and JOSEPH WILSON LOWRY. With 23 Plates and upwards of 300 Woodcuts. Reprint of Fourth Ed., 1880. Cr. 8vo, 7$. 6d. cl. " A most valuable storehouse of conchological and geological information." Science Gossip. Geology. RUDIMENTARY TREATISE ON GEOLOGY, PHYSICAL AND HISTORICAL. Consisting of " Physical Geology " which sets forth the leading Principles of the Science ; and " Historical Geology," which treats of the Mineral and Organic Conditions of the Earth at each successive epoch, especial reference being made to the British Series of Rocks. By RALPH TATE, A.L.S.. F.G.S.. &c. With 250 Illustrations, izmo, 5$ cloth. " The fulness of the matter has elevated the book Into a manual. Its Information is exhaustive and well arranged."-^S<-A SON'S CATALOGUE. Bread and Biscuit Baking. THE BREAD AND BISCUIT BAKER'S AND SUGAR- BOILER'S ASSISTANT. Including a large variety of Modern Recipes. With Remarks on the Art of Bread-making. By ROBERT WELLS, Practical Baker. Second Edition, with Additional Recipes. Crown 8vo, zs. cloth . " A large number of wrinkles for the ordinary cook, as well as the baker." Saturday Review Confectionery. THE PASTRYCOOK AND CONFECTIONER'S GUIDE. For Hotels, Restaurants and the Trade in general, adapted also for Family Use. By ROBERT WELLS, Author of " The Bread and Biscuit Baker's and Sugar Boiler's Assistant." Crown 8vo, as. cloth. " We cannot speak too highly of this really excellent work. In these days of keen competition our readers cannot do better than purchase this book." Bakers' Times. Ornamental Confectionery. ORNAMENTAL CONFECTIONERY: A Guide for Bakers, Confectioners and Pastrycooks ; including a variety of Modern Recipes, and Remarks on Decorative and Coloured Work. With 129 Original Designs. By ROBERT WELLS. Crown 8vo, 55. cloth. "A valuable work, and should be in the hands of every baker and confectioner. The illus trative designs are alone worth treble the amount charged for the whole work." Bakers' Times. Flour Confectionery. THE MODERN FLOUR CONFECTIONER. Wholesale and Retail. Containing a large Collection of Recipes for Cheap Cakes, Biscuits, &c. With Remarks on the Ingredients used in their Manufacture, &c. By R. WELLS, Author of "Ornamental Confectionery," "The Bread and Biscuit Baker," " The Pastrycook's Guide, 1 ' &c. Crown 8vo, 2s. cloth. Laundry Work. LA UN DRY MANAGEMENT. A Handbook for Use in Private and Public Laundries, Including Descriptive Accounts of Modern Machinery and Appliances for Laundry Work. By the EDITOR of " The Laundry Journal," With numerous Illustrations. Crown 8vo, zs. 6d. cloth. CHEMICAL MANUFACTURES & COMMERCE. New Manual of Engineering Chemistry, ENGINEERING CHEMISTRY; A Practical Treatise for the Use of Analytical Chemists, Engineers, Iron Masters, Iron Founders, Students, and others. Comprising Methods of Analysis and Valuation of the Principal Materials used in Engineering Work, with numerous Analyses, Examples, and Suggestions. By H. JOSHUA PHILLIPS, F.I.C., F.C.S., Analytical and Consulting Chemist to the Great Eastern Railway. Crown 8vo, 320 pp., with Illustrations, IDS. 6d. cloth. {Just published. " In this work the author has rendered no small service to a numerous body of practical men. .... The analytical methods may be pronounced most satisfactory, being as accurate as the despatch required of engineering chemists permits." Chemical News. Analysis and Valuation of Fuels. FUELS: SOLID, LIQUID AND GASEOUS, Their Analysis and Valuation. For the Use of Chemists and Engineers. By H. J. PHILLIPS, F.C.S., Analytical and Consulting Chemist to the Great Eastern Railway. Crown 8vo, 35. 6d. cloth. " Ought to have its place in the laboratory of every metallurgical establishment, and wherever fuel is used on a large scale." Chemical News. " Cannot fail to be of wide interest, especially at the present time." Railway News. Alkali Trade, Manufacture of Sulphuric Acid, etc. A MANUAL OF THE ALKALI TRADE, including the Manufacture of Sulphuric Acid, Sulphate of Soda, and Bleaching Powder. By JOHN LOMAS. 390 pages. With 232 Illustrations and Working Drawings. Second Edition. Royal 8vo, i los. cloth. "This book is written by a manufacturer for manufacturers. The working details of the most approved forms of apparatus are given, and these are accompanied by no less than 232 wood en- gravings, all of which may be used for the purposes of construction." Athenaum. AGRICULTURE, FARMING, GARDENING, etc. 35 The Blowpipe. THE BLOWPIPE IN CHEMISTRY, MINERALOGY, AND GEOLOGY. Containing all known Methods of Anhydrous Analysis, Work- ing Examples, and Instructions for Making Apparatus. By Lieut. -Col. W. A. Ross, R.A. With 120 Illustrations. New Edition. Crown 8vo, 55. "The student who goes through the course of experimentation here laid down will gain a better insight into inorganic chemistry and mineralogy than if he had 'got up' any of the best text-books of the day, and passed any number of examinations in their contents." Chemical News. Commercial Chemical Analysis. THE COMMERCIAL HANDBOOK OF CHEMICAL ANA- LYSIS; or, Practical Instructions ior the determination of the Intrinsic or Commercial Value of Substances used in Manufactures.Trades, and the Arts. By A. NORMANDY. New Edition by H. M. NOAD, F.R.S. Cr. 8vo, 125. 6d. cl. "Essential to the analysts appointed under the new Act. The most recent results are given, and the work is well edited and carefully written." Nature. brewing. A HANDBOOK FOR YOUNG BREWERS. By HERBERT EDWARDS WRIGHT, B.A. New Edition, much Enlarged. [In the press. Dye-Wares and Colours. THE MANUAL OF COLOURS AND DYE- WARES : Their Properties, Applications, Valuation, Impurities, and Sophistications. For the use of Dyers, Printers, Drysalters, Brokers, &c. By J. W. SLATER. Second Edition, Revised and greatly Enlarged. Crown 8vo, js. 6d. cloth. "A complete encyclopaedia of the inateria. tinctoria. The information given respecting each article is full and precise, and the methods of determining the value of articles such as these, so liable to sophistication, are given with clearness, and are practical as well as valuable." Chemist and Druggist. " There is no other work which covers precisely the same ground. To students preparing or examinations in dyeing and printing it will prove exceedingly useful." Chemical News. Pigments. THE ARTIST'S MANUAL OF PIGMENTS. Showing their Composition, Conditions of Permanency, Non-Permanency, and Adul- terations ; Effects in Combination with Each Other and with Vehicles ; and the most Reliable Tests of Purity. By H. C. STANDAGE Second Edition. Crown 8vp, 2s. 6d. cloth. "This work is indeed ntrtltum-in-parvo, and we can, with good conscience, recommend it to all who come in contact with pigments, whether as makers, dealers or users." Chemical Review. Gauging. Tables and Rules for Revenue Officers, Brewers, etc. A POCKET BOOK OF MENSURATION AND GAUGING : Containing Tables, Rules and Memoranda for Revenue Officers, Brewers, Spirit Merchants, &c. By J. B. MANT (Inland Revenue). Second Edition, Revised. Oblong i8mo, 43. leather, with elastic band. " This handy and useful book is adapted to the requirements of the Inland Revenue Depart- ment, and will be a favourite book of reference." Civilian. " Should be in the hands of every practical brewer." Brewers' Journal. AGRICULTURE, FARMING, J2ARDENING, etc. Youatt and Burn's Complete Grazier. THE COMPLETE GRAZIER, and FARMER'S ant? CATTLE- BREEDER'S ASSISTANT. Including the Breeding, Rearing, and Feeding of Stock ; Management of the Dairy, Culture and Management of Grass Land, and of Grain and Root Crops, &c. By W. YOUATT and R. SCOTT BURN. An entirely New Edition, partly Re-written and greatly Enlarged, by W. FREAM, B.Sc.Lond., LL.D. In medium 8vo, about 1,000 pp. [/ra the press. Agricultural Facts and Figures. NOTE-BOOK OF AGRICULTURAL FACTS AND FIGURES FOR FARMERS AND FARM STUDENTS. By PRIMROSE McCoNNELL, late Professor of Agriculture, Glasgow Veterinary College. Third Edition. Royal samo, 45. leather. " The most complete and comprehensive Note-book for Fanners and Farm Students that we have seen. It literally teems with information, and we can cordially recommend it to all connected with agrcuilture." North British Agriculturist. 36 CROSBY LOCK WOOD & SON'S CATALOGUE. Flour Manufacture, Milling, etc. FLOUR MANUFACTURE: A Treatise on Milling Science and Practice. By FRIEDRICH KICK, Imperial Regierungsrath, Professor of Mechanical Technology in the Imperial German Polytechnic Institute, Prague. Translated from the Second Enlarged and Revised Edition with Supplement. By H. H. P. POWLES, A.M.I.C.E. Nearly 400 pp. Illustrates with 28 Folding Plates, and 167 Woodcuts. Royal 8vo, 255. cloth. " This valuable work is, and will remain, the standard authority on the science of milling. , . The miller who has read and digested this work will have laid the foundation, so to speak, of a suc- cessful career ; he will have acquired a number of general principles which he can proceed to apply. In this handsome volume we at last have the accepted text-book of modern milling in good, sound English, which has little, if any, trace of the German idiom." The Miller. " The appearance of this celebrated work in English is very opportune, and British millers will, we are sure, not be slow in availing themselves of its pages." Millers' Gazette. Small Farming. SYSTEMATIC SMALL FARMING; or, The Lessons of my Farm. Being an Introduction to Modern Farm Practice for Small Farmers in the Culture of Crops; The Feeding of Cattle; The Management of the Dairy, Poultry and Pigs, &c. &c. By ROBERT SCOTT BURN, Author of " Out- lines of Landed Estates' Management." Numerous Illusts., cr. 8vo, Cs. cloth. "This is the completes! book of its class we have seen, and one which every amateur farmer will read with pleasure and accept as a guide." Field. " The volume contains a vast amount of useful information. No branch of farming is left untouched, from the labour to be done to the results achieved. It may be safely recommended to all who think they will be in paradise when they buy or rent a three-acre farm." Glasgow Herald. Modern Farming. OUTLINES OF MODERN FARMING. By R. SCOTT BURN. Soils, Manures, and Crops Farming and Farming Economy Cattle, Sheep, and Horses Management of Dairy, Pigs and Poultry Utilisation of Town-Sewage, Irrigation, &c. Sixth Edition. In One Vol., 1,250 pp., half- bound, profusely Illustrated, 125. " The aim of the author has been to make his work at once comprehensive and trustworthy, and in this aim he has succeeded to a degree which entitles him to much credit." Morning Advertiser. " No fanner should be without this book." Banbury Guardian. Agricultural Engineering. FARM ENGINEERING, THE COMPLETE TEXT -BOOK OF. Comprising Draining and Embanking; Irrigation and Water Supply ; Farm Roads, Fences, and Gates ; Farm Buildings, their Arrangement and Con- struction, with Plans and Estimates; Barn Implements and Machines ; Field Implements and Machines; Agricultural Surveying, Levelling, &c. By Prof. JOHN SCOTT, Editor of the " Farmers' Gazette," late Professor of Agriculture and Rural Economy at the Royal Agricultural College, Cirencester, &c. &c. In One Vol., 1,150 pages, half-bound, with over 600 Illustrations, I2S. "Written with great care, as well as with knowledge and ability. The author has done his work well ; we have found him a very trustworthy guide wherever we have tested his statements. The volume will be of great value to agricultural students," Mark Lane Express. "For a young agriculturist we know of^no handy volume likely to be more usefully studied. Bell's Weekly Messenger. English Agriculture. THE FIELDS OF GREAT BRITAIN : A Text-Book of Agriculture, adapted to the Syllabus of the Science and Art Department. For Elementary and Advanced Students. By HUGH CLEMENTS (Board of Trade). Second Ed., Revised, with Additions. i8mo, 2$. 6d. cl. "A most comprehensive volume, giving a mass of information." Agricultural Economist. " It is a long time since we have seen a book which has pleased us more, or which contains such a vast and useful fund of knowledge." Educational Times. Tables for Farmers 9 etc. TABLES, MEMORANDA, AND CALCULATED RESULTS for Farmers, Graziers, Agricultural Students, Surveyors, Land Agents Auc- tioneers, etc. With a New System of Farm Book-keeping. Selected and Arranged by SIDNEY FRANCIS. Second Edition, Revised. 272 pp., waist- coat-pocket size, is. 6d. limp leather. "Weighing less than i oz., and occupying no more space than a match box, it contains a mass of facts and calculations which has never before, in such handy form, been obtainable. . Every operation on the farm is dealt with. The work may be taken as thoroughly accurate, the whole of the tables having been revised by Dr. Fream. We cordially recommend it." Bell's Weekly Messenger. " A marvellous little book. . . . The agriculturist who possesses himself of it will not be disappointed with his investment." The Farm. AGRICULTURE, FARMING, GARDENING, etc. 37 Farm and Estate Boolc-Jceeping. BOOK-KEEPING FOR FARMERS 6- ESTATE OWNERS. A Practical Treatise, presenting, in Three Plans, a System adapted for all Classes of Farms. By JOHNSON M. WOODMAN, Chartered Accountant. Second Edition, Revised. Cr. 8vo, 35. 6d. cl. bds. ; or 2S. 6d. cl. limp. " The volume is a capital study of a most important subject." Agricultural Gazette. " Will be found of great assistance by those who intend to commence a system of book-keep- ng, the author's examples being clear and explicit, and his explanations, while full and accurate, being to a large extent free from technicalities." Live Stock Journal. Farm Account Boo/c. WOODMAN'S YEARLY FARM ACCOUNT BOOK. Giving a Weekly Labour Account and Diary, and showing the Income and Expen- diture under each Department of Crops, Live Stock, Dairy, &c. &c. With Valuation, Profit and Loss Account, and Balance Sheet at the end of the Year, and an Appendix of Forms. Ruled and Headed for Entering a Com- plete Record of the Farming Operations. By JOHNSON M. WOODMAN, Chartered Accountant. Folio, 75. 6d. half bound. [witure. "Contains every requisite form for keeping farm accounts readily and accurately." Agri Early Fruits, Flowers and Vegetables. THE FORCING GARDEN ; or, How to Grow Early Fruits, Flowers, and Vegetables. With Plans and Estimates for Building Glass- houses, Pits and Frames. By SAMUEL WOOD. Crown 8vo, 35. 6d. cloth. "A good book, and fairly fills a place that was in some degree vacant. The book is written with great care, and contains a great deal of valuable teaching." Gardeners' Magazine. " Mr. Wood's book is an original and exhaustive answer to the question ' How to Grow Early Fruits, Flowers and Vegetables ? ' "Land and Water. Good Gardening. A PLAIN GUIDE TO GOOD GARDENING ; or, How to Grow Vegetables, Fruits, and Flowers. With Practical Notes on Soils, Manures, Seeds, Planting, Laying-out of Gardens and Grounds, &c. By S. WOOD. Fourth Edition, with numerous Illustrations. Crown 8vo, 35. 6d. cloth. "A very good book, and one to be highly recommended as a practical guide. The practical directions are excellent." Athenaum. " May be recommended to young gardeners, cottagers, and specially to amateurs, for the plain, simple, and trustworthy information it gives on common matters too often neglected." Gardeners' Chronicle. Gainful Gardening. MULTUM-IN-PARVO GARDENING; cr, How to make One Acre of Land produce 620 a-year by the Cultivation of Fruits and Vegetables ; also, How to Grow Flowers in Three Glass Houses, so as to realise 176 per annum clear Profit. By S. WOOD. Fifth Edition. Crown 8vo, is. sewed. "We are bound to recommend it as not only suited to the case of the amateur and gentleman's gardener, but to the market grower." Gardeners' Magazine. Gardening for Ladies. THE LADIES' MULTUM-IN-PARVO FLOWER GARDEN, and Amateurs' Complete Guide. By S. WOOD. With Illusts. Cr.8vo, 3$. 6d. cl. " This volume contains a good deal of sound, common sense instruction." Florist. " Full of shrewd hints and useful instructions, based on a lifetime of experience." Scotsman. Receipts for Gardeners. GARDEN RECEIPTS. By C. W. QUIN. I2mo, is. 6d. cloth. "A useful and handy book, containing a good deal of valuable information." Athenaum. Market Gardening. MARKET AND KITCHEN GARDENING. By Contributors to " The Garden." Compiled by C. W. SHAW, late Editor of "Gardening Illustrated." i2mo, 35. 6d. cloth boards. " The most valuable compendium of kitchen and market-garden work published." Farmer. Cottage Gardening. COTTAGE GARDENING; or, Flowers, Fruits, and Vegetables for Small Gardens. By E. HOBDAY, izmo, is. 6d. cloth limp. Potato Culture. POTATOES : How to Grow and Show Them. A Practical Guide to the Cultivation and General Treatment of the Potato. By JAMES PINK. Second Edition. Crown 8vo, as. cloth. 38 CROSBY LOCK WOOD 6- SON'S CATALOGUE. LAND AND ESTATE MANAGEMENT, LAW, etc. Hudson's Land Valuer's Pocket-Book. THE LAND VALUER'S BEST ASSISTANT: Being Tables on a very much Improved Plan, for Calculating the Value of Estates. With Tables for reducing Scotch, Irish, and Provincial Customary Acres to Statute Measure, &c. By R. HUDSON, C.E. New Edition. Royal 32mo, leather, elastic band, 45. "This new edition includes tables for ascertaining- the value of leases for any term of years ; and for showing how to lay out plots of ground of certain acres in forms, square, round, &c., with valuable rules for ascertaining the probable worth of standing timber to any amount ; and is of incalculable value to the country gentleman and professional man." Farmers' Journal. Ewart's Land Improver's Pocket-Book. THE LAND IMPROVER'S POCKET-BOOK OF FORMULAE, TABLES and MEMORANDA required in any Computation relating to the Permanent Improvement of Landed Property. By JOHN EWART, Land Surveyor and Agricultural Engineer. Second Edition, Revised. Royal samo, oblong, leather, gilt edges, with elastic band, 45. " A compendious and handy little volume." Spectator. Complete Agricultural Surveyor's Pocket-Book. THE LAND VALUER'S AND LAND IMPROVER'S COM- PLETE POCKET-BOOK. Consisting of the above Two Works bound to- gether. Leather, gilt edges, with strap, 75. 6d. " Hudson's book is the best ready-reckoner on matters relating to the valuation of land and crops, and its combination with Mr. Ewart's work greatly enhances the value and usefulness of the latter-mentioned. ... It is most useful as a manual for reference." North of England Farmer. Auctioneer's Assistant. THE APPRAISER, A UCTIONEER, BROKER, HOUSE AND ESTATE AGENT AND VALUER'S POCKET ASSISTANT, lorthe Valua- tion for Purchase, Sale, or Renewal of Leases, Annuities and Reversions, and of property generally; with Prices for Inventories, &c. By JOHN WHEELER, Valuer, &c. Fifth Edition, re-written and greatly extended by C. MORRIS, Surveyor, Valuer, &c. Royal 32010, 53. cloth. " A neat and concise book of reference, containing an admirable and clearly-arranged list of prices for inventories, and a very practical guide to determine the value of furniture, &c. "Standard. " Contains a large quantity of varied and useful information as to the valuation for purchase, sale, or renewal of leases, annuities and reversions, and of property generally, with prices for Inventories, and a guide to determine the value of interior fittings and other effects." Builder, Auctioneering. AUCTIONEERS: THEIR DUTIES AND LIABILITIES. A Manual of Instruction and Counsel for the Young Auctioneer. By ROBERT SQUIBBS, Auctioneer. Second Edition, Revised and partly Re- written. Demy 8vo, I2S. 6d. cloth. "The position and duties of auctioneers treated compendiously and clearly." Builder. "Every auctioneer ought to possess a copy of this excellent work." Ironmonger. " Of great value to the profession. . . . We readily welcome this book from the fact that it treats the subject in a manner somewhat new to the profession." Estates Gazette. Legal Guide for Pawnbrokers. THE PAWNBROKERS', FACTORS' AND MERCHANTS' GUIDE TO THE LAW OF LOANS AND PLEDGES. With the Statutes and a Digest of Cases on Rights and Liabilities, Civil and Criminal, as to Loans and Pledges of Goods, Debentures, Mercantile and other Se- curities. By H. C. FOLKARD, Esq., Barrister-at-Law, Author of "The Law of Slander and Libel," &c. With Additions and Corrections. Fcap. 8vo, 35. 6d. cloth. " This work contains simply everything that requires to be known concerning the department of the law of which it treats. We can safely commend the book as unique and very nearly perfect." Iron. " The task undertaken by Mr. Folkard has been very satisfactorily performed. . . . Such ex- planations as are needful have been supplied with great clearness and with due regard to brevity." City Press. LAND AND ESTATE MANAGEMENT, LAW, etc. 39 Law of Patents. PATENTS FOR INVENTIONS, AND HOW TO PROCURE THEM. Compiled for the Use of Inventors, Patentees and others. By G. G. M. HARDINGHAM, Assoc.Mem.Inst.C.E., &c. Demy 8vo, cloth, price zs. 6d. Metropolitan Hating Appeals. REPORTS OF APPEALS HEARD BEFORE THE COURT OF GENERAL ASSESSMENT SESSIONS, from the Year 1871 to 1885. By EDWARD RYDE and ARTHUR LYON RYDE. Fourth Edition, brought down to the Present Date, with an Introduction to the Valuation (Metropolis) Act, 1869, and an Appendix by WALTER C. RYDE, of the Inner Temple, Barrister- at-Law. 8vo, i6s. cloth. " A useful work, occupying a place mid-way between a handbook for a lawyer and a guide to the surveyor. It is compiled by a gentleman eminent in his profession as a land agent, whose spe- cialty, it is acknowledged, lies i the direction of assessing property for rating purposes." Land Agents' Record. " It is an indispensable work of reference for all engaged in assessment business." Journa of Gas Lighting. House Property. HANDBOOK OF HOUSE PROPERTY. A Popular and Practi- cal Guide to the Purchase, Mortgage, Tenancy, and Compulsory Sale of Houses and Land, including the Law of Dilapidations and Fixtures; with Examples of all kinds of Valuations, Useful Information on Building, and Suggestive Elucidations of Fine Art. By E. L. TARBUCK, Architect and Surveyor. Fourth Edition, Enlarged. i2mo, 55. cloth. " The advice is thoroughly practical." La-w Journal. 'For all who have dealings with house property, this is an indispensable guide." Decoration. " Carefully brought up to date, and much improved by the addition of a division on fine art. " A well-written and thoughtful work." Land Agents Record. Inwood's Estate Tables. TABLES FOR THE PURCHASING OF ESTATES, Freehold, Copyhold, or Leasehold; Annuities, Advowsons, etc., and for the Renewing of Leases held under Cathedral Churches, Colleges, or other Corporate bodies, for Terms of Years certain, and for Lives ; also for Valuing Reversionary Estates, Deferred Annuities, Next Presentations, &c. ; together with SMART'S Five Tables of Compound Interest, and an Extension of the same to Lower and Intermediate Rates. By W. INWOOD. 23rd Edition, with considerable Additions, and new and valuable Tables of Logarithms for the more Difficult Computations of the Interest of Money, Discount, Annuities, &c. , by M. FEDOR THOMAN, of the Societe Credit Mobilier of Paris. Crown 8vo, 8s. cloth. "Those interested in the purchase and sale of estates, and in the adjustment of compensation cases, as well as in transactions in annuities, life insurances, &c., will find the present edition of eminent service." Engineering. " ' Inwood's Tables ' still maintain a most enviable reputation. The new issue has been enriched by large additional contributions by M. Fedor Thoman, whose carefully arranged Tables cannot fail to be of the utmost utility. "Mining Journal. Agricultural and Tenant-Hight Valuation. THE AGRICULTURAL AND TENANT-RIGHT-VALUER'S ASSISTANT. A Practical Handbook on Measuring and Estimating the Contents, Weights and Values of Agricultural Produce and Timber, the Values of Estates and Agricultural Labour, Forms of Tenant-Right-Valua- tions, Scales ol Compensation under the Agricultural Holdings Act, 1883, &c. &c. By TOM BRIGHT, Agricultural Surveyor. Crown 8vo, 35. 6d. cloth. "Full of tables and examples in connection with the valuation of tenant-right, estates, labour, contents, and weights of timber, and farm produce of all kinds." Agricultural Gazette. " An eminently practical handbook, full of practical tables and data of undoubted interest and value to surveyors and auctioneers in preparing valuations of all kinds." Farmer. Plantations and Underwoods. POLE PLANTATIONS AND UNDERWOODS: A Practical Handbook on Estimating the Cost of Forming, Renovating, Improving and Grubbing Plantations and Underwoods, their Valuation for Purposes ot Transfer, Rental, Sale or Assessment. By TOM BRIGHT, F.S.Sc., Author of "The Agricultural and Tenant-Right-Valuer's Assistant," &c. Crown 8vo, 35. 6d. cloth. [Just published. " Will be found very useful to those who are actually engaged in managing wood." BelCs Weekly Messenger. ' To valuers, foresters and agents it will be a welcome aid." North British Agriculturist. "Well calculated to assist the valuer in the discharge of his duties, and of undoubted interest and use both to surveyors and auctioneers in preparing valuations of all kinds." Kent Herald. 46 CROSBY LOCK WOOD & SON'S CATALOGUE. A Complete Epitome of the Laws of this Country. EVERY MAN'S OWN LAWYER: A Handy-Book of the Principles of Law and Equity. By A BARRISTER. Twenty-eighth Edition. Revised and Enlarged. Including the Legislation of 1890, and including careful digests of The Bankruptcy Act, 1890; the Directors' Liability Act, 1890; the Partnership Act, 1890; the Intestates' Estates Act, 1890; the Settled Land Act, 1890 ; the Housing of the Working Classes Act, 1890; the Infectious Disease (Prevention) Act, 1890; the Allotments Act, 1890; the Tenants' Com- pensation Act, 1890; and the Trustees' Appointment Act, 1890; while other new Acts have been duly noted. Crown 8vo, 688 pp., price 6s. 8d. (saved at every consultation ! ), strongly bound in cloth. [Just published. VTHE BOOK WILL BE FOUND TO COMPRISE (AMONGST OTHER MATTER) THE RIGHTS AND WRONGS OF INDIVIDUALS LANDLORD AND TENANT VENDORS AND PURCHASERS PARTNERS AND AGENTS COMPANIES AND ASSOCIATIONS MASTERS, SERVANTS AND WORKMEN LEASES AND MORTGAGES CHURCH AND CLERGY, RITUAL LIBEL AND SLANDER CONTRACTS AND AGREEMENTS -BONDS AND BILLS OF SALE- CHEQUES, BILLS AND NOTES -RAILWAY AND SHIPPING LAW BANKRUPTCY AND IN- SURANCEBORROWERS. LENDERS AND SURETIES CRIMINAL LAW PARLIAMENTARY ELECTIONS- COUNTY COUNCILS MUNICIPAL CORPORATIONS PARISH LAW, CHURCH- WARDENS, ETC. INSANITARY DWELLINGS AND AREAS PUBLIC HEALTH AXD NUISANCES FRIENDLY AND BUILDING SOCIETIES-COPYRIGHT AND PATENTS TRADE MARKS AND DESIGNS HUSBAND AND WIFE, DIVORCE, ETC. TRUSTEES AND EXECU- TORSGUARDIAN AND WARD, INFANTS, ETC. GAME LAWS AND SPORTING-HORSES, HORSE-DEALING AND DOGS INNKEEPERS, LICENSING, ETC. FORMS OF WILLS, AGREEMENTS, ETC. ETC. NOTE. The object of this work is to enable those who consult it to help them- selves to the law; and thereby to dispense, as far as possible, with professional assistance and advice. There are many wrongs and grievances which persons sub- mit to from time to time through not knowing how or where to apply for redress ; and many persons have as great a dread of a lawyer's office as of a lion's den. With this book at hand it is believed that many a SIX-AND-EIGHTPENCE may be saved ; many a wrong redressed ; many a right reclaimed ; many a law suit avoided ; and many an evil abated. The work has established itself as the standard legal adviser of all classes, and also made a reputation for itself as a useful book of reference for lawyers residing at a distance from law libraries, who are glad to have at hand a work em- bodying recent decisions and enactments. %* OPINIONS OF THE PRESS. " It is a complete code of English Law, written in plain language, which all can understand. . . Should be in the hands of every business man, and all who wish to abolish lawyers' bills.'' Weekly Times. " A useful and concise epitome of the law, compiled with considerable care." Law Magazine. "A complete digest of the most useful facts which constitute English law." Globe. " This excellent handbook. . . . Admirably done, admirably arranged, and admirably cheap." Leeds Mercury. ' A concise, cheap and complete epitome of the English law. So plainly written that he who runs may read, and he who reads may understand." Figaro. " A dictionary of legal facts well put together. The book is a very useful one." Spectator. " A work which has long been wanted, which is thoroughly well done, and which we most cordially recommend." Sunday Times. " The latest edition of this popular book ought to be in every business establishment, and on every library table." Sheffield Post. Private Bill Legislation and Provisional Orders. HANDBOOK FOR THE USE OF SOLICITORS AND EN- GINEERS Engaged in Promoting Private Acts of Parliament and Provi- sional Orders, for the Authorization of Railways, Tramways, Works for the Supply of Gas and Water, and other undertakings of a like character. By L. LIVINGSTON MACASSEY, of the Middle Temple, Barrister-at-Law, and Member of the Institution of Civil Engineers; Author of" Hints on Water Supply." Demy 8vo, 950 pp., price 255. cloth. " The volume is a desideratum on a subject which can be only acquired by practical experi- ence, and the order of procedure in Private Bill Legislation and Provisional Orders is followed. The author's suggestions and notes will be found of great value to engineers and others profession- ally engaged in this class of practice." Building News. " The author's double experience as an engineer and barrister has eminently qualified him for the task, and enabled him to approach the subject alike from an engineering and legal point of view. The volume will be found a great help both to engineers and lawyers engaged in promoting Private Acts ot Parliament and Provisional Orders." Local Government Chronicle. OGDEN, SMALE AND CO. LIMITED, PRINTERS, GREAT SAFFRON HILL, B.C. LONDON, 1862, THE PRIZE MEDAL Was awarded to the Publishers of "WHALE'S SERIES." A NEW LIST OF WEALE'S SERIES RUDIMENTARY SCIENTIFIC,EDUCATIONAL, AND CLASSICAL. Comprising nearly Three Hundred and Fifty distinct -works in almost every department of Science, Art, and Education, recommended to the notice of Engineers, Architects, Builders, Artisans, and Students generally, as "well as to those interested in Workmen's 'aries, Literc, and Scientific Institutions, Colleges, Schools, Science Cla ses, &*c., drc. IS 5 * " WEALE'S SERIES includes Text-Books on almost every branch of Science and Industry, comprising such subjects as Agriculture, Architecture and Building, Civil Engineering, Fine Arts, Mechanics and Mechanical Engineering, Physical and Chemical Science, and many miscellaneous Treatises. The whole are constantly undergoing revision, and new editions, brought up to the latest discoveries in scientific research, are constantly issued. The prices at which they are sold are as low as their excellence is assured." American Literary Gazette. " Amongst the literature of technical education, WEALE'S SERIES has ever enjoyed a high reputation, and the additions being made by Messrs. CROSBY LOCKWOOD & SON render the series more complete, and bring the informa- tion upon the several subjects down to the present time." Mining Journal. " It is not too much to say that no books have ever proved more popular with, or more useful to, young engineers and others than the excellent treatises comprised in WEALE'S SERIES." Engineer. "The excellence of WEALE'S SERIES is now so well appreciated, that it would be wasting our space to enlarge upon their general usefulness and value." Builder. "The volumes of WEALE'S SERIES form one of the best collections of elementary technical books in any language." Architect. " WEALE'S SERIES has become a standard as well as an unrivalled collection of treatises in all branches of art and science." Public Opinion. PHILADELPHIA, 1876, THE PRIZE MEDAL Was awarded to the Publishers for Books : Rudimentary, Scientific, "WEALE'S SERIES," ETC. CROSBY LOCKWOOD & SON, 7, STATIONERS' HALL COURT, LUDGATE HILL, LONDON, E.G. WEALE S RUDIMENTARY SERIES. WEALE'S RUDIMENTARY SCIENTIFIC SERIES. *** The volumes of this Series are freely Illustrated with Woodcuts, or otherwise, where requisite. Throughout the fol- lowing List it must be understood that the books are bound in limp cloth, unless otherwise stated ; but the -volumes marked with a \ may also be had strongly bound in cloth boards for 6d. extra. N.B. / ordering from this List it is recommended, as a means of facilitating business and obviating error, to quote the numbers affixed to the -volumes, as -well as the titles and prices. CIVIL ENGINEERING, SURVEYING, ETC. No. 31. WELLS AND WELL-SINKING. By JOHN GEO. SWINDELL, A.R.I.B.A., and G. R. BURNELL, C.E. Revised Edition. With a New Appendix on the Qualities of Water. Illustrated. 2s. 35- THE BLASTING AND QUARRYING OF STONE, for Building and other Purposes. By Gen. Sir T. BURGOYNK, Bart. is. 6d. 43. TUBULAR, AND OTHER IRON GIRDER BRIDGES, par- ticularly describing the Britannia and Conway Tubular Bridges. By G. DRYSDALE DEMPSEY, C.E. Fourth Edition, zs. 44. FOUNDATIONS AND CONCRETE WORKS, with Practical Remarks! on Footings, Sand, Concrete, Beton, Pile-driving, Caissons, and Cofferdams, &c. By E. DOBSON. Fifth Edition, is. 6d. 60. LAND AND ENGINEERING SURVEYING. By T. BAKER, C.E. Fourteenth Edition, revised by Professor T. R. YOUNG. 2S.i 80*. EMBANKING LANDS FROM THE SEA. With examples and Particulars of actual Embankments, &c. By T. WIGGINS, F.G.S. 2s. 8 1. WATER WORKS, for the Supply of Cities and Towns. With a Description of the Principal Geological Formations of England as in- fluencing Supplies of Water, &c. By S. HUGHES, C.E. New Edition. 45.* 118. CIVIL ENGINEERING IN NORTH AMERICA, a Sketch of. By DAVID STEVENSON, F.R.S.E., &c. Plates and Diagrams. 35. 167. IRON BRIDGES, GIRDERS, ROOFS, AND OTHER WORKS. By FRANCIS CAMPIN, C.E. 2s. 6d4 197. ROADS AND STREETS. By H. LAW, C.E., revised and enlarged by D. K. CLARK, C.E., including pavements of Stone, Wood, Asphalte, &c. as. 6d. 203. SANITARY WORK IN THE SMALLER TOWNS AND IN VILLAGES. By C. SLAGG, A.M.I.C.E. Revised Edition. 3 s.t 212. GAS- WORKS, THEIR CONSTR UCTIQN AND ARRANGE- MENT; and the Manufacture and Distribution of Coal Gas. Originally written by SAMUEL HUGHES, C.E. Re-written and enlarged by WILLIAM RICHARDS, C.E. Seventh Edition, with important additions. 53. 6d.t 213. PIONEER ENGINEERING. A Treatise on the Engineering Operations connected with the Settlement of Waste Lands in New Coun- tries. By EDWARD DOBSON, Assoc. Inst. C.E. 45. 6d.J 216. MATERIALS AND CONSTRUCTION; A Theoretical and Practical Treatise on the Strains, Designing, and Erection of Works of Con- struction. By FRANCIS CAMPIN, C.E. Second Edition, revised. 354 219. CIVIL ENGINEERING. By HENRY LAW, M.Inst. C.E. Including HYDRAULIC ENGINEERING by GEO. R. BURNELL, M.Inst. C.E. Seventh Edition, revised, with large additions by D. KINNEAR CLARK, M.Inst. C.E. 6s. 6d., Cloth boards, 7 s. 6d. 268. THE DRAINAGE OF LANDS, TOWNS, <^ BUILDINGS. By G. D. DEMPSEY, C.E. 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