LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 
 Deceived. MAY... 5 1894 
 
NEW SERIES OF HANDBOOKS FOR 
 STUDENTS AND PRACTICAL ENGINEERS. 
 
 THE 
 
 SPECIALIST'S SERIES 
 
 Edited by Dr. PAGET HIGGS, 
 
 AND 
 
 Professor CHARLES FORBES. 
 
 HE Series is intended to impart information on 
 recent Technical subjects in a manner suited to the 
 average individual intelligence. This will not include a merely 
 popular treatment of each subject a mode that usually 
 avoids all points of difficulty and exaggerates those that 
 happen to be phenomenal but it is held out as the object 
 to be attained that every subject shall be fully explained, 
 as well in its theory as in its practice, yet that this shall be 
 done in language and in a fashion (following the Baconian 
 advice), u to be understanded of the common people." 
 
 Following out this idea, the reader will find a complete 
 explanation of the principles involved in each subject, so 
 made as not to necessitate a knowledge of mathematics nor 
 of more abstruse general science ; whilst the mathematical 
 student will find, in those pages that the general reader will 
 avoid, a synopsis of the chief formulae involved. It is hoped 
 by following this course, to enable the general reader to 
 become more familiar with mathematical exposition, and the 
 mathematical student to see clearly the relations expressed 
 by his symbols, and as well to reach the practical man 
 desirous of learning how these relations are expressed by 
 the best authorities. And it is desired to do this without 
 following a distinct didactic method. 
 
 Each volume will be written by, as far as possible, 
 perfectly independent authority, unflavoured with the taint 
 of commercial advocacy, and will give the results of 
 practical experience. 
 
 The Series is elegantly printed in crown 8vo, and the price regulated 
 by the extent of each volume. The volumes will follow in succession, at 
 110 fixed periods, but as early as is consistent with the necessary care in 
 their production. 
 
 London: SYMONS & CO., 27, Bouverie Street, E.G. 
 
 1884. 
 
THE SPECIALISTS SERIES. 
 
 Vol. I. DYNAMO- AND MAGNETO-ELECTRIC 
 MACHINES. By PAGET HIGGS, LL.D., 
 D.Sc., &c., &c. With the use of the German 
 Original by GLASER DE CEW, translated by 
 F. KROHN. Crown 8vo, pp. xiii. 301, with 61 
 Illustrations, cloth, $s. [Ready. 
 
 This volume contains the theory, brief description of, and results 
 obtained, with the best constructions of Dynamo-Electric and Magneto- 
 Electric Machines, and with electrical " storage," so far as this latter may 
 be considered as an auxiliary in the regulation of the current of such 
 machines. 
 
 Vol. II. GAS ENGINES. By WILLIAM MACGREGOR. 
 
 [Ready November. 
 
 This is the first English work containing a popular treatment of the 
 principles involved in that exceedingly useful commercial motor, the Gas 
 Engine. All the principal engines before the public are described, and 
 the differences of construction pointed out. Those historical gas motors 
 that have led to the present development of the engine are dealt with 
 according to their merit. Also the users of Gas Engines will find valuable 
 information as to the management of these motors. 
 
 Vol. III. BALLOONING. By G. MAY. A concise His- 
 tory and Outline of the Principles of the Art of 
 Ballooning, compiled from the best Continental 
 and English sources. [Ready December. 
 
 This deals, not with the possibilities of Aeronautics on vague assump- 
 tion, but gives information from a practical view of what has been done, 
 showing the present position. 
 
 Vol. IV. PRIMARY BATTERIES. By PAGET HIGGS, 
 LL.D., D.Sc., Telford Medalist, and CHARLES 
 FORBES, B.Sc., M.A. [In the press. 
 
 The title of " Primary Batteries " has been selected to express those 
 electric generators depending on chemical or other destructive action, as 
 distinguished from "Secondary Batteries," or "Accumulators" (which 
 are described in Vol. I.) where reconstruction is non-mechanical. The 
 volume contains a full description of all batteries, giving practical results 
 that have been used for the purposes of Telegraphy, the Electric Light, 
 and Electro-Motive power. 
 
 Vol. V. ARC AND INCANDESCENT ELECTRIC 
 LAMPS. By Dr. JULIUS MAIER. [In the press. 
 
 This volume describes those forms and principles of Arc and Incan- 
 descent Lamps that have met with practical application in Europe or 
 America. 
 
 Full Prospectus of each Work post free on application. 
 
 London : SYMONS & CO., 27, Bouverie Street, E.G. 
 
 1884. 
 
MAGNETO- AND DYNAMO- 
 ELECTRIC MACHINES. 
 
LONDON : 
 
 PRINTED BY J. OGDEN AND CO., 
 172, ST. JOHN STREET, E.G. 
 
THE SPECIALISTS' SERIES. 
 
 Edited by Dr. PAGET HIGGS and Professor CHARLES FORBES. 
 
 VOLUME I. 
 
 MAGNETO- ^ 
 
 AND 
 
 DYNAMO-ELECTRIC 
 MACHINES: 
 
 WITH 
 
 A DESCRIPTION OF ELECTRIC ACCUMULATORS 
 
 FROM THE GERMAN OF GLASER DE CEW, 
 BY F. KROHN; 
 
 AND SPECIALLY EDITED, WITH MANY ADDITIONS, BY 
 
 PAGET HIGGS, LL.D., D.Sc. 
 
 SYMONS & CO., 27, BOUVERIE STREET, E.G. 
 EDINBURGH: YOUNG PENTLAND, WEST NICHOLSON STREET. 
 
 1884. 
 
n 
 
 GrL 
 
 Engineering 
 Library 
 
PREFACE. 
 
 THE author of the German original of the greater part of 
 this book says : " Few years only have elapsed since 
 magneto- and dynamo-electric 'generators began to be 
 employed in practice, and the experience gained with 
 regard to them is, therefore, comparatively limited. But 
 we are beginning to see that the machines as yet con- 
 structed are still capable of considerable improvement, 
 and that by a rational construction we shall be able to 
 increase their value." For a considerable period, it was 
 the aim of the constructors of dynamo machines to arrive 
 at some novelty, or to attain some hitherto unapproached 
 dimension, in order to secure a valid patent or to impress 
 the public. The rational development of the practical 
 construction of these machines was left in the hands of 
 the very few who, from position or inclination, were inde- 
 pendent of the financial furore for the time attaching to 
 all matters electrical. Now that the public has become 
 educated (and very dearly they have paid for this educa- 
 tion), the dynamo machine is likely to take a fair stand 
 
vi PREFACE, 
 
 in the rank of useful machines ; for a time it was a ma- 
 chine regarded as likely to revolutionise all the mechanical 
 world ; now it is coming to be considered in its true light 
 as a very valuable aid and auxiliary to steam and other 
 prime movers, extending their sphere, and making more 
 easy their application. P'or these reasons, it is assumed 
 that the public interested in such technical matters are 
 desirous of a more intimate knowlege of the principles of 
 these machines, and this knowledge it is the object of the 
 present handbook to supply. 
 
 THE EDITOR. 
 
Dept. Mech Eng. 
 
 CONTENTS. 
 
 PAGE 
 
 Electrical Units . . * * < . . xiii 
 
 Introduction: the historical development of magneto- and 
 dynamo-electric generators Induction phenomena The prin- 
 ciple of Pixii's generator The commutator Stb'hrer's magneto- 
 electric generator Siemens' cylinder Pacinotti's ring Currents in 
 a ring armature Direct influence of poles Construction of Pacinotti's 
 machine Wilde's machine Principle of dynamo-electric machines 
 Ladd's machine with two cylinders ..... 1 28 
 
 CHAPTER I. 
 
 Machines generating alternating currents The Alliance ma- 
 chine Dr. Meritens' machine Holme's machine Weston's plating- 
 machine Mohring and Bauer's plating-machine Gramme's alternat- 
 ing current-machine Siemens' alternating current-machine Brush's 
 dynamo **.*....'* 2949 
 
 CHAPTER II. 
 
 Machines generating direct currents Gramme's ring and collec- 
 tor Generator with laminated magnet^ Gramme's dynamo Path of 
 the current in the coils of tripolar magnets Fein's generator 
 Schuckert's generator Heinrich's generator with grooved ring- 
 armature Fitzgerald's generator Jiirgensen's generator Glilcher's 
 dynamo Hefner- Altenecks drum-armature Course of the current 
 in the drum-armature Magneto-electric machine with drum-armature 
 Siemens' dynamo Dynamo-electric generator for obtaining pure 
 metals The latest dynamo-electric generator of Siemens and Halske 
 Connections in this generator Weston's dynamo Maxim's dynamo 
 Wallace-Farmer's generator Lontin's dynamo Blirgin's dynamo 
 Niaudet's generator The large Edison machine . . . 50 87 
 
viii CONTENTS. 
 
 CHAPTER III. 
 Particular applicability of the various electric generators 
 
 Alternating current machines Direct current machines Magneto- 
 electric machines Dynamo-electric generators : their disadvantages 
 Advantages of magnetorelectric generators with electro-magnets 88 94 
 
 CHAPTER IV. 
 
 Automatic switches and current regulation Siemens' switch 
 Maxim's regulator Doublerwound machines Self-regulating ma- 
 chines Storage necessary ....... 95 103 
 
 CHAPTER V. 
 
 Electrical storage! Planters elements Their constructions Forming 
 of the Plante element The Elwell-Parker accumulator Faure's 
 batteries Comparison of the Plante and Faure elements Trustworthy 
 data as to the efficiency of accumulators Reynier's statements Swan, 
 Sellon-Volckinar accumulators Brush's accumulator Theory of action 
 in accumulators Applications of accumulators Their use as reservoirs 
 and regulators Their limited use as portable stores Calculation of 
 their value for electric railways and tramways Their application in 
 permanent connection with an electromotor . . . 104 139 
 
 CHAPTER vi. 
 
 The physjqa! laws bearing on the construction of electric 
 generators, and their practical application. Relation of the 
 electromotive force of a generator to the external work-^-Theoretical 
 deduction of the law bearing on this point Modification of the theo- 
 retical data in practice Internal resistance and external resistance in 
 theory and practice Relation of the strength of current to the number 
 of turns of wire on the armature The rate of rotation and its influence 
 The increase of temperature of the coils, and the calculation of the 
 resistance thus caused The intensity of the magnetic field Special 
 laws for the calculation in the case of dynamo-electric generators Sir 
 William Thomson's theory with regard to the advantageous dimensions 
 of the armature coils and electro-magnet cores of dynamos. 140 163 
 
 CHAPTER VII. 
 Construction of the several parts of electric generators. 
 
 The field-magnets The manufacture of steel magnets Haker and 
 Elias' coefficient for the portative power of a magnet Jamin's investi- 
 gations on the distribution of free magnetism Frankenheim's investi- 
 gations Elias' method for making steel magnets Deprez' small 
 
CONTENTS. ix 
 
 electro-magnetic motor The coefficients found for various kinds of iron 
 by Pliicker and Barlow The construction of the armature Varia- 
 tion Period of change in the magnetisation of the iron core Position 
 of the brushes Heating of the iron core, and reasons therefor Most 
 advantageous way of placing the armature with respect to the magnetic 
 poles Collectors and commutators Diminution of the surfaces of fric- 
 tion Distribution of the formation of sparks, Edisons' pollector 
 Mechanical construction of electric generators , . . 164 181 
 
 CHAPTER VIII. 
 
 The employment of electric generators, for producing the 
 electric I ight. Special rules for the construction of electric light gene- 
 rators The "Trinity House " report Advantages of large generators 
 Tables of comparison Report of the Military College at Chatham 
 Comparison between the Gramme and the Siemens generators Com- 
 mittee of the Franklin Institute in America Tresca's experiments on 
 expenditure of work and efficiency Gramme's experiments with electric 
 light generators 182202 
 
 CHAPTER IX r 
 
 Various applications of electric generators. Generators for 
 galvano-plastic purposes Current interrupters and circuit closers 
 Efficiency of some galvanoplastic generators Generators for obtainipg 
 pure metals and preparing ozone Employment of electric generators 
 for the melting of irfdium, platinum, and steel Sir William Siemens' 
 smelting apparatus Schwendler's experiments in telegraphy Arrange- 
 ments of the " Western Union Company " in New York Employment 
 of small generators worked by hand or foot Ejeptrical transmission of 
 energy and its future . ...... 203 211 
 
 APPENDICES, 
 
 CHAPTER X. 
 
 Formulae for the construction of electro-magnets General 
 formulae for electro-magnets Dependence of the magnetic moment and 
 the power of attraction on the resistance of the coil The most advan- 
 tageous diameter of wire The best ratio of the magnetising coil to the 
 diameter of the iron core Conditions for maximum on shunt cir- 
 cuits . 212225 
 
x CONTENTS. 
 
 CHAPTER XI. 
 
 Instruments for measurements in connection with electric 
 generators. Ayrton and Perry's dynamometer The commutator 
 Ammeter Commutator Voltmeter Ammeter and Voltmeter without 
 commutator Ammeter and Voltmeter with springs Ammeter and 
 Voltmeter with cogwheel and gear Energy measurer Dr. Tobler's 
 formulae for taking measurements in connection with dynamo -electric 
 generators Measurements for dynamos whose magnets are excited by 
 the main current Measurements for dynamos whose magnets are excited 
 by a shunt-current 225241 
 
 CHAPTER XII. 
 
 Latest constructions of generators Jablochkoffs "Elliptic" 
 machine Gordon's alternating current system Gordon's estimate for 
 lighting a town Ferranti machine Hopkinson-Edison machine 
 Mordey's Victoria machine Isenbeck's experiments Theory of proper 
 distribution of potential differences on the collector of a dynamo Best 
 dimensions of pole pieces in multipolar machines Advantages of multi- 
 polar machines Comparison of Gramme's and Pacinotti's rings The 
 Elphinstone- Vincent machine Crompton-Biirgin-Kapp machines 
 
 242262 
 
 CHAPTER XIII. 
 
 Clausius' complete mathematical theory of magneto- and dynamo-electric 
 machines 263280 
 
LIST OF ILLUSTRATIONS. 
 
 TA6X 
 
 Fig. 1. Diagrams explaining induction phenomena ^ , . . 2 
 Fig. 2. Pixii's magneto-electric generator . . . . .4 
 Fig. 3. Path of current in Pixii's generator ..... 5 
 Fig. 4. Diagrams explaining the mode of action of a commutator . 7 
 Fig. 5. Stohrer's magneto-electric generator ..... 8 
 Fig. 6. Figures explaining the construction of a cylinder armature . 10 
 Fig. 7 Small Siemens generator with cylinder armature . . .11 
 
 Fig. 8. Ring armature .12 
 
 Fig. 9. Diagram explaining the course of the current in a ring armature 13 
 Fig. 10. Diagram for explaining the action of the permanent pole on 
 
 the coils of the ring armature. (N.B. In this figure the 
 
 full black lines are supposed to lie on the other side of the 
 
 plane of the figure, whilst the dotted lines are supposed 
 
 to lie on the front. ) t .'., . . . .16 
 
 Fig. 11. Diagrams explaining the mode of leading away the current in 
 
 a ring armature and in a battery coupled up for quantity . 19 
 Fig. 12. Mode of winding the coils and of connecting them with the 
 
 collector in Pacinotti's ring 20 
 
 Fig. 13. Pacinotti's generator ........ 21 
 
 Fig. 14. Wilde's generator . . 23 
 
 Fig. 15. First form of the Siemens dynamo-electric generator . . 25 
 Fig. 16. Ladd's generator with two cylinder armatures . .27 
 
 Fig. 17. The Alliance machine 30 
 
 Fig. 18. De Meritens' machine 33 
 
 Fig. 19. Figure explaining the construction of De Meritens' generator 35 
 Fig. 20. Position of the field-magnets and armature-magnets in 
 
 Weston's plating machine ...... 36 
 
 Fig. 21. Cross-section of the Gramme alternating current generator . 40 
 Fig. 22. Longitudinal section of the Gramme alternating current 
 
 generator . . , ' 41 
 
 Fig. 23. Siemens' alternating current generator with small dynamo 
 
 for exciting the field-magnets , 44 
 
 Fig. 24. Brush machine . . . . . . . .45 
 
 Fig. 25. Figure showing the construction of the iron core of the 
 
 armature in Brush's generator ...... 48 
 
xii LIST OF ILLUSTRATIONS. 
 
 PAOB 
 
 Fig. 26. Diagram explaining the construction of the commutator in 
 
 Brush's generator . . . . . . . .48 
 
 Fig. 27. Figure showing the construction of the Gramme ring and 
 
 collector 51 
 
 Fig. 28. Gramme's generator with laminated magnet . . .52 
 Fig. 29. Gramme's light machine ...... .53 
 
 Fig. 30. Diagram explaining the path of the current in Gramme's 
 
 light machine . . . . . < . . .55 
 Fig. 31. Fein's dynamo-electric generator ..,.<. 57 
 
 Fig. 32. Schuckert's flat ring generator 59 
 
 Fig. 33. Giilcher's dynamo-electric generator ..... 62 
 Fig. 34. Figure showing the construction of a Siemens' drum armature 63 
 Fig. 35. Diagram explaining the course of the current in the drum 
 
 armature ,* , . . . ; , . . .64 
 
 Fig. 36. Diagram showing the course of the current in a coil of the 
 
 drum armature . .65 
 
 F>'g. 37. Siemens' small magneto-electric generator With drum armature 67 
 
 Fig. 38 . Siemens' light generator 69 
 
 Fig. 39. Siemens' generator for obtaining pure metals . . .71 
 Fig. 40. Figure showing the action of the field-magnets on the 
 
 armature bobbins in Siemens' coreless armature . . 72 
 Fig. 41. Diagram explaining the connection of the armature bobbins 
 
 with the collector in Siemens' coreless armature . . 73 
 Fig. 42. Weston's dynamo-electric light generatdr * . . .77 
 Fig. 43. Maxim's generator, with current regulator . < . .78 
 
 Fig. 44. Wallace-Farmer's generator 80 
 
 Fig. 45. Figure explaining the construction of Lontin's generator . 81 
 Fig. 46. Niaudet's magneto-electric generator , . . 83 
 
 Fig. 47. Edison's large dynamo-electric generator . . . .85 
 Fig. 48. Figure ' showing the Construction of a Plante secondary 
 
 element .....<.... 105 
 Fig. 49. Faure's secondary element . . < ; . . .111 
 
 Fia. 50. Edison's collector 177 
 
 Fig. 51. Ayrton and Perry's dynamometer < 227 
 
 Fig 52. Ayrton and Perry's Commutator ammeter , 228 
 
 Fig. 53. Ayrton and Perry's cog-wheel ammeter .... 235 
 Fig. 54. Diagrams explaining the measurements in connection 
 
 with dynamo-electric generators ..... 238 
 Fig. 55, JablochkoflTs " Elliptic " machine . . . . . 243 
 Fig. 56. Gordon's alternating current generator . . . .246 
 Fig. 57. Diagram of Ferranti's alternating current generator . . 250 
 Fig. 58. Ferranti's alternating current generator .... 250 
 
 Fig. 59. Mordey's Victoria "machine 258 
 
 Fig. 60. Elphinstone-Vincent machine . . . . . . 259 
 
 Fig. 61. Elphinstone-Vincent machine, construction . . . 260 
 
UNITS EMPLOYED IN ELECTRICAL MEASUREMENTS. 
 
 I. The absolute or C. G. S. (ceiitimetre-grainme-second) units. 
 
 1. Unit of length, 1 centimetre. 
 
 2. Unit of time, 1 second. 
 
 3. Unit of force. The unit of force is that force which, acting 
 on a freely movable mass of one gramme during one second 
 imparts 10 that mass a velocity of 1 centimetre per second. 
 
 4. The unit of work is the work done by the unit of force in traversing 
 the space of 1 centimetre. In Paris, this unit = '00101 915 centi- 
 metre-gramme, or. in other words, in order to raise one gramme 
 one centimetre high, 980*868 units of work are necessary. 
 
 5. The unit of electrical quantity is that quantity of electricity 
 which, acting on an equal quantity of electricity at a distance 
 of 1 -centimetre, exerts a force equal to the unit of force. 
 
 6. The unit of potential difference or of electromotive force exists 
 between two points, when the unit quantity of electricity, in 
 moving from the one point to the other, requires a unit force to 
 overcome the electrical repulsion. 
 
 7. The unit of resistance is that which, in one second, only allows 
 the passage of unit quantity between two points, between 
 which there exists unit potential difference. 
 
 II. The practical units for electrical measurements. 
 
 1. Weber, unit of magnetic quantity = 10 8 C. G. S. units. 
 
 2. Ohm*, unit of resistance, 10 9 C. G. S. units. 
 
 3. FbKt, unit of electromotive force = 10 8 C. G. S. units. 
 
 4. Ampere^., unit of strength of current = 10 1 C. G.'S. units. 
 
 5. Coulomb, unit of electric quantity = 10 ~ * C. G. S. units. 
 
 6. Watt$, unit of work = 10 7 C. G. S. units. 
 
 7. Farad, unit of capacity = 10 9 C. G. S. units. 
 
 * 1 ohm is about equal to tne resistance of 48'5 m. of pure copper wire, 1 mm. 
 in diameter, at Q C. 
 
 t 1 volt is about 5 to 10 per cent, less than the electromotive force of a l)aniell 
 cell. 
 
 % The current which, driven by the unit electromotive force, is able to traverse 
 the unit of resistance in one second, is = 1 ampere. 
 
 amp. x volt 
 
 1 Watt = ampere x volt; 1 H. P. = ^ ; 1 cheval de vapeur = 
 
 amn. x volt 
 735 
 
Dept. Mech. Eng. 
 
 INTKODUClTON. 
 
 HISTORICAL DEVELOPMENT OF MAGNETO-ELECTRIC AND 
 DYNAMO-ELECTRIC MACHINES. 
 
 So long as only galvanic batteries were employed in 
 practice for generating electric currents, that is, so long 
 as these currents were obtained solely by chemical action, 
 it was but natural that, for doing large quantities of work, 
 the application of electrical energy should be very limited 
 For the cost of maintaining a battery is too high as 
 compared with its efficiency, and it is almost impossible 
 to obtain in this way constant currents of great quantity 
 and intensity. A larger field for the application of 
 electrical energy was opened up when use began to be 
 made of electric currents, produced by the conversion of 
 mechanical energy, through the invention of electric 
 machines. 
 
 Faraday's researches on the phenomena of induction, 
 formed the theoretical basis for the construction of 
 electric machines. 
 
 He had shown that when a current circulates in a wire, 
 A A f , Fig. 1, a, forming part of a circuit, momentary 
 currents will under certain circumstances be induced in 
 a neighbouring wire, B B', parallel to the first. These 
 
 B 
 
2 INTRODUCTION. 
 
 currents will flow in the direction of the primary current, 
 A A', or in an opposite direction, according to circum- 
 stances ; and this direction can easily be observed by the 
 deflections of the needle of a galvanometer connected 
 with the wire B B' . 
 
 A current in a direction opposite to that of the primary 
 current, that is in a direction from B' to B, will be 
 generated : (1) at the moment when the primary current 
 
 Fig. 1. 
 
 is started; (2) when the wires A A' and B B' are ap- 
 proached to each other ; and (3) when the current in A A' 
 is strengthened. 
 
 A current is set up in the same direction as that of the 
 primary current, that is from B to B' : (1) at the moment 
 when the current in A A r is interrupted ; (2) when the 
 .wires A A' and B B' are moved away from each other ; 
 (3) when the current in A A' is weakened. 
 
 The discovery of the currents generated on the approach 
 of the wires to each other (approximation currents), and 
 on their being moved away from each other (retrocession 
 
INDUCED CURRENTS. 3 
 
 currents), was of special importance for the construction 
 of electric machines. 
 
 Far stronger induction currents are generated if the 
 primary wire, as well as the wire in which currents are to 
 be induced (the secondary wire) are coiled into spirals, 
 or helices, and if both are so placed that the separate 
 turns of the one can act on those of the other, as shown, 
 for example, in Fig. 1,6. In this case, the strength of the 
 induced current B B r increases, generally with the num- 
 ber of turns or convolutions in the two wires ; for under 
 the conditions assumed, small currents are induced by 
 each turn of the primary wire A A', in every neighbour- 
 ing turn of the secondary wire B B r , and these unite to 
 form a total strong current. 
 
 The practical importance of this fact is only fully learned 
 from the results of investigations by Ampere, who dis- 
 covered that a magnet may be considered to be a piece of 
 iron perpetually encircled by parallel electric currents, 
 and that by approaching a magnet to a conducting wire 
 or by moving the magnet away, currents can be induced 
 in the wire, in the same way as if there were used a wire 
 spiral through which a current is flowing. 
 
 It is to Pixii that the honour is due of having made 
 the first practical application of this discovery. He con- 
 structed the first magneto-electric machine in 1832. The 
 mode of action of this machine, illustrated in Fig. 2, will 
 be made clear from what follows. 
 
 According to Ampere every magnet is encircled by 
 parallel electric currents in such a way that if the north 
 pole is pointed towards the observer, they circle in a 
 direction opposite to that of the hands of a clock, whilst, 
 if the observer faces the south pole, the currents flow in 
 the direction of the hands of a clock. 
 
INTRODUCTION. 
 
 Fig. 2. 
 
 In Pixii's machine, Fig. 2, there is a compound horse- 
 shoe magnet which can revolve on its axis, and above the 
 poles of this magnet is fixed the armature. This consists 
 of two wire coils, whose convolutions form a continuous 
 helix. These coils contain two soft iron cores, which at 
 every approach of the poles of the magnet are themselves 
 
 converted into magnets. 
 Fig. 3 shows more clearly 
 in what way the coils of 
 wire are wound, and this 
 figure serves better for 
 explanation. Whenever 
 the pole Nof the magnet 
 approaches the soft iron 
 core a of one of the coils, 
 a will become a south 
 pole, for a magnet always 
 magnetises a piece of iron 
 close to (but not touch- 
 ing) it in such a way that 
 a south pole is induced 
 opposite the north pole, 
 and a north pole opposite 
 the south pole. At the 
 same time, according to 
 Ampere's law, electric currents will be generated, and 
 these will then circulate round the iron core of the coil 
 in the direction of the hands of a clock. But as soon 
 as these currents are started, they will induce others in 
 the turns of the wire coil, which are seen in the figure 
 to flow from right to left. 
 
 Simultaneously, however, b will become a north -pole 
 on account of the pole S approaching it, and Amperian 
 
PIXII'S MACHINE. 
 
 Fig 3. 
 
 currents will commence encircling the iron core of the 
 second coil from right to left. The moment these are 
 started, they induce currents in the coils surrounding the 
 iron core, which flow in the direction of the hands of a 
 clock. 
 
 A careful examination of Fig. 3 will show that the two 
 currents simultaneously generated in the two coils, 
 though seeming to flow 
 in opposite directions, 
 really form one current 
 in the wire system, as 
 indicated by the arrows. 
 This current traverses 
 the wire system in the P 
 same direction, from p to 
 p', and can be conducted 
 away by the terminal 
 wires p and p r . An 
 opposite current, one 
 from p f to p, is induced 
 in the wire system of the 
 coils as soon as the poles 
 of the magnet, N S, begin 
 to move away from the iron cores a and 6, in continuing 
 their revolution. For the resulting gradual demagne- 
 tisation of the iron cores causes a weakening of the 
 Amperian currents encircling them, and, according to 
 Ampere's law, this weakening must induce currents in 
 the surrounding turns of wire of the opposite direction. 
 
 Finally, the poles of the magnet will again approach 
 the iron cores, in such a way that N approaches 6, and S 
 approaches a, and since a now becomes a north-pole and 
 6 a south-pole, a current will be induced in the wire coils 
 
6 INTRODUCTION. 
 
 opposite in direction to the original current of approach, 
 but which is only a continuation of the current produced 
 by the preceding demagnetisation of the iron cores. All 
 this the reader will easily perceive if he makes an 
 analysis of the separate processes. After the second 
 current of approach follows a retrocession current, and 
 so on. From what has been said, it will be seen that 
 in every complete revolution of the magnet N S round its 
 axis, the current in the turns of the wire coils changes 
 its direction twice, the changes taking place at the 
 moments when the poles N S pass the ends of the iron 
 cores. 
 
 In order to convert the two opposite currents, gene- 
 rated during each complete revolution of the magnet N S, 
 into a current of single direction, where this is desirable, 
 a commutator is added to the machine. Fig. 4 shows the 
 principle on which it is constructed. 
 
 One end of the conducting wire of the armature coil is 
 connected with the metallic segment A, Fig. 4, a ; the 
 other end of the wire is. connected with segment B. The 
 segments are separated from each other by a strip of 
 insulating material, i i, and the commutator is fixed in 
 such a way that it revolves once round its axis simulta- 
 neously with the magnet (or simultaneously with the 
 armature in the machines to be subsequently described). 
 
 Now, if the induction current be supposed to flow 
 through the turns of the helix, in the direction from A to 
 By when the pole N approaches a, and the pole S ap- 
 proaches 6, it is clear that it will flow in the direction from 
 L to L' in the conducting wire L L f , whose terminals 
 bear on the metallic segments. When the poles N and S 
 recede from a and 6, and the retrocession current is started, 
 the current in the spiral changes its direction, and now 
 
COMMUTATOR. 7 
 
 traverses the latter from B to A. In order to avoid a 
 change of current in the conducting wires, the com- 
 mutator is arranged so that at the moment when there 
 occurs the change of current, and when the helix is 
 momentarily currentless, the conducting wires L L' bear 
 on the insulating portion of the commutator, Fig. 4 b. 
 Simultaneously with the commencement of the new cur- 
 rent, L bears on A, and L' on B ; consequently, although 
 the current in the spiral of the armature flows from B to 
 
 g 
 
 <D 
 P 
 
 A, it will continue to flow in the original direction in the 
 conducting wires, that is, from L to L'. Thus the two 
 opposite currents, generated during each complete revolu- 
 tion of the magnet, are made to flow in the same direction 
 in the external circuit by means of the commutator. 
 
 Pixii's machine had this practical disadvantage, that the 
 heavy compound magnet rotated in front of the armature. 
 Subsequent constructors, as Saxton, Clarke, and others, 
 modified the machine, making the lighter armature rotate 
 in front of the magnet. Besides this, Saxton placed the 
 magnet as well as the bobbins of the armature in a hori- 
 
8 INTRODUCTION. 
 
 zontal position, whilst Clarke retained the vertical position 
 of the magnet, but placed it with the poles downwards, 
 and made the bobbins of the armature rotate at its side. 
 It seems also, that Saxton was the first to employ the 
 commutator previously described. 
 
 Stohrer considerably increased the efficiency of magneto- 
 
 Fig. 5. 
 
 electric machines by increasing the number of the magnets 
 as well as the number of armature-bobbins. 
 
 In this machine six armature-bobbins rotate before the 
 six poles of three compound magnets. The coils of the 
 bobbins are wound in such a way that at each approach 
 of the coils to the magnet poles currents flowing in the 
 same direction are generated, and these unite to form one 
 current ; again, every time the bobbins of the armature 
 recede from the poles of the magnets, currents are induced 
 
STUHRER'S MACHINE. g 
 
 which flow in the coils in a direction opposite to that of 
 the currents of approach. Accordingly, in each complete 
 revolution of the armature six compounded currents of 
 approach, and six compounded currents of retrocession 
 are generated in the wire coils of the armature-bobbins, 
 and each of these, again, is composed of six elementary 
 currents. By means of a commutator, connected with the 
 machine, these alternating currents can be rectified before 
 reaching the external circuit. 
 
 The results obtained with Stohrer's machine were so 
 satisfactory that subsequent inventors, adopting his idea, 
 continued to increase the number of the armature-bobbins 
 and magnet-poles, and in this way succeeded in obtaining 
 currents of remarkable strength, following each other in 
 rapid succession. Thus, by degrees, were developed the 
 large magneto-electric machines for alternating currents, 
 such as those of the " Alliance Company " constructed by 
 Nollet, and the machines of Holmes, Lontin and others, 
 which, side by side with the machines for continuous cur- 
 rents, are still, under certain circumstances, used in 
 practice, especially for the electric light in lighthouses. 
 All these machines, which in principle are only enlarged 
 Pixii machines, will be dealt with in the chapter on 
 " Machines generating alternating currents." 
 
 A notable modification in the construction of magneto- 
 electric generators was made by Dr. Werner Siemens, of 
 Berlin, in 1857, who greatly improved the shape of the 
 armature-bobbins. 
 
 Experiment soon showed that the strength of the cur- 
 rents produced by a magneto-electric generator is in- 
 creased when the coils of the armature are brought as 
 near as possible to the magnetic poles ; and that the 
 efficiency of a machine depends further on the interruption 
 
io INTRODUCTION. 
 
 being as short as possible when the current changes its 
 direction. Siemens took both these experimental laws 
 into account in the construction of his armature, the 
 simplest form of which is represented in Fig. 6. 
 
 An iron cylinder, a 6, Fig. 6 a, is provided with two 
 grooves, and the spirals of the conducting wire are wound 
 round this cylinder, parallel with its axis, in such a way 
 that the two grooves are filled up, the complete cylindrical 
 
 Fig. 6. 
 
 jsr 
 
 form being thus restored, Fig. 6 6. One of the terminal 
 wires is connected with the shaft of the armature, whilst 
 the other is connected with a ring which is insulated from 
 the shaft. Two springs, one of which bears on the in- 
 sulated ring, and the other on the shaft, conduct the cur- 
 rents to the external circuit. 
 
 In Fig. 7, a small Siemens machine is illustrated, and 
 from this figure can be seen the position that the rotating 
 cylinder takes up between the poles of the magnets. The 
 magnets are usually numerous. The poles of the magnets, 
 
SIEMENS' ARMATURE. n 
 
 Fig. 6 c, have semi -circular pieces cut out, so that the 
 cylinder is well-surrounded ; in fact in the whole con- 
 struction of Siemens' machine, the inductive action of the 
 permanent magnets is far more completely utilised than 
 in the magneto-electric generators previously described. 
 
 One special advantage in the form of the cylindrical 
 armature is that not only is the armature magnetised as 
 completely as possible, but the poles of the steel magnets 
 
 Fig. 7. 
 
 can also directly exert a strong inducing action on the 
 spirals of the wire coils, and this considerably strengthens 
 the currents induced by the magnetism of the soft iron core. 
 Besides, in the cylindrical armature the time during 
 which the current is interrupted is reduced to a minimum, 
 as the change of poles takes place in an extremely short 
 interval of time, when the cylinder is rotated rapidly ; and 
 this circumstance greatly increases the efficiency of the 
 machine. 
 
 The form of cylindrical armature just described (proba- 
 
INTRODUCTION. 
 
 Fig 
 
 bly now used in Siemens' alarm bell indicator only), was 
 later on considerably modified, and so much improved 
 that cylindrical armatures still very successfully hold 
 their position, and have not been supplanted by the 
 " ring " armature, which we now proceed to describe. 
 
 The ring armature, which caused quite a revolution in 
 the construction of electric generators, was invented by 
 
 Dr. Antonio Pacinotti, 
 of Florence, in 1860, 
 and by its means he 
 succeeded, for the first 
 time, in obtaining, 
 with an electric ma- 
 chine, continuous elec- 
 tric currents flowing in 
 a constant direction, 
 without making use of 
 a commutator. As 
 Pacinotti's ring arma- 
 ture is to be found in 
 principle in all ma- 
 chines constructed on 
 the " Gramme " sys- 
 tem, and as the prin- 
 ciple of its construction is employed in almost all 
 continuous-current machines, a careful analysis of its 
 action will be necessary. 
 
 When a ring of soft iron, Fig. 8, is placed between two 
 magnetic poles, N $, a south pole will be induced oppo- 
 site the north pole N, and a north pole opposite the 
 south pole. Now, if the iron ring is caused to revolve 
 round its centre from right to left, new portions of the 
 ring will in turn be magnetised, whilst the portions of 
 
RING ARMATURES. 13 
 
 the ring previously magnetised will lose their magnetism. 
 Accordingly, the poles of the iron will travel along the 
 ring from left to right. If this ring, as shown in Fig. 8, 
 be encircled by a continuous coil of copper wire, insulated 
 from the iron ring, currents will be induced in the wire, 
 and the direction will be different in the several turns 
 of the coil, accordingly as these are nearing the north 
 pole or the south pole of 
 the iron ring ; moreover, 
 as the poles of the ring 
 change, in consequence of 
 its rotation, the currents 
 also in the convolutions of 
 wire surrounding it will 
 change their direction. To 
 understand better what 
 takes place during the re- 
 volution of the ring, it may 
 be considered that the ring 
 is fixed. For, in any case, 
 its poles will always lie in 
 the line N S 9 and it can be 
 assumed that the windings 
 of the coil move from left 
 to right round the ring, and thus are brought under 
 the maximum inducing action of the poles N and 
 S. For the sake of simplicity, the inducing effect on a 
 single turn of the coil need only be considered, and it 
 may be supposed that the ring is divided in two, so that 
 two north poles meet opposite S 9 and two south poles 
 opposite N. 
 
 In this case, Amperian currents will circle round the 
 ring, as indicated by the arrows in Fig. 9. Let us com- 
 
i 4 INTRODUCTION. 
 
 mence our observation at the moment when the turn x y 
 is at the point where the dotted line h cuts the ring, and 
 when it commences to move from left to right. Con- 
 sidering only the nearest portions of the ring, we see that 
 the turn or loop approaches the divisions A and 5, re- 
 ceding at the same time from divisions G and H. Now let 
 us call the current + when its direction is from the circum- 
 ference towards the centre of the ring ; and when its direc- 
 tion is from the centre towards the circumference. Let us 
 also denote the current induced in the loop by the two ad- 
 joining segments of the ring by 4- 2 or 2, and that in- 
 duced by the portions of the ring which are more than 45 
 away by -f 1 or 1. We shall then be able to express the 
 current induced in the loop at the moment when it com- 
 mences to move from h towards the right by the sum of the 
 factors + 1 +221, i.e., by ; for a current of retreat 
 will be induced in the loop x y by its moving away 
 from the segments of the ring G and H, and, according 
 to the law of induction, this current will flow in the same 
 direction as the Amperian currents in the iron ring. On 
 the other hand, by its approach to the segments A and B, 
 a current will be induced in the loop, traversing the 
 latter in a direction opposite to that of the Amperian 
 currents in these portions of the ring. Accordingly the 
 two currents will neutralise each other at the moment 
 when the loop quits h, for they will be of equal strength. 
 
 If the loop has arrived at the point a, and commences 
 its further course round the ring, it will be possible to 
 express the current of approximation induced in it by the 
 segments B and (7, together with the current of retrocession 
 induced by the segments H and A as the sum of the 
 following factors, + 1+22 + 1=4-2. When the 
 loop x y leaves 6, the sum equals +1+2 + 2 + 1, 
 
RING ARMATURE THEORY. 15 
 
 that is, = -f 6. On quitting c, the induced current can 
 be represented by-f 12 + 2 4-1 = +2, and again, 
 when the loop has passed c2, we can express the action 
 by the sum of the factors 1 2 4-2+ 1, that is, 
 by 0, and the loop has, therefore, no current induced 
 in it. 
 
 Now, when the loop reaches the point e and continues to 
 move towards that portion of the ring which is most 
 strongly influenced by the north pole JV, the current in- 
 duced in it after it leaves e will be expressed by the sum of 
 the factors 1 2 + 2--1, that is, by 2, the cur- 
 rent, therefore, has changed its previous direction. At / 
 the current, which is now flowing in a new direction, will 
 reach its maximum, and be equal to 6 ; at g its 
 strength will again have fallen to 2 ; and after the 
 strength at h has sunk to 0, a change of current will again 
 take place, and the expressions for the strength of the 
 induction currents will have the sign + prefixed. 
 
 What we have said of the one turn x y of the coil, of 
 course equally applies to turns or groups of turns which 
 come into the respective positions ; and from the preceding 
 considerations we see that the whole wire system which 
 surrounds the ring can be regarded as being traversed by 
 two opposite total currents meeting at p and p' y Fig. 8. 
 Besides, according to the explanation, we shall be able to 
 denote that current by + , which is compounded of all the 
 separate currents in the turns which surround the portion 
 A B G D of the ring, whilst the other current, which is 
 compounded of the currents traversing the turns surround- 
 ing the section E F G H of the ring may be distinguised 
 by the prefix . The rotation of the ring only so far 
 changes the condition of things that new turns and groups 
 of wires constantly come into the regions where the two 
 
i6 
 
 INTRODUCTION. 
 
 opposite currents dominate, and accordingly in every 
 complete revolution of the ring, each turn passes both the 
 neutral points once. 
 
 What has been said, however, refers only to the inducing 
 action that the magnetised iron ring exerts on the wire 
 coils surrounding it ; all that we have now to do is to 
 analyse the action of the fixed poles S and N 9 Fig. 8, on 
 the wire system rotating between them. 
 
 We shall retain the position of the poles as shown in 
 Fig. 8. 
 
 Fig. 10. 
 
 In this position the turns of the coils are perpendicular 
 to. the plane of cross-section of the poles when they pass 
 the latter. 
 
 Fig. 10 will serve best for an explanation. In this A B 
 represents a portion of the rotating ring, the turns of wire 
 " on which have been assumed to be moved a little asunder, 
 though in reality they are very close together. S indi- 
 cates the south pole, which in the figure is supposed to 
 be under the ring. The arrows indicate the direction in 
 which the Amperian currents encircle the ring. We will 
 suppose the ring to be moving in the direction from A to 
 By and will only consider those portions of the coils that 
 
RING ARMATURE THEORY. 17 
 
 are on the outside of the ring, and indicated by full lines 
 in the figure ; the portions on the inside of the ring are 
 indicated by dotted lines, and are omitted from con- 
 sideration for the present. We then perceive that in 
 turns I. and II., currents of approach will be generated, 
 having a direction opposite to that of the Amperian 
 currents at x (from top to bottom in the figure), whilst 
 in the , turns VIII. and IX., currents of retrocession will 
 be generated (also flowing from top to bottom in the 
 figure) that are due to the direction of the Amperian 
 currents at y, from which they are moving away. 
 
 In other words, currents of the same direction are in- 
 duced in all the turns, left and right of the south pole, 
 and this direction is exactly the same as that of the cur- 
 rents induced by the magnetism of the iron ring. 
 
 Now, if we take those portions of the turns into con- 
 sideration that lie on the inner side of the ring, which 
 are indicated by the dotted lines, we see that, if the iron 
 core of the coils were not present, the south pole, S 9 would 
 induce currents which would also flow from top to bottom 
 in the figure. Accordingly, the currents induced in the 
 internal and external portions of the turns would oppose 
 each other ; and if the portions of the turns on the inside 
 of the ring were as close to the pole of the magnet as the 
 portions lying on the outside, the induced currents in the 
 inner portions would be equally as strong, and would 
 destroy the others. This, however, is not the case, for, 
 firstly, the portions of the turns which are on the inside of 
 the ring are farther away from the pole 8 than the por- 
 tions on the outside, and the currents induced in the latter 
 would, therefore, in any case, have the greater power, 
 even if the iron core were not present ; secondly, the iron 
 ring really does separate the inside portions of the turns 
 
 C 
 
1 8 INTRODUCTION. 
 
 from the magnet, and completely annuls the action of the 
 magnet on those portions, so that the currents generated 
 in the parts of the turns lying on the outside of the ring 
 act unopposed. As these currents flow in exactly the 
 same direction as those induced by the magnetised iron 
 ring, they considerably strengthen its action. 
 
 In our explanation we have, however, only spoken of the 
 turns lying right and left of the pole, and we have not con- 
 sidered the turns III., IV., V., VI. and VII. The action 
 of the pole S on these turns is equal to zero, as can be 
 seen from what follows. 
 
 The current induced in turn IV. will principally be a 
 retrocession current from x, and it will accordingly flow in 
 the direction of the Amperian current at x. In turn VI. a 
 current of approach will predominate, and this will flow in 
 the same direction as the previous one, because its direc- 
 tion must be opposite to that of the Amperian current at 
 y. The receding from x and the approach to y will 
 exert an equally powerful influence on turn V that is, a 
 current of double strength will be generated in it, flow- 
 ing in the same direction as the currents in IV. and VI. 
 Now, if all the turns are the same distance apart from 
 each other, which is the case in the figure and in reality, 
 the opposite currents in II. and IV. will have the same 
 strength, and will neutralise each other, and a change of 
 current will take place in turn III., for which reason this 
 turn will be currentless. Similarly, there will be no cur- 
 rent in turn VII., on account of the currents in VI. and 
 VIII., which neutralise each other ; and as currents I. 
 and IX. are equidistant from V., the double current in 
 V. will be annulled by currents I. and IX., which are 
 opposite in direction to it ; all the turns from III. to VII. 
 will accordingly be currentless. As a result, therefore, 
 
RING ARMATURE, CONNECTIONS. ig 
 
 we only obtain the currents generated in the turns right 
 and left of the south pole, and this, as we have observed, 
 strengthens the current generated in the coils of wire, by 
 the magnetism of the iron core. It need scarcely be added 
 that the action of the north pole on the neighbouring 
 turns is quite analogous, and, from the preceding con- 
 siderations, we can clearly see that the two total currents 
 of opposite direction, generated by the magnetism of the 
 iron ring unite with the currents produced by the direct 
 
 Fig. 11. 
 
 influence of the magnet poles on the coils, and which also 
 flow in contrary directions. 
 
 The two intensified currents which are thus generated 
 in the wire system surrounding the ring can be collected 
 at the neutral points, Fig. 8, p p', where their directions 
 meet ; and as shown in Fig. 11, a, they can be united into 
 a single current and be conducted away, like as the cur- 
 rent from the cells of a galvanic battery, connected for 
 quantity, Fig. 11, 6. Pacinotti has effected this collection 
 by dividing the wire coiling surrounding the ring- 
 armature into groups, and by giving to the separate parts 
 of his machine the form shown in Figs. 12 and 13. 
 
20 
 
 INTRODUCTION . 
 
 Fig. 12. 
 
 The iron ring, which moves between two magnetic poles, 
 has sixteen grooved spaces in it, and these serve to receive 
 sixteen wire coils, Fig. 12, all wound in the same direction. 
 The end of each coil is soldered on to the commencement 
 of the next, so that the turns of all the coils unite to 
 form one continuous helix. Wooden wedges are driven 
 into the recesses of the iron ring, and separate the coils 
 from each other. From the joints at which the terminal 
 
 wire of one coil and the 
 wire commencing the next 
 are soldered together, cop- 
 per wires branch off and 
 run from the inner side of 
 the ring to the shaft. 
 There these lead to several 
 brass terminal pieces, in- 
 sulated from each other, 
 and forming a ring, fixed 
 to the shaft of the ma- 
 chine, Fig 13. Two con- 
 tact rollers, k k, bear on 
 this ring, and are placed 
 in such a position that 
 
 they are always in contact with those brass pieces that 
 are attached to branch wires leading from the solderings, 
 p p', Fig. 8, momentarily at the neutral points. 
 
 If the conducting wires are connected with these contact 
 rollers, sixteen total currents will traverse the circuit at 
 every revolution of the ring ; for every one of the sixteen 
 solderings passes each of the neutral points once. All these 
 currents will flow in the same direction without a com- 
 mutator being necessary ; here, then, is a basis for the 
 construction of electric machines for continuous currents. 
 
PACINOTTI'S MACHINE. 21 
 
 The construction of the ring-armature was afterwards 
 considerably improved by the Belgian inventor, Gramme, 
 and the ring-armature employed by him will be more fully 
 described in the chapter on machines generating con- 
 tinuous currents. 
 
 A further advance in improvement of electric machines 
 was made by H. Wilde, of Manchester, in 1866. Wilde 
 conducted the currents generated in a Siemens' cylinder- 
 
 armature, c c, Fig. 14, by the permanent magnets M M, 
 through the coils of a large electro-magnet, E E, after 
 they had been rectified by a commutator. This electro- 
 magnet induced currents in a second Siemens cylinder- 
 armature, K K, and these, of course, were of considerable 
 intensity, because the armature was moving in a very 
 powerful magnetic field. With a machine constructed in 
 this way results were obtained such as had not been ap- 
 proached previously by any electric machine. W r ilde later 
 on constructed a machine with which he obtained still 
 stronger currents. This he did by leading the currents 
 
22 INTRODUCTION. 
 
 induced in the armature K K through the coils of a 
 second electro-magnet of very great dimensions, and by 
 making this magnet act on a third cylinder-armature, in 
 the wire of which was generated the current to be used for 
 doing work. 
 
 Wilde's machines soon found wide application in 
 practice, and a number of them were employed in the 
 celebrated galvano-plastic works of Elkington, in Bir- 
 mingham, for obtaining galvano-plastic deposits on a 
 large scale ; some were used for the production of the 
 electric light in photographic studios, and others again 
 were employed in Whitechapel for preparing ozone as a 
 bleaching agent. 
 
 Nevertheless, even these machines left much to be de- 
 sired. It appears that through the heating of the iron cores, 
 the current was considerably weakened after a working 
 time of several hours, and it could not be kept constant 
 long enough to be employed with advantage in the pro- 
 duction of the electric light for lighthouses. The causes 
 of the heating of the iron cores are discussed in another 
 part of this book. 
 
 In all the machines yet described, the electric currents 
 were induced by means of steel magnets, or, as in Wilde's 
 machine, by magnets that were magnetised by the cur- 
 rent produced in another machine. Such machines are 
 usually called " magneto-electric " machines, to distinguish 
 them from the " dynamo-electric " machines. In the 
 latter the inducing magnets, " field " magnets, as these 
 are termed, have cores of soft iron, which, at starting, only 
 possess a very small trace of magnetism ; this trace is 
 however, sufficient to induce a weak current in the coils 
 of the rotating armature, which current is then used to 
 strengthen the magnetism of the field or inducing 
 
WILDE'S MACHINE. 
 
 magnets. This is done by the current being conducted 
 through the wire coils surrounding the soft iron cores, 
 which are accordingly magnetised more strongly, and now 
 
 Fig. 14. 
 
 induce a new but stronger current in the coils of the 
 armature. The new current again increases the mag- 
 netism of the iron cores, by being conducted, like the 
 previous one, through their wire coils. By this reciprocal 
 
24 INTRODUCTION. 
 
 action, currents are generated in the armature-coils far 
 surpassing in strength any that can be produced with 
 machines of the same size, having only steel field-magnets. 
 The machines without permanent magnets have been 
 named dynamo-electric machines, or, shortly, dynamos. 
 
 Siemens, in Berlin, and Wheatstone, in London, almost 
 simultaneously discovered the principle of the dynamo- 
 electric machines. Siemens, perhaps, deserves the right of 
 priority, as in December, 1866, he had made experiments, 
 before several Berlin scientists, with a machine in which 
 there were no permanent magnets.* In the middle of 
 January, 1867, he communicated his discovery to the 
 Berlin Academy of Science : whilst it was only in February 
 that Wheatstone communicated the result of his dis- 
 covery to the Koyal Society in London, in a paper 
 entitled : " On the Augmentation of the Power of a 
 Magnet by the Eotation thereon of Currents induced by 
 the Magnet itself." These results agreed fully with those 
 obtained by Siemens. Curiously enough, the discovery of 
 the Berlin physicist was made known by his brother Dr. 
 William Siemens, at the same meeting of the Koyal 
 Society as that at which Wheatstone delivered his lecture ; 
 and Wheatstone's communication immediately followed 
 that of Siemens. 
 
 The simplest kind of dynamo is shown in Fig. 15. 
 
 E E are two plates of soft iron, each about 60 cm. long 
 50 cm. wide, and 10 cm. thick. They are united at one 
 end by a third plate, P. Each of the plates E E is sur- 
 
 * The German scientific writers have, in their good fellowship for their 
 countryman, generally overlooked the fact that Wheatstone must also have 
 experimented ; and there are several scientific men who claim to have seen 
 his machine at work at the earlier time indicated as that occupied by 
 Siemens with exhibition in Berlin. The honour, however can well be 
 divided. Editor. 
 
DYNAMO-ELECTRIC PRINCIPLE. 25 
 
 rounded by coils of well-insulated and rather thick copper 
 wire, about 27m. long. The coils on each plate are wound in 
 such a way that they may be considered as constituting a 
 single coil, whose terminals, c, d, lead to the binding screws 
 b and a. I is a Siemens' cylinder-armature, which rotates 
 between the projecting ends of the iron plates. One ter- 
 minal of its coil is connected with the shaft A, and the 
 other terminal is connected with a copper ring, fixed to 
 the shaft, but insulated from it. A spring, 2, in connection 
 
 Fig. 15. 
 
 with the screw 6, bears on the shaft A 9 whilst a spring, 
 1, connected with the screw a, bears on the copper ring 
 R. Before using the machine for the first time, the soft 
 iron plates E E are slightly magnetised, by connecting 
 the wires c and d with a galvanic cell, and causing a cur- 
 rent to traverse the coils surrounding the iron cores ; when 
 this ceases a small quantity of residual magnetism is left. 
 However, it is not necessary to do even this, for through 
 the influence of terrestrial magnetism, a slight magnetic 
 polarity is induced in all soft iron plates that lie in a 
 certain position, and this magnetism is quite sufficient to 
 induce the first current in the armature of a dynamo- 
 
26 INTRODUCTION. 
 
 electric machine. After such a machine has once been 
 made to give a current, there is always enough magnetism 
 remaining, at any time, to generate electric currents. 
 
 If the cylinder-armature is set in motion, alternating 
 currents will be generated in its coils, during its revolu- 
 tion between the poles. These currents are rectified by 
 means of a commutator, omitted in the figure ; and as 
 the terminals of the armature-bobbin are in connection 
 with the terminal wires of the coils surrounding the iron 
 cores, through the screws a and 6, the currents encircle 
 the iron cores, which will finally, after a certain speed of 
 revolution of the armature has been attained, be mag- 
 netised to the maximum extent possible ; in other words, 
 the machine reaches the maximum of its efficiency, and 
 the powerful currents generated in the armature manifest 
 themselves by a great spark if the circuit is broken at any 
 point. This spark can, for instance, be used to explode 
 mines or torpedos, and so forth. Or the powerful currents 
 of the machine can be used as in Siemens' " alarm-bell 
 inductor," to ring large signal-bells in stations, and to 
 work other signalling apparatus. 
 
 An important modification of the dynamo-electric ma- 
 chine was carried out by an Englishman, Ladd, only four 
 weeks after the date of the papers previously mentioned. 
 He sent a description of his dynamo, to the Koyal Society 
 on the 14th of March, 1867, and exhibited it at the Paris 
 Exhibition in the middle of May, 1867. 
 
 The specialty of this machine was that the two iron 
 plates were not connected with each other, but were con- 
 verted into two electro-magnets, between whose poles 
 rotated two armatures, Fig. 16, one of which served to 
 strengthen the magnetism of the iron plates, according 
 to the dynamo-electric principle, whilst the currents from 
 
LADD'S MACHINE. 27 
 
 the other could be used in doing work, that is, in pro- 
 ducing the electric light, or obtaining galvano-plastic 
 deposits. 
 
 Later, the firm of Siemens and Halske, of Berlin, also 
 constructed machines with several armatures, and obtained 
 particularly good results with a machipe consisting of 
 three pairs of plates lying horizontally and parallel to each 
 other. These were converted into six electro-magnets 
 when the machinery was set in motion. Six armatures 
 
 Fig. 16. 
 
 revolved between the twelve poles, and the currents 
 generated could be combined in the most varied ways by 
 means of specially-constructed commutators. 
 
 Other constructors, too, gradually changed and im- 
 proved the dynamo-electric machines in various ways. 
 All these improvements, however, contained nothing new 
 in principle, and only dealt with the arrangement of the 
 separate parts. A change in the principle of the electric 
 machine has not taken place since the discovery of the 
 
28 INTRODUCTION. 
 
 dynamo-electric principle. Accordingly, all the machines 
 described in subsequent chapters, and at present used in 
 practice, depend on modifications and combinations of the 
 historical apparatus we have considered. 
 
CHAPTER I. 
 
 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 ALTHOUGH electric machines may be classified in various 
 ways, as they may be considered from different points of 
 view, and although they are usually divided into magneto- 
 electric and dynamo-electric machines, yet, for a rational 
 classification, it is preferable to group them according to 
 the nature of the currents generated. In the two follow- 
 ing chapters, therefore, they have been divided under 
 " Machines generating alternating currents," and ' Ma- 
 chines generating continuous currents. 
 
 The first large alternating current machines were con- 
 structed by the " L' Alliance " Company, and were intended 
 for the production of the electric light in lighthouses. 
 They have become known as the Alliance machines. The 
 inventor of the Alliance machines, which are still manu- 
 factured by the same Company, was Nollet, Professor of 
 Physics at the Military College of Brussels. Nollet'a 
 machine has been much modified and improved, on the 
 one hand by Professor Masson, who, amongst other 
 things, omitted the commutator, formerly employed with 
 this machine ; on the other hand, by Van Malderen, 
 engineer to the Alliance Company. 
 
 The following is the construction of the present pattern 
 of Alliance machine (Fig. 17). 
 
30 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 Several brass disks are fixed to the shaft of the machine, 
 one behind the other. Each of these carries 16 armature 
 bobbins, which are attached at equal intervals, and each 
 disk revolves, with its bobbins, between the poles of strong 
 compound permanent magnets. These magnets are fixed 
 radially to the horizontal bars of the cast-iron frame, so 
 
 Fig. 17. 
 
 that two opposite poles face each other, and that the 
 magnets arranged in a line are of alternate polarity. By 
 rneans of this arrangement each bobbin is brought, when 
 the brass disks revolve, between poles of opposite polarity, 
 and the iron cores are converted into magnets, which 
 induce powerful currents in the wire coils of the armature- 
 bobbins. These coils are wound in such a manner that 
 they may be considered to form a single large helix, one 
 
"ALLIANCE" MACHINES. 31 
 
 end of which is fixed to the shaft of the machine, the 
 other leading to a ring fixed on the shaft, but insulated 
 from it. The alternating currents are conducted into the 
 external circuit through springs which bear on the ring 
 and shaft. 
 
 The Alliance machines usually carry, on the shaft, 4 
 or 6 of the brass disks, and accordingly the number of 
 armature-bobbins, that move past the poles of the 40 or 
 56 magnets, is 64 or 96. As, in each revolution of the 
 disks, each side of the 16 armature-bobbins passes 16 mag- 
 netic poles, it follows that the current changes 16 times 
 in each revolution ; and as in practice the shaft makes 
 400 revolutions per minute, when a steam-engine of about 
 5-horse power is used, there are about 100 changes of 
 current per second. The intervals between the currents 
 are, therefore, so short that they scarcely come into con- 
 sideration, and, for certain purposes, the currents, taken 
 together, may be regarded as a single current. 
 
 As regards the dimensions and construction of the 
 separate parts of the Alliance machine, the following 
 data, given by Count du Moncel, may be of interest. 
 
 The horseshoe magnets are made at the works of 
 Alvarre ; each weighs 20 kgrs., and each is composed of 
 5 or 6 steel laminae about 1 cm. thick, screwed together. 
 In order to have the poles as uniformly magnetised as 
 possible, bars of soft iron are attached to the ends of the 
 steel magnets. Each complete compound magnet can 
 carry three times its own weight. 
 
 The bobbins of the Alliance machine have gradually 
 undergone much modification. At present they consist 
 of iron tubes, which are slit through the whole length. 
 These are enclosed in brass cylinders, also slit along the 
 middle, and on which the wire-coils are wound. Each 
 
32 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 bobbin is 10 cm. long, and has a diameter of 4 cm. 
 The length and cross-section of the wire depends on the 
 resistance of the external circuit, also on the number 
 of bobbins and the work that the machine is intended 
 to do. 
 
 Fig. 18. 
 
 In the machines for the electric light, strands of wire 
 are used, which consist of 8 wires, each about 1 mm. 
 thick and 30 m. long. The wires are wound with cotton ; 
 and, to insure as perfect insulation as possible, they are 
 dipped, before winding, into a solution of resin and tur- 
 pentine, a very good insulating solution, which only very 
 slightly increases the thickness of the wires. 
 
DE MERITENS' MACHINE. 33 
 
 With an Alliance machine of this construction, having 
 a shaft carrying 4 disks, a light can be obtained, when a 
 steam-engine of 5-horse power is employed, equal in 
 intensity to that of 1,110 candles or 150 Carcel lamps 
 (one Carcel lamp being equivalent to 7*4 standard candles). 
 If a machine with 6 disks is used, a light of 1,480 
 candle-power can be obtained. 
 
 The results obtained with the Alliance machines are 
 good, and the machines are used for the electric light in 
 many lighthouses (those of Cape La Heve, near Havre ; 
 Cape Grriz-Nez, near Calais ; Kronstadt, Odessa, and 
 others) ; but only a small number are made, for the con- 
 struction is very complicated and costly, compared with 
 that of more recent machines. 
 
 De Meritens' Machine is considered by many en- 
 gineers to be the best alternating current machine, and 
 certainly very good results are obtained with it. This 
 machine, especially the latest pattern, is not unlike the 
 Alliance machine in appearance, but differs considerably 
 in the peculiar construction of the armature. 
 
 The armature consists of an eight-spoked wheel, to the 
 rim of which 16 bobbins are fixed in such a way that the 
 iron core of one bobbin forms the prolongation of the 
 iron core of that preceding it. All the iron cores together 
 form a ring, as shown in Fig. 18. 
 
 The cores consist of 50 iron plates, 1 mm. thick, and at 
 each end they have iron pole-pieces composed of similar 
 plates, Fig. 19. The pole-pieces of each bobbin are con- 
 nected with those adjoining by bars of copper. All 
 the coils of these bobbins are wound round the iron 
 cores in the same direction, forming a single long helix, 
 whose terminals lead to two copper rings on the shaft of 
 
 the machine, but insulated from it and from each other. 
 
 D 
 
34 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 Two copper springs bear on these rings and conduct the 
 current into the outer circuit. 
 
 The 8 inducing, or field, magnets, which are fixed to the 
 outer framework of the machine, Fig. 18, are compound steel 
 magnets, and are provided with pole-pieces, Fig. 19, so 
 that the armature-bobbins revolve as near the magnetic 
 poles as possible. The magnets are placed in such a way 
 
 Fig. 19. 
 
 that poles of opposite polarity are always nearest to each 
 other. When the armature is caused to revolve, the 
 bobbins pass close uncler the poles of the magnets ; the 
 soft iron cores are magnetised, and alternating currents 
 are induced in the wire coils, which are intensified by the 
 direct action of the magnets on the coils. 
 
 This arrangement, which -brings the wire coils of the 
 armature into the direct magnetic field of the permanent 
 magnets, is one of the chief advantages of the De Meritens 
 machine. The construction is also particularly prae- 
 
WESTON'S PLATING MACHINE. 35 
 
 ticable, as the separate parts of the armature can, if 
 necessary, be easily removed, without disturbance of the 
 other parts, an absolute impossibility in many other 
 machines. 
 
 Another generator, which closely resembles the Alliance 
 machine, is that of Holmes. Indeed, it is almost identical 
 in construction with the Alliance machine, only that 
 Holmes, who has constructed a number of different pat- 
 terns, has, in his last, replaced the steel magnets by 
 V-shaped cores of soft iron, wound with wire coils, to form 
 electro-magnets under the current from the machine. 
 The cores of soft iron are attached to a disk which 
 rotates in front of a second fixed disk, to which the 
 armature-bobbins are bolted. The coils of these bobbins 
 are not connected with each other, but are united in 
 groups, so that the machine can generate several currents 
 at the same time, each of which can be used independently, 
 so that one machine can work several separate electric 
 lights at the same time. 
 
 In order to rectify the currents, the machine is provided 
 with a commutator. 
 
 Weston's machine for galvano - plastic purposes 
 (Weston's light-machine is described in Chap. II.) con- 
 sists of an iron drum, on the inner surface of which 
 six cast-iron electro-magnets are fixed radially, each 
 reaching to about the middle of the radius of the drum. 
 Six smaller magnets, fixed radially to the hub and shaft of 
 the machine, revolve close under the poles of the larger 
 magnets, Fig. 20, These smaller electro-magnets form 
 the armature, and the coils of two are united into one 
 circuit, so that three horseshoe magnets are obtained, 
 in the coils of which alternating currents are generated, 
 and these are collected and rectified by a specially-con 
 
36 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 Fig. 20, 
 
 structed commutator. The wire coils of the six field- 
 magnets form one circuit ; but the wires are wound so that 
 adjacent poles are of opposite polarity. In order to mag- 
 netise these electro-magnets, the currents generated in 
 the armature are conducted through their coils on the 
 dynamo-electric principle. 
 
 To prevent the coils of the electro-magnets becoming 
 overheated, their iron cores are made hollow, and are in 
 
 connection with a cir- 
 culating water system. 
 
 In Weston's machine, 
 the commutator, which 
 rectifies the currents 
 generated in the coils 
 of the armature, con- 
 sists of a broad cylin- 
 drical wheel, fixed on 
 the shaft, having three 
 teeth, and into the 
 spaces between these 
 teeth metal plates are 
 inserted. These are con- 
 nected with each other, but are insulated from the wheel. 
 Three terminal wires, of the same sign, lead from the 
 armature to the teeth, whilst the other three are con- 
 nected with the little metallic plates. As each of the 
 metallic plates is diametrically opposite to a tooth of the 
 wheel, it is only necessary to let two springs bear on the 
 commutator, directly opposite each other, to collect the 
 currents. These will, at the same time, be rectified, for 
 the metallic plates are alternately in connection with one 
 or the other of the springs. 
 
 This construction of Weston's machine is principally 
 
MOHRING AND BAUR'S MACHINE. 37 
 
 used for galvano-plastic purposes, and it is provided with 
 a " current interrupter," the object of which is instantly 
 to interrupt the electric circuit, so that any current 
 generated by the polarisation of the electrodes in the 
 galvanic bath, cannot reach the coils of the electro- 
 magnets, when the machine is going too slow or stops. 
 Under certain circumstances, this would reverse the 
 polarity of the machine, and currents would be induced in 
 the armature, whose action would redissolve the galvano- 
 plastic deposit. 
 
 This current interrupter is described amongst the 
 apparatus in Chap. IV. 
 
 Weston's machine was improved by H. Or. Mohring, of 
 Frankfort-on-the^Maine, and Gustav Baur, of Stuttgart. 
 
 The dynamo - electric machine of Mohring and 
 Baur also has 6 field-magnets, and an armature consist- 
 ing of 6 electro-magnets. The magnets are, however, 
 attached to the inner surface of the cover of a cylinder, 
 and, by means of a screw, the armature-magnets can 
 be approached to or moved away from the fields-magnets, 
 thus making it possible to regulate the machine at any 
 time. 
 
 Besides this, the coils of the field-magnets do not form 
 a single helix, as in Weston's machine; but each helix sur- 
 rounding a field-magnet is separate from the others. 
 The currents induced in the turns of the armature-bobbins, 
 are conducted to an insulated pin, after leaving the com- 
 mutator, and thence they enter the six wires, leading to 
 the coils of the field-magnets, which are magnetised as in 
 Weston's machine, so that adjoining magnets are of dif- 
 ferent polarity. The currents pass from the six terminal 
 wires of the magnet coils to a second pin, and thence flow 
 into the external circuit. If required, the currents can 
 
38 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 be conducted separately through different circuits and 
 can then be united. 
 
 This machine is also provided with a current-interrupter, 
 as it is intended for galvano-plastic purposes. 
 
 Lontin's alternating current machine resembles that 
 of Weston very much in the arrangement of the separate 
 parts, excepting that the twenty-four field-magnets are 
 fixed to the hub of a wheel on the shaft, and revolve in 
 front of twenty-four armature-magnets, which are attached 
 radially to the inside of a drum-like frame, and converge 
 towards the centre ; as do the field-magnets in Weston's 
 machine. The wire coils of the inducing electro-magnets 
 form a connected helix, and opposite poles are placed next 
 to each other, as in the machines previously described. 
 The current for magnetising the magnets is produced in a 
 separate Lontin machine for continuous currents (see 
 Chap. II.), the star-shaped wheel of which is fixed to the 
 principal shaft of the alternate current generator. The 
 coils of the armature-bobbins are connected with each 
 other in pairs, and in such a way that, together, their cores 
 form horseshoe magnets. One of the terminal wires leads 
 from each to a binding screw on the right-hand side of the 
 machine ; and the second leads to a binding screw on the 
 left-hand side. Conducting wires branch off from the 
 different binding screws on both sides of the machine, 
 and twelve alternating currents are sent through them 
 during each revolution. By a very simple commutating 
 apparatus these currents can be combined for quantity or 
 intensity, or they can be united into smaller groups. 
 
 The special advantage of this machine is that neither a 
 commutator nor contact brushes are necessary to con- 
 duct the main currents away. Brushes, or contact pieces, 
 usually wear rapidly, for the sparks which occur burn or 
 
GRAMME'S ALTERNATING CURRENT MACHINE. 39 
 
 very much oxidize the metal parts, if the currents are 
 strong. This machine also possesses the advantage that 
 if necessary the separate parts can be easily replaced with- 
 out the necessity of taking the machine to pieces. 
 
 When the working rate is 320 revolutions per minute 
 Lontin's machine generates 12 currents, each of which is 
 able to produce an electric light of 740-candle power. 
 
 A very efficient alternating current machine has also 
 been constructed by M. Grainme, the inventor of the well-- 
 known machines for continuous currents, with the object 
 of producing a suitable generator for the Jablochkotf 
 candles. 
 
 The following is the construction of Gramme's 
 alternating current machine. Eight electro-magnets, 
 K K (Figs. 21 and 22), provided with pole-pieces, are 
 fixed to a steel shaft, fl, by means of two cast-iron 
 crowns, H, and an eight-sided cast-iron hub, /. In 
 the older patterns of the generator, the current traversing 
 the coils of these magnets was obtained from a small 
 separate exciting machine, and conducted through two 
 brushes bearing on two insulated rings. In the newest 
 pattern this current is generated in a Gramme's ring- 
 armature, which is attached to the principal shaft of the 
 machine, and is brought under the influence of two electro- 
 magnets. 
 
 The armature of Gramme's alternating current machine 
 consists of a broad ring of soft iron, on which are wound 
 thirty-two bobbins completely separated from each other, 
 their turns running parallel to the axis of rotation. These 
 bobbins are divided into eight groups, and at certain 
 periods, during the revolution of the field-magnets, each 
 of these groups is opposite the pole of one of the magnets, 
 and the polarity of the magnets alternates from one 
 
40 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 to another. Accordingly, when one of the groups of the 
 armature is opposite a north pole, each of the adjoining 
 groups is opposite a south pole, and vice-versa. The posi- 
 tion of the coils, with respect to the magnetic poles, is so 
 
 Fig. 21. 
 
 symmetrical that when the field-magnets pass before them, 
 currents of equal intensity are induced in all the coils, a ; 
 similarly, the currents induced in the coils b are equal to 
 each other in intensity ; and currents are induced in the 
 coils c and d, their strength corresponding to their posi- 
 tion. If the direction of the currents, therefore, is to be 
 
GRAMME'S MACHINE. 41 
 
 the same in all the similarly lettered coils, all that is 
 necessary is that the bobbins, which are situated opposite 
 different polarities, during the rotation of the field-mag- 
 nets, should be coiled in opposite directions. As the 
 terminals of each coil lead to separate binding screws, 
 attached to the frame of the machine, it is possible to 
 
 Fig. 22. 
 
 conduct thirty-two separate alternating currents from the 
 machine, or to combine these currents for quantity or 
 intensity, as desired. 
 
 The framework consists of a cast-iron standard, D, at 
 front and back, and both nearly circular. These are fixed to 
 a cast-iron base, R, their rigidity being further ensured by 
 eight brass bars, E, and an iron support, U. To protect the 
 electro-magnet bobbins from injury, by action of centri- 
 
42 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 fugal force, two thin disks, T, are attached to them, and 
 these are firmly connected with the shaft. Gramme con- 
 structs three sizes of this pattern of alternating current 
 generator. 
 
 The machine described generates current for sixteen 
 Jablochkoff candles, and to work it 16-horse power is neces- 
 sary. Its length, including the driving pulley, is 89 cm. ; 
 width, 76 cm, and height, 78 cm. ; it occupies a space of 
 ^ cub. m., and weighs 650 kg., 103 kg. of which are the 
 copper wire. The maximum velocity of rotation is 600 
 revolutions per minute. 
 
 The next size is intended for six Jablochkoff candles. To 
 work it 6-horse power is necessary ; it is 70 cm. long, 40 
 cm. wide, and 52 cm. high, occupying a space of 0*15 
 cub. m. It weighs 280 kg., 40 kg. being due to the weight 
 of the copper wire. The maximum velocity of rotation is 
 700 revolutions per minute. 
 
 The third size supplies four Jablochkoff candles, and re- 
 quires 4-horse power. It is 55 cm. long, 40 cm. wide, 
 and 48 cm. high, and occupies a space of 0*18 cub. m. 
 The weight is 190 kg., of which 28 kg. are copper wire, 
 and the maximum velocity of rotation is 800 revolutions in 
 the minute. 
 
 As already stated, the latest pattern of Gramme's 
 machine for alternating currents contains the generator for 
 magnetising the field-magnets in itself. Gramme made 
 this change because in the generator previously de- 
 scribed transmission of the power by belt was difficult, 
 and a disturbance was frequently caused in the uniformity 
 of the light. 
 
 In the latest pattern, Gramme's ring-armature (see 
 Chap. II.) is fixed to the shaft of the machine, and two of 
 the eight field-magnets are directed radially towards this 
 
SIEMENS-HALSKE MACHINE. 43 
 
 ring, and are provided with pole-pieces, which generate two 
 travelling poles in it (see Pacinotti's ring). The current 
 produced in the coils of the ring is then conducted through 
 ii copper wire, which can be replaced by another of different 
 oross-section and length, if the strength of current in the 
 1 wo machines is to be modified. The current, as in the 
 older pattern, is then taken to two annular disks, both of 
 which are insulated from the shaft and from each other ; 
 and from these, it passes into the coils of the field-mag- 
 nets. Two sizes are built of this pattern. 
 
 The largest machine of. this kind weighing 470 kg., 
 generates current for twenty-four candles each of 148 to 
 220 candle power, or for sixteen candles each of 296 to 
 370 candle power. The smaller generators weigh 280 kg., 
 and supply twelve candles each of 148 to 220 candle 
 power, or eight candles each of 296 to 370 candle power. 
 
 Experience with the new machines shows that they are 
 superior to the machines of the older type, especially in 
 the production of a uniform, steady light. The firm 
 Siemens and Halske also construct machines for alter- 
 nating currents. 
 
 The Siemens^Halske alternating current machines 
 have also been gradually modified ; the fundamental 
 principle has not, however, been changed. 
 
 The following is the construction of the latest pattern : 
 Cast-iron standards are fixed to a base, and are held to- 
 gether at the top by a bar. Each of these standards carries 
 twenty-four magnets on its inner face, and they obtain their 
 magnetising current from a small Siemens continuous cur- 
 rent exciting machine. This current magnetises the iron 
 cores in such a way that adjacent magnets, as well as mag- 
 nets facing each other, are of opposite polarity. The pro- 
 jecting ends of the iron cores of the electro-magnets are 
 
44 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 provided with pole-pieces, consisting of flat pieces of iron, 
 and these serve to strengthen the inducing action on the 
 armature-coils. 
 
 In the older pattern the armature-coils are wound on 
 an iron ring, somewhat as in the Gramme machine. In 
 
 Fig. 23. 
 
 the new machine, shown in Fig. 23, they a,re fixed to 
 the rim of a wheel, and do not contain any iron, but have 
 wooden cores, which are perforated for the sake of ven- 
 tilation. This so far gives the machine a considerable 
 advantage over those previously described, as there is no 
 change of polarity in its movable iron parts. The heating 
 of the armature -coils, which would otherwise occur, is 
 
SIEMENS-HALSKE MACHINE. 
 
 45 
 
 obviated, and there is not the waste of work due to this 
 heating and change of magnetism. 
 
 Another advantage arises from the arrangement of the 
 different parts, by which the wire coils are made to rotate 
 through fields of high magnetic intensity, formed by the 
 powerful electro-magnets placed opposite each other. 
 
 The number of armature-bobbins, and of the magnetic 
 fields, produced by the pairs of opposite poles of the field- 
 magnets which face each other, is the same ; the coiling of 
 
 Fig. 24. 
 
 the bobbins changes from one to another. If by a we denote 
 all the bobbins in which the coils are wound in one direc- 
 tion, and 6, all those which are coiled in the opposite 
 direction, we see that at a given moment, as the armature 
 revolves, all the alternate bobbins a will be opposite the 
 north poles on the anterior side of the machine, and all 
 the bobbins 6 opposite the south pole. Immediately 
 afterwards the bobbins a will be opposite the south poles 
 on the same side, and the bobbins 6 will be opposite the 
 north poles. Accordingly, the current will change with 
 each change of position of the bobbins ; the number, 
 
46 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 therefore, of alternating currents generated will be equal 
 to the number of armature-bobbins or of magnetic fields. 
 The alternating currents induced in the armature-coils 
 are conducted to contact rings, which are fixed to the 
 shaft, but are insulated from the latter and from each 
 other. They are then conducted to the external circuit by 
 means of contact springs or brushes, which are connected 
 with the conducting wires leading to the external circuit. 
 
 For electric lighting, the Siemens alternating current 
 machine renders good service, and it has proved of special 
 use in connection with the Hefner-Alteneck differential 
 lamps. 
 
 Brush's Machine is, perhaps, the most original, and, 
 at any rate, the most efficient of the machines that pri- 
 marily generate alternating currents (Figs. 24, 25, 26), 
 The armature of this machine is very much like Paci- 
 notti's ring in outward appearance ; but the connection of 
 the wire coils is different. The cast-iron core of the 
 armature contains a vertical groove, shown in Fig. 25, 
 which nearly completely divides it; it also has deep 
 recesses of rectangular section on both sides, which are 
 meant to receive the coils. The teeth thus formed are 
 again traversed by three deep grooves. This grooving of 
 the solid iron core serves, on the one hand, to prevent in- 
 terfering induction currents being generated in the ring, 
 which would weaken the current and heat the iron ; and, 
 on the other hand, it aids ventilation during the revolu- 
 tion of the armature, and serves thus to keep cool the wire 
 coils. 
 
 The wire coils, of which there are eight, completely fill 
 the rectangular recesses in the iron core, and every pair of 
 diametrically opposite coils are connected with each other, 
 whilst the terminal wires are conducted to the four com- 
 
BRUSH'S MACHINE, 47 
 
 mutator rings, where they are attached to two segments, 
 insulated from each other. The current generated in the 
 two bobbins is conducted from these segments by means 
 of brushes, consisting of slit pieces of sheet copper. Fig. 
 24 illustrates a machine for lighting sixteen arc-lamps. 
 
 The commutator, which consists of four copper rings, 
 differs considerably from all those that have been de- 
 scribed, and is undoubtedly one of the most interesting 
 features of the Brush machine. 
 
 The construction of a commutator ring is shown in 
 Fig. 26. Every ring consists of two segments, S S, which 
 approach each other very closely at one point. They are 
 there insulated from each other, by a small air space, 
 whilst between the other two ends there is a piece of 
 metal, T, which is insulated from them, and correspond- 
 ing to ^-revolution. This is called the " insulator," and 
 serves to exclude that pair of bobbins from the circuit 
 whose coils are at the moment in the neutral position, 
 during the revolution of the armature. For when the 
 bobbins are in this position, one of the brushes presses 
 against the " insulator," the pair of bobbins is excluded 
 from the principal circuit, and, what is more important, 
 no current can traverse their coils, as there is no closed 
 circuit. 
 
 The four brushes, each of which bears on two of the 
 commutator rings, can be shifted concentrically around 
 the shaft of the machine, the proper regulation of the 
 generator at any time being thus possible. They are 
 pressed against the commutator rings by strong clamps. 
 The conductors leading from the brushes are of thick 
 strips of copper. 
 
 The armature, whose coils are separated by segmental 
 cylindrical sections of the iron ring, similar to th? 
 
48 MACHINES GENERATING ALTERNATING CURRENTS. 
 
 wooden wedges in Pacinotti's ring, rotates very near to 
 and between the poles of a pair of powerful horizontal 
 horseshoe magnets, the iron cores of which are a little 
 flattened, and have similar poles facing each other. To 
 prevent the shaft of the machine from being displaced 
 lengthways, it has grooved bearings in the journals as in 
 the case of the shafts of screw-steamers. The segmental 
 ring-shaped pole-pieces exert a very powerful inducing 
 
 Fig. 25. 
 
 Fig. 26. 
 
 action on the whole armature, with the exception of the 
 bobbins in the neutral position. 
 
 In a lecture given by Brush in America, he explains 
 that the arrangement of the field-magnets is such that 
 the current generated by each pair of coils is alternately 
 conducted through the coils of the electro-magnet and 
 the external circuit. Thus, during each complete revolu- 
 tion, every pair of bobbins once supplies the magnets with 
 a current and once the lamps. In one position of the 
 ring some of the armature -coils send their current 
 through the coils of the magnets, and the others are in 
 
BRUSH'S MACHINE. 49 
 
 connection with the external circuit. During the next 
 eighth part of the revolution of the ring, those bobbins 
 that were connected with the coils of the magnets send 
 their current into the circuit, and vice versa. 
 
 According to Brush, the armature of the sixteen- 
 light machine offers a resistance of about 4 ohms, and 
 with a speed of 750 revolutions per minute, will supply 
 16 to 18 lamps, each of which has an arc of about 2 mm, 
 and offers a resistance of 4J ohms ; so that the machine 
 generates a current which is able to overcome an external 
 resistance, including that due to the electro-magnets, of 
 about 80 ohms, or a resistance nearly twenty times greater 
 than that of the armature. 
 
 A larger Brush machine has been constructed for forty 
 lights ; and (according to Brush) actuated by 30-horse 
 power, it gives a current of 10 amperes, with an electro- 
 motive force of 2,200 volts. 
 
 In "Engineering," Vol. 31, 1881, p. 55, the following 
 data are given in connection with the sixteen-light 
 machine represented in Fig. 24. 
 
 The diameter of the ring is 20 ins. ; the wire on the 
 eight bobbins is No. 14, B. W. Gr. (= 2'15 mm. diameter); 
 the weight of the wire in each coil is about 20 Ib. 
 (= 91 kgrs.); length of wire in one coil is about 900 ft. 
 (= 275 m.) ; resistance of the four limbs of the elec- 
 tro-magnets is 6 ohms ; the resistance of the machine 
 from binding-screw to binding-screw is 10*55 ohms. 
 
 When working sixteen lamps, the machine made 770 
 revolutions a minute, and the working power was 15*5 
 horse power ; the electro-motive force was 839 volts, the 
 strength of current 10 amperes, and the resistance of one 
 lamp 4-5 ohms. 
 
CHAPTER II. 
 MACHINES GENERATING DIRECT CURRENTS. 
 
 THE fundament on which nearly all direct current genera- 
 tors are constructed is Pacinotti's ring-armature, which, 
 however, only attains its full importance in connection 
 with Gramme's ingeniously constructed collector.* 
 
 Zenobe Theophile Gramme, whose alternating current 
 generator was described in the previous chapter, was 
 formerly one of the employes of the " Alliance " company, 
 and independently constructed a ring-armature in 1871, 
 without knowledge of Pacinotti's work. In principle it 
 agreed with the ring-armature invented by the latter. 
 
 The following is the construction of Gramme's armature 
 and collector (perhaps incorrectly termed commutator by 
 Pacinotti.) 
 
 In order to prevent interfering, heating, false, or so- 
 called Foucault currents, the core of the ring is con- 
 structed of annealed iron wires, and the wire system 
 wound round it is composed, as in the Pacinotti ring, of 
 groups of helices. These, however, are not separated 
 from each other by projecting iron teeth, but follow one 
 another closely. The wire commencing each coil is con- 
 
 * This assertion by the Author is undoubtedly correct as a commercial 
 fact, but technically the collector constructed by Pacinotti is of even 
 greater merit. Editor. 
 
GRAMME ARMATURE. 
 
 nected with the wire ending the previous one, and con- 
 sequently all the coils together form one continuous 
 circuit. The number of coils varies in different machines, 
 and each consists of 300 or more turns. The points of 
 junction all lie on the same side of the ring, as shown in 
 Fig. 27, and are connected with strips of copper, bent at 
 right angles, one arm of which, _R, lies radially and edge- 
 wise along the side of the wooden hub, whilst the other 
 arm is within this 
 
 ring and runs parallel Fi S' 2 ?- 
 
 to the shaft. These 
 copper strips, which 
 are equal in number 
 to the bobbins, are 
 separated from each 
 
 other by an insulating 
 material, and their 
 horizontal arms form 
 a hollow cylinder 
 (compare Fig. 29) 
 through which the 
 shaft passes. Two 
 
 contact brushes, consisting of fine copper wires, bear 
 on this cylinder, and are always in contact with those 
 strips that are in connection with the points of junction 
 in the neutral positions, p p r , Fig. 8, that is the points 
 through the connection of which the two total currents 
 generated in the wire system flow in the same direction. 
 Direct currents, consequently, flow through the two 
 brushes when they are in contact with the respective 
 collector strips. 
 
 Gramme constructs his ring-armature machine in 
 several sizes, and with various modifications. Some of 
 
52 MACHINES GENERATING DIRECT CURRENTS. 
 
 them are arranged to be worked by hand or foot power, 
 and are intended only for laboratory use, or for 
 small quantities of work ; others are constructed to be 
 driven by steam, and differ more or less from one another, 
 according to the object for which they are intended. As, 
 
 Fig. 28. 
 
 however, the principle is the same in all these generators, 
 a brief description of some of the most useful and most 
 frequently employed types will suffice. 
 
 Of the machines intended for use in physical labora- 
 tories, the pattern shown in Fig. 28 is the best ; it is 
 constructed by Breguet, of Paris. This is a magneto- 
 electric machine, the field magnet of which is a so-called 
 
JAMIN'S MAGNETS. 53 
 
 laminated magnet, consisting of several steel plates, held 
 together by clamps, a 6, but dividing out a little at the 
 poles. These plates are provided with massive pole-pieces, 
 that nearly enclose the ring-armature which revolves be- 
 tween them. The French physicist Jamin, to whom the 
 
 Fig. 29, 
 
 construction of this kind of magnet is to be attributed, 
 calls it a normal magnet, as in it the maximum magnetL 
 sation of the steel plates is attained. It therefore pos- 
 sesses far greater portative power than magnets of the 
 same size composed of simple steel bars. 
 
 The Gramme generator with steel magnet, as con- 
 
54 MACHINES GENERATING DIRECT CURRENTS. 
 
 structed by Breguet, gives a current equal to that from 
 three Bunsen's cells of ordinary size. 
 
 Amongst the large Gramme generators, we shall specially 
 mention those for the electric light. 
 
 The framework of these generators consists of two iron 
 standards, held together at top and bottom by two stout 
 cylindrical cross-bars of soft iron. These cross-bars are 
 converted into tripolar magnets, when the current induced 
 in the ring-armature traverses the coils surrounding them. 
 These coils are wound in such a way that all the poles of 
 the tripolar magnets, opposite each other, are of different 
 polarity. A glance at the direction of the current in Fig. 
 30 will make this clear. 
 
 When the current generated in the coils of the ring- 
 armature enters the helices of the lower tripolar electro- 
 magnet at p', and traverses them in the direction of the 
 arrows the right-hand half of the lower magnet has a 
 south pole induced at s', and a north pole at n r . If we 
 follow the course of the current further, we see that there 
 are formed in the right-hand half of the upper tripolar 
 magnet, a south pole, s', and a north pole, n' f Again, the 
 left-hand half of the upper magnet, n, becomes a north pole, 
 and s a south pole ; and in the left-hand half of the lower 
 magnet, a north pole is obtained at n, and a south pole at 
 s. Therefore, in the middle of the upper tripolar magnet, 
 a north pole, N, is produced, consisting of the portions 
 n n r , and in the middle of the lower tripolar magnet, 
 a south pole, $, is formed, of the two portions s s f . 
 This is the action in the electro-magnet cores of the 
 Gramme machine, represented in Fig. 29, and in order to 
 utilise the double poles more completely, they are pro- 
 vided with heavy pole-pieces of soft iron. These nearly 
 enclose the ring-armature, which is constructed as 
 
GRAMME'S MACHINES. 
 
 55 
 
 described, and revolves on a steel shaft. The brushes and 
 collector are shown in Fig. 29, on the right-hand side of 
 the machine, and the currents, which the brushes conduct 
 away, are not only employed to do work in the external 
 circuit, but also to excite the field-magnets on the dynamo- 
 electric principle, already explained. 
 
 Generators of this kind weigh 180 kgrs. ; are O60 m. 
 high, 0*35 m. wide, and 0-65 m. long (including the belt- 
 Fig. 30. 
 
 pulley, shown on the left-hand side of the figure). The 
 copper wire used for the field-magnets weighs 28 kgrs., 
 whilst the copper wire coils of the ring weigh 4-5 kgrs. 
 The generator usually works at a speed of 900 revolutions 
 per minute, and produces a current which will maintain an 
 electric light of 10,656 candle power. 
 
 Gramme's plating-machine, constructed in 1873, also 
 deserves mention. This generator weighs 177'5 kgrs., 
 47 kgrs. of which are due to the weight of the copper. 
 It is 0'60 m. in height, and has a width and breadth of 
 0-55 m. With it a deposit of 600 grs. of silver per hour 
 
56 MACHINES GENERATING DIRECT CURRENTS. 
 
 is obtained in an electrolytic bath, and to do this, f horse- 
 power is necessary for driving the machine. The field- 
 magnets are not wound with copper wires, as in the 
 machine previously described, but both halves of each 
 tripolar magnet are completely surrounded with a copper 
 sheet, so that altogether the copper conductors of the 
 field-magnets consist only of four broad copper strips or 
 sheets. 
 
 The coils of the ring-armature, which is almost com- 
 pletely enclosed by the pole-pieces, as in the light-machine, 
 consist of thick wire, flattened. The armature is thus 
 made very strong, and is protected against the action of 
 centrifugal force. 
 
 This arrangement of the copper windings is suitable for 
 a generator for galvano-plastic purposes, such generators 
 having to produce currents of low intensity, but in large 
 quantity, and this object is to be attained only by means 
 of coiling with thick copper wire, offering a low resistance. 
 The field-magnets obtain their exciting current from the 
 armature, on the dynamo-electric principle, and an auto- 
 matic current interrupter is connected with the generator, 
 as in Weston's and Mohring's generators. This prevents 
 polarisation currents reaching the machine from the baths, 
 and traversing it in the opposite direction. 
 
 Gramme's generator for the electrical transmission 
 of power, differs somewhat from the other machines of 
 the same constructor, in that four pairs of electro-magnets 
 are used, which are fixed to the inside of an octagonal 
 frame. Of these magnets, two adjacent are at right- 
 angles to each other, and at the point where they con- 
 verge, carry a common pole-piece. 
 
 In this way four poles are generated, which are alter- 
 nately of opposite polarity, and nearly completely sur- 
 
FEIN'S MACHINE. 
 
 57 
 
 round the ring-armature, generating four travelling 
 poles. 
 
 One of the deficiencies which some inventors claim to 
 exist in Gramme's machines is that only the portion of 
 the coils situated on the outside of the ring-armature is 
 exposed to the inducing action of the fixed magnets. This 
 Fein, of Stuttgart, endeavours to avoid. 
 
 Fig. 31. 
 
 Fein's dynamo, Fig. 31, contains a cylindrical ring- 
 armature, R R, the core consisting of a number of very 
 thin strips of iron, insulated from each other ; it is fixed 
 to a brass star-shaped hub, S 8 9 through the centre of 
 which the shaft passes. The terminals of the coils pass 
 through openings in the star, 8 8, provided with collars 
 or thimbles of insulating material, and are led to the 
 collector, (7, which is attached to the portion of the shaft 
 shown on the right-hand side in the figure. 
 
58 MACHINES GENERATING DIRECT CURRENTS. 
 
 The field-magnets, as in Gramme's dynamo, have iron 
 cores, which are converted into tripolar magnets by the 
 method of winding the coils. These are provided with 
 pole-pieces, M M', which approach the external portions of 
 the armature coils. In addition, the peculiarly-shaped 
 prolongations, A A, are screwed on to these pole-pieces. 
 They enclose the inside and back portions of the windings 
 of the coils, so that nearly every part of the wire is under 
 the inducing action of the magnetic poles. 
 
 The construction of Schuckert's flat-ring generator, 
 Fig. 32, is, too, such that the inducing action of the 
 magnets on the coils is more completely utilised than in 
 Gramme's machine. The way in which this is effected 
 differs from that followed in Fein's machine. 
 
 Whilst in Fein's machine the ring has a cylindrical 
 form, Schuckert has made use of a flattened ring. This 
 flat ring is nearly completely surrounded by the pole- 
 pieces of the field electro-magnets. The core of the iron 
 ring consists of thin insulated plates of sheet-iron ; and 
 the collector and wire brushes are similar in construction 
 to the corresponding parts of Gramme's machine. 
 
 Schuckert constructs various sizes and patterns of his 
 generators, as well as machines for galvano-plastic pur- 
 poses, which, with the exception of the flat ring, are 
 almost identical in construction with Gramme's machines. 
 He also constructs generators with two collectors, one 
 placed at each end of the shaft. 
 
 This arrangement is also employed by Gramme, and 
 makes it possible for only a portion of the current to be 
 used for exciting the field-magnets, and the larger part of 
 the current solely for doing work. The advantage is that 
 when these machines are used for galvano-plastic pur- 
 poses, a polarisation current, entering the machine from 
 
SCHUCKERTS MACHINE. 59 
 
 the baths, cannot produce an inversion of the polarity of 
 the field-magnets. 
 
 For the same purpose Schuckert constructs generators 
 with two flat rings ; and these are also provided with an 
 arrangement for combining the currents for intensity or 
 quantity. 
 
 Heinrich's generator is another design for better 
 
 Fig. 32, 
 
 utilising the inducing action of the magnets on the 
 armature. In this machine, the ring-armature, the core 
 of which is composed of a bundle of thick iron wires, has 
 a horse-shoe shaped cross-section, and the wire coils 
 which surround it only lie close upon it on the outside, 
 crossing over the hollow on the inside. 
 
 In order to bring those parts of the wire that lie on 
 the outside of the iron ring as completely as possible 
 under the inducing action of the electro-magnets, the 
 
60 MACHINES GENERATING DIRECT CURRENTS. 
 
 pole-pieces form nearly a complete ring, interrupted in 
 two places. The cross-section of this, too, is horse-shoe 
 shaped, and it thus very nearly surrounds the armature 
 on the outside The hollowing of the armature is in- 
 tended to aid ventilation. 
 
 Desmond G. Fitzgerald's generator has an arma- 
 ture somewhat similar to Brush's ring. The coils are 
 separated from each other by iron wedges, and the electro- 
 magnets, which completely surround the ring, consist, 
 for this purpose, of several pieces, which together make 
 up a hollow ring. In this class of generators, however, 
 when the armature is intended to rotate as close as 
 possible to the magnetic poles, and if, at the same time, 
 very rapid revolution is required, the builder has to over- 
 come a great many technical difficulties. For, unless 
 these machines are built very symmetrically, there is great 
 danger of the armature and pole-pieces of the electro- 
 magnets rubbing against each other, and, of course, this 
 would soon remove the insulation, and make the machine 
 useless. 
 
 A better solution of the problem, how to utilise the 
 armature coils as completely as possible, is obtained in 
 Jiirgensen's generator. In this generator there are 
 electro-magnetic field-magnets inside as well as outside 
 the ring, but as the cross section of the ring and wire 
 spirals is comparatively small, it is only important that 
 the horizontal portions of the wire coils should be ex- 
 posed to the inducing action of the magnetic poles ; and 
 the short vertical portions can be neglected ; the poles of 
 the magnets need not, therefore, take any particularly 
 complicated shape. 
 
 To prevent Foucault's currents, the core of the arma- 
 ture in Jiirgensen's generator is composed of separate 
 
GULCH ER'S MACHINE. 61 
 
 rings, which are insulated from each other, and consist of 
 iron wire ; and it is worth mentioning that the wire coils 
 of the electro-magnets increase in thickness towards the 
 poles, to obtain a greater concentration of magnetism at 
 those places. 
 
 A generator noteworthy for its thorough practical 
 construction is Giilcher's dynamo. The dimensions 
 of the few thick copper coils surrounding the electro- 
 magnet cores, and composed of wire strands, show that 
 the machine is intended for currents of large quantity, 
 but low intensity. 
 
 The flat ring-armature, which is wound much in the 
 style of Pacinotti's ring, as may be seen from Fig. 33, 
 rotates between four pole-pieces, which enclose it like 
 clamps. Proceeding round the armature, the polarity of 
 these changes from one to the other, and each unites two 
 of the electro-magnets, whose similar poles face each other. 
 
 The four currents induced in the coils of the armature 
 are united for quantity, and are conducted into the 
 external circuit by means of two contact brushes. 
 
 The generator, shown in Fig. 33, will supply six Gulcher 
 lamps of 1,300 candle power, when working at the rate of 
 940 revolutions per minute, and using 10-horse power. 
 Amongst the advantages of the machine are that its 
 magnet-coil resistance is very small, on account of the 
 four pairs of electro-magnets being coupled parallel to 
 each other ; and that, through the arrangement of the 
 coils, the internal resistance of the machine is only 
 0'265 ohm, for both the ring and the electro-magnets. 
 
 The dynamo-electric generator of the firm of Siemens 
 and Halske, in which the drum-armature invented by 
 Hefner-Alteneck is used, differs very much from the 
 machines previously described. 
 
62 MACHINES GENERATING DIRECT CURRENTS. 
 
DRUM ARMATURES. 63 
 
 The simplest form of drum-armature is shown in 
 Fig. 34. In this figure N N and S S are the poles of 
 the field-magnets, whilst s s, n n include a hollow 
 cylinder, which rotates with the shaft, and round which 
 the wires are wound parallel with the axis of rotation. 
 Now, as travelling poles are induced in the cylinder during 
 its rotation, as in the case of Gramme's ring, and as the 
 interval between the poles of the magnets and the arma- 
 ture is very small, the coils move in a field of high in- 
 tensity. 
 
 The turns of wire wound on to the armature-drum 
 
 Fig. 34. 
 
 parallel to the axis of rotation are divided into from eight 
 to twenty-eight groups, and form a continuous wire circuit. 
 The terminal wires of the separate groups are connected 
 with the segments of the collector, which has as many 
 segments as there are groups of wire on the drum. The 
 method of connection of the terminals with the parts of 
 the collector is such that the two total currents of opposite 
 direction, generated in the wire system, always meet in 
 two opposite segments of the collector, and can thence be 
 conducted into the external circuit by means of contact 
 brushes. 
 
 The way in which the connections are made, for this 
 purpose, is shown in Fig. 35. This figure represents a 
 
64 MACHINES GENERATING DIRECT CURRENTS. 
 
 drum-armature, on which are wound eight wire groups. 
 The separate segments of the collector are denoted by the 
 
 letters a, 6, x' 9 c, d, e, x 9 /, and the several portions of the 
 same group are denoted by similar numbers. 
 
DRUM ARMATURES. 65 
 
 If we start from the collector, and follow the course of 
 the wire of a coil in the figure, we see that when the wire 
 leaves the segment under consideration, it runs to the 
 circumference on the front of the cylinder, then runs 
 parallel to the axis along the cylinder, again crosses the 
 back of the cylinder, and runs along the opposite side, and 
 is finally connected with another segment of the collector. 
 
 During the rotation, one half of such a rectangularly-bent 
 group or coil is exposed to the influence of the north pole 
 of the inducing field-magnets, and the other half is ex- 
 posed to the influence of the south pole ; accordingly, cur- 
 rents of opposite direc- 
 tion are generated in Fig. 36. 
 both halves. For in- 
 stance, in the lower 
 half of the wire, the 
 current will flow from 
 left to right, whilst in 
 the upper half, it will 
 
 be directed from right to left ; yet both together, form a 
 current of the same direction, as may be seen at a glance, 
 from Figure 36. However, as the drum rotates, that half 
 of the coil, which at one moment was at the top, will, after 
 a semi-revolution, form the lower half. In other words, 
 during a complete revolution of a coil, each half turn of 
 wire gets once into the position where the north pole 
 dominates, and once into the position where the south 
 pole dominates. The current will be reversed immedi- 
 ately after the two sides of the coils have passed the 
 neutral points, which are equidistant from the north and 
 south pole. The collector serves to conduct all currents of 
 one direction simultaneously to one terminal, whilst it 
 conducts the currents of the opposite direction to the 
 
 F 
 
66 MACHINES GENERATING DIRECT CURRENTS. 
 
 other terminal ; that is, the currents of opposite directions 
 are, by it, united to form currents of the same direction. 
 This is made possible by the ingenious manner in which 
 the inventor of this collector has arranged the connection 
 of the wires of different coils with the separate segments of 
 the collector. This arrangement is such that the opposite 
 currents meet, as in Gramme's collector, in two diametri- 
 cally opposite segments of the collector, and they are, as it 
 were, coupled for quantity. If by 4- we denote, in Fig. 
 35, the ends of the wire in which the current flows from 
 the circumference of the collector disk to the centre, and 
 by , the ends in which it has a direction from the 
 centre to the circumference, we see that two -h wires 
 unite at the collector segment x, and two wires at the 
 collector segment x' . In Fig. 11, we have already shown 
 how it is possible to obtain a direct current by connecting 
 the conducting wires with the respective segments. The 
 method of conducting the current away is, accordingly, 
 exactly the same in the Siemens-Halske drum generator, 
 as that employed in the Gramme generator ; that is, 
 the conducting wires are always in contact with the two 
 metallic segments of the commutator in which the 
 currents meet ; and through the revolution of the drum, 
 all the commutator segments come into this position in 
 turn. 
 
 The drum-armature now described is employed in a 
 large number of generators constructed by the firm 
 Siemens and Halske ; and as generally, these machines 
 have a similar construction, it will be sufficient to describe 
 only a few of them. 
 
 Fig. 37 represents a magneto-electric generator by 
 this firm. This machine is constructed to be driven with 
 a belt, and is very similar to the small magneto-electric 
 
SIEMENS-HALSKE MACHINE. 
 
 67 
 
 generators of the same firm, which are worked by the 
 hand or foot. 
 
 The drum-armature of this machine rotates between 
 the pole-pieces, which closely clasp it, of fifty V-shaped 
 steel magnets, twenty-five of which are at the top, and 
 
 Fig. 37. 
 
 twenty-eight at the bottom, placed with their similar poles 
 opposite each other. 
 
 The poles of the top and bottom pairs are connected 
 by soft iron pole-pieces, screwed on ; and magnetic fields 
 of fairly high intensity are thus produced, in which the 
 drum-armature rotates. The collector and brushes are 
 shown on the right-hand of the figure. 
 
 When the drum is caused to rotate, currents are in- 
 
68 MACHINES GENERATING DIRECT CURRENTS. 
 
 duced in the coils surrounding it, both by the direct 
 action of the field magnets, as well as by the travelling 
 poles generated in the iron cylinder. These currents 
 are made to flow in the same direction by the collector, and 
 are conducted to the external circuit by the contact brushes, 
 R R' . From the description of the construction of the 
 drum-armature, it will easily be perceived that the inducing 
 Action of the magnets is more completely utilised in 
 Siemens' generators than in Gramme's. For, all parts of 
 the wire coils of the armature move in the magnetic fields, 
 a.nd no portion ii situated inside the cylinder.* 
 
 In order to prevent the heating of the iron cylinder, 
 (which occurs in machines for generating large quantities 
 of electricity, in consequence of an undivided metallic 
 mass moving in the magnetic field), Siemens and Halske 
 constructed generators in which the iron core of the drum 
 is fixed. In these generators, the armature coils are wound 
 on a drum consisting of a sheet of german- silver, which 
 rotates round the iron drum, at a little distance from it 
 and from the enclosing magnetic poles. The position of 
 the magnetic poles is the same as shown in Fig, 38, and 
 the magnets (the horizontal portions of which are round 
 in the older patterns) aje magnetised on the dynamo- 
 electric principle. 
 
 The generators with a fixed iron drum are 110^ cm. 
 long, 32 cm. high, and 46J cm. in width. TJie rate of 
 rotation is 450 revolutions per minute, at which is pro- 
 duced a light of 14,000 candles, with an expenditure of 6- 
 horse power. 
 
 * That the inside wire of a Gramme ring is ineffective has not yet been 
 demonstrated, even by any marked superiority of machines specially 
 constructed to place these inside wires under direct magnetic influence. 
 Editor. 
 
SIEMENS' DYNAMO-MACHINE. 69 
 
 In one respect the fixing of the iron core of the cylinder 
 is a great improvement, but experience has shown that 
 the construction of the machines is made far more difficult, 
 especially in the winding of the armature-coils. Accord- 
 ingly, this construction is now seldom employed, and in 
 the small generators and in those of medium size, the 
 
 Fig. 38. 
 
 
 coils are wound directly on to a cylinder composed of iron 
 wires. The complicated connection, too, of the separate 
 coils is not retained in all Siemens' generators. Thus, in 
 the well- known Siemens machines with flat magnets, Fig. 
 38, a drum-armature is used, the wire coils of which are 
 divided into a great number of groups connected similarly 
 to Gramme's method, and lead to a collector of the Gramme 
 pattern. In these generators, as in that shown in Fig. 37, 
 metallic contact brushes are used, and not contact rollers, 
 
70 MACHINES GENERATING DIRECT CURRENTS. 
 
 as in the older generators. Siemens and Halske construct 
 generators of this kind in various sizes. One size is 757 
 mm. long, 700 mm. wide, and 284 mm. high. The drum 
 is wound with 28 wire coils, and the collector consists of 
 56 pieces. The generator weighs 200 kgrs. Its maximum 
 velocity of rotation is 700 revolutions per minute, and 3^ 
 horse power is necessary to work it. It will generate an 
 arc light of 4,000 candles. 
 
 The smaller generators of this pattern are 698 mm. 
 long, 572 mm. wide, and 233 mm. high. The armature 
 in these generators is also wound with 28 wire coils, and 
 accordingly the collector consists of 56 pieces. The weight 
 of the generator is 115 kgrs. Its maximum speed of 
 rotation is 900 revolutions per minute, and 1^ horse power 
 is necessary to drive it. With these generators a light of 
 1,400 candles is obtained. 
 
 Small machines of this kind are also constructed with 
 vertical electro-magnets, as shown in the exciting machine, 
 Fig. 23. 
 
 A very interesting type, the Siemens plating 
 machine, is represented in Fig. 39. 
 
 These generators are for the preparation of pure metals, 
 and there are three employed in the Koyal Foundries, at 
 Oker. With each of these five to six hundredweight of 
 copper is precipitated daily, eight to ten horse-power 
 being required. 
 
 The electro-magnets of these machines are encircled by 
 thick, square- sectioned copper bars, which make seven 
 turns round each limb of the magnets. The armature 
 also carries only one layer of windings of the bands of 
 copper, which correspond to the coils in the other genera- 
 tors, and are connected with the collector by suitably bent 
 pieces. The contact-brushes which bear on the collector 
 
SIEMENS' PLATING MACHINE. 71 
 
 are of stout plates of copper. The several copper parts are 
 insulated with asbestos ; therefore the insulation is not 
 
 destroyed however hot the copper conductors of the 
 machine may become. 
 
 In outward appearance the latest dynamo designed by 
 the firm of Siemens and Halske is very like the Siemens 
 
72 MACHINES GENERATING DIRECT CURRENTS. 
 
 alternating current generator. It is constructed as 
 follows. 
 
 Two iron standards are fixed to a sole-plate, and each 
 of these carries an even number of electro-magnets, 
 arranged in such a way that each is of opposite polarity 
 both to the magnet facing it and to those right and left. 
 The coils which surround the cores of the magnets form 
 
 Fig. 40. 
 
 ./A 
 
 a continuous circuit, and in the magnetic fields of the 
 poles (provided with flat pole -pieces) there revolve the 
 armature- coils, wound on wooden cores, as in the alternat- 
 ing current generator. However, the number of these 
 bobbins is two less than the number of the magnets attached 
 to each of the standards. 
 
 The distances, therefore, between the bobbins are greater 
 than the intervals laterally between the magnets ; and 
 during revolution the bobbins do not all simultaneously 
 arrive directly opposite the magnetic poles. This is 
 only the case with two of them, whilst the others are 
 
SIEMENS' CORELESS ARMATURE. 
 
 73 
 
 at greater or less distance from the magnetic poles which 
 they are about to approach. The maximum strength of 
 current does not, therefore, occur at the same moment in 
 all the bobbins ; bat occurs at successive intervals of time 
 in successive bobbins. 
 
 The coils of the armature form a single uninterrupted 
 circuit, but the coiling changes in direction from bobbin 
 
 Fig. 41. 
 
 J^WrrrsJr 
 
 to bobbin. The direction of the currents induced in the 
 bobbins during the revolution of the armature is easily 
 determined if we suppose the armature coils and magnets 
 to be turned lengthwise to the observer, as in Fig. 40, 
 when we compare the direction in which the wire of the 
 armature-bobbins is coiled with the direction of the 
 Amperian currents circulating round the iron cores of the 
 field-magnets. 
 
 If on a certain side of a bobbin the rh'naqtitiiViin which 
 
74 MACHINES GENERATING DIRECT CURRENTS. 
 
 the wire is wound is the same as that of the Amperian 
 currents of the magnetic pole that this side of the bobbin 
 is approaching, a current will be induced in the wire 
 opposite in direction to its mode of coiling. On the other 
 hand, when the direction of the coiling of the bobbin, and 
 the direction of the Amperian currents of the magnet, 
 are opposite on the sides facing each other, currents will 
 be induced circulating in the direction of the coiling. 
 
 Let us denote all the bobbins and all the magnetic 
 fields by similar symbols, when the bobbins are so placed 
 between magnetic poles that the direction of the coils of 
 the bobbins corresponds with the direction of the Amper- 
 ian currents of the poles opposite them. The position 
 occupied by the armature-bobbins, with respect to the 
 magnetic fields, will be seen from the diagram, Fig. 41. 
 
 In this diagram, the small black and white circles repre- 
 sent the bobbins, and the rectangular figures the magnetic 
 fields. We see that all the bobbins that approach corre- 
 sponding magnetic fields lie in one half of the rotating 
 armature, whilst all bobbins which approach opposite 
 fields are situated in the other half; and whatever the 
 position we give to the armature, such a division will 
 always be possible. 
 
 In that half in which bobbins and magnetic fields 
 correspond, a current will traverse the bobbins, flowing in 
 the direction of the coiling. 
 
 Since the coils of the separate bobbins form a single 
 uninterrupted circuit, currents of opposite direction will 
 meet at two points in it, as in the coils of Pacinotti's ring. 
 All, therefore, required is to unite the two currents in one 
 circuit. This is done in the following way. 
 
 If only eight bobbins are present, as in the case illus- 
 trated by the diagram, eight insulated metallic rings are 
 
SIEMENS' CIRCULAR DYNAMO. 75 
 
 fixed to the shaft of the generator, one behind the other. 
 From the points at which two bobbins are soldered to- 
 gether, wires branch off, and are in metallic contact with 
 the rings. In the diagram, these points of junction are 
 denoted by the numbers 1 to 8, placed on the circle 
 representing the armature between the symbols for the 
 bobbins. They are so connected with the rings that the 
 point of juncture 1 is connected with ring 1 ; juncture 
 2 with ring 2, and so on. Besides these rings, there 
 is also a collector cylinder, and it is composed of forty 
 pieces. This cylinder, too, is represented in the diagram, 
 and its position is correct as regards the angle that its 
 separate parts make with the position of the armature- 
 bobbins and magnetic poles at the given moment. The 
 forty parts of the collector are divided into five groups, 
 each of which contains the numbers 1 to 8. All parts 
 numbered 1 are connected, by wires, with the ring 
 1 on the shaft, and that again is connected with the 
 point of junction number 1, by the branch wires ; all 
 divisions numbered 2 are connected with the ring which 
 is in connection with juncture number 2, and so on. 
 
 It has been stated that the position of the armature - 
 bobbins relatively to the magnetic poles is such that, when 
 the armature-system rotates, it is divided into two equal 
 parts, in which currents of opposite direction are induced, 
 and that where these currents meet they can be conducted 
 away and be united. In Fig. 41 the armature is supposed 
 to be revolving from left to right ; and at the given 
 moment, all bobbins to the right of the dotted line (pass- 
 ing through the points of juncture 3 and 7) are 
 approaching like magnetic poles, and those to the left of 
 the line are approaching unlike poles. Therefore, accord- 
 ing to the explanation previously given, the currents must 
 
76 MACHINES GENERATING DIRECT CURRENTS. 
 
 meet at the junctures 3 and 7 ; and as these are in 
 metallic connection with all parts of the collector num- 
 bered 3 and 7, the currents can be conducted away 
 at all those places. As shown in the diagram, the collect- 
 ing brushes, which are indicated by the arrows marked 
 -f- and , are situated opposite two such collector portions 
 numbered 3 and 7 ; and as the position of the collector- 
 cylinder remains constant relatively to the armature- 
 bobbins, with which it simultaneously revolves, the brushes 
 will always bear on such portions of the collector as 
 are connected with those points of junction in which op- 
 posite currents meet. Accordingly, currents of the same 
 direction will always reach the circuit. 
 
 The number of armature -bobbins and magnetic fields 
 can be varied according to certain laws, without change to 
 the mode of action of the generator. For instance, instead 
 of using n bobbins (as in the case given), and n + 2 mag- 
 netic fields, we can have n + 2 bobbins, and n magnetic 
 fields or keeping n + 2 magnetic fields, we can use 2n 
 bobbins ; that is, we can double the number of bobbins. 
 
 One great advantage of machines constructed on this 
 principle is that, as in Siemens' alternating current 
 generator, the mode of coiling is extremely simple, and the 
 bobbins being wound on wooden cores, Foucault's currents 
 are prevented. 
 
 Western's dynamo-electric light machine, Fig. 42, 
 is also worth noting on account of its advantageously 
 constructed armature. The iron core of the armature 
 consists of 36 thin perforated iron disks, which have 16 
 indentations on their circumferences, so that they look 
 like 16 toothed wheels. These disks are fixed one behind 
 the other on the shaft in such a way that, when looked at 
 along the shaft, all the teeth cover each other. The disks, 
 
WESTON'S MACHINE. 77 
 
 however, are not directly connected with each other, but 
 are separated by the insertion of small washers, and, con- 
 sequently, after the wire coils have been wound on, a 
 current of air can constantly circulate in the interior of the 
 armature, and most effectively counteracts the heating of 
 the wires. The wire coils are wound like those in Siemens' 
 cylinder armature; and they lie in the 16 grooves formed 
 by the indentations in the rims of the 36 disks. 
 
 In a new pattern of the generator, 12 cylindrical field- 
 Fig. 42. 
 
 magnets are united into 6 pairs, of which the three upper 
 ones carry a common pole-piece, whilst the three lower 
 pairs are also united by a common pole-piece of opposite 
 polarity. The magnet coils form an uninterrupted circuit, 
 which receives its current on the dynamo-electric principle. 
 The way the electro-magnets of this machine act is 
 especially characterised by their inducing action not 
 being the same simultaneously on all parts of a wire, but 
 proceeding from the centre to the ends, and inversely. 
 This is brought about by the pole-pieces, between which 
 the cylinder -armature moves, being composed of parallel 
 
78 MACHINES GENERATING DIRECT CURRENTS. 
 
 tongues of the same length, the ends of which form an 
 elliptical figure on each side of the armature. 
 
 The collector of Weston's generator has quite a special 
 shape. It does not consist of separate segments running 
 
 Fig. 43. 
 
 parallel with the shaft, as in Gramme's collector, but the 
 segment-strips, although parallel to each other, form 
 spirals. By this means the contact brushes (which consist 
 of from 10 to 12 elastic copper plates, divided into 3 parts 
 by slits), are made to bear simultaneously on several seg- 
 ment-strips and the current is thus taken up very 
 uniformly. 
 
MAXIM'S MACHINE, 79 
 
 In outward appearance Maxim's dynamo - electric 
 generator is like a Siemens generator, of the pattern 
 shown in Fig. 38, whose electro-magnets are placed 
 vertically. It is represented in Fig. 43, with its regulator, 
 which will be described in Chapter IV. The armature of 
 this generator consists of a cylinder-ring, round which the 
 coils are wound as in the method employed by Gramme. 
 Each coil, however, has four layers of wires, and the 
 terminals of each layer are connected with two segments 
 of the collector. For this purpose the collector consists 
 of 64 parts. 
 
 In some of Maxim's generators there are two collectors, 
 one at each end of the machine, and the coils are connected 
 so that coils 1, 3, 5, etc., are in connection with one, and 
 bobbins, 2, 4, 6, etc., with the other collector. There is 
 also an arrangement by which the currents obtained from 
 the two collectors can be coupled up for quantity or 
 intensity* 
 
 A generator favourably known in the United States is 
 that of Wallace Farmer (Fig. 44). The armature of 
 this machine consists of two disks, which are fixed to the 
 shaft, close together ; and on the outer sides these disks carry 
 25 flattened bobbins, with perforated cores. The coils of 
 these form an uninterrupted circuit. Each bobbin contains 
 four separate coils, the wires of which are connected 
 in series. From the point where the wires of two bobbins 
 are soldered together branch-wires lead to the segments 
 of a collector, as in Gramme's machine. 
 
 There are four field magnets, and these are united 
 in pairs by the iron standards of the framework, forming 
 horseshoe magnets. Poles of opposite polarity face each 
 other, and induce currents of the same direction in the 
 armature bobbins. These currents, after traversing the 
 
8o MACHINES GENERATING DIRECT CURRENTS. 
 
 coils of the electro -magnets for the purpose of exciting 
 them, pass into the circuit. 
 
 Fig. 45 represents Lontin's dynamo - electric 
 generator. The armature of this generate rconsists of 
 a cylinder of soft iron, which carries one or more series of 
 conical bars of iron fixed radially, and forming the cores of 
 the armature-coils. The field-magnets are two vertical 
 iron columns placed one on each side of the armature. 
 
 Fig. 44. 
 
 All the armature-bobbins are coiled in the same direction, 
 and the terminal wire of each is connected with the wire 
 commencing the next ; their wires accordingly form an 
 uninterrupted circuit. From the points at which the wires 
 of every two coils are joined, branch wires lead to the seg- 
 ments of the collector ; and by means of springs or brushes, 
 the direct currents generated in the armature are conducted 
 into the external circuit. As in Pacinotti's ring, these 
 currents are, of course, composed of two opposite and 
 parallel ones, and the internal process in Lontin's generator 
 
SURGING MACHINE. 8r 
 
 is exactly the same, when the bobbins are coiled as described, 
 as that in the coils of the ring. 
 
 In order to convert this generator into one for alternating 
 currents, it is necessary only to change the direction of 
 coiling, from bobbin to bobbin. 
 
 A generator with which very excellent results are 
 obtained in practice is Burgin's dynamo. The arm- 
 ature of this generator consists of eight six-sided iron 
 
 Fig. 45. 
 
 wire wheels fixed to the same shaft, one behind the other. 
 Looked at from the front, however, their sides do not cover 
 each other, for every wheel is displaced 7J relatively to 
 the one preceding it. The 6 sides, or chords, of each 
 wheel-rim form the cores of armature bobbins, and 
 accordingly, there are 48 of these. The cores of the 
 bobbins are wound with 6 coils of copper wire, each of 
 which contains 15 m. of wire of 1/5 mm. diameter. The 
 several coils are connected with each other in such a way 
 
 G 
 
82 MACHINES GENERATING DIRECT CURRENTS. 
 
 that if we imagine all 48 projected on a plane, the terminal 
 of each bobbin is connected with the wire of the bobbin 
 following next. The wire coiling of the armature, accord- 
 ingly, forms an uninterrupted circuit. From the points of 
 junction of two coils a wire branches off to a segment of 
 the collector ; and, as in the generators previously described, 
 the current is first conducted through the coils of the 
 electro-magnets, on the dynamo-electric principle, and 
 then into the external circuit. The strength of the induced 
 current is greatly increased by the armature-coils of 
 Burgin's machine moving close between the pole-pieces of 
 the field-magnets. The resistance of the armature in the 
 Burgin generator is 1/6 ohms, and that of the 4 electro- 
 magnets, 1/2 ohms ; total resistance, therefore, of the 
 generator is 2*8 ohms. When the machine is making 
 1,500 revolutions the electro-motive force of the current 
 generated is 195 volts, and it attains 206*5 volts, when the 
 rate is 1,600 revolutions ; the resistance of the external 
 circuit being 13' \ 6 ohms. 
 
 The generator is about 0-863 m. long, 0*342 m. high, 
 and 0*711 m. wide ; it weighs about 6*5 cwt.* 
 
 An efficient magneto-electric machine for continuous 
 currents is that of Niaudet, Fig. 46. In outward ap- 
 pearance it somewhat resembles Clarke's generator. Two 
 parallel horseshoe magnets are fixed to the base of the 
 machine by one of their limbs, and are so placed that poles 
 of opposite polarity face each other. A disk rotates between 
 the 4 poles, and on one of its sides there are 12 perpen- 
 dicular iron bars, arranged in a circle, and forming the cores 
 of as many armature-bobbins. The coils of these bobbins 
 
 * These machines have since been greatly improved by R. A. Crompton 
 and by Gisbert Kapp. Some further details will be found in the Chapter 
 dealing with recent machines. Editor. 
 
NIAUDET'S MACHINE. 83 
 
 are all wound in the same direction, and the terminal of 
 each coil is connected with the wire commencing the next. 
 On the outside of the disk, 12 metallic strips, on each 
 of which the wires of two coils are joined together, 
 converge radially towards the centre, being insulated one 
 from another. Two springs bear on these strips and take 
 up the currents. 
 
 Suppose the disk of the armature to be rotating in the 
 direction of the arrow, and that the anterior horseshoe 
 
 Fig. 46. 
 
 magnet has a south pole at the top and a north pole at the 
 bottom. Then with reference to this magnet (the magnet 
 behind only strengthens the action) all bobbins left of a 
 line that halves the disk and passes through the poles, are 
 retreating from the north pole and approaching the south 
 pole. In the lower ones a retrocession current will pre- 
 dominate, and in the upper ones, an approximation current ; 
 both currents will however have the same direction. On 
 the other hand, in all the bobbins to the right of the line, 
 retrocession currents will be induced, relatively to the south 
 
84 MACHINES GENERATING DIRECT CURRENTS. 
 
 pole, and currents of approximation, relatively to the north 
 pole. These currents too will flow in the same direction, 
 but this will be opposite to that of the currents circulating 
 in the bobbins on the left half of the disk. The two 
 opposite currents will accordingly meet at those points of 
 junction in the armature which are exactly opposite the 
 north and south pole, that is, at both ends of the vertical 
 diameter of the armature disk. The springs which serve 
 to, bring these currents to a single direct current and to 
 the outer circuit, must therefore bear on the metallic 
 strips which are situated on this diameter as shown in 
 Fig. 46. 
 
 Niaudet's generators have not found any very wide 
 distribution in practice. 
 
 Edison's dynamo-electric generator is remarkable for 
 its dimensions, and well deserves the attention of the 
 technologist on account of its practical construction, which 
 follows certain theoretical laws. 
 
 Fig. 47 represents one of the 12 large generators that 
 are at present set up in New York, in a large central 
 station whence a portion of the city receives the current 
 for lighting with incandescent lamps. 
 
 The armature of Edison's generator is a Siemens 
 cylinder armature, the construction of which has, however, 
 undergone slight modification. 
 
 The core of the cylinder consists of iron plates, which 
 are fixed to the shaft, one behind the other. They do not 
 touch, but are insulated from each other with paper. Fou- 
 cault currents are thus prevented. The copper coiling of 
 the armature does not consist of insulated wires, as is 
 generally the case, but of thick copper bars, as in Siemens' 
 generator for depositing metals. These bars have a 
 trapezoidal section, and are insulated from the iron cores 
 
EDISON'S MACHINE. 85 
 
 and from each other by air spaces. At its anterior end 
 each bar is connected with a copper disk, which has the 
 same diameter as the disks that compose the core ; this 
 disk again is connected with a bar, which lies diametrically 
 opposite the first ; and this bar also is connected with a 
 copper disk situated at the back of the cylinder. This 
 disk is connected with a third bar, and so on. Accord- 
 ingly all the bars and copper disks, together represent an 
 
 Fisr. 47. 
 
 uninterrupted circuit. Of course the copper disks, like 
 the bars, are insulated from each other, and together with 
 the disks of the core form a solid cylinder, thus considerably 
 increasing the mechanical strength of the armature. The 
 special advantage of the copper disks is that by their use 
 the internal resistance of the generator is reduced to a 
 minimum, especially at the ends of the armature on which 
 the magnets cannot exert any inducing action. 
 
 In order to protect the bars (which run parallel to the 
 axis of the generator) against destruction from the centri- 
 
86 MACHINES GENERATING DIRECT CURRENTS. 
 
 fugal force during the rotation of the armature, they are 
 held together, at different points, by ties. 
 
 The cylinder armature of the generator has a diameter 
 of 27*8 ins., and a length of 61 ins. without, and of 79 ins. 
 with the commutator. The diameter of the commutator 
 is 12f ins. The steel shaft round which the armature 
 revolves is 10 ft. 3 ins. long, and 6 ins. diameter. All 
 these dimensions show that the armature is very strongly 
 made, and that disturbances in its working will in conse- 
 quence not be likely to occur so frequently as in generators 
 of a more complicated pattern. 
 
 Water circulates under the journals in which the shaft 
 turns, so as to prevent their getting over-heated. Besides 
 this, there are arrangements for automatically oiling the 
 machine, by which the oil is carried along the shaft, whilst 
 it is carried off before it reaches the commutator, where 
 on account of its insulating properties, it would interfere 
 in the electric conduction between the commutator and 
 the brushes. 
 
 The field-magnets are 12 cylindrical cores of soft iron, 
 excited by coils arranged on the dynamo-electric principle, 
 and connected with each other on one side by 4 connect- 
 ing pieces. Eight of these iron cores terminate in an 
 upper pole-piece and 4 in a lower pole-piece, between 
 which the armature rotates. 
 
 The width of the pole pieces is 49 ins., and they are 
 61 J ins. high. The length of the soft iron cores is 57 ins., 
 the diameter of the 8 upper cores is 8 ins., and that of 
 the 4 lower ones 9 ins. The connecting pieces are 1 1 ins. 
 wide and 9 ins. thick, and the total length of the field- 
 magnet is 94 ins. 
 
 The system of field-magnets is insulated magnetically 
 from the iron sole plate by a zinc plate 3 ins. thick. 
 
EDISON'S MACHINE. 87 
 
 The weight of the parts is distributed thus : 
 Armature and shaft * . . 9,800 Ibs. 
 Shaft journals .... 1,340 Ibs. 
 System of field-magnets . . 33,000 Ibs. 
 
 Zinc base 680 Ibs. 
 
 Total weight 44,820 Ibs. 
 
 3440 Ibs. of this is the weight of the copper : 
 The copper bars of the armature weigh 590 Ibs. 
 The copper disks of the armature . 1,350 Ibs. 
 The wire coils of the magnets . . 1,500 Ibs. 
 
CHAPTEK III. 
 
 PARTICULAR APPLICABILITY OP THE VARIOUS ELECTRIC 
 GENERATORS. 
 
 THE last two chapters will have given the reader a general 
 idea of the construction of different electrical generators, 
 and he may now naturally ask " What are the particular 
 advantages of the various kinds of machines." 
 
 If we follow the division in Chapters I. and II., the ques- 
 tion can be answered somewhat as follows. 
 
 The alternating current machines are necessary in electric 
 lighting with JablochkofF, Jamin and other " candles." 
 They are always preferable to other machines when it is 
 more desirable to burn away the carbon points in the lamps 
 evenly, and to prevent residual magnetism in the electro- 
 magnets of these lamps, than to advantageously utilise the 
 energy employed. Accordingly the improved patterns of 
 these machines, for instance, de Meritens' machines are 
 extensively employed in lighthouses. 
 
 When, however, it is principally a question of illuminat- 
 ing a large area, as, for instance, in the lighting of streets 
 or large halls, then the machines for generating continuous, 
 or direct, currents are preferable, as in this case the uneven 
 consumption of the carbons in the lamps, is an advantage ; 
 for when the carbons have a vertical position, and the 
 upper carbon point is the positive pole, the " crater " 
 which is there formed plays the part of an efficient 
 
RELATIVE ADVANTAGES. 89 
 
 reflector and directs a considerable part of the rays of 
 light downwards. Numerous experiments have also 
 proved that the machines for continuous currents are 
 always to be preferred when it is desired to obtain the 
 largest possible yield of work. For the conditions of 
 resistance and rate of rotation being the same, these 
 machines give about 35% more effect in the luminous 
 arc than the alternating-current machines. Besides, 
 machines for continuous currents will always have to be 
 employed in cases where direct currents are absolutely 
 necessary, for instance, in galvano-plastic operations, or in 
 the preparation of pure metals. For alternating current 
 machines, whose currents have to be rectified by a 
 commutator, are not, as a rule, so efficient as other 
 machines under similar circumstances. For not only is a 
 considerable percentage of the current lost in the com- 
 mutation, but, as we have before pointed out, the 
 commutator very quickly wears, on account of the 
 production there of sparks, whence constant disturbances 
 occur in the working of the machine. 
 
 If we divide electric machines into magneto-electric 
 and dynamo-electric generators and if we compare these 
 two classes we can but arrive at the conclusion that, in 
 principle, magneto-electric machines, and especially those 
 in which the field magnets are electro-magnets, are the 
 most advantageous. 
 
 We shall now try to establish the above statement. 
 
 First of all, as far as alternating- cur rent machines are 
 concerned, it scarcely needs proving that for working 
 electric candles they are absolutely necessary. This 
 follows from the construction of the electric candles them- 
 selves, and the very fact that the application of electric 
 candles for illuminating purposes, is gradually increasing, 
 
go PARTICULAR APPLICATIONS. 
 
 makes it necessary to construct alternating -current 
 machines. For through the use of these candles the 
 problem of the distribution of light in moderately powerful 
 foci has been successfully solved. In fact, constructors 
 like Gramme and Siemens whose specialty is really the 
 construction of direct-current generators, were obliged to 
 make alternating- current generators as well> so as not to 
 lose the manufacture. At the present time, it is true, 
 great improvements in the lamps of other constructors, 
 and especially the invention of the Hefner- Altenech 
 differential lamp, has driven the Jablochkoff candle 
 considerably into the background, as the electric exhibi- 
 tion in Paris proved. Through this the alternating- 
 current generators lose some of their importance. 
 
 The table subsequently given (taken from the " Keport 
 of the Trinity House"), shows that, economically, 
 alternating-current machines are far inferior to those 
 giving direct currents. From this table we see that 
 notwithstanding its costliness and comparatively large 
 size, the Alliance machine generated only a current 
 capable of producing a concentrated beam of 465 to 593 
 candles per horse power, whereas the current of the small 
 Siemens generator, No. 68, produced a concentrated beam 
 of light of 2,080, and Gramme's generator, No. 2, a beam 
 of 1,257 candles. 
 
 It cannot be denied that the recent alternating-current 
 generators give much better results; nevertheless 
 economically, they are still very far behind the continuous- 
 current machines. In a number of operations too, for 
 which electric generators are used, alternating currents 
 cannot be employed, so that this restricts the construction 
 of alternating-current generators. 
 
 We now return to our statement relative to the 
 
RELATIVE ADVANTAGES. 91 
 
 magneto-electric and dynamo-electric generators. Experi- 
 ence has shown that the latter have great imperfections, 
 for which as yet, no radical remedy has been found. 
 
 As explained in the introduction, the magnetism of the 
 field magnets in dynamos depends on the strength of the 
 currents generated in the armature coils ; and, as this 
 again depends on the greater or less 'rate of rotation of the 
 armature, it follows that the intensity of the magnetic 
 field fluctuates with every change in the rate of rotation ; 
 of course, again causing a corresponding reaction on the 
 currents produced in the armature. The result is, that 
 the strength of the current cannot remain constant, as 
 long as a constant rate of rotation of the armature is not 
 maintained, and this is scarcely possible even with the 
 best steam engine or other motor. For these motors never 
 work with perfect uniformity, and there are difficulties 
 in the uniform transmission of the motion by belting, &c. 
 Each irregularity, however, in the working (caused by 
 the slipping of the strap or some similar occurrence) 
 is accompanied by a corresponding irregularity in the 
 strength of the current of the dynamo. Variations of 
 current strength from the cause of inequality in the rate 
 of rotation can, however, be easily maintained below 5%. 
 
 Another still more fatal source of disturbance in the 
 strength of current of a dynamo, are the changes which 
 occur in the external circuit. If, for instance, the current 
 is used for generating the electric light between two 
 carbon rods, each change in the arc, not only causes a 
 corresponding but a proportionally increased variation in 
 the strength of the current of the generator. 
 
 Before the lamps are lighted the carbon points are in 
 contact with each other, and a comparatively weak current 
 only should be necessary for starting the light at their 
 
92 PARTICULAR APPLICATIONS. 
 
 point of contact. In a well-constructed regulator-lamp, 
 the small electro-magnets ought then immediately to 
 separate the carbon points, thus instantly employing the 
 strong currents produced in the mean time in the dynamo- 
 electric generator. If, however, the carbons do not 
 instantly separate, the intensity of the magnetic field in 
 the generator rises with each revolution of the armature, 
 and rapidly increases to such an extent that the armature 
 can be moved through the magnetic field only with great 
 difficulty, and often the machine is brought to a stop. 
 But even if the carbon points are instantly separated, the 
 strength of current is constantly subjected to disturbing 
 influences. For the automatic regulation of the lamp 
 by the regulator produces a continuous reaction on the 
 machines, causing fluctuations in the strength of current, 
 and thus again fluctuations in the length of the arc. 
 
 The most disagreeable part, however, in this interdepend- 
 ence of strength of current on the varying resistance in the 
 circuit, is that the current is weakened just when strength 
 is most wanted, whilst it is increased, when there is no 
 necessity for a strong current. Thus for instance when 
 combustion increases the distance between the carbon points 
 the arc gets longer, and when, therefore, a stronger current 
 is wanted to overcome the greater resistance, this increased 
 resistance weakens the current ; again when the carbon 
 points are very near together, and a weaker current would 
 suffice, the strength of current in the generator is 
 increased. 
 
 A good regulator lamp, it is true, modifies these 
 occurrences ; but as yet no lamp has been constructed so 
 perfect as quite to prevent a disturbance in the strength 
 of current. 
 
 Other changes in the resistance of the circuit, whatever 
 
SOME DIFFICULTIES. 
 
 93 
 
 their nature, react in a similar way on the strength of 
 current generated. If, for instance, oil or dirt gets be- 
 tween the brushes and the commutator, or if the binding 
 screws get dirtied, the resistance of the circuit is in- 
 creased, and the current of the generator weakened. 
 Although these occurrences can be reduced to a minimum 
 by careful supervision, and by great cleanliness in the 
 handling, as well as by employing uniformly working 
 motors, and a method of uniform transmission of work, 
 there still remains this defect in dynamo-electric gene- 
 rators, that the intensity of their magnetic fields, and 
 consequently the current, varies with the resistance in 
 the curcuit. In our next chapter we shall see by what 
 preventive arrangements these fluctuations can be modi- 
 fied ; they are not present in magneto-electric machines 
 with steel magnets. 
 
 The magnetic fields of these machines are of constant 
 intensity, and do not depend on the rate of rotation of the 
 armature. Also magneto-electric generators, with electro- 
 magnets, which are excited by currents from a separate 
 generator, are not influenced by the disturbances in the 
 circuit a circumstance which gives this arrangement 
 great advantage over the ordinary dynamo-electric ma- 
 chines. 
 
 If the question be asked, what are the special ad- 
 vantages of the various generators described in Chapters* 
 I. and II., the answer is not so easy. For although gene- 
 ral conclusions can be arrived at as to the efficiency of the 
 various machines from a consideration of their construc- 
 tion, trustworthy data are wanting. There are, it is true, 
 numerous reports, which seem to give the reader a good 
 idea of the advantages and drawbacks of the several ma- 
 chines, but, as a rule, the data given are vitiated by 
 
94 PARTICULAR APPLICATIONS. 
 
 private or national interests. For the data are either 
 taken from reports of constructors, or from reports of 
 national committees, and naturally in these an absence of 
 party feeling is scarcely to be expected. Besides, the 
 basis of comparison of the several machines varies in 
 almost all published reports, and tables of comparison, 
 which would be of real value to electro-technical science, 
 could only be constructed by an international committee, 
 provided with all the necessary facilities. It is much to 
 be regretted that nothing was done in this respect during 
 the Paris Exhibition, although a comparative investigation 
 of the several machines would have been easy at that 
 time ; but however great, in other respects, the utility of 
 this exhibition was, absolutely nothing was done for the 
 advancement of electro-technical science, to throw light 
 on the mysterious darkness which prevents a clear com- 
 prehension of the efficiency of the various magneto and 
 dynamo-electric generators. 
 
 As, however, some of the data given by national com- 
 mittees, and by constructors and physicists known for 
 their veracity, are a useful aid to the technologist, those 
 most important have been reprinted and explained in a 
 subsequent chapter. 
 
CHAPTEE IV. 
 
 AUTOMATIC SWITCHES AND CURRENT REGULATION. 
 
 To prevent the extremely troublesome disturbances men- 
 tioned in the last chapter, as occurring in the working 
 of dynamo-electric generators, in consequence of changes 
 in the external circuit, various devices have been de- 
 signed. 
 
 To these belong the so-called " switches," by which an 
 artificial resistance is inserted in the circuit, actuated 
 either by an overseer or automatically, and generally when 
 for some cause the external circuit is interrupted. 
 
 Siemens, Sawyer and other constructors employ these 
 switches. That of Siemens depends on the action of a 
 small extra magnet, through the coils of which the 
 current is conducted when the machine is working 
 regularly, and which, during this time, holds a small 
 keeper connected with an extra circuit. As soon as the 
 current in the external circuit is interrupted, a spring 
 pulls away the keeper from the magnet ; this action 
 introduces into the circuit of the machine the extra 
 circuit, which has the same resistance as the external 
 circuit. 
 
 Many of the switches in use are constructed on a 
 similar principle. 
 
 Another method of regulating strength of currents to 
 follow the requirements of the circuit, is exemplified by 
 
g6 CURRENT REGULATION. 
 
 Hiram Maxim's current regulator, which excited great 
 interest at the electric exhibition in Paris. It is re- 
 presented in connection with the generator in Fig. 43. 
 
 As already mentioned, the electro-magnets of Maxim's 
 generator are excited by a current from a small machine. 
 In order to supply the electro-magnets with a weak or 
 strong current as required, so as to regulate the current of 
 the generator itself, the collector-brushes of the exciting- 
 machine are fixed to a rocking frame, by means of which 
 they can be shifted round the collector-cylinder. As the 
 strength of the current taken up by the brushes depends 
 on their being more or less advantageously situated with 
 respect to the sectors of the collector, this current in- 
 fluences the strength of current of the generator. In 
 order to alter the position of the brushes according to the 
 requirements of the generator, the current of the latter is 
 conducted to an electro-magnet connected with the 
 regulator of the exciting-machine, and according to 
 Schellen, the following action takes place (vide Schellen's 
 " Die Magnet-elektrische und Dynamo-elektr. Maschinen,'' 
 p. 509) ; " The electro-magnet lifts a pawl by means of 
 a keeper attached to the end of a lever, which moves up 
 and down between two set-screws. The pawl is caused to 
 catch in the lower or upper of two ratchet-wheels, and is 
 moved backwards and forwards by an oscillating bar, 
 moved by a small crank which has a comparatively slow 
 rotatory motion imparted to it from the shaft of the 
 generator. If the pawl catches in one of the ratchet- 
 wheels, the motion of the latter, as it turns, is transferred 
 to a horizontal pin, and thence to the carrier of the 
 brushes of the exciting-machine, by bevel pinions. The 
 rocking-frame is turned in one or the other direction 
 when the light-producing current is too weak or too 
 
MA XI M '5 REG ULA TOR. 97 
 
 strong. The keeper of the electro-magnet of the regulator 
 is pulled down more or less, and in consequence, the 
 upper or lower ratchet-wheel is turned. This, first of all, 
 strengthens or weakens the exciting current, and next, 
 the current for generating the electric light." 
 
 A very effective method for preventing a sudden rise in 
 the strength of current from a dynamo consequent upon 
 the resistance in the external circuit being lowered, is 
 that of exciting the electro-magnets by a shunt current, 
 which was first recommended by Wheatstone, in England, 
 and afterwards applied by Siemens and others with the 
 most satisfactory results. 
 
 In this arrangement, with a lighting machine, for 
 instance, only the lamp, the armature -coils and conduct- 
 ing wires are united to form the main circuit ; the 
 electro -magnets are inserted in a branch-circuit, generally 
 taken from one brush of the collector to the other. If 
 the resistance in the external circuit is reduced to zero, a 
 small portion only of the current passes into the coils of 
 the electro-magnets, and as the inducing action of the 
 latter is thus weakened, the strength of the current is at 
 the same time reduced. 
 
 The reader should here note that with a. machine con- 
 nected on this " shunt " method, the removal of resistance 
 from the working circuit causes a decrease of current in 
 this circuit ; but that with a machine connected with the 
 electro-magnets in the same circuit in which work is 
 done, or in " series," as this arrangement is termed, the 
 removal of resistance from the working circuit is produc- 
 tive of an increase of current in this circuit. In other 
 words, with these two systems of connection, the same 
 action of removing resistance from the working circuit 
 produces opposite results. 
 
 H 
 
g8 CURRENT REGULATION. 
 
 To prevent reversal of current in the external circuit 
 influencing the magnets, C. F. Brush surrounds the latter, 
 in some of his generators for plating purposes, with a 
 second coil of very fine wire which is connected with the 
 collector-brushes, and thus forms a shunt circuit to the 
 main or working circuit. 
 
 This system of double-winding of the electro-magnets 
 of dynamo-machines as employed by Brush for preventing 
 the demagnetisation of the " field "-magnets, was first 
 used by Paget Higgs, in 1880-81, to maintain a constant 
 electromotive force, under variations caused in the ex- 
 ternal circuit by addition or removal of lamps from the 
 circuit. When electric lamps are ranged along the two 
 conducting-wires leading from the dynamo, side by side, 
 one of the two terminals of the lamp being connected to 
 each conducting wire, the lamps are said to be put in 
 " parallel arc " or in " multiple arc." The greater the 
 number of lamps, the greater therefore the number of 
 ways for the electric current to flow from the positive to 
 the negative conductor ; and the greater the number of 
 ways, the greater will be the total flow of current. Now, 
 with a " series " machine (in which the electro-magnets 
 are included directly in the working circuit), the greater 
 number of lamps causing an increased flow of current, a 
 higher electromotive force is obtained, consequent upon 
 heightened magnetic intensity of the field-magnets, 
 caused by the increased current circulating in the electro- 
 magnet coils. If this increase of magnetism were pro- 
 portioned to the number of lamps added or to the flow of 
 current, all would be easy work for the electrical engineer ; 
 unfortunately for him, the increase of magnetism does not 
 follow any such convenient law. Besides, let us suppose 
 that ten units of flow of current were necessary to pro- 
 
DOUBLE-WOUND MACHINES. gg 
 
 duce a certain intensity of magnetism, to which would 
 correspond the electromotive force necessary to properly 
 light the lamps, then it is quite clear that five lamps 
 would not open ways sufficient to cause enough flow of 
 current to magnetise the magnets to that intensity neces- 
 sary to produce the proper electromotive force (which for 
 all practical purposes we may consider to be the same for 
 one lamp as for one hundred, when the lamps are arranged 
 in parallel arc). And if more than ten lamps are in- 
 cluded in the circuits between the two main conductors, 
 then it is also pretty evident that a higher intensity of 
 magnetism would occur from the greater flow of current 
 around the magnets, and a higher electromotive force 
 would result, and this would cause too much current 
 to be forced through the lamps, probably more than 
 they were intended to withstand, ending in their destruc- 
 tion. 
 
 On the other hand, if the electro- magnets were in- 
 cluded in a " shunt " circuit taken from one of the 
 conducting mains to the other^ or from one brush of the 
 machine to the other the electro-magnets being thus in 
 parallel arc to the lamps increase of the number of 
 lamps above the normal number would cause a too great 
 number of ways to be opened for the current to pass by 
 the electro-magnets, subtracting current from these 
 magnets, and therefrom the magnetism would be de- 
 creased, with the consequence that the electromotive force 
 would also be decreased (in a much more than a pro- 
 portional amount), resulting that the lamps would de- 
 crease in the amount of light given by each by this 
 addition to their number. 
 
 We see that adding lamps, in the one case of the " series " 
 machine would cause the destruction of those already 
 
ioo CURRENT REGULATION. 
 
 arranged in circuit from too high excitation, and in the 
 other case of a " shunt " machine, reduction of current 
 and light ensues : from these opposite effects it is not 
 difficult to comprehend that a possible combination of 
 these two methods of arranging the electro-magnets 
 " shunt " and " series " would result in maintaining, under 
 the case of adding, or subtracting, lamps in the circuit, a 
 constant magnetic intensity and consequently a constant 
 electromotive force. Such is the principle of the ma- 
 chines termed compound wound, or self -regulating ; and 
 in these machines a constant speed being given, with the 
 lamps arranged in parallel arc, very great variations in the 
 external circuit may occur, without variation in the 
 electromotive force. 
 
 The steady maintenance of a constant electromotive 
 force, with only one unit of current passing over the coils 
 of the electro-magnets (ten units being supposed to main- 
 tain saturation under a " series " arrangement), clearly 
 necessitates that the magnetic field shall initially be 
 raised to its proper intensity. This need of an " initial 
 field " was first proved mathematically by M. Marcel 
 Deprez, in 1881, independently of Paget Higgs (but 
 several months after application for patent by the latter), 
 in a valuable contribution to the French journal La 
 Lumiere Electrique. M. Marcel Deprez proposed to 
 maintain this initial field by employing two machines, one 
 being the generator, the electro-magnets of which were 
 wound with two equal and similar wires ; the other an 
 exciting machine. One of the wire circuits on the electro- 
 magnets of the generator was put into connection with 
 the exciting machine, only to maintain the " initial field ;" 
 the other wire circuit was arranged in " series " in the 
 main circuit in which work was to be done. The system 
 
SELF-REGULATING MACHINES. 101 
 
 adopted by Paget Higgs at once gave similar results, with 
 the use of only one machine. 
 
 It is frequently astonishing to find how nearly earlier 
 inventors were in attaining results that have finally been 
 produced with so much thought and labour. An old ma- 
 chine by Hjorth, a Swede, was patented thirty years pre- 
 viously, in which permanent magnets were used in com- 
 bination with electro-magnets in the same machine. The 
 permanent magnets were then doubtless intended to give 
 the necessary magnetism to start the electric current, the 
 dynamo-electric principle being then unknown ; but to- 
 day, constructed in proper proportion, Hjorth's machine 
 could be used to give constant electromotive force, or as 
 a self-regulating machine. Indeed, Professors Ayrton and 
 Perry have recently perfected a dynamo, in which perma- 
 nent magnets are employed to produce an initial field 
 with electro-magnets to provide current for the remainder 
 of the work. An objection to such a machine will be pro- 
 bably found in the great size required, which is one of the 
 most detrimental drawbacks to magneto-machines with 
 permanent magnets. 
 
 Self-regulating compound wound dynamo-machines 
 have been usually constructed with the main circuit, or 
 " series " electro-magnet coils wound on the same arm or 
 limb of the electro-magnet, as contains the " shunt " 
 coils ; some makers, like R. E. Crompton, putting the 
 main coils, of thick wire, on first, the " shunt " coils, of 
 finer wire, being wound above or over these other coils ; 
 Siemens, on the contrary, puts the main coils outside and 
 the shunt coils nearest the core of the electro-magnet. 
 Paget Higgs, however, prefers to assign one limb of the 
 electro-magnet to the shunt coils, and the other limb to 
 the series or main coils ; very many more points that occur 
 
102 CURRENT REGULATION. 
 
 in practice are covered by this arrangement, and it has 
 been shown to be possible by a suitable combination to 
 obtain a machine so regulated as to produce a normal 
 current only, any deviation of a marked character from 
 this normal current causing a cessation, or great diminu- 
 tion of current. The first published mathematical con- 
 sideration of double-wound machines is due to Mr. E. H. 
 Bosanquet, of St. John's College, Cambridge, and to this 
 reference will be made in a subsequent chapter. 
 
 M. Marcel Deprez, to whom electricians are indebted 
 for the first logical enunciations of the laws relating to 
 current electromotive force in dynamo machines, has also 
 shown that with a properly-arranged initial field, and with 
 the remaining coils of the electro-magnets in a circuit 
 shunted from the main or working circuit, it is possible to 
 maintain a constant current (the former arrangement 
 referred to maintaining a constant electromotive force\ 
 flowing through a " series " of lamps -that is through a 
 succession of lamps on a single circuit when the number 
 of lamps is varied, provided the speed of rotation of the 
 armature of the machine is maintained constant. But 
 this has only been successfully accomplished with two 
 machines, one being used as an exciting machine, and the 
 other, the chief generator, wound as to its electro-magnets 
 with two equal and similar wire circuits. One of these 
 circuits is connected to the exciting machine, the other is 
 arranged as a shunt from main to main of the working 
 circuit. 
 
 In all these double-wound machines, certain relations 
 have to be maintained between the resistances of electrical 
 circuits of the machine itself, and between the amount of 
 current and number of turns of wire led around the 
 electro-magnets, but to this it is not now necessary to refer. 
 
STORAGE NECESSARY. 103 
 
 So far, however, these methods of regulation have not 
 furnished us with an absolutely reliable remedy, especially 
 as to any variation in the speed of the motor or irregu- 
 larity of its motion. However, a comparatively short 
 time ago, great advance was made in electro-technology, 
 which renders it possible, to completely sever the connection 
 of the electric generator with the circuit in which elec- 
 tricity is converted into work. This advance is the em- 
 ployment of the improved secondary batteries as reservoirs 
 of electrical energy. 
 
 In this respect the recent improvements have made the 
 subject of storage batteries sufficiently important to re- 
 ceive separate consideration. 
 
io 4 
 
 CHAPTEE V. 
 
 ELECTRICAL STORAGE. 
 
 WHEN two platinum electrodes are immersed in hydric 
 sulphate, and are connected with a galvanometer, after a 
 
 T current has been sent through the whole voltametric 
 arrangement, a current is found to flow from one electrode 
 
 ., to the other, in a direction opposite to that of the original 
 current. This current is called a polarisation current, 
 and was first observed by Grantkerot in 1802. It is pro- 
 
 . duced by the evolution of hydrogen at one pole, oxygen 
 at the other ; these gases change the potential of the 
 electrodes, by partly adhering to the metallic surfaces, 
 and partly by penetrating into the metal ; and as 
 soon as metallic contact in the external circuit between 
 the electrodes is established, a current flows tending to 
 reproduce electrical equilibrium. 
 
 This polarisation current may be very powerful ; and 
 as early as 1803, the German physicist Eitter, of Jena, 
 constructed a kind of voltaic battery in which only one 
 metal was employed, the disk-electrodes of which were 
 rendered active by polarisation. This secondary battery, 
 by Eitter, can be regarded as the first electric storage 
 battery or accumulator. 
 
 Plante, the celebrated French physicist, however, de- 
 serves the merit of having been the first who applied the 
 polarising of electrodes to the construction of an efficient 
 
PLANTERS ACCUMULATOR. 
 
 105 
 
 battery that could be used in practice. In 1859, he con- 
 structed a secondary or storage battery, the efficiency of 
 which depended on the chemical behaviour of lead. 
 
 The following is the construction of Plante's Element, 
 Fig. 48. A broad sheet of rolled lead is placed on a 
 second sheet of the same size, so that one sheet covers 
 the other. However, to prevent contact between the two 
 sheets, thick strips of indiarubber are laid between them. 
 Each strip of rubber is 1 cm. wide, 0*5 cm. thick, and of 
 the same length as the lead sheets ; when similar india- 
 
 Fig. 48. 
 
 rubber strips have been laid on -the upper lead sheet, 
 the two sheets are rolled into a spiral on a wooden 
 cylinder. To make the arrangement stronger, the lead 
 spiral is held together at one end by gutta-percha clamps. 
 The construction of the element is completed by placing 
 this roll of lead, each sheet of which is provided with a 
 connecting strip, in a cylindrical vessel, closed with an 
 ebonite cover. The cover is provided with openings for 
 the connecting strips, and an opening for pouring in the 
 liquid, which consists of water containing ten per cent, of 
 hydric sulphate. 
 
io6 ELECTRICAL STORAGE. 
 
 Now, if the poles of such an element are connected with 
 the poles of two Bunsen's elements, so as to cause a cur- 
 rent to circulate through the Plante cell, lead peroxide 
 (Pb O) will be formed on the lead sheet by which the 
 current enters the cell, or the anode ; and, on the other 
 hand, on the lead sheet, or the cathode, hydrogen will be 
 generated, tending to precipitate lead in the metallic 
 state. The cathode obtains thus a rough granular sur- 
 face, and the anode a brown coating. 
 
 Now, when the Bunsen battery is removed, after the 
 current has been allowed to work for some time (the 
 current should only be allowed to traverse the Plante 
 element till small bubbles of oxygen show themselves at 
 the anode), if the poles of the Plante element are joined, 
 a strong current results; for now the oxygen of the 
 peroxide powerfully attracts the hydrogen of the hydric 
 sulphate ; and the peroxide is de-oxidised ; whilst the 
 oxygen liberated combines with the lead of the cathode, 
 and oxide of lead is formed there. The current continues 
 as long as the cathode takes up oxygen. When the dis- 
 charge current ceases, the conditions for a new polarisa- 
 tion current can be again obtained by recharging with the 
 Bunsen elements ; and as the discharge need not take 
 place immediately, but can be proceeded with after several 
 days, it appears that in a Plante cell we really have a 
 reservoir for electrical energy. 
 
 This element, however, cannot take up a large charge 
 immediately, but its efficiency increases to a useful de- 
 gree with repeated charging and discharging. The 
 element has to be " formed," as Plante expresses it, and 
 this " forming " is a long, troublesome process. 
 
 When first charged, only a small quantity of peroxide is 
 formed; and accordingly, in the discharge, a current of 
 
PLANTS 'S ACCUMULATOR. 107 
 
 but short duration is obtained. The poles have now to be 
 reversed ; that is, the pole which was previously negative 
 must now be oxidised, and the pole which was previously 
 positive must be reduced. The reduced lead sheet now 
 takes up oxygen, and lead peroxide is formed on it ; whilst 
 the plate which was previously oxidised is reduced by the 
 hydrogen. According to Plante, this process of reversion 
 must be repeated frequently. On the first day the element 
 must be charged and discharged from six to eight times, 
 commencing with a quarter of an hour, and gradually in- 
 creasing the length of time to an hour ; the element is 
 allowed to stand charged over night. On the second day 
 it is discharged, and then recharged in the opposite way 
 during two hours ; again discharged, recharged afresh in 
 opposite direction, and finally is allowed to stand charged 
 for eight days. After eight days it is again charged 
 during some hours without being reversed, and is then 
 allowed to stand charged for fourteen days, and so on. 
 In this way the capacity of the element is more and more 
 increased. With a well-formed Plante element, a thick 
 platinum wire of 1 mm. diameter can be made to glow, 
 and can be kept glowing during ten minutes ; a platinum 
 wire of T *o mm. diameter can be kept glowing for an 
 hour. 
 
 On account of the spiral arrangement of the electrodes, 
 the Plante element has very small internal resistance. It 
 has a high electromotive force as well, and accordingly its 
 construction is very advantageous. The results obtained 
 with the elements would undoubtedly have ensured their 
 extensive application in practice, had not their " forma- 
 tion " offered such a great obstacle. This "forming" is 
 the reason why this original Plante element is scarcely 
 employed in practice, excepting for galvano-caustic pur- 
 
loS ELECTRICAL STORAGE. 
 
 poses, although it is an extremely convenient source of 
 electricty when once formed. 
 
 In 1883, M. Graston Plante patented a process- for the 
 rapid formation of the well-known secondary battery, and 
 it consists in immersing the sheets of lead (similar to 
 those devised by him in 1860) in nitric acid, diluted with 
 from once to twice its volume of water, for about twenty- 
 four hours before submitting them to the action of the 
 primary current. The cells are then emptied, thoroughly 
 washed, filled with water acidulated with about one-tenth 
 of sulphuric acid, and submitted to the action of the 
 current from the primary source of electricity of which 
 they are intended to accumulate and store up the energy. 
 By this preliminary immersion in nitric acid, a small 
 quantity of lead is, of course, dissolved, but the thickness 
 of the sheets suffers no sensible diminution as, by reason 
 of their metallic porosity, the chemical action is not 
 limited to the mere surfaces of the sheets of lead, but 
 penetrates into the interior of the metal, creating new 
 interstices and enlarging the natural pores already exist- 
 ing, and consequently facilitating the ulterior electro- 
 chemical action produced by the primary current. 
 
 The sheets of lead intended to be employed in the 
 construction of these secondary cells may be submitted to 
 the action of the dilute nitric acid and washed before 
 being rolled up or arranged in cells ; but the process is 
 equally applicable to cells already constructed. 
 
 Secondary cells thus formed, after having been submitted 
 for a few hours to the action of the primary current, give 
 off a discharge current lasting for a long period, whereas 
 when they have not previously been attacked by the nitric 
 acid, several weeks of electric action are required, as has 
 been shown, before they will give the same results. Ke- 
 
ELWELL-PARKER ACCUMULATOR. 109 
 
 versing the direction of the primary current, which is so 
 useful for the operation that Graston Plante described 
 in 1872 under the name of " formation," is equally 
 efficacious in the present case, without it being necessary 
 to so frequently effect this change. About the same time 
 that M. Plante made his remarkable discovery, Mr. 
 Bedford Elwell and Mr. Parker, of Wolverhampton, hit 
 on nearly the same thing. They found that by immersing 
 lead plates in a dilute mixture of nitric and sulphuric 
 acids very important advantages were secured. 
 
 The method of making the Elwell-Parker secondary 
 battery may be thus described : Strips of sheet lead 9 ins. 
 wide and any convenient length, weighing 2*16 Ib. to the 
 square foot, are passed through a machine which first 
 punches holes entirely through them, and then impresses 
 them with indentations, which act as distance pieces to 
 keep the layers of each plate apart. The holes secure a 
 free circulation to the electrolyte. These strips are then 
 rolled spirally into cylinders containing, in the small 
 cells, three thicknesses of plate each, the joints being 
 made secure by fusing with a soldering iron, and a con- 
 ducting piece of much thicker lead being fused on at the 
 same time. Each cell contains eight of these cylinders 
 in. apart. The lead cylinders are first placed in a bath 
 containing a dilute solution of nitric and sulphuric acids, 
 and left there for twenty-four hours. The effect of this 
 bath is to minutely honeycomb the lead plates, putting 
 them into the most favourable condition for " formation " 
 by the electric current. There is also formed upon the 
 surface of the plates a deposit of sulphate of lead, the 
 greater part of which is subsequently reduced to peroxide, 
 part of it being first washed off. The plates on being 
 taken from the bath are washed, and then placed in the 
 
no ELECTRICAL STORAGE. 
 
 ordinary dilute sulphuric acid solution in the cell. They 
 are then charged in one direction for six hours with a 
 current of 12 amperes, discharged in about three hours 
 through ten Swan 45 volt, 20 candle lamps twenty- 
 two cells give 45 volts and charged again in the reverse 
 direction. They are now ready for use. There is then 
 no sulphate visible, the peroxide plate being of a rich, dark 
 brown colour, smooth, hard, and crystalline in appearance, 
 and the negative plate presenting a clean surface of 
 ordinary lead colour. 
 
 The plates or cylinders are retained in position by 
 notched vulcanite frames underneath, and notched dis- 
 tance pieces of the same material on the top, thus leaving 
 the centre space between the plates, and a space under- 
 neath them, open for the free circulation of the electrolyte. 
 Earthenware cells are generally used, but the company 
 manufacturing under the patent also use wood cells, 
 coated inside with a composition of gutta percha, which 
 are preferable where strength and lightness are required. 
 The quantity these cells will give out at an electromotive 
 force of two volts, or rather more, is about 40 ampere- 
 hours when sent from the works, that is, supposing an 
 accumulator is required to give a current at an electro- 
 motive force of 45 volts, twenty-two of these cells will 
 give a current of 10 amperes for four hours before any of 
 the cells are exhausted. But the capacity of the cell may 
 be greatly increased by occasionally reversing the charging 
 current, as in the original Plante cell. The arrangement 
 of the battery is very workman-like and convenient. A 
 cell can be taken to pieces and put together again in 
 a.bout two minutes ; and the way in which the cylinders 
 are put together gives great stiffness and prevents 
 deflection or bending, while the plates being free 
 
FA ORE'S ACCUMULATOR. in 
 
 to expand or contract, can do so without losing their 
 shape. 
 
 It is to a Frenchman named Faure that the honour is 
 due of having in practice and by somewhat mechanical 
 means rendered the long " forming " of the elements un- 
 necessary. He uses lead in a powdered condition for the 
 
 Fig. 49. 
 
 construction of his elements. These consist of two lead 
 plates, each 200 mm. wide, one 600, the other 400 mm. long, 
 and 1 and 0-5 mm. thick, which he coats as thickly as 
 possible with a paste of red lead (Pb 3 4 ) and water. On 
 the larger plate he puts 800 grms., on the smaller are 700 
 grms. of red lead. To keep the paste on the metallic 
 plates, he places over them strips of parchment paper, and 
 
ii2 ELECTRICAL STORAGE. 
 
 on that a strip of felt. He then rolls up the whole system 
 as in the Plante element, and places it in a cylindrical 
 vessel, Fig. 49. The liquid is the same as that used 
 in the Plante element. 
 
 When the element is thus prepared, a current is passed 
 through it, and a thin layer of lead peroxide and lead 
 sulphate is, according to Dr. Aron, formed on the outer 
 surface of the red lead. This layer of sulphate then gets 
 reduced to lead, whilst on the other plate pure lead 
 peroxide is formed. In due course the stratum of red 
 lead beneath gets attacked, and the action goes on till by 
 degrees the cell is made capable of taking up a large 
 charge. 
 
 Charging the element two or three times is sufficient 
 to make it ready for use ; the coating of red lead on one 
 electrode has then changed completely into lead peroxide, 
 whilst the red lead on the other electrode has been re- 
 duced to lead. 
 
 There were few trustworthy data with regard to the 
 efficiency of the Faure batteries up to the beginning of 
 last year ; and whilst, on the one hand, Faure's improve- 
 ment of the Plante battery was lauded to the skies in 
 ridiculous advertisements, on the other hand, in conse- 
 quence of this quackery, so unworthy of a scientific in- 
 vention, physicists were inclined to think lightly of the 
 Faure battery. One of the first to truly investigate the 
 merits of the Faure batteries was Mr. Frank Geraldy, who 
 published the results of experiments carried out by him, 
 in partnership with Mr. Hospitalier, in the electrical 
 journal, La Lumiere Electrique, in which he showed that 
 a Plante element is almost as efficient as a Faure's element 
 of the same weight. The advantage of the Faure element 
 over the Plante element, consists in the former being 
 
FAURE'S ACCUMULATOR. 113 
 
 ready for use almost immediately after its construction, 
 whereas the latter requires the tedious " forming." We 
 have now reliable data as to the value and efficiency of 
 Faure's elements of the newest construction. These data 
 are given in the journal mentioned, Vol. VI., No. 10, in 
 which there is a full report of experiments made by a 
 French committee, with Faitre's batteries at the Conserva- 
 toire des Arts et Metiers. 
 
 The committee were Messrs. Allard, Blanc, Joubert, 
 Potier, and Tresca, and a memoir on their experiments was 
 also placed before the French Academy of Sciences on 
 March 10, 1882. 
 
 The battery placed at the disposal of the committee 
 consisted of thirty-five Fairfe elements of the newest 
 construction ; each element, with its liquid, weighed 43' 7 
 kgs., the lead-electrodes were covered with red lead in the 
 proportion of about 1 kgr. to the square metre. The 
 liquid consisted of distilled water containing about 
 10 per cent, by volume of hydric sulphate. The gene- 
 rator placed at their disposal by FauTe was a Siemens 
 dynamo. 
 
 The resistance of the armature was 0-27 ohm, that of 
 the field-magnets 19-45 ohms. The coils of the latter 
 were supplied by a shunt Current. By means of a regula- 
 ting apparatus, employed by Fau're, the exciting current 
 was kept during the entire experiment at a strength 
 varying between two and five amperes. 
 
 The object of the experiments was to measure: 1. 
 The mechanical work necessary to charge the battery. 2. 
 The quantity of electrical energy stored during the charg- 
 ing. 3. The electrical work actually performed during the 
 discharge. 
 
 For this object the electro-motive force and the resis- 
 
 I 
 
ELECTRICAL STORAGE. 
 
 SejSS 
 
 
 -8* 
 
 000 
 o o o 
 
 o 
 o 
 
 1-1 OO vo'OO 
 
 >q- iy\Vt> V*A 
 
 ON 
 
 vO 
 
 H 
 
 M 
 
 H 
 
 8 
 
 8 
 
 8 
 
 8 8 
 
 
 
 
 00 
 
 vO 
 
 CO 
 
 ^O 
 
 ^C 
 
 
 
 
 
 f-^. 
 
 
 
 
 
 oo 5 
 
 
 VO 
 
 u- 
 
 
 00 
 
 
 
 
 
 H 
 
 I 
 
 8 
 
 O 
 
 
 
 O 
 
 
 
 o 
 
 
 
 
 
 00 
 
 CO 
 
 VC 
 
 
 2 
 
 -f 
 
 
 O 
 
 00 
 
 00 
 
 CN 
 
 
 
 VO 
 
 
 M 
 
 M 
 
 
 
 ^o 
 
 
 
 
 
 i 
 
 
 
 
 
 H 
 
 sqraojnoQ m 
 Xq dn 
 jo 
 
 O O O O 
 0000 
 ^OO rO O 
 vo O Tj- r 
 
 10 
 
 * 
 
 ON 
 
 vo 
 
 saiadray u,i q.uaij;noSai ^-oo oo 
 J " 
 
 ly ui ^u9janQ Sm 
 
 m 
 
 jo 
 
 jo - 
 
 ON 
 
 H- OO HN \O 
 00 O ON O 
 M ft' M 
 
 ON ON ON 
 
 CO 
 
 Xq 
 
 a^nmin aad suoT^n^OA9'jj 1^.^.0000 
 o o o o 
 
 t^ N M 00 
 O ON ** N 
 ON N 00 t^ 
 ^- N VO 10 
 
 M ^h t 
 
 * 1^. ^ M 
 
 N N PO M 
 
 oo o 
 
 ON VO 
 
 t^ r^ 
 
 ON 00 
 
 vO O 
 VOOO 
 
 ON 
 
 ff II 
 
 00 
 
 a a a a 
 
 1 v 
 
 to 1 PO <* 
 
 ,4 rd & ^ 
 
 10 t^ t^ e 
 
 rf- IOVO 
 
 1 1 
 
 
 
 a 
 
 88 
 
 O O 
 
 O 
 
 
 o 
 
 W H 
 
 00 M 
 
 ON 
 
 ^" fi 
 
 
 
 O 
 
 d .3 
 
 vO N 
 
 OO 
 
 JOJ 
 
 N M 
 
 c/2 
 
 g 
 
 
 
 '5 
 
 O 
 
 o 
 
 ?i 
 
 o o 
 
 oo oo 
 
 C> ON 
 
 
 
 vO 
 ON 
 
 f^^**^ 
 
 rj- M 
 
 vO 
 
 .3 
 
 
 
 
 3 
 
 d 
 
 
 
 II 
 
 
 J 3 
 
 00 vo 
 
 &B"^ 
 
 -< M 
 
 .S 
 
 vb vb 
 
 a> ! 
 
 M M 
 
 ectromotive Force 
 iattery, in Volts. 
 
 ON 00 
 
 F- M 
 
 VO vo 
 
 3 
 
 
 s 
 
 a s 
 
 a 
 
 CH -|J 
 
 ON O 
 
 ON 
 
 fl 
 
 M (4 
 
 
 I! 
 
 A A 
 
 4 
 
 II 
 
 t^ co 
 
 O 
 
 H 
 
 a * 
 3 
 
 
 
 <fr ON 
 
 
FA U RE'S ACCUMULATOR. 
 
 tance of the battery had to be constantly controlled, and 
 as the current traversed a number of Maxim's incan- 
 descent lamps, the changes in the resistance and bright- 
 ness of the lamps had to be kept in view. 
 
 The measurements of the mechanical work were effected 
 by means of an Easton-Anderson integrating dynamo- 
 meter. To measure the intensity of the light a Foucault 
 photometer was employed. The electrical measurements 
 were carried out with a Deprez galvanometer, with, which 
 the total current, and, from time to time, the exciting cur- 
 rent were measured ; with a Siemens electro-dynamo- 
 meter, which was employed in measuring the barging 
 currents, and with a graduated electrometer, according to 
 Joubert's method, which was used for determining the 
 difference of potential between the poles of the bat- 
 tery. 
 
 The readings of the instruments were a.t first taken 
 every quarter of an hour, and every 7-| minutes during the 
 later period. 
 
 Mean Intensity and Quantity of Electricity. The 
 mean intensity during a certain tim is the arithmetical 
 mean of the intensities taken every quarter of an 
 hour. 
 
 The product of the number of seconds, and of the mean 
 intensity in amperes, gives the quantity of electricity 
 generated during the time. 
 
 
 Mean Intensity. 
 
 Seconds. 
 
 Coulombs. 
 
 4 January . 
 
 IO*Q7O 
 
 19800 
 
 2 l6AOO 
 
 c 
 
 7'Q7O 
 
 25 200 
 
 2OO8OO 
 
 6 
 
 / y 1 w 
 7*Q76 
 
 27OOO 
 
 2 IA7OO 
 
 7 
 
 6-360 
 
 99OO 
 
 69000 
 
 In order to arrive at correct conclusions, the same cal- 
 
n6 
 
 ELECTRICAL STORAGE. 
 
 culations have to be made with regard to the exciting 
 -current. 
 
 
 Mean Intensity. 
 
 Seconds-. 
 
 Coulombs. 
 
 4 January 
 
 2*46 
 
 19800 
 
 48700 
 
 c 
 
 2*8l 
 
 25200 
 
 72800 
 
 6 
 
 2' ?"? 
 
 27000 
 
 62000 
 
 7 
 
 2-18 
 
 QQOO 
 
 21600 
 
 Calculations of the Electrical Work. As long as 
 the difference of potential between the two poles of the 
 battery remains unchanged, the electrical work employed 
 in charging the battery is equal to the product of the 
 quantity of electricity and the difference of potential, 
 divided by the acceleration due to gravity, g. When 
 this difference changes, each observed intensity has to 
 be multiplied by the corresponding difference of po- 
 tential, again divided by g, and the arithmetical mean of 
 all the results has to be taken. 
 
 In this way were calculated the numbers in columns 8 
 and 9, Table I., and those in column 5, Table II. 
 
 Column 8 gives the electrical work T' spent in conduct- 
 ing the quantity of electricity to the battery, with which 
 the latter was charged. 
 
 ELECT&ICAL WORK DURING THE CHARGING. 
 
 
 Difference of 
 Potential. 
 
 Quantity of 
 Electricity. 
 
 Work. 
 
 4 January 
 
 82'2I 
 
 2 1 6400 
 
 1814600 
 
 c 
 
 QI'oS 
 
 2OO8OO 
 
 TO/17 IOO 
 
 " 
 
 6 
 
 7 
 
 y A 
 92-91 
 
 Q2*o6 
 
 2I43OO 
 
 6-2000 
 
 2028800 
 
 coi6oo 
 
 
 
 
 ^y j. www 
 
 
 
 
 6382100 
 
 Column 9, Table I., shows the work spent in exciting the 
 electro-magnets . 
 
RESULTS OBTAINED. 
 ELECTRICAL WORK FOR EXCITING. 
 
 117 
 
 
 Difference of 
 Potential. 
 
 Quantity of 
 Electricity. 
 
 Work. 
 
 4 January . 
 
 82-21 
 
 48700 
 
 408400 
 
 5 ,, 
 
 01-08 
 
 72800 
 
 676-100 
 
 6 
 
 Q2-QI 
 
 62900 
 
 ?g6ioo 
 
 7 t> 
 
 92*06 
 
 21600 
 
 K>7 
 2O28OO 
 
 
 
 
 I88360O 
 
 Column 10 shows the value of the electrical work T" r 
 in the armature calculated for each day, by multiplying 
 the resistance of the armature, 0*27 ohm, by the square of 
 the total intensity observed in the galvanometer, and 
 multiplied by the number of seconds. 
 
 Resistance of 
 the Ring. 
 
 Strength of 
 Current. 
 
 Number of 
 Seconds. 
 
 Electrical Work in 
 the Armature. 
 
 0*27 
 0-27 
 
 0*27 
 0-27 
 
 | 13-29 
 10-78 
 10.26 
 
 8'54 
 
 . 
 
 19800 
 25200 
 
 27000 
 9900 
 
 94400 
 79100 
 76800 
 19500 
 
 269800 
 
 When the sum of these different amounts of electrical 
 work has been ascertained, and when to this is added the 
 work of transmission, , obtained by direct measurement, we 
 find that between this sum and the work T read off from 
 the dynamometer, there is only a small difference of about 
 2 per cent. 
 
 The Electromotive Force and the Resistance of the 
 Battery. The electromotive force of the battery is given 
 directly by the electrometer, for open circuit. Let E be 
 this value, and e the readings of the electrometer, when 
 the circuit is closed ; let R be the resistance of the bat- 
 tery, and F the intensity of the current, then eE RF 
 according as the battery is being charged or discharged. 
 
n8 
 
 ELECTRICAL STORAGE. 
 
 As E, e and F are known for the same moment of time, 
 jR, the total resistance can be easily found. 
 
 During the charging, J varied between 72 to 75-8 volts, 
 that is, between 2'057 and 2*165 for each element ; the 
 mean of e was a little below 90 volts, and the mean in- 
 tensity of the current was 8 '55 amperes. 
 
 During the discharge E went back from 75 '6 to 72 volts ; 
 e sank to about 60 volts, with a current of 16' 16 amperes. 
 
 During the charging, the resistance of each element 
 varied between 0-023 and 0-075 ohm, and between 0-006 
 and 0-040 ohm, during the discharge ; at the commence- 
 ment of the discharge, the change in direction of the 
 current suddenly caused this resistance to sink from 0*075 
 to 0-006 ohm. 
 
 
 Electromotive Force of the 
 Open Battery Circuit. 
 
 Resistance of 
 Battery. 
 
 At com- ' 
 mencement. 
 
 At end. 
 
 At com- 
 mencement. 
 
 At end. 
 
 4 January 
 
 5 
 6 
 
 7 
 
 72*00 
 73-10 
 72*10 
 74*5 
 
 75' 10 
 75-60 
 
 75*50 
 75'So 
 
 0'8o 
 1-41 
 2-58 
 
 2'6l 
 
 1-28 
 2-32 
 2'6l 
 
 2-63 
 
 Duration of the Discharge. The discharge took place 
 on the 7th and 9th of January, lasting altogether ten hours 
 thirty-nine minutes. There were 1 1 Maxim lamps in the 
 circuit. The experiments were commenced with only 
 thirty elements. After six hours two new elements were 
 added, and after about two hours the three remaining 
 elements were added for only a quarter of an hour. During 
 this time the current was too strong for the normal burn- 
 ing of the lamps. 
 
 On the first day the discharge experiments were inter- 
 rupted after seven hours fifteen minutes, and they were 
 
RESULTS OBTAINED. 
 
 119 
 
 taken up again only the day but one following. After the 
 new discharge had lasted three hours and twenty minutes, 
 the battery was in its original condition. 
 
 Electrical Measurements. The data referring to the 
 total amount of electricity given out were the following : 
 
 
 Mean Intensity. 
 
 Seconds. 
 
 Coulombs. 
 
 7 January . . , 
 
 16-128 
 
 26340 
 
 424800 
 
 9 ,, 
 
 16-235 
 
 I200O 
 
 194800 
 
 
 
 
 619600 
 
 The condition of the battery will be seen from the 
 following numbers : 
 
 
 Electromotive Force in 
 Volts of the Battery, con- 
 sisting of 33 Elements 
 on Open Circuit. 
 
 Resistance of the Battery 
 in Ohms. 
 
 At com- 
 mencement. 
 
 At end. 
 
 At com- 
 mencement. 
 
 At end. 
 
 7 January 
 9 
 
 75'o j 
 72-50 
 
 72'00 
 
 0'2I 
 0'26 
 
 ' 2 5 
 1-41 
 
 Resistance of the Lamps. If by r we denote the 
 resistance of the external circuit during the discharge, 
 we obtain e = E R F=r F, from which expression, the 
 value of r can easily be found ; for the value of e and F 
 can be ascertained at each moment, by observation. 
 
 Photometric Determination. With regard to the 
 expenditure of work per second per Carcel-burner (7*4 
 candle power), it is affirmed in the article in " La Lumiere 
 Electrique" from which these data are taken, that this 
 work has a value of 8 kgrs.-mm. This, however, 
 does not agree with the statement that on an average 
 each Maxim lamp represented an illuminating power of 
 1-40 Carcels (10-36 candles). 
 
120 ELECTRICAL STORAGE. 
 
 Taking this statement as a basis, we obtain, if the 
 average intensity of light during ten hours thirty-five 
 minutes is 1*40 Carcel-burners, a value equal to that of 
 163*9 Carcel-burners power during one hour. 
 
 Now, from Table II. we see, that as the whole of the 
 electrical work done by the battery was equal to 3,809,000 
 kgrs.-mm., each Carcel power per hour cost 3 8 9 ? 
 ( = 23,229) kgrs,-mm. per hour, or 6*4 kgrs.-mm.per second. 
 
 Conclusions. From a comparison of the data given 
 in the foregoing tables, we immediately perceive that of 
 the quantity of electricity equal to 694,500 coulombs, 
 stored in the battery, 619,600 coulombs were returned 
 during the discharge. Accordingly, there was a loss of 
 10*8 per cent. only. 
 
 With regard to the work expended and returned, 
 Table I. shows that the mechanical work spent corre- 
 sponds to 9,570,000 kgrs.-mm. ; of this only 6,382,000 
 kgrs.-mm. were stored ; and 3,809,000 kgrs.-mm. of 
 this store could again be used during the discharge ; 
 that is, -f|fS ( = 0-40) of the whole work expended, and 
 ttimjTHy (=0-60) of the work stored. 
 
 The final result of the experiments can accordingly be 
 stated thus : 
 
 The charging of the battery required the expenditure 
 of l*558-horse power of mechanical work during a period 
 of 22 hours 45 minutes ( = 1,365 minutes), and this 
 corresponds to an expenditure of work of one-horse 
 power during 1*558 x 1,365 = 2,126 minutes =35 hours 
 26 minutes ; 44 per cent, of this work was lost through 
 passive resistance and in the work of exciting the 
 generator, and only -jHrrij&C- ( = 66 per cent.) was really 
 employed in the charging of the battery. 
 
 Of the 6,382,000 kgrs.-mm., however, which were stored 
 
5 WAN, SELLON-VOLCKMAR ACCUMULATORS. 121 
 
 in the battery, only 60 per cent, were effective in the 
 external circuit during the discharge. 
 
 Accordingly, in employing the Faure battery to supply 
 the electric lamps, instead of directly using the dynamo- 
 electric generator, 40 per cent, of the work given out by the 
 generator was lost. We thus see that the secondary battery 
 is by no means an economical apparatus, and that the con- 
 venience offered by its use has, according to these results, 
 to be paid for pretty dearly. Nevertheless, in making 
 the external circuit independent of the electric generator, 
 and the generator independent of the electric circuit, the 
 secondary batteries render invaluable service ; and apart 
 from the fact that doubtless in time the construction of 
 these batteries will be so improved that a much smaller 
 loss of work will accompany their employment, they are 
 even now of great value in practice in those cases where 
 the working power, and consequently the production of 
 the electric current is cheap. 
 
 A very great improvement in storage batteries is due 
 to Mr. Swan, and to Messrs, Sellon and Volckmar. One 
 of the great defects of the Faure accumulator is the 
 interposition of the felt ; and in fact any porous separator 
 by adding to the internal resistance of the battery more 
 than proportionally reduces the economy. In practice 
 also, the lead-oxide became detached from the plates, and 
 fell to the bottom of the parchment paper bags or covers, 
 causing these to bulge out into contact with the bag or 
 cover on the opposed plate ; a short circuit was there- 
 from frequently established in a cell. Messrs. Swan, 
 Sellon and Volckmar introduced a grid, or perforated 
 plate, into the holes of which the red lead paste is forced 
 and there held. The plates are then separated by rubber 
 stops, and immersed in the usual solution of dilute acid. 
 
122 ELECTRICAL STORAGE. 
 
 These plates are about of an inch in thickness and 
 10 inches square. Fourteen pairs give 1^ electrical horse- 
 power hours in actual use. A great advantage has accrued 
 from thus dispensing with the felt and with the danger of 
 detachment of the lead -oxide from the plate ; whilst in 
 consequence of expansion during the formation of per- 
 oxide, the red lead paste becomes very firmly gripped by 
 the surrounding grid-work. Mr. Sellon has, however, 
 several patents for bevelling the edges of the holes so as 
 to hold in the paste, an improvement that it does not 
 appear necessary to put into practice. 
 
 Having made, at the Stevens Institute of Technology, 
 tests and measurements of the Sellon -Volckmar electrical 
 storage batteries sent to him, and manufactured by the 
 Electrical Power Storage Company, Professor Henry 
 Morton found the following results in reference to their 
 capacity to store and retain energy, afterwards delivered 
 by them as electric current. 
 
 The cells were of the pattern called " one-horse power " 
 cells, because they contain, when fully charged, an amount 
 of energy equal to 1,980,000 foot-pounds, or one-horse 
 power for one hour. 
 
 These cells were externally rectangular wooden boxes, 
 12^ inches high, 11-J inches wide, and 5f inches thick. 
 
 Two of them, side by side, as they would stand when 
 in use, occupied about one cubic foot of space. 
 
 Each cell contained sixteen plates, whose united weight 
 was 48 Ibs., and with the lead-lined box and liquid, the 
 entire weight of the cell, when in use, was 79^ Ibs. 
 
 One of these cells fully charged gave, as found by 
 careful experiment, a current of 32*5 amperes at the 
 beginning, and 31-2 amperes at the close of a continuous 
 discharge for nine hours. 
 
SELLON-VOLCKMAR ACCUMULATOR. 123 
 
 This amounts to 286*5 ampere-hours of current, and if 
 even short interruptions or periods of repose occurred in 
 the use of the current, a larger total amount could b* 
 obtained. 
 
 An Edison incandescent lamp of high resistance, giving 
 a light of 16 candles, requires a current of '73 of an 
 ampere to supply it. Such a current, therefore, as these 
 batteries gave for nine hours at a time sufficed for 44 such 
 lamps. 
 
 To secure sufficient electromotive force or propelling 
 power to overcome the resistance of these lamps would, 
 however, require about 50 of such cells. So that a battery 
 of 50 of these cells connected in series, would operate 
 44 lamps for nine hours, or for even a longer time in the 
 aggregate, if the use were interrupted, as it would be in 
 practice. 
 
 If fewer lamps were used with the same battery they 
 would be operated for a proportionately longer time. 
 
 Thus, 11 lamps would be supplied by a 50 cell battery 
 for thirty-six hours of continuous action ; or, as lights 
 are commonly used in private houses on the average for 
 five hours each nightj such a battery once charged, would 
 operate 11 lamps for a week. 
 
 To express the relation between weight of battery and 
 power of maintaining a light, we may therefore say that 
 for each lamp operated for nine hours 1-f cells of battery 
 would be required, or a weight of about 90 Ibs. of battery. 
 This would be for each hour of burning each lamp, 10 Ib. 
 of battery. 
 
 This makes a very simple rule for calculating the 
 weight of battery required for any number of lamps for 
 any time. 
 
 Thus, suppose we wish a battery to operate 25 lamps 
 
124 ELECTRICAL STORAGE. 
 
 for five hours each night, the battery being recharged 
 during the day. We have 25 x 5 x 10=1,250 Ibs. as the 
 weight of battery required. Comparing the efficiency of 
 this storage battery with that of other similar arrange- 
 ments, such as the Faure battery, measured and reported 
 upon by M. Tresca, of the Conservatoire des Arts et 
 Metiers, it shows a marked superiority. 
 
 Thus, in M. Tresca's experiments, a cell weighing 
 95 lb., yielded a current representing 793,791 foot- 
 pounds of energy where this battery yielded 1,826,168 
 foot-pounds, and only weighed 80 lb. 
 
 Even the experiments made by Professors Ayrton and 
 Perry, on other Faure accumulators, though the con- 
 ditions were rendered as favourable as possible, by dis- 
 tributing the discharge over three periods of six hours 
 each on three successive days, do not show a much better 
 result. In this case the weight of the battery-plates only 
 is given, and that is eighty-one pounds. Reducing the 
 results proportionally for batteries whose plates weigh 
 forty-eight pounds, Professor Morton has found that by 
 the experiments of Professors Ayrton and Perry, each 
 cell of this weight should give 853,333 foot-pounds of 
 energy. 
 
 This, again, is less than half the amount of energy 
 recently repeatedly obtained. 
 
 Passing .next to the efficiency of the batteries, as re- 
 gards their delivery of nearly the same current as was 
 used to charge them, Professor Morton found that the 
 loss in this relation is less than ten per cent. In other 
 words, he has obtained from these batteries ninety to ninety- 
 one per cent, of the current used to charge them. This 
 far exceeds the results obtained by M. Tresca, or by Pro- 
 fessors Ayrton and Perry with the Faure batteries. 
 
SELLON-VOLCKMAR ACCUMULATOR. 125 
 
 Tresca reports that he recovered only sixty per cent, 
 of the current used to charge the battery, and Ayrton and 
 Perry found the loss in charging and discharging to be 
 " not greater than eighteen per cent.," and in some cases 
 of very slow discharge, to be only ten per cent. 
 
 Professor Morton found the loss to be less than ten per 
 cent., with a rapid discharge of thirty-two amperes. 
 
 Lastly comes the very important question as to the re- 
 tention of charge during a long time. To test this, three 
 cells were charged, and locked in a closet, where they 
 remained fifteen days, when at the rate of thirty-two 
 amperes, there were obtained 266*7 ampere-hours of 
 current. 
 
 Comparing this with the 286*5 ampere-hours of cur- 
 rent obtained from the other cells discharged soon after 
 charging them, shows a loss of seven per cent, caused by 
 standing for sixteen days. 
 
 The above measurements and comparisons show that 
 this storage battery has attained a degree of efficiency 
 which will render it applicable to a number of uses. 
 
 Thus, Professor Morton suggests that on steam-boats, 
 by the use of such storage batteries, the irregular and 
 occasionally interrupted motion of the main engine might 
 operate a relatively small dynamo-electric machine, so as 
 to charge the batteries during the entire twenty-four 
 hours, and the current from these batteries would then 
 supply light, with perfect steadiness, during the relatively 
 brief time in which it is required. In this way, the cost 
 of supplying and running a special and large engine, 
 which would be needed for operating the same lights 
 directly without the storage battery, would be avoided, 
 and also the necessity for extreme steadiness in running 
 the dynamo, and all risk of extinction of the lights from a 
 
ia6 ELECTRICAL STORAGE. 
 
 momentary interruption of motion in any part of the 
 machinery would be removed, as the battery would secure 
 an absolutely steady and continuous supply of current, no 
 matter how little regular might be the action of the 
 engine or dynamo-electric machine. 
 
 Again, in larger buildings, the engine used to operate 
 the elevator or lift, or to do any other work, if of suf- 
 ficient power, could charge the storage battery without 
 interrupting its regular work, and thus supply the light 
 needed at a minimum cost for special machinery and 
 skilled supervision. 
 
 In private houses, where the running of a large engine 
 with extreme smoothness and absolute certainty during 
 the hours when light is needed, would be out of the ques- 
 tion, a small engine, operated at convenient intervals, and 
 with no need of regularity or of fixed hours, would accom- 
 plish all that was required, if a storage battery was em- 
 ployed with it. 
 
 Mr. C. F. Brush, the inventor of the well-known system 
 of arc lighting bearing his name, has carefully investi- 
 gated the chemical and mechanical action involved in 
 the process of formation, and has arrived at a satisfactory 
 explanation of the results produced. 
 
 The formation of peroxide of lead on one of the plates 
 continues indefinitely as long as the exciting current is 
 maintained, becoming constantly slower as the metallic 
 surface acquires an increasing protection against further 
 action by the constantly increasing thickness of the coat- 
 ing of peroxide. 
 
 Peroxide of lead being a good conductor of electricity, 
 the coating becomes a part of the conducting-plate or 
 element of the battery, and free oxygen is evolved at the 
 surface of the coating. Now, if the exciting current be 
 
BRUSH'S ACCUMULATOR. 127 
 
 stopped, " local action," somewhat similar to that in gal- 
 vanic batteries, and electrical in its nature, commences 
 between the peroxide of lead and the backing or support 
 of metallic lead with which it is in contact. By this 
 " local action," the peroxide of lead is gradually reduced 
 to a lower state of oxidation, while more of the metallic 
 lead of the plate is oxidised by the oxygen thus made 
 available. 
 
 The fresh lead thus oxidised doubtless acquires the same 
 condition of oxidation that the original peroxide finally 
 assumes. But the peroxide is never by this action re- 
 duced to the state of protoxide, as is proven by the colour 
 of the coating, and the non-action on it of the ever pre- 
 sent sulphuric acid. 
 
 When peroxide of lead is thus reduced to a state of 
 lower oxidation, it becomes useless for the development of 
 a secondary current until freshly charged or re-oxidized. 
 Thus is explained, so far as the oxygen .plate is concerned, 
 the cause of the gradual loss of charge observed in lead 
 secondary batteries. 
 
 Further, since the conducting power of peroxide of lead 
 rapidly decreases as its oxygen is removed, the reason of 
 the high electrical resistance of the oxidized plates after 
 long standing uncharged is also explained. When such a 
 plate, that is, one having gradually lost its original charge 
 by local action, is re-charged by an electrical current as at 
 first, it will hold a larger charge than before ; because all 
 of the lower oxide of lead is now raised to the condition of 
 peroxide, and thus more of the latter is present than at 
 the previous time of charging. This explains why the 
 oxygen plate of secondary batteries constantly increases in 
 capacity, even though the exciting current be applied at 
 long intervals. 
 
128 ELECTRICAL STORAGE. 
 
 Let us now consider what takes place at the opposite 
 side of the secondary battery, that is the action on the 
 lead plate where the hydrogen appears. Here the hydro- 
 gen is absorbed at the surface of the plate, being simply 
 occluded, or more probably forming a definite but feeble 
 chemical combination with the lead. If such a combina- 
 tion exists, it is a nearly or" quite stable one, so far as 
 " local action " is concerned, for experience shows that the 
 capacity of the plate for the reception of hydrogen in- 
 creases very slowly, if at all, when the plate is left charged 
 a long time, but without the action of the exciting cur- 
 rent ; even the continued action of the exciting current 
 increases the capacity of the hydrogen plate Very slowly 
 indeed, as compared with the improvement of the oxygen 
 plate during the same time. 
 
 The capacity of the hydrogen plate never becotrtes at all 
 considerable when it is subjected to the above action 
 alone. Hence, in practice, the oxygen plate soon acquires 
 much greater capacity than the hydrogen plate ; but this 
 is of no advantage, since its usefulness is limited by that 
 of the hydrogen plate. But if now the charge of the two 
 plates be reversed, by changing the direction of the ex- 
 citing current, the former" hydrogen plate will absorb 
 oxygen freely as did the other" plate at first, while the 
 former oxygen plate will have its coating of oxide of lead 
 reduced to the metallic state of the nascent hydrogen 
 evolved upon it, and will thus be left with at corresponding 
 coating of porous lead. This porous metal is now in a 
 condition to absorb and retain an amount of available 
 hydrogen, about equivalent to the available oxygen which 
 it before held. 
 
 Thus it will be seen that the simple act of reversing the 
 charge of the two plates increases the capacity of the 
 
BRUSH'S ACCUMULATOR. 129 
 
 apparatus up to a point attained only by the oxygen plate 
 before the reversal. Again, what is now the oxygen plate 
 continues to improve, as in the first instance, while the 
 hydrogen plate remains nearly or quite stationary in this 
 respect. 
 
 Hence, after a time, a further increase of capacity in the 
 apparatus may be affected by another reversal. Thus is 
 explained the reason for the many reversals of charge 
 customary in " forming " the plates. 
 
 When a previously excited secondary battery is dis- 
 charged, the peroxide of lead is reduced to a state of lower 
 oxidation, as already explained in connection with the 
 spontaneous loss of charge. Thus, what was at first a good 
 conducting coat on the metal, is now reduced to a poor 
 conductor, as previously explained, while at the same time 
 pure water is formed within the mass of lead oxide by the 
 combination of hydrogen with a portion of the oxygen of 
 the peroxide of lead ; and, since pure water is a very poor 
 conductor of electricity, a further barrier to the passage of 
 current between the sulphuric acid solution and the 
 metallic plate within the envelope of lead-oxide is raised. 
 
 These two causes (lower oxidation and presence of pure 
 water) account, so far as the oxygen plate is concerned, for 
 the increase of resistance in secondary batteries during 
 their discharge, and especially toward the end of the pro- 
 cess. 
 
 In the case of the hydrogen plate, pure water is also 
 formed by the union of oxygen with its hydrogen, where- 
 by the necessary liquid conductor within the porous metal 
 has its resistance largely increased. 
 
 The cause of the gradual spontaneous loss of charge, in 
 case of the hydrogen plate of secondary batteries, is not 
 the same as that already described in connection with the 
 
 K 
 
1 30 ELECTRICAL STORAGE. 
 
 oxygen plate. The hydrogen in this case seems to be 
 gradually dissolved and carried away from its plate by the 
 dilute sulphuric acid, which then discharges it gradually 
 into the atmosphere. 
 
 If, in charging a hydrogen plate, a chemical component 
 of lead and hydrogen is formed, this compound would ap- 
 pear to be gradually decomposed in the presence of the 
 acid water, giving up its gas to the latter. 
 
 There are certain evils incident to the above-described 
 process of " forming " the lead plates of secondary bat- 
 teries, which attendant evils prevent the attainment of the 
 best results and limit the ultimate capacity of the appa- 
 ratus to a comparatively small field of usefulness. 
 
 The coating of peroxide of lead which is formed on one 
 of the plates, necessarily occupies more space than did the 
 metallic lead which it contains. The shell of oxide must 
 then expand in forming. To accommodate this expansion, 
 which evidently occurs in all directions, the structure of 
 the deposit must be more or less broken up at numerous 
 points, or else the lead plate itself must expand. The 
 occurrence of the latter action may be readily observed 
 when the lead sheet is thin. When, now, the direction of 
 charge is reversed, by which operation the oxide of lead is 
 reduced to the metallic state, the previously-expanded mass 
 shrinks. Both the expansion and subsequent shrinkage 
 may be illustrated by treating one side only of a sheet of 
 lead, the other side being protected from action by varnish, 
 or otherwise. When such a plate is oxidized, the exposed 
 side becomes convex ; when the oxide is subsequently re- 
 duced, this side becomes concave. 
 
 During the process of reduction the shrinkage does not 
 occur in all parts of the mass at once, as the reduction is 
 not simultaneous in all parts at once, but is progressive. 
 
BRUSH'S ACCUMULATOR. 131 
 
 The converse of this is true when the reduced lead is again 
 oxidized. Hence there is a disintegrating action in the 
 changing mass itself, as well as between it and the solid 
 plate behind it. This alternate expansion and contraction 
 of the active and valuable portion of the lead plate does 
 not lead to serious disturbance when it is allowed to 
 occur only once, or a very small number of times. But 
 if these changes are many times repeated, the coating 
 peels off from the lead plates to a considerable extent, 
 and thus becomes useless. This evil is especially notice- 
 able in the case of thick deposits. 
 
 Again, every time the deposit of oxide of lead is re- 
 duced, a notable quantity of sulphate of lead is formed 
 within the mass. This inert and useless substance, when 
 allowed thus to form, soon exercises a very deleterious in- 
 fluence, wasting in its formation the otherwise available 
 oxide of lead, stopping the pores of the essentially porous 
 mass, and tending to disintegrate the latter by occupying 
 a much larger space than the oxide of lead from which it 
 is formed. 
 
 The reduction of the oxide of lead is also attended with 
 danger of separating the mass from its supporting lead 
 plate, by the liberation of gas between the two, especially 
 when the reducing current is of sufficient strength to 
 effect the change at all rapidly. 
 
 The frequent reversal of charge is also expensive, in 
 that much energy of charging current is wasted at each 
 operation. 
 
 Further, it will be seen that the oxygen, which is the 
 active though slow agent in improving the plates, acts 
 not on both plates simultaneously, but on only one at a 
 time. 
 
 The method or process of " forming " the plates or 
 
132 ELECTRICAL STORAGE. 
 
 elements of secondary batteries, which has been adopted 
 by Mr. Brush, has been so adopted with a view to avoid 
 or eliminate these evils enumerated almost entirely. 
 
 The process consists in charging the plates which are 
 ultimately to constitute the battery in such a manner 
 that a coating of peroxide of lead of sufficient thickness 
 is formed on both of them ; these plates are then asso- 
 ciated together in the usual manner, and an electric 
 current passed through the apparatus in the manner 
 customary in charging ; one of the plates remains un- 
 changed, and constitutes the oxygen element of the 
 battery, while the other has its charge reversed, and now 
 constitutes the hydrogen element of the battery. 
 
 The plates, while acquiring their coating of peroxide of 
 lead, may, for this purpose, be charged continuously ; or, 
 equally effective and more convenient, they may be 
 charged at intervals only, short at first, which may be in- 
 creased in length as the process progresses, thus allowing 
 the local action between the peroxide of lead already 
 formed and the metallic lead to continue the oxidizing 
 process during the time the changing current is not 
 acting. 
 
 Several months of continuous or intermittent charging 
 is required when ordinary sheet lead alone is employed 
 for the plates, in order to produce a satisfactory coating 
 of peroxide of lead. 
 
 This process of " forming " the plates of secondary 
 batteries, is applicable not only to the flat or plain plates 
 ordinarily used, but equally so to corrugated and to 
 ribbed, honeycombed, perforated, slotted, or otherwise 
 fashioned plates, also to plates coated or filled with 
 spongy or porous, or reduced lead. 
 
 Another of Mr. Brush's improvements consists in pro- 
 
BRUSH'S ACCUMULATOR. 133 
 
 viding the plates with a suitably thick coating of elec- 
 trically-deposited coherent metal previous to the process 
 of " forming." 
 
 In coating the plates, the coherent porous lead is 
 deposited by electrical action as in any ordinary process 
 of electro-plating ; the plates to be coated first being 
 made chemically clean, and the plating solution consist- 
 ing of oxide of lead dissolved in a solution of a caustic 
 alkali, or of an equivalent solution of lead. Any solution 
 of lead may be used, provided it is such as to produce a 
 coherent deposit of metal, and not a spongy or non- 
 coherent deposit. The latter kind of deposit is always 
 produced when the sulphate, chloride, acetate, nitrate, 
 and some other salts of lead are reduced electrically, and 
 possesses properties different from those of the coherent 
 form of metal; being vastly inferior to the latter in 
 efficiency as a material for secondary batteries. 
 
 The coherent metal may be deposited with greater or 
 less rapidity as may be found most expedient or desirable 
 in practice, the character of the deposit varying to some 
 extent according to the rate and other circumstances of 
 its formation. 
 
 Corrugated or perforated plates are well adapted to 
 receive and retain the coherent coating, and the corruga- 
 tions or other spaces or cavities in the plates may be 
 entirely filled with the deposit if desirable. When such 
 plates are treated to a deposit of coherent lead in the 
 manner customary, the interior of the cells or cavities 
 or corrugations will receive a less heavy deposit than the 
 more exposed portions. This difficulty is avoided by 
 adopting the following method of working : 
 
 The plate being first thoroughly cleaned, has the 
 grooves or cavities on one of its sides filled with pro- 
 
134 ELECTRICAL STORAGE. 
 
 toxide or other suitable compound of lead, either dry or 
 made into a paste with water or saline solution. 
 
 The plate is then placed horizontally, prepared side up, 
 in a suitable vessel containing a solution of caustic soda 
 or potassa, or other alkali, when protoxide of lead is used 
 in the grooves. 
 
 In the same solution, but not touching the plate, is 
 suspended or placed a lead or equivalent plate. Current 
 is then passed through the apparatus in the proper 
 direction until the lead-oxide in the grooves or corruga- 
 tions is exhausted, and its metal deposited on the sides 
 and bottom of the grooves. More lead-oxide is added if 
 it is desired to increase the deposits. 
 
 Plates of other metals than lead might be employed to 
 receive and support the deposited lead ; thus, if gold or 
 platinum were used the oxygen element of the battery, if 
 fully peroxidized, could not lose its charge by spontaneous 
 '" local action." 
 
 When lead plates coated with deposited coherent lead 
 are associated together in a secondary battery and charged, 
 the reduced metal is peroxidized much faster than 
 ordinary cast or rolled lead, but not nearly so fast as 
 spongy or non-coherent lead ; while the coherent lead of 
 the other plate absorbs hydrogen more freely than cast or 
 rolled lead, but not nearly so fast as the other plate of the 
 battery absorbs available oxygen. 
 
 It becomes advisable, then, to resort to a "forming 
 process." 
 
 The plates of secondary batteries can be provided with 
 a suitably thick coating of porous metal, reduced from 
 the oxide, through the agency of a suitable reducing gas, 
 and at a temperature insufficient to cause the reduced 
 metal to assume a compact or fluid condition through fusion. 
 
APPLICATIONS OF ACCUMULATORS. 135 
 
 Either of the gases, carbonic oxide or hydrogen, will do 
 this readily. The plates having been made chemically 
 clean, are placed in a horizontal position and covered to 
 a sufficient depth with lead oxide. This is applied pre- 
 ferably in the form of a paste, with nitric acid, which 
 partially dissolves the oxide> and when evaporated leaves 
 the latter in a coherent compact condition. 
 
 After the plates are coated with oxide, they are packed, 
 sufficiently separated from each other, in a chamber, 
 where they are raised to a high temperature, and exposed 
 for a sufficient length of time to the action of a reducing 
 gas. 
 
 Mr. Brush also proposes to construct the plates of 
 metallic lead in a pulverised or finely-divided state, and 
 to allow the surface of the lead particles to become 
 oxidized, either by exposure to the air, or by any artificial 
 oxidizing process. 
 
 Or, instead of employing the superficially-oxidized 
 particles of lead as above specified, to take particles of 
 metallic lead and oxide of lead and effect a thorough 
 mechanical mixture of the two. 
 
 In either of the above cases, lead and lead oxide are 
 thoroughly intermingled, and, under heavy pressure, the 
 particles are consolidated into a compact mass. 
 
 The mass thus formed consists of metallic lead having 
 minute veins of oxide of lead everywhere ramifying and 
 extending through it ; and these veins of lead oxide 
 within and throughout the mass greatly facilitate the 
 penetration of the electrical action in " forming " the 
 plates for operative use in secondary batteries. 
 
 Applications of Secondary Batteries. The special 
 applications of secondary batteries can be classed under 
 two headings, according as we wish to use the battery 
 
136 ELECTRICAL STORAGE. 
 
 as a fixed electrical reservoir, or as a portable vessel 
 charged with electrical energy. 
 
 As a fixed reservoir, these batteries can be used, even 
 in their present incomplete condition, in all cases where a 
 uniform, continuous current is absolutely necessary for 
 the work to be done ; and the loss of work will then be 
 counterbalanced by the steady results obtained, for the 
 secondary batteries are undeniably excellent regulators. 
 If, for instance, instead of supplying a circuit directly 
 from an electric generator, we do so aided by a secondary 
 battery connected with it, then, however irregularly the 
 generator may work, there will always be a uniform cur- 
 rent in the circuit ; and, similarly, no variations in the 
 circuit will, in this case, affect the working of the gene- 
 rator. 
 
 If, however, it is desired to make use of the secondary 
 batteries, in their present form, as portable vessels, 
 charged with electricity, it will only be possible to em- 
 ploy them with real advantage when a comparatively 
 small number of elements have to be transported. The 
 great weight of the batteries, which for the most part 
 consist of lead, is a considerable obstacle to this use ; 
 for, in many cases, the cost of carriage will annul the ad- 
 vantages offered by the battery. 
 
 If the advertisements of the " Societe la Force et la 
 Lumiere," in Paris, could be trusted, or even if Reynier's 
 statements had proved correct, we should be led to sup- 
 pose that the results obtained with the Faure batteries 
 would be but little influenced by the weight of the appa- 
 ratus ; and, two years ago, some persons went so far as to 
 assert that it would pay to send batteries charged with 
 electricity to the houses of the inhabitants of a town. 
 After use, the exhausted batteries were to be replaced by 
 
APPLICATIONS CRITICISED. 137 
 
 those freshly charged, somewhat in the way that is done 
 with bottles of beverages. 
 
 However, on a little calm reflection, and by making the 
 data obtained in the experiments given above the basis 
 of decision, it will be seen that lead-batteries can find 
 only a limited application as portable accumulators. 
 
 According to Eeynier's statements, a Faure's element, 
 weighing 8 kg., gives out work at the rate of 4-4 kgrs. m. 
 per second ; that is, 0-55 kgrs. m. to each kg. of weight ; 
 the data obtained by the French committee, however, 
 showed that the thirty-two elements, of which each 
 weighed 43-7 kg., and whose total weight accordingly 
 came to 1398-4 kg., stored 6,382,000 kg. m. of work ; 
 and during the discharge, which lasted ten hours thirty- 
 nine minutes, they gave out 3,809,000 kg. m. of work. 
 So that, during this time, ^W 00 = 2,725 kg. m. cor- 
 responded to each kilogram of weight ; and -^W^ 
 0-071 kilo, to one kilogrammetre per second; that is, 
 the work given out per kilogram of the battery, only 
 constitutes an eighth (7'7th) part of the value stated by 
 Reynier. 
 
 If it were intended, for instance, to employ a Faure 
 battery for the purpose of setting an electric railway in 
 motion, and if we assume that the elements are to work 
 during ten hours thirty-nine minutes (this is, perhaps, 
 rather a long period, considering the object, but we shall 
 retain it in order to make use of the data given above), 
 it is easy to determine the efficiency of the battery per 
 kilogram of weight. We will assume that the speed 
 of the train is to be ten kilometres an hour (equal to 
 three metres per second), and that the coefficient of 
 friction is that usually taken in the case of railways on 
 which the rails are good, and are kept clean namely, -5^. 
 
138 ELECTRICAL STORAGE. 
 
 In this case, a force of T f-^ kg. m. = O012 kg. m. 
 would be necessary to make one kilogram move with 
 a velocity of three metres per second. Now, as each 
 kilogram of the battery, as we have seen, is able to do 
 0-07 kg. m. of work, it will be able to pull five kilos., 
 besides its own weight. 
 
 This rather favourable result, however, only refers to 
 the case when the secondary battery is used to move car- 
 riages that run on smooth, clean fails. If the battery is 
 to be used for tramway carriages, which have to run on 
 rails in whose grooves dirt accumulates, and where ac- 
 cordingly the friction is comparatively great, the co- 
 efficient of friction is much more unfavourable, and it can 
 be denoted by about T -J-Q. 
 
 In this case, therefore, the moving of a kilogram would 
 require O03 kgr. m. to be exerted, if the carriage is to 
 travel ten kilometres per hour ; accordingly a battery 
 giving out 0-07 kilogrammetres of work per kilo, would 
 not be able to set double its weight in motion. 
 
 It is evident, therefore, as constructed at present, 
 secondary batteries offer comparatively few advantages 
 as portable accumulators ; and if it is desired to em- 
 ploy such batteries in carriages, it will be better to limit 
 the number of elements as much as possible, and to re- 
 charge them more frequently, instead of carrying a large 
 number. 
 
 When the secondary batteries are to be employed 
 in the lighting of railway carriages, the axle of a car- 
 riage can be connected with a dynamo. During the 
 journey, the secondary battery will be charged by the 
 current, and from it the lamps will be supplied. The 
 latter will continue to burn steadily, even when the train 
 stops, being only indirectly connected with the electric 
 
APPLICATIONS. 139 
 
 generator. In this way many applications of secondary 
 batteries will be found, and it will always be possible to 
 make good use of them, if it is not forgotten that the 
 weight of the battery has to be kept as low as possible 
 when there is any question of moving it. 
 
CHAPTEE VI. 
 
 THE PHYSICAL LAWS BEARING ON THE CONSTRUCTION OF 
 ELECTRIC MACHINES; AND THEIR APPLICATION IN 
 
 PRACTICE. 
 
 IN the previous chapters we gave to some extent a sum- 
 mary of what has been done in electro-technology as 
 relates to magneto and dynamo-electric machines and 
 their auxiliary apparatus ; and the reader will have 
 gathered that the results achieved are extremely en- 
 couraging. 
 
 Nevertheless the construction of electro-generators is 
 still in its infancy, and many improvements will have to 
 be carried out before the manufacture will have reached 
 that stage it must undoubtedly attain. Accordingly, in a 
 book such as this, intended for the use of technologists, it 
 will be necessary to discuss those theoretical principles on 
 which depends the efficient construction of an electric 
 generator. 
 
 It may be objected that as a rule the theoretical 
 electrician considers cases which only occur in practice 
 with great modifications. Nevertheless the conclusions of 
 the physicist can be easily modified for practical application 
 if the cases on which they are based are accurately com- 
 pared with those under consideration, and when the 
 differences are accurately taken into account. It ought 
 not to be forgotten that, although theory does not always 
 put means into the hands of the practical man to carry 
 
AS TO MAXIMUM EFFECT. 141 
 
 out his problems, it, at any rate, points out the way by 
 which these means can be found, and thus saves the 
 constructor much time and trouble, which he would 
 otherwise often spend unsuccessfully in trying to find an 
 answer empyrically to the questions that come before him. 
 Consequently, before we pass to the various details of 
 construction we shall try to develop briefly the principal 
 physical laws that affect the construction of an electro- 
 generator. 
 
 These laws specially bear on the following points : 
 
 (1). The relation of the electromotive force of a 
 generator to the work to be done. 
 
 (2). The ratio of the internal resistance of a generator 
 to the resistance in the external circuit. 
 
 (3). The interdependence of the electromotive force 
 and quantity of current : 
 
 (a) on the number of convolutions in the armature ; 
 (6) on the rate of rotation of the armature ; 
 (c) on the intensity of the magnetic field in which 
 the armature moves. 
 
 To commence by considering the first point, and to try 
 to get an answer, by theoretical methods, to the question : 
 
 I. What must be the ratio of the electromotive force of 
 a generator to the external work done, in order to obtain 
 maximum effect ? 
 
 For this purpose we will assume that an electro-generator 
 is to be used for obtaining galvano-plastic deposits, and 
 that we know the resistance of the galvano-plastic bath 
 and of the generator. 
 
 Let E be electromotive force of the generator, R the 
 
 total resistance that the current has to overcome, and / 
 
 the quantity of current. Then from Ohm's law we have, 
 
 IR = E. (1) 
 
M2 CONSTRUCTIONAL LAWS. 
 
 Now, if, instead of the galvano-plastic apparatus we, for 
 the present, insert an insulated conducting wire having 
 exactly the same resistance, a quantity of heat will be 
 evolved, when the current traverses the wire, corresponding 
 to a definite amount of work , and according to Joule's 
 law this work is 
 
 7T2 
 
 L = E . I = ~. (2) 
 
 Now, when, instead of the substituted resistance, we 
 insert the galvano-plastic bath, it might be supposed from 
 a superficial consideration, that the quantity of current 
 would be the same, because the resistance had remained 
 unchanged. This however is not the case ; the quantity 
 of current diminishes, for it is partially annulled by an 
 opposing electromotive force arising in the bath during 
 the work. We will denote the new strength of current by 
 /' and putting t for the time during which we obtain ;is 
 large a quantity of electricity from the generator, as we 
 did in unit time when the corresponding resistance was 
 inserted in place of the galvano-plastic bath, we shall have 
 / = t I'. (3) 
 
 That is, in unit time, only the part of the effective 
 electrical energy is converted into real work I, that cor- 
 responds to the quantity /', whilst the remaining portion, 
 which we will call L', is distributed in the circuit as heat. 
 
 Now, because the current is proportional to the work 
 (or to the corresponding amount of heat), we obtain from 
 equation (3) 
 
 L = (L' + l)t (4) 
 
 Eliminating , in equations (3) and (4) we get 
 
 L L' + I ... 
 
 T = - 7 ,-- (5) 
 
 The reason why only part of the current is converted 
 
RELATIVE RESISTANCES. 143 
 
 into work, whilst the other part manifests itself as heat, 
 has to be sought in the existence of the opposite electro- 
 motive force which we shall call e. 
 In this case we get 
 
 77 E e Tl (E e) ,* 
 
 ~T ' ~~ET 
 
 and from equations (5) and (2) 
 
 or lR=e(E-e). (7) 
 
 Now, writing e = R i, where 
 
 i = i-r 
 
 we get from equations (7) and (1) 
 
 I = R i (I - i) = R i P 
 and as it follows from equation (1), that 
 
 i I' 
 
 then puttings and y for the quotients y and y respec- 
 tively, we get 
 
 Consequently as x and y are the roots of the quadratic 
 equation 
 
 JL * > 
 
 It becomes evident, therefore, that the ratio -y can 
 
 never be greater than -j- ; that is, when the current has 
 no other work to do, and has only to overcome the in- 
 ternal and external resistance, ^ only of the electrical 
 
I 4 4 CONSTRUCTIONAL LAWS. 
 
 energy can be converted into another form of energy (in 
 our case, into the work of chemical decomposition). 
 
 When this maximum of the conversion of electrical 
 energy into work is reached 
 
 or, the quantity of current, and the electromotive force 
 are only half as great as when the current has no other 
 work to do, the resistance being the same ; and from this 
 follows the important principle : 
 
 The efficiency of an electro-generator is greatest when 
 its electromotive force is twice as great as the opposing 
 force that arises whilst the current is doing work. 
 
 In the case we have taken, where the generator is 
 intended for galvano-plastic purposes, the electromotive 
 force of the current ought to be twice as great as the 
 opposite electromotive force generated in the galvanic 
 bath by polarization. 
 
 The same principle also holds good when the generator 
 is employed to do dynamic or magnetic work, but has to 
 be modified when the generator is intended for illuminating 
 purposes. 
 
 Although in the case of the luminous arc, Edlund 
 discovered that an electromotive force is generated by 
 the polarization of the electrodes, and acts counter to the 
 electromotive force of the generator, yet it does not 
 behave otherwise than as a resistance of the circuit. 
 Both generate radiant energy, and where the resistance 
 of the arc is great, as compared with the electromotive 
 force due to polarization, the preceding law for the 
 greatest efficiency loses its importance. 
 
 In practice we have to see that we get as much energy 
 as possible in the external circuit, and this is attained by 
 
RELATIVE RESISTANCES. 145 
 
 making the internal resistance of the generator as small 
 as possible. 
 
 In fact we have in practice to modify the theoretical law 
 thus: the electromotive force of the generator shall be always 
 greater than the opposing electromotive force that arises. 
 
 The question bearing on the second point mentioned 
 at the beginning of this chapter would be- 
 
 ll. What internal resistance is best, in order to obtain 
 the greatest efficiency with a given external resistance ? 
 
 The answer to this question can also be found by a 
 theoretical method. 
 
 We will assume that an armature has n armature-coils, 
 all having the same resistance and the same electromotive 
 force, and the question is how are we to couple up the 
 bobbins so as to make the greatest possible use of the 
 current of the generator. 
 
 For this purpose let n be the number of armature-coils, 
 e the electromotive force, and r the resistance of each. 
 The total electromotive force of the armature will accord- 
 ingly be ne, and its resistance nr, when the bobbins are 
 coupled up in series. 
 
 If the coils, however, are coupled up for quantity, or if 
 their similar poles are connected, then the electromotive 
 force of the armature will only equal that of a single 
 bobbin, namely e, but the internal resistance will be 
 
 The coils can also be arranged in groups. The elements 
 of each group can be coupled up for quantity and the 
 groups themselves for intensity. 
 
 When each group contains the same number of similar 
 elements, this mode of connection corresponds to a like 
 arrangement of a voltaic battery. 
 
 L 
 
146 CONSTRUCTIONAL LAWS. 
 
 Let x be the number of elements in a group, e the 
 
 electromotive force of each group, and its internal 
 
 X 
 
 resistance. Accordingly, we can express the electromotive 
 
 TL 
 
 force of the whole armature by - - e, and its internal 
 
 $ 
 
 . , , n r 
 resistance by x . 
 7 x x 
 
 Now, the problem is to determine x in such a way that 
 the current generated in the n armature-coils shall attain 
 its maximum in the circuit. 
 
 If R represents the resistance in the external circuit and 
 
 y the current which we obtain when we have made 
 
 x 
 
 groups out of the number of armature-coils, then from 
 Ohm's law we have the equation 
 
 n 
 
 e 
 x 
 
 nr 
 
 nxe 
 = 
 
 Hence # 2 Ry nxe + nry = and 
 
 X = 2v R \ ne - r n* e? - 
 
 - nr R 
 
 Of course as we have not to deal with imaginary values 
 we may put 
 
 in order to obtain the maximum value for y. 
 Consequently y = -|- y -^= 
 
 l/^rn nr 
 
 and x = y _, or R = ~tf' 
 
RELATIVE RESISTANCES. 147 
 
 Therefore, the maximum efficiency of an electro- 
 generator is obtained when its internal resistance is equal 
 to the resistance in the external circuit. 
 
 In practice, however, this law of the maximum theoretical 
 efficiency has to be modified. Although this is the best 
 way of obtaining the greatest amount of work with the 
 generator, yet in practice the object is (for instance, in 
 electric lighting) to obtain the largest amount of work 
 in the external circuit. This, however, would not be 
 the case if the internal resistance of the generator were 
 equal to that of the external circuit. In this case, 
 because as much of the effect is lost in the internal 
 circuit, through heating, as is gained in the external 
 circuit, only 50 per cent of the electrical energy is 
 employed in the latter. For practical purposes this is 
 far too little, and as Uppenborn has pointed out, the 
 internal resistance ought never to be greater than f of 
 the external resistance. 
 
 We now come to the question 
 
 III. In what way does the number of convolutions in the 
 armature affect the strength of current and the electro- 
 motive force of a generator ? 
 
 This question would, for instance, obtain if we had to 
 construct a magneto-electric generator, in which we had 
 ascertained the intensity of the magnetic-field, and 
 where we wished to work at a constant velocity ; with 
 reference to which however we desired to know how many 
 turns of wire we must wind on to the armature in order to 
 get the maximum effect. 
 
 The answer to this question is given in the principle 
 established by the law of Lenz and Jacobi. 
 
 This law says : With a constant intensity of the 
 magnetic-field and a constant rate of rotation, the 
 
148 CONSTRUCTIONAL LAWS. 
 
 electromotive force of a generator is directly proportional 
 to the number of windings and is quite independent of 
 their radii, as well as independent of the thickness and 
 the specific conductivity of the wire. 
 
 However, each new turn of wire or each new layer of 
 turns wound on the armature not only increases the 
 electromotive force of the generator but has its definite 
 resistance, which depends on the length and diameter of 
 the wire, and this has to be taken into consideration in 
 the construction. 
 
 If the groove which receives the coil is rectangular in 
 section, all the turns in the same layer are of the same 
 length, and this varies from layer to layer by a constant 
 quantity. Consequently, the armature rotating at a con- 
 stant rate in a magnetic-field of constant intensity, may 
 be regarded as a series of electro-generators connected 
 in series, their electromotive force being the same, and 
 their total resistance being a multiple of m. In deter- 
 mining the number of turns, and layers of turns, and the 
 thickness of wire, we must get the internal resistance of 
 the circuit into a practically useful ratio to the external 
 resistance. Once this ratio is fixed, it is easy to calculate 
 the number of turns and layers by putting ne for the 
 electromotive force, and np for the internal resistance of 
 the generator, whilst for p we substitute the expression 
 
 4 k G 
 
 , where k represents the specific resistance of the 
 
 wire, and G the mean length of a wire turn, which depends 
 on the shape and dimensions of the armature. 
 
 The thickness of the insulating coating can be de- 
 noted by a, in which case the thickness of the insulated 
 wire is = x -f 2a, and the normal section of the groove 
 which receives the coil must accordingly have an 
 
CONVOLUTIONS; RATE OF ROTATION. 149 
 
 area = n (x + 2a) 2 and a capacity = n C (x + 2a) 2 ; from 
 these two values the two dimensions of its cross-section 
 can be got. 
 
 Further, by dividing the height by x -f 2a, we get the 
 number of layers, and dividing the width by the same 
 value, we get the number of turns that ought to be in a 
 layer. 
 
 If the armature is to have several coils, it is best to 
 arrange them so that they can be coupled up for quantity 
 or intensity, and the calculation of their mode of action 
 is then effected as previously described. 
 
 The next question which arises in practice is : 
 
 IV. What relation has the current and electromotive 
 force of a generator, in whose armature there is a given 
 number of turns of wire, to the rate of rotation of the arma- 
 ture ; the intensity of the magnetic-field being constant? 
 
 The answer is : We may assume that if the intensity of 
 the magnetic-field and the resistance are both constant, 
 the current will increase in direct proportion with the rate 
 of rotation of the armature. 
 
 Accordingly, if the real influence of the speed of a 
 generator is to be known, we have to determine the 
 increase of the resistance. 
 
 For this purpose the fact has to be taken into considera- 
 tion in the calculation that the heat generated in the 
 coils of the armature increases with the current in pro- 
 portion to the square of the electromotive force, and also 
 in proportion to the square of the rate of rotation of the 
 armature, and that with this, the temperature and resist- 
 ance of the coil increases. In practice we may also assume 
 that the absolute temperature of the wire increases 
 proportionally to the square of the number of revolutions 
 per minute of the armature. In what way the resistance 
 
150 
 
 CONSTRUCTIONAL LAWS. 
 
 of the wire increases with the rise of its absolute tempera- 
 ture can then be calculated from Siemens' formula 
 
 when the coefficient of resistance at C. is known for 
 the metal employed. In this formula T denotes the 
 absolute temperature of the metal (273 + t\ and r the 
 resistance. The values for the coefficients a ]3 y are to be 
 obtained from the following table ; the formula is calculated 
 for Siemens' units, and for wires 1 m. long and of 1 sq. 
 mm. cross-section. 
 
 Metal. 
 
 a 
 
 f 
 
 7 
 
 Platinum 
 Copper 
 Iron 
 Aluminium ... ... 
 Silver 
 
 0-039369 
 0*026577 
 0-072545 
 0-0595144 
 '0060907 
 
 0-00216407 
 0-0031443 
 0-0038133 
 0*00284603 
 
 'oo5538 
 
 o 24127 
 0-29751 
 1-23971 
 0-76492 
 0-07456 
 
 When from this formula we have calculated the increase 
 of resistance of the coil for every rise in its temperature 
 by a fixed amount, it is easy to state an equation, taking 
 Ohm's law into consideration, by which a maximum can 
 be found for /. We can also determine the ideal efficiency, 
 as well as make the calculation by which the rate of 
 rotation of the armature can be so modified that the 
 largest possible amount of evolution of energy may be 
 obtained in the external circuit. 
 
 We have now considered the effect of the number of 
 turns of wire in the armature and its rate of rotation; 
 there still remains the third factor, namely, the intensity 
 of the magnetic field. 
 
 The question to be answered would, therefore, be : 
 
 V. What is the relation of the electromotive force of a 
 generator to the intensity of the magnetic-field when the 
 
MAGNETIC FIELD. 151 
 
 armature has a given number of wire windings and rotates 
 at a constant rate ? 
 
 The answer is : Under these circumstances the electro- 
 motive force is proportional to the intensity of the 
 magnetic-field ; and the most important questions with 
 reference to magneto-electric generators are thus satisfied, 
 for the intensity of the magnetic-field is constant in these 
 generators, and only depends on the position of the 
 armature relative to the magnetic-poles and the judicious 
 construction of the inducing steel-magnets or electro- 
 magnets. But we have not yet found the answer with 
 regard to the effect of the speed of the armature in a 
 dynamo-electric generator; for in these generators the 
 intensity of the magnetic-field is not constant, but directly 
 depends on the rate of rotation of the armature, whilst 
 the processes in the interior of the generator are rather 
 more complicated. As regards a dynamo, therefore, we 
 shall still have to answer three important questions. 
 
 VI. What is the ratio between current and rate of 
 rotation in dynamo-electric generators ? 
 
 VII. What relation has the effective magnetism in 
 dynamo-electric generators to the rate of rotation of the 
 armature, and to the increase of current ? 
 
 VIII. How many turns of wire must be wound on the 
 field-magnets, and on the armature, in dynamo- electric 
 generators, in order to obtain the maximum efficiency ? 
 
 The answers to questions VI and VII are given in 
 an extremely interesting article by Dr. 0. Frohlich, in 
 the " Monatshefte " of the Berlin Academy of Science, 
 published 30th November, 1880. This article explains a 
 theory based on a large number of experiments, and is of 
 great value. We shall now discuss the most important 
 points of this theory. 
 
152 CONSTRUCTIONAL LAWS. 
 
 According to Ohm's law, 
 
 in which equation, as previously, / represents the 
 quantity of current, E the electromotive force, R the 
 resistance. 
 
 The electromotive force, however, as already men- 
 tioned, is proportionate to the number of windings (ri) 
 on the armature, and its rate of rotation (v\ and to the 
 intensity of the magnetic field ; or, as Dr. Frohlich ex- 
 presses it, to the " effective magnetism (M )." Ohm's 
 law can, therefore, be written thus : 
 
 '; /= T .-'.'.. 0) 
 
 In magneto-electric generators, with steel magnets, the 
 effective magnetism is constant, and depends only on the 
 strength of the magnets. In magneto-electric generators 
 with electro-magnets, it depends on the current travers- 
 ing the coils of the magnet. In dynamos this is also the 
 case ; but then we have, in addition, that it is a function 
 of the same current, 7, which it generates in the coils of 
 the armature. 
 
 This can be written as 
 
 M=f(I). 
 
 Dividing equation (1) by Jf, we get 
 / nv 
 
 I V 
 
 Now, as ^TT\ is a function of 7, n -~- depends only on 
 
 v 
 /, and inversely 7 depends on n -- 
 
FROHLICITS THEORY. 153 
 
 This can be expressed as follows : 
 
 <>) 
 
 Or the current depends on the relation of the rate of 
 rotation of the armature to the resistance. 
 
 This is the fundamental equation for dynamo-electric 
 
 v 
 generators ; and once the relation ^ is known for a gene- 
 
 _/~L 
 
 rator, all practical questions with reference to this gene- 
 rator can be answered. 
 
 v 
 To determine the ratio -= we proceed, as Dr. Frohlich 
 
 -V 
 
 has done for Siemens' generators, to work the generator 
 under investigation at as many different rates as possible, 
 inserting the most varied resistances, and measuring the 
 respective quantities of current. We then determine the 
 
 v 
 ratios -~ for each experiment, and represent them all 
 
 nj 
 
 graphically (making n ^ the abscissa, and the quantity 
 
 of current the ordinate). This gives us a curve, which 
 Dr. Frohlich calls the " current " curve, from which the 
 desired data can easily be deduced. 
 
 We shall presently refer to a curve somewhat differ- 
 ently constructed, called the " characteristic " curve of 
 a machine, the means M. Marcel Duprez has adopted to 
 elucidate the internal processes of dynamo-electric gene- 
 rators. 
 
 If v and R are known, and we wish to find /, we look 
 
 v 
 
 for the abscissa n -7, in the curve, and in the corre- 
 Jti 
 
 spending ordinate we obtain the value for J; if 7 is 
 known, we look for the corresponding ordinate, and get 
 
i 54 CONSTRUCTIONAL LAWS. 
 
 the value for n -~- from the abscissa ; if, besides this, we 
 
 know the value for v 9 which is always the case in prac- 
 
 v 
 tice, we can deduce the value for R from v and n -^ ; 
 
 if R is given, we obtain the value for v from R and 
 
 v 
 n ~R- 
 
 Immediately /, v, and R are known, it is easy to 
 deduce the values for E and M from Ohm's law. 
 
 In practice, however, the labour of determining the 
 current curve experimentally for each generator would 
 involve much loss of time. But this is not necessary, 
 as Dr. Frohlich points out, for in practice we neither 
 employ very weak nor extremely strong currents ; and for 
 currents of medium strength the curve may be regarded 
 as a straight line. In the fact that, within the limits 
 occurring in practice, the current curve is a straight line, 
 is expressed the statement that in this case / (the quan- 
 tity of current) may be regarded as a linear function 
 
 77 
 
 of n -^ . (The direction of the straight line corresponding 
 
 to the curve is, of course, found by determining the end 
 points experimentally.) 
 
 If the quantity of current is a linear function of n -^-, 
 we can lay down the equation : 
 
 In this equation a and b are constants ; a denotes the 
 " dead revolutions " of the armature ; that is, those 
 revolutions the generator makes during the " start," 
 and during which no effective current is generated ; 
 
"DEAD" REVOLUTIONS. 155 
 
 and when a is known, 6 is obtained from the equa- 
 tion 
 
 v 
 
 after the values for / and n -^ have been determined for 
 
 JK 
 
 some one point in the straight line representing the curve. 
 If we wish to determine how far the " effective mag- 
 netism " depends on the quantity of current, we obtain 
 from equation (3), 
 
 1 R 
 
 M / - (compare equation 1 ), 
 
 V 
 
 and by eliminating ^ 
 
 From this equation we find that is the relation of 
 
 a 
 
 the effective magnetism to the current when the latter is 
 very weak, and that -j- is the relation when the current 
 
 is very strong. (This, it is true, is not quite correct, for 
 we have arrived at this statement on the supposition that 
 
 v 
 
 I is a linear function of n -~-> which is only true for cur- 
 rents of medium strength. Nevertheless, these statements 
 tend, in general, to give a correct view of the processes.) 
 
 The dependence of the electromotive force can also be 
 deduced from the curve by the equation 
 
 E = -i/ v a R \ 
 With regard to the effective magnetism, in the cases 
 
156 CONSTRUCTIONAL LAWS. 
 
 occurring in practice, Dr. Frohlich has shown that it is 
 incorrect to suppose that in dynamo-electric generators 
 its increase is proportional to the current in the arma- 
 ture. At first, certainly, this is the case ; but as the rate 
 of rotation and the quantity of current go on increasing, 
 the increase of the effective magnetism begins to differ 
 more and more from the rate of rotation, and the effective 
 magnetism finally reaches a maximum. For still larger 
 currents, its strength actually falls off from this maxi- 
 mum. 
 
 The reason of this phenomenon is that the magnetism 
 of the field-magnets not only depends on the magnetising 
 effect of the wire -windings on their limbs (this, it is 
 true, is the principal source), by which both these limbs 
 and the armature (by induction) are magnetised, but 
 also that the windings of the armature have a consider- 
 able magnetising effect on the iron of the field-magnets ; 
 which, however, counteracts that due to the coiling on 
 the limbs, by rotating the magnetic axis of the armature, 
 and by weakening the magnetism, especially that of the 
 armature. Dr. Frohlich's experiments with the Siemens 
 generators showed that the effective magnetism of the 
 generator is diminished by one-fourth in consequence of 
 the magnetising influence of the coiling of the armature, 
 more than it would be without this opposing influence. 
 The armature acts more and more detrimentally on the 
 field-magnets when the rate of rotation is increased beyond 
 a certain limit. For when the limbs of the electro-magnets 
 have been magnetised to a maximum, the influence of the 
 current on the magnetism of the armature must still go on 
 increasing, and the total effective magnetism therefore 
 must decrease. This is, however, only the case with cur- 
 rents which far exceed in strength any employed in prac- 
 
THOMSON'S LAW. 157 
 
 tice. As a rule, therefore, we may assume that the effec- 
 tive magnetism finally reaches a constant maximum. 
 
 With regard to question VIII., as to the most advan- 
 tageous ratio between the turns of wire in the armature 
 and those of the field-magnets, the well-known physicist 
 Sir William Thomson put forward a hypothesis before 
 the Paris Academy of Science on the 19th September, 
 1881 :- 
 
 In the field-magnets, let 
 
 L be the length of the wire ; 
 
 B the volume of the wire and insulating material ; 
 
 n the ratio of this total volume to that of the copper 
 
 alone (that is, B volume of copper) ; 
 
 A the total cross-section of the wire ; and 
 
 R the resistance of the wire. 
 
 The same values for the armature may be respectively 
 denoted by L', B', n r , A', R. Furthermore, let 8 be the 
 specific resistance of copper. 
 
 Then, 
 
 B = AL 
 
 , , K /1N 
 
 Therefore ^ * (1) 
 
 , ,, Vn's'B' K 
 
 and Am 
 
 In these equations K and K' denote constants. 
 
 Now, let c be the quantity of current in the field- 
 magnet, c', the current generated in the armature, v the 
 velocity of some point on the armature, and p the mean 
 
158 CONSTRUCTIONAL LAWS. 
 
 electromotive force at both ends of the armature-wire ; 
 then we have the equation 
 
 *-.P = *-Z*l,* (3) 
 
 Here / denotes a co-efficient, which depends on the 
 form, dimensions, and relative positions of B and B', and, 
 besides on the magnetic capacity of iron. / decreases 
 with this capacity, when the current increases, and also 
 when R and R undergo variations, which increase the in- 
 tensity of the magnetisation. 
 
 In dynamo-electric generators with a simple circuit 
 c' = c. This is, however, not the case with shunt-wound 
 dynamo-electric generators. In both cases, however, the 
 mechanical equivalent of the electrical work done is equal 
 to p c', or, according to equation (3) ; 
 
 J JT'" W 
 
 and putting the values found for A and A r , in this equa- 
 tion, we get 
 
 Icc'v^RR ,_. 
 
 KK 
 
 Part of this work is wasted in the heating of the wires in 
 the coils ; the other part is made use of in the external 
 circuit. Their respective values are : 
 
 R c 2 + R c' 2 (6) 
 
 for the work lost, and 
 
 (7) 
 
 for the useful work. 
 
 If v is very large, we can make the ratio of (6) to (7), 
 that is, of the loss of work to the useful work, as small as 
 we like. 
 
THOMSON'S LA WS. 159 
 
 The problem we now have to solve is, what relative 
 values must be given to R and R', in order, with any 
 given velocity, to reduce to a minimum the ratio of the 
 wasted work to the useful work ; or, in other words, if 
 this ratio is given, to reduce the velocity to a minimum. 
 In order to solve this question, we will call r the ratio of 
 the total work to the loss of work. 
 
 According to (5) and (6), we then have the relation 
 
 _ I V RR cc' v 
 '' * ''* X 1 ' 
 
 In the simple dynamo-electric generator, we have 
 c f = c y and for (8) we obtain the equation 
 I STIR' v 
 R + R x KK' 
 
 IV R(S R) ,--. 
 
 r = - , - (10) 
 
 if we put 8 = R + R. (11) 
 
 Now, let us assume that S is given, and that / is con- 
 stant for a moment. Then, in order that r may become 
 a maximum for a given v 9 or v a minimum for a given r, 
 R (S R) must become a maximum. 
 
 This takes place as soon as R = S 9 that is, when the 
 
 & 
 
 resistance of the armature is equal to the resistance of 
 the magnet. /, however, as a fact, is not constant, but 
 decreases as the magnetising force increases. In general, 
 1 depends principally on the soft iron of the field electro- 
 magnet, but comparatively little on the iron of the 
 armature. 
 
 In most cases, therefore, / will decrease as R increases, 
 
 A 
 
 and R diminishes ; consequently, the maximum for - 
 
i6o CONSTRUCTIONAL LAWS. 
 
 according to equation 10, requires R' should be greater 
 
 than 8. We cannot deduce the ratio of R' to R' 
 2 
 
 from the formula, without knowing the law of the varia- 
 tions of /. By experiments, as well as by practical pre- 
 disposition, constructors were led to make the resistance 
 of the field electro-magnets in most dynamos rather lower 
 than the resistance of the armature, and this agrees with 
 theory as developed. 
 
 As the useful work of a generator manifests itself as 
 light, mechanical work, heat, or electrolytic work, we can 
 simplify consideration in all these possible cases by sub- 
 stituting the typical case, where the terminals of the 
 generator are connected by a conductor of resistance, E. 
 Following the general custom, we call this conductor the 
 external circuit, an expression which briefly denotes that 
 portion of the whole circuit situated outside the dynamo- 
 electric generator. If we have a dynamo with a simple 
 circuit, the current traversing the external circuit is 
 equal to that (c r ) traversing the armature. 
 
 According to Ohm's law, we then get the equation : 
 
 c ' = E + R+R 
 but according to equations (3), (1) and (2) 
 
 KK'(E 
 
 
 Now, if we put c' = c, (14) 
 
 T KK'(E -^R + R) 
 
 The case where c' = is the one in which 
 KE>(]l + R+R) 
 
 ' { ' 
 
FIELD-MAGNET RESISTANCE. 161 
 
 where I denotes that value of /, for which c' = 0. In 
 order to understand this, we must remember that we do 
 not assume any residual magnetism. For all velocities 
 corresponding to equation (16), no current is generated. 
 As soon, however, as this limit is passed, the electrical 
 equilibrium of the circuit becomes stable. The slightest 
 current then started in one or the other direction by 
 any cause, will rapidly increase to a limiting value, de- 
 termined by equation (15), in consequence of the diminu- 
 tion of T, which diminution coincides with the increase of 
 the current. If we consider / to be a function of c, we 
 have in equation (15) a mathematical expression for the 
 current generated from the dynamo in its stationary 
 condition. Putting equation (15) into equation (9), we 
 
 get ' - = 
 
 an equation given by Joule forty years ago. 
 
 In a shunt-wound dynamo, the current c', generated in 
 the armature, divides into two, c in the electro field- 
 magnet and (c f - c) in the external circuit. The quan- 
 tities of current are inversely proportional to the resist- 
 ances they traverse. Accordingly, always calling the 
 resistance of the external circuit E, we have the equation 
 
 c M = (c' - c) E, 
 jji 
 
 from which follows : c = j^ - =^ c'. (18) 
 
 H + ti 
 
 Therefore, according to Joule's law, the work done in 
 unit time iii the three parts of the circuit is 
 R c' 2 for the armature. 
 
 the field-magnet. , , (19) 
 
 E ( P , F ) c ' 2 f r the external circuit. 1 
 
 M 
 
162 CONSTRUCTIONAL LAWS. 
 
 From this it follows that if r represent the ratio of the 
 total work to the useful work, 
 
 (20) 
 
 and, again, from this it follows that 
 
 R*T = - + (It + R'}E+ R(2$' + R). (21) 
 
 Now, let us assume that R and R' are given, and that E 
 is required. In order that r may become 3, minimum, 
 it must happen that 
 
 R+R' 
 We, therefore, have 
 
 (23) 
 
 R' 
 If we put ~R 6 ( 24 ) 
 
 equations (22) and (23) become 
 
 and r = I + 2Ve(l+e) + 2e, (26) 
 
 For the sake of efficiency, r must approach unity 
 as closely as possible, and consequently e must be 
 very small. The value for the shunt circuit approxi- 
 mately equals 
 
 E = 
 
FIELD-MAGNET RESISTANCE. 163 
 
 Now, if we assume, for example, that the resistance of 
 the field-magnet is 400 times as great as that of the 
 armature, or that e = 400, we have approximately 
 
 E = - 
 
 Or the resistance of the external circuit is twenty times as 
 great as that of the armature, and the useful work in the 
 
 external circuit is about equal to ^y of the work wasted 
 
 in the generator by the heating of the wires. 
 
 We have now become acquainted with the more im- 
 portant laws bearing on the construction of magneto- 
 electric and dynamo-electric generators, and there is no 
 doubt that it is only possible to construct a good and 
 efficient generator when these laws are fully considered. 
 
 Nevertheless the constructor has also to take into ac- 
 count a large number of particulars of great importance in 
 building an electric generator, and relating to its several 
 parts. The most important of these are given in the next 
 chapter. 
 
CHAPTER VII. 
 
 THE CONSTRUCTION OF THE SEVERAL PARTS OF 
 ELECTRIC GENERATORS. 
 
 THE most important parts of an electric generator are the 
 field-magnets and the armature. It is on their construc- 
 tion and advantageous relative arrangement that the 
 valite of an electric machine principally depends. 
 
 1. The field-magnets. The principal theoretical laws 
 bearing on the general construction of magnets are given 
 in the Appendix, and it will only here be necessary to 
 give a few practical hints on the manufacture of mag- 
 nets. 
 
 We shall take first the manufacture of steel-magnets. 
 Steel bars can be magnetised by stroking them with 
 steel-magnets, or 1 by the electrical method. 
 
 In the first of these cases, we distinguish between two 
 methods ; namely, the simple stroke or the double and 
 separate stroke. 
 
 In the simple stroke, we lay the piece to be magnetised, 
 with one of its broader surfaces, on the opposite poles of 
 two steel magnets, and, with the corresponding pole of a 
 third magnet, we stroke the bar, in one way, in the 
 direction of its longer axis. We then turn it round, so 
 that the lower side comes atop, and repeat the operation. 
 In the case of the double-stroke method, we place the 
 opposite poles of two steel magnets on the middle of the 
 bar, and stroke with both magnets, away from the middle 
 towards the ends. 
 
PARTS OF GENERATORS. 165 
 
 If we wish to magnetise the bar by the electrical 
 method, we place it inside a wire helix, which is tra- 
 versed by a current. A south pole will then be generated 
 in the piece of steel at that end of the helix at which 
 when it is turned towards the observer the current 
 circles in the direction of the hands of a clock ; at the 
 other end, a north pole will be formed. 
 
 The strength of a magnet principally depends on its 
 dimensions, its shape, and the quality of the steel.* 
 Coulomb determined that the magnetic moment of 
 geometrically similar magnets, composed of the same 
 material, is nearly proportional to the cube of their homo- 
 logous dimensions, and that, in cylindrical magnets of 
 the same length, the free magnetism is proportional to) 
 the diameter. 
 
 According to the first statement, the magnetic moment 
 of a magnet would be proportional to its volume. 
 
 Haker arrived experimentally at the result that, for 
 horse-shoe magnets, Q = 10-33 Pf, in which equation 
 Q denotes the portative power of the magnet, and p its 
 weight in kilogrammes. 
 
 According to this equation, therefore, a magnet of 
 1,102 kgs. would be able to carry its own weight ; and 
 the smaller a magnet, the greater would be its portative 
 power compared with its weight. 
 
 The co-efficient 10*33, however, is perhaps a little too 
 small. Elias determined the value of this co-efficient to 
 be 13-23. 
 
 But the practical value of this co-efficient is not very 
 great, for the magnets obtained in commerce rarely attain 
 the efficiency given by the above formula ; yet, on the 
 other hand, by special care in their construction, and by 
 
 * Compare Appendix. 
 
i66 CONSTRUCTIONAL LAWS. 
 
 selecting good steel, it is possible to make magnets of 
 double this strength. 
 
 Jamin has made a series of very important experi- 
 ments, with the object of ascertaining the distribution of 
 the free magnetism in prismatic and cylindrical magnets, 
 as well as in magnetic batteries, and also of determining 
 the conditions for their greatest efficiency. These in- 
 vestigations are too extensive to be given here, even in 
 abstract ; they are, however, of great practical import- 
 ance, as illustrated by the construction of the laminated 
 magnet (described page 53), which is a result of the in- 
 vestigations.* 
 
 According to Frankenheim* the length of time during 
 which the magnetising current acts on steel magnets does 
 not influence the So-called "permanent moment" (the mag- 
 netism of steel magnets is not permanent in the true 
 sense of the word), but this can be increased by repeating 
 the magnetisation several times. 
 
 This can be done either by taking the piece of steel 
 out of the magnetising helix and replacing it several 
 times, or by opening and closing the magnetising circuit 
 several times. By this operation the magnetic moment 
 is increased, but, of course^ only up to a certain limit. 
 
 When Frankenheim applied this method to pieces of 
 steel which had been freshly annealed, he found that the 
 permanent magnetism that the steel acquires after being 
 magnetised x times, bears a certain relation to the 
 magnetism that can be obtained with the magnetic field 
 in question. This relation is perfectly independent of 
 the intensity of the field, as well as of the dimensions 
 and the coercive force of the bars. Fromme asserts that 
 
 * Comptes Rendus de 1' Academic des Sciences de Paris, Vol. LXXV. to 
 LXKVI1., and Journal de Physique, Vol. V., 1876. 
 
PARTS OF GENERATORS. 167 
 
 he obtained these results with bars which had not been 
 annealed. 
 
 A method for making very powerful steel magnets is 
 the following, as given by Elias. 
 
 A copper wire 7-8 m. long, and about 3 mm. diameter, 
 is wound into a cylindrical helix, and the current of a 
 large Bunsen's or Grove's cell, whose internal resistance 
 is equal to that of the helix, is allowed to traverse it. 
 The steel bar to be magnetised is placed within the helix, 
 and the latter is then moved several times backwards and 
 forwards from end to end of the bar. With horseshoe 
 magnets, two helices are used, with which both limbs are 
 magnetised simultaneously. 
 
 The distribution of the magnetism on the surface of 
 the core is found from the equation given by Biot and 
 Coulomb, the accuracy of which Jamin confirmed in the 
 experiments previously mentioned. The equation is 
 
 and it expresses the mean magnetic density at the cir- 
 cumference of a cross section, at distance x from one of 
 the ends of the magnet, whose length is t. 
 
 According to Jamin, the co-efficient A principally de- 
 pends on the chemical composition of the magnet ; fc, on 
 the other hand, depends on its molecular constitution and 
 on the hardness (particularly in the case of steel). 
 When I is very large, the equation assumes the simpler 
 
 form 
 
 ^ 
 y = -p^, since k is always ^ 1. 
 
 In practice, the importance, of the distribution of 
 the magnetism is usually under-estimated, because, in 
 
168 CONSTRUCTIONAL LAWS. 
 
 most generators with steel magnets, the inductive power 
 of the poles only is employed. Marcel Deprez, how- 
 ever, has proved, in his small electro-motor, that this 
 is erroneous; for with this motor very powerful effects 
 are obtained, the inventor having placed a Siemens 
 cylinder armature between the branches of a horseshoe 
 magnet, with its axis parallel to these branches. The 
 rotating armature is thus influenced by the longest por- 
 tions of the limbs. 
 
 We give here the dimensions of one of the small 
 motors, as well as the values of its working power. 
 
 The length of the horseshoe magnet, measured 
 
 from the faces of the poles to the top of the 
 
 bend , f f , , , 145 mm. 
 ^j The distance between the limbs . . 33 
 The thickness of the magnetic battery . 25 
 Diameter of the cylinder armature . . 32 
 Length of the iron core . . . 60 
 
 Weight of the fiekUmagnet . . . 1-70 kg. 
 
 Weight of the whole motor . . . 2*83 ,, 
 
 With a motor having these dimensions, Deprez obtains, 
 using the apparatus as a generator, all the effects that 
 can be produced with three Bunsen's elements. On the 
 other hand, if it is used as an electro-magnetic motor, 
 the work produced is as follows : ^- 
 
 With 1 Bunsen's cell . . . O04 kg. metres. 
 
 2 cells . f r 0-20 
 
 3 . 0*45 
 
 4 , 0-75 
 
 5 . MO 
 
 8 . . 1*80 
 
 In making electro-magnets, the construction of which 
 
PARTS OF GENERATORS. 169 
 
 is important both for the inducing portion and for the 
 armature of electric generators, it is necessary to take 
 carefully into account the formulae given in the previous 
 chapter, and in the Appendix, as well as to select good 
 material. 
 
 Unfortunately, the value of the co-efficient fc, with 
 which the intensity of the field and the volume of the 
 magnetic core have to be multiplied, to obtain the mag- 
 netic moment, is not known with certainty for all kinds 
 of iron ; from the investigations of Barlow and Pliickner, 
 however, we know the following values, taken from 
 Fleeming Jenkin's work.* 
 
 Soft wrought iron , , , . k = 32*8 
 
 Cast iron . . , . . k = 23-0 
 
 Soft steel , , , , . k = 21-6 
 
 Hardened steel f , . k = 17*4 
 
 Soft cast steel k = 23*3 
 
 Hard , , , , . k = 16-1 
 
 Nickel k = 15-3 
 
 Cobalt . , . , . . k = 32-8 
 
 If we wish to construct an electro -magnet, it is best to 
 use another electro-magnet as a pattern-, and to make the 
 dimensions proportional. Then, according to Dub's laws, 
 the quantity of current required to saturate the core of 
 the new magnet is proportional to that of the pattern 
 electro-magnet, in the ratio of the cubes of the homo- 
 logous dimensions of the two cores. 
 
 The dimensions of the coil are calculated by the laws 
 given in Chapters VI. and X., taking into account the 
 external resistance. 
 
 Professor Sylvanns P. Thomson, in his " Cantor Lec- 
 
 * Electricity and Magnetism, p. 124. 
 
170 CONSTRUCTIONAL LAWS. 
 
 tures " points out that to magnetise a piece of iron requires 
 the expenditure of energy ; but when once it is magnet- 
 ised, it requires no further expenditure to keep it 
 magnetised, provided the magnet is doing no work. Even 
 if it be doing no work, if the current flowing round it be 
 not steady, there will be loss. If it do work, say, in 
 attracting a piece of iron to it, then there is an immediate 
 and corresponding call upon the strength of the current 
 in the coils, to provide the needful energy. This point 
 Professor Thomson illustrates by the following experi- 
 ment : Let a current from a steady source pass through 
 an incandescent lamp, and also through an electro- 
 magnet, whose cores it magnetises. If now the magnet 
 is allowed to do work in attracting an iron bar toward 
 itself, the light of the lamp is seen momentarily to fade. 
 When the iron bar is snatched away, the light exhibits a 
 momentary increase ; in each case resuming its original 
 intensity when the motion ceases. Now, in a dynamo 
 where, in many cases, there are revolving parts con- 
 taining iron, it is of importance that the approach or a 
 retrocession of the iron parts should not produce such re- 
 actions as these in the magnetism of the magnet. Large, 
 slow-acting field-magnets are, therefore, advisable. And 
 the body of the field-magnets should be solid. Even in the 
 iron itself currents are induced, and circulate round and 
 round whenever the strength of the magnetism is altered. 
 These self-induced currents tend to retard all changes in 
 the degree of magnetisation. They are stronger in pro- 
 portion to the square of the diameter of the magnet, if 
 cylindrical, or to its area of cross-section. A thick 
 magnet, will, therefore, be a slow-acting one, and will 
 steady the current induced in its field. 
 
 It is important to have a sufficient mass, that satura- 
 
PARTS OF GENERATORS. 171 
 
 tion may not be too soon attained. The softest possible 
 iron should be used for field-magnets. Long magnets 
 steady the magnetism, and therefore steady the current. 
 A long magnet takes a longer time than a short magnet 
 to magnetise and demagnetise. It costs more than a short 
 magnet, it is true, and requires more copper wire in the 
 exterior coil ; but the copper wire may be made thicker 
 in proportion, and will offer less resistance. The mag- 
 netism so obtained should be utilised as directly as 
 possible, therefore Professor Thomson advises to place the 
 field-magnets or their pole-pieces as close to the rotating 
 armature as is compatible with safety in running. 
 
 Avoid edges and corners on the magnets and pole- 
 pieces if you want a uniform field. 
 
 Pole-pieces.* The pole-pieces should be heavy, with 
 plenty of iron in them, for reasons similar to those urged 
 above. 
 
 The pole-pieces should be of shapes really adapted to 
 their functions. If intended to form a single approximately 
 uniform field, they should not extend too far on each 
 side. The distribution of the electromotive force in the 
 various sections of the coils on the armature depends 
 very greatly on the shape of the pole-pieces. 
 
 Pole-pieces should be constructed so as to avoid, if 
 possible, the generation in them of useless Foucault 
 currents. The only way of diminishing loss from this 
 source is to construct them of laminae, built up so that 
 the mass of iron is divided by planes in a direction per- 
 pendicular to the direction of the currents, or of the 
 electromotive forces tending to start such currents. 
 
 If the bed-plates of dynamos are of cast iron, care 
 
 * "Cantor Lectures." 
 
172 CONSTRUCTIONAL LAWS. 
 
 should be taken that these bed-plates do not short-circuit 
 the magnetic lines of force from pole to pole of the field- 
 magnets. Masses of brass, zinc, or other non-magnetic 
 metal may be interposed ; but are at best a poor resource. 
 In a well-designed dynamo, there should be no need of 
 such devices. 
 
 The Armature. In connection with this portion of an 
 electric generator, another important point regarding 
 electro-magnets has to be considered, that is, the periods 
 of change in the magnetisation of an iron core. A magnet 
 does not acquire its magnetism instantaneously, nor lose 
 it instantaneously. When the circuit is closed or the 
 current is started, the magnetic moment of the core in- 
 creases rather rapidly, and reaches a maximum ; again on 
 opening the circuit or stopping the current, the magnetic 
 moment decreases and reaches a limit more or less nearly 
 zero. The magnetism never entirely disappears, but a small 
 amount of " residual " magnetism remains. The dura- 
 tion of the increase and decrease of the magnetism 
 depends on various circumstances ; the principal is, that 
 the coercive force of iron is never equal to zero. The 
 separate molecules of the metal possess a certain inertia 
 that prevents their instantly resuming the position they 
 had before the iron was magnetised. Another reason is 
 the occurrence of extra currents produced by induction. 
 These have the same direction as the principal current, 
 when the circuit is opened or the current disappears, 
 consequently, they tend to prolong the primary current, 
 as well as its magnetising action. 
 
 From this fact it follows that the magnetic maximum 
 of the iron core in the armature of an electric generator 
 does not begin to decrease when, according to theory, it 
 should do so, but at another point. If, for instance, we 
 
PARTS OF GENERATORS. 173 
 
 take Fig. 8 for the basis of our consideration, and assume 
 that the ring moves in a direction opposite to that of the 
 hands of a clock, then the maximum magnetisation of 
 the iron core, and therefrom the maximum current, does 
 not decrease immediately after the turns of wire have 
 passed the poles S and N ; but the magnetism of the iron 
 core, and the current in these turns of the wire, remain at 
 the same intensity for a few moments, so that the decrease 
 commences a few degrees to the left of S and to the right 
 of JV. The neutral points also are displaced in con- 
 sequence, and have to be sought beldw p and above p f , 
 and not at p and p'. This makes it necessary to change 
 the position of the brushes, and not place them at the 
 ends of the horizontal line joining the points p and p', 
 but at those points which are really neutral. Affairs are 
 made still more complicated by the fact that the amount 
 of displacement of the neutral points depends on the 
 greater or less rate of rotation of the armature. For 
 when the armature rotates rapidly from right to left, each 
 of the respective points of the ring has advanced some 
 distance before the decrease of the magnetism of the iron 
 core, and of the current induced in the wire windings, 
 has reached the minimum J on the other hand, when the 
 armature moves slowly, the theoretical and actual neutral 
 points of the armature lie closer together. The difference 
 in the position of the neutral points is further increased 
 when the rate of rotation is rapid, because the magnetism 
 of the field-magnets, and of the iron core of the armature, 
 and consequently also the reaction on the armature coils, 
 is increased, whereas when the rotation is slow these 
 factors are of small value. It is therefore obvious that 
 we should seek an automatic arrangement of the brushes 
 to place them always on the points which are for the time 
 
I 7 4 CONSTRUCTIONAL LAWS. 
 
 being neutral. This is already partially effected by some 
 regulators. 
 
 Another consequence of the fact that the maximum 
 magnetism does not immediately disappear, is the heating 
 of the iron core of the armature, which greatly influences 
 the efficiency of an electric generator. In any case it is 
 necessary to prevent the peripheral current in the mass of 
 iron of the core. This is effected to some extent by slitting 
 the iron cores, that is, in other words, by structurally 
 dividing the core in planes normal to the circuits round 
 which currents are induced, which statement may be 
 generally accepted as meaning, in planes at right angles 
 to the direction of the wire windings, or in planes parallel 
 to the lines of force to the direction of the motion. Cores 
 are also built up of varnished or insulated iron wire, or of 
 thin sheet iron separated by varnish, asbestos-paper, or 
 mica, to realise the required condition. 
 
 The heating of the armature, however, may not be a 
 consequence of the residual magnetism in the iron core, 
 but may arise from the resistance of the armature being too 
 great. Also a part of the armature-coils are not exposed 
 to the action of the field-magnets, and oppose a great re- 
 sistance to the current which has to traverse these coils. 
 To overcome the resistance, work is necessary, which 
 manifests itself as heat. 
 
 One of the principal problems for the constructor is, 
 where possible, to expose all parts of the coils of the 
 armature simultaneously to the influence of the field- 
 magnets, or where this cannot be done to temporarily 
 exclude those parts of the armature from the circuit 
 which are not accessible to the influence of the field-mag- 
 nets, or are in the neutral positions, as is attained for 
 instance in Brush's generator. 
 
PARTS OF GENERATORS. 17$ 
 
 The hollowing of the armature core and the conducting 
 of water through it, is a very incomplete remedy against 
 heating. The injurious consequences can thus, it is true, 
 be modified, but the work lost in the heating is not re- 
 gained. Similarly the perforation of the armature for the 
 sake of cooling by ventilation cannot be recommended, as 
 the surface of the armature is thus increased, and the 
 work which has to be spent in overcoming the atmos- 
 pheric resistance, is lost as far as the efficiency of the 
 generator is concerned. The rational remedy for this evil 
 of the heating of electric generators is not to be found in 
 modifying the consequences of the heating, but in avoid- 
 ing the causes. 
 
 The position of the Armature with respect to the mag- 
 netic poles must be such that the armature moves in as 
 strong a magnetic field as possible, and this will be the 
 case when it revolves as close as possible to the magnetic 
 poles ; for the intensity of a magnetic field is equal to the 
 magnetising force of the pole divided by the square of the 
 distance from the pole. 
 
 In order that the armature may rotate as close as 
 possible to the pole, the parts of its surfaces which are 
 turned towards the pole must be comparatively even, and 
 we must therefore wind the coiling of the armature very 
 symmetrically, or bring its core very close to the pole-pieces 
 of the field-magnets by a suitable construction, as in 
 Paccinotti's generator. 
 
 The collectors and commutators of electric generators 
 are the parts which perhaps require most care in their 
 construction. If they are badly constructed they wear 
 out quickly in consequence of friction and the for- 
 mation of sparks, and badly constructed collectors 
 or commutators are the cause that a large amount 
 
176 CONSTRUCTIONAL LAWS. 
 
 of the working power of a generator is spent use- 
 lessly. 
 
 The loss of energy through the friction of the rubbing 
 parts of a generator is proportional to the number of 
 revolutions of the shaft and to the diameter of the rub- 
 bing surfaces. For these reasons the surfaces ought to be 
 diminished as much as possible, not only in the journals 
 of the generators but also, as Professor Perry suggests, in 
 the conducting brushes and commutators. But, besides, 
 we must diminish the destructive action in these parts 
 caused by sparking. This can be done by distributing the 
 sparking over various portions of the collector, so that 
 only small sparks can be formed, which are unable to melt 
 or oxidize. 
 
 In order to reduce the sparking oti the collectors of 
 large generator's to a minimum, Edison increases the 
 width of the insulation a l9 a 2 a s ( n g" 50), between the 
 segments of the collector. He makes the conducting 
 sectors b 19 b%, by narrower at one end of the collector- 
 cylinder J., and on each side of this portion of the cylin- 
 der, he places a single brush e which he calls the insulated 
 brush, the contact point of whieh is not in a line with the 
 principal brushes. The insulated brush is not directly 
 connected with the principal brushes, d d, but first with 
 an interruption cylinder B by means of the brushes h 19 A 2 . 
 This cylinder has conducting and insulating sectors which 
 correspond with those on which the insulated brush e 
 bears, and it can be attached separately to one end of 
 the shaft of the generator, or may form a continuation of 
 the collector-cylinder A, as shewn in the figure, in which 
 case its conducting strips c l9 c 2 must be insulated from 
 those of the collector-cylinder A. In working the 
 generator the local current and part of the principal cur- 
 
PARTS OF GENERATORS. 177 
 
 rent continue to flow through each of the insulated 
 brushes, and across each commutator segment, after having 
 ceased traversing the principal brushes, so that no sparks 
 are generated at the ends of the latter. When an insulated 
 brush quits a strip of the collector, the current traversing 
 it is interrupted on the interruption-cylinder B, and as the 
 same thing occurs simultaneously on the collector-cylinder 
 
 Fig. 50. 
 
 J., through the insulated brush e, the spark is thus greatly 
 subdivided and much weakened. 
 
 All the hints given in this chapter, with reference to 
 the construction of the separate parts of electric genera- 
 tors, are of great importance to the manufacturer. They 
 do not, however, by any means exhaust the details which 
 he has to take into consideration. For the difficulties 
 which the constructor has to overcome are of too varied 
 a nature to be all mentioned here. 
 
 We have only been able to draw attention to the prin- 
 
 N 
 
1 78 CONSTRUCTIONAL LAWS. 
 
 cipal points, which, if kept in view, form the basis of 
 good construction. 
 
 The constructor has, besides, to attend to peculiarities 
 of construction connected, 
 
 (1). With strength and simplicity of mechanical con- 
 struction. 
 
 (2). With easy access to and repair of the several parts 
 of the generator. 
 
 (3). With the cost. 
 
 A discussion of these points, however, does not come 
 within the scope of a technological work. We shall 
 only mention a few examples which may be regarded 
 as typical of what has to be attended to, and of what 
 has to be neglected under the three headings we have 
 mentioned. 
 
 The generators of Brush and Edison, and the collector 
 of Gramme's generator, and soine of their imitations, 
 are specially noteworthy for strength and simplicity of 
 construction. 
 
 Brush's generator too serves as a very good type, in 
 which the parts are very accessible and easily repaired. 
 With regard to the latter advantage, however, we must 
 specially mention the alternating-current generator and 
 the latest dynamo-electric generator of Siemens and 
 Halske, in which each bobbin can be replaced without dis- 
 turbing the other parts. This is also true of the Burgin 
 generator. 
 
 The question of cost is at present one of the principal 
 obstacles in the way of an extensive application of electric 
 generators, and again indirectly depends on complicated 
 or simple construction. It is to be expected that there 
 will be a considerable reduction in this direction as soon 
 as the dimensions of generators are increased. For as 
 
DIMENSIONS OF GENERATORS. 179 
 
 regards their efficiency, large generators are much cheaper 
 than small ones, as will be seen from the details in the 
 next chapter ; and upon the whole, experience has taught 
 that it is always advantageous to concentrate as large 
 an amount of working-power at one point as possible, 
 and then to distribute it in different directions. The 
 secondary batteries described in Chapter V. promise to 
 be of great service in this particular. 
 
 As regards the relation of size to efficiency, Professor 
 Thomson has pointed out, in the Cantor Lectures, de- 
 livered by him before the Society of Arts, the much more 
 than proportional efficiency of large machines. If we 
 assume that the size of any machine can be increased n 
 times in every dimension, and that though the dimensions 
 are increased the velocity of rotation of the shaft remains 
 the same, whilst the intensity of the magnetic field, per 
 square centimetre, is also constant, the following laws of 
 increase of size will hold good. The area the machine 
 stands on will be increased n* times, and its volume and 
 weight n s times. 
 
 The cost will be less than n s , but greater than n times. 
 
 If the same increase of dimensions in the armature 
 coils be observed (the number of layers and of turns re- 
 maining the same as before), there will be in the armature 
 coils a length n times as great, and the area of cross 
 section of the wire will be n 2 times as great as before ; the 
 
 resistance of these coils will be th part of the original 
 
 resistance. 
 
 If the field magnet coils are increased similarly, they 
 
 will offer only - th the resistance of those of the original 
 machine. 
 
i8o CONSTRUCTIONAL LAWS. 
 
 The electromotive force will be increased ri 2 times, the 
 speed of the shaft being the same. 
 
 To correspond, we may assume the whole circuit to be 
 increased in section, so that its wire will carry the larger 
 
 current, its resistance will then be th of its previous 
 
 value. 
 
 If our theoretical machine is " series " wound, an 
 
 electromotive force, n 2 , working through resistance 
 
 Yl/ 
 
 will give a current n* times as great as before. In this 
 respect, as the iron of our field magnets is n s times as 
 great in mass, we need not so nearly saturate it as before 
 to gain the same magnetic field, or to get n* times the 
 area of surface magnetised to the former average intensity 
 per square centimetre. Hence, the numbef of coils may 
 
 be reduced in the proportion of n s to n 2 , or to th of its 
 
 already diminished value, correspondingly reducing the 
 resistance on which work has to be done. 
 
 As in the larger machine, therefore, the electromotive 
 force is increased n 2 times, and the current n s times, the 
 work of the machine will be n s x w? = n 5 times greater 
 than with the smaller machine. Or, a machine doubled 
 in all its linear dimensions will not cost eight times as 
 much, and will be electrically thirty-two times more 
 powerful than the smaller machine. 
 
 If the machine be " shunt " wound, then to produce 
 the field of force of n* times as many square centimetres 
 area, will require (if the electromotive force be 7i 2 times 
 as great) that the absolute strength of the current remain 
 the same as before in the field magnet coils. This can be 
 effected by using wire of the same size as before, and in- 
 
DIMENSIONS OF GENERATORS. 181 
 
 creasing its length n? times, to allow for n times as many 
 turns, of n times as great a diameter each, in the same 
 number -of layers of coils as before. The current being 
 the same, therefore, in the shunt circuit as before, but 
 under n 2 the e.m.f., the work here is only n* times as 
 great ; whilst in the whole machine it is n 5 times greater 
 than with the smaller machine. 
 
 Following wholly different lines of reasoning, M. Marcel 
 Deprez has arrived at the conclusion that for similar 
 machines, the " statical effort " increases as the fourth 
 power of the linear dimensions. But as this " statical 
 effort " is a force of mutual reaction between two elements 
 of the system of conductors ; and as work is represented 
 by force multiplied by distance ; and as, again, in the 
 similar machine whose dimensions are increased n times, 
 the available distance through which the new force 
 can act is also n times greater, the value n 5 also here 
 obtains. 
 
CHAPTEE VIII. 
 
 THE EMPLOYMENT OF ELECTRIC GENERATORS FOR PRODUCING 
 THE ELECTRIC LIGHT. 
 
 ALTHOUGH it is not our intention to discuss fully the 
 applications of electric generators^ we think it advisable 
 to briefly review these applications, as far as this will con- 
 tribute to the understanding of the properties of the 
 electric generators. We have also included in this chap- 
 ter the more important Comparative experiments relating 
 to the efficiency of the light-generators ; fo*, from the data 
 as to the intensity of the light, the construction of the 
 light-machines and the expenditure of motive power, 
 tolerably correct conclusions can be drawn as to the in- 
 dividual value of the various generators. 
 
 The most important Use to which electric generators 
 have been put is undoubtedly their employment in the 
 production of the electric light, and it was only by the 
 invention of electric generators that electric illumination 
 became possible on a large scale. 
 
 As has already been said, generators intended for the 
 purpose of electric illumination must not only produce a 
 powerful current in the external circuit, but the current 
 must also be at considerable tension, and this again 
 must be maintained within certain limits, for if the 
 tension is too great the luminous arc becomes unsteady, 
 
SPECIAL DETAILS. 183 
 
 therefore, the internal resistance of the generators must 
 be judiciously arranged. 
 
 The internal resistance of the normal Siemens light- 
 machine is about O7 or O7o ohms ; Gramme's generators 
 have on the average a resistance of about 1 ohm, but 
 Gramme also constructs generators which have a resist- 
 ance of only 0*6 ohm. Of Course^ the greater the in- 
 ternal resistance of a generator > the greater, generally, the 
 intensity of the current, and with generators that pro- 
 duce a current of low intensity, we can only supply one 
 arc-light in series ; as for instance with the normal 
 generators of Siemens and Bur'gin. The Brush generator, 
 on the other hand, is capable of producing a current of 
 such intensity that 20, and even 40 lamps can be insertel 
 in a single circuit. From a Certain point of view, how- 
 ever, this is no advantage, for currents of such high in- 
 tensity very considerably affect the Colour as well as the 
 steadiness of the light. 
 
 With currents of comparatively large quantity arid low 
 intensity the light is steady, and in its colour resembles 
 sunlight ; for a greater part, of its lighting-power is due 
 to the incandescence of the electrodes. 
 
 It is difficult to determine accurately the Comparative 
 values of the generators which have as yet been constructed 
 for the purpose of electric lighting; for, as we already 
 pointed out in Chapter IIL> there is a lack of measure- 
 ments that are impartial and founded on the same basis 
 of comparison. 
 
 One of the most interesting communications on com- 
 parative experiments with light-machines of various con- 
 struction is to be found in the report by Tyndall and 
 Douglass, known as the " Keport to the Trinity House," 
 which embodies the results of experiments by an English 
 
184 ELECTRIC LIGHT GENERATORS. 
 
 committee, in 1877, with generators for producing the 
 light in light-houses.* 
 
 The generators employed in these experiments were 
 
 1. A Holmes magneto-electric generator, for producing 
 alternating currents. 
 
 2. An Alliance machine, also for generating alternating 
 currents. 
 
 3. A Gramme generator. 
 
 4. Two Gramme generators, coupled up. 
 
 5. A large Siemens generator. 
 
 6. A small Siemens generator. 
 
 The Gramme and Siemens generators were dynamos, 
 producing continuous or direct currents. 
 
 The Siemens generators were from the works of 
 
 X, Siemens Brothers, in London, and the Gramme generators 
 
 had been furnished by the " British Telegraph Manufac- 
 
 .. :J tory " in London, conducted by Eobert Sabine, to whom 
 
 % many suggestions as to the mode of measuring the light 
 
 are due. 
 
 The Alliance and the Holmes machines were already in 
 use at the South Foreland lighthouses, where the experi- 
 
 "} ments were carried out. 
 
 t 
 
 After various preliminary experiments, the generators 
 were tried on January 18th, with respect to the intensity 
 of the light produced. These intensities were determined 
 for diffused light, and for the light concentrated by re- 
 flectors. However, in the following table, we have to 
 deduct about sixty per cent, from the intensity of illu- 
 mination obtained with the dynamos, if we wish to regard 
 
 * These experiments, although at this date to be regarded as old, and 
 as made with machines the absolute efficiency of which has been consider- 
 ably increased, are yet the most valuable to the student. To the 
 engineer, who can sift for himself, there are, of course, later measure- 
 ments, such as those made at Munich, Vienna and Paris. EDITOR. 
 
SPECIAL DETAILS. 185 
 
 the light-intensity as a sign of the efficiency of the gene- 
 rator; for the carbons in the lamps were placed more 
 advantageously for these generators than for the alter- 
 nating current generators. 
 
 The table contains the mean value of the intensity of 
 light obtained from several experiments. 
 
 Concentrated light. Diffused light. 
 
 *- r J 
 
 Standard Candles. 
 
 1. Holmes' Generator . , 1494 1494 
 
 2. 2721 2721 
 
 3. Alliance . . 1953 1953 
 
 4. Gramme . . 5333 3215 
 
 5. 9126 5501 
 
 6. Siemens . . 14573 8784 
 
 7. 5920 3568 
 
 The intensity of illumination by a Gramme generator 
 to that of the small Siemens generator (No. 58) was in the 
 ratio of 100 to 100-6, and of the Holmes generator to the 
 Siemens generator in the ratio of 100 to 384. 
 
 The intensity of illumination with the No. 58 Siemens 
 generator to that with No. 68 generator was in the ratio 
 of 100 to 109-5. 
 
 The two lighthouses on South Foreland have different 
 heights ; the light of the one was 211-7 m., and that of 
 the other 180-6 m. distant from the engine-room. This 
 difference in distance was accordingly employed to 
 measure the loss of illuminating power for each generator 
 when the current was conducted from the engine-room to 
 the lamps, on the high and the low lighthouse. The 
 cable employed was made up of two cables, connected 
 with each other, each consisting of seven copper wires of 
 No. 14 Birmingham wire-gauge, and the circuit was led 
 
186 ELECTRIC LIGHT GENERATORS. 
 
 from the engine-room through both lighthouses, and back 
 to the lamp in the engine-room. 
 
 The loss of illuminating power, due to the resistance 
 interposed by these cables, was, 
 
 With the Holmes generator * . 29*8 per cent. 
 
 Gramme . 58*6 
 
 Siemens . . 80-4 
 
 On March 6th, the measurements were continued, after 
 the collector and the brushes in the Siemens generators 
 had been replaced by new ones J the intensity of illumi- 
 nation then was 
 
 With No. 58 Siemens gerierator, 4,446 standard candles. 
 
 With No. 68 Siemens generator > 6,513 
 
 For both generators together, 
 
 therefore . . . 11,009 
 
 When generators 58 and 68 were coupled together 
 electrically, they gave a light of 13,179 standard candles, 
 i.e., 19'7 per cent more than the sum of the intensities of 
 illumination with the separate generators. 
 
 The Holmes and the Alliance machine, which had both 
 been put up in the lighthouses in 1872, had lost con- 
 siderably since then in strength of current and lighting 
 power by the weakening of the magnetism of the steel 
 magnets the Holmes machine about 22 per cent., and 
 the Alliance machine about ten per cent. 
 
 Various other experiments were tried, which we cannot 
 here describe. 
 
 The results are apparent from the adjoining Table I. 
 
 We must not, however, forget that the report of these 
 experiments refers to generators of older construction. 
 Since then electric generators, and especially the Gramme 
 generators, have been much improved, as can. be seen 
 from the results which were obtained with them, accord- 
 
SPECIAL DETAILS. 
 
 187 
 
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188 
 
 ELECTRIC LIGHT GENERATORS. 
 
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SPECIAL DETAILS. 189 
 
 ing to the report on the experiments carried out at the 
 School of Military Engineering at Chatham, in the winter 
 1879-80. 
 
 This report is important in so far as the data given 
 were obtained from a large number of carefully-executed 
 experiments ; it is, however, impossible here to reproduce 
 the whole. 
 
 The results of this report are given in Table II., from 
 which we see that, calculating the mean intensity of 
 illumination per horse-power obtained with the several 
 generators, the Gramme generators this time gave the 
 best results. The intensity of illumination per horse- 
 power in standard candles is as follows : 
 
 For two Siemens generators, coupled side by 
 
 side 1428 
 
 Gramme-generator, type D * . . . 1821 
 
 (7 .... 2048 
 
 Two Gramme-generators, coupled side by side . 1916 
 
 Wilde's generator 877 
 
 The general advantages and disadvantages of the 
 Gramme generator D and of the Siemens generators are 
 summed up in the following criticisms : 
 
 GEAMME, TYPE D. 
 
 Advantages : 
 
 1. This generator gives a considerably stronger light 
 than any of the other generators tried. 
 
 2. The generator can be entrusted to less experienced 
 persons without fear of the wires suffering from heating 
 or sparking. 
 
 3. During six hours continuous working, under the 
 same conditions as with the Siemens generators coupled 
 side by side, and with a current of 58-5 amperes, the tern- 
 
i go ELECTRIC LIGHT GENERATORS. 
 
 perature of the wires only increased by 71F. Under the 
 same conditions the temperature of the drum of the 
 Siemens generators was raised 110F. and that of the 
 electro-magnets 85 Q F., with a current of 55 amperes. 
 The electro-magnets of the Gramme generator get more 
 heated than the revolving ring, so that the maximum 
 rise of temperature can be observed without stopping the 
 machine. 
 
 4. Absence of sparks. The sparking at the brushes is 
 "extremely feeble and often imperceptible; and con- 
 sequently the wear of the collector and brushes is very 
 slight. The brushes can easily be brought into the right 
 position, and are so arranged that if necessary they can 
 be shifted parallel to the axis of the collector. 
 
 5. Simplicity. The connections are very simple and 
 can be easily followed, 
 
 6. With a circuit of 0<498 ohm external resistance, 
 47*8 per cent, of effective work was done in the arc. 
 
 7. The number of revolutions is less than in the two 
 medium-sized Siemens generators, and less than half of 
 the number in the Gramme machine (1200) ; in con- 
 sequence, there is less wear and tear of the generator 
 and of the rubbing parts. 
 
 Disadvantages : 
 
 The cost of a Gramme generator, type D, is 360, and, 
 accordingly, about 1J times as great as that of the 
 Siemens generator. 
 
 GRAMME, TYPE C. 
 
 Advantages : 
 
 1. The generator can be attended to by persons who 
 have not much experience, without fear of the wires being 
 damaged by over-heating. In this respect, this generator 
 surpasses all the others experimented with. 
 
SPECIAL DETAILS. igi 
 
 2. During six hours continuous working, under the 
 same conditions as with the two Siemens machines and 
 the Gramme, type D, and with a strength of current of 
 about 83*15 amperes, the temperature of the wire in- 
 creased only 30 F. 
 
 3. Absence of sparks, see advantage 4 of Gramme D. 
 
 4. Compactness, see advantage 7 of Gramme D. 
 
 The price of this generator is 240, which is about 
 the same as that of two Siemens medium-sized gene- 
 rators. 
 
 Disadvantages : 
 
 1. The intensity of illumination is only 19,500 candles, 
 which is about as great as that of the two Siemens gene- 
 rators, and about 30 per cent, less than that of the 
 Gramme D, when making 500 revolutions. 
 
 2. The great speed of 1,200 revolutions per minute 
 would probably cause considerable wear of the machine 
 and its rubbing parts.* 
 
 Two A GRAMMES, coupled side by side. 
 Advantages : 
 
 1. Cheapness. The price of the two generators is 
 only 170. 
 
 2. These generators have about the same slight amount 
 of heating as the other Gramme machines. 
 
 3. Absence of sparks, see advantage 4 of Gramme D. 
 
 4. Using the generators separately, two lights can be 
 
 produced. 
 
 Disadvantages: 
 
 1. The amount of light obtained with these generators 
 is only 18,500 candles, and this is not sufficient for 
 military purposes. 
 
 * This increased wear of the rubbing parts of properly-constructed high 
 speed machines does not accrue in practice. EDITOR. 
 
ig 2 ELECTRIC LIGHT GENERATORS. 
 
 2. When the generators are coupled side by side an 
 inversion of the magnetism easily occurs, thus causing 
 great disturbances and much loss of time. 
 
 Two SIEMENS machines of medium size, coupled 
 
 up side by side. 
 
 Advantages : 
 
 1. By using the generators separately, two lights can 
 be produced. 
 
 2. The intensity of illumination is considerably greater 
 than with the other machines that were tried, excepting 
 the Gramme generators D and (7. 
 
 Disadvantages : 
 
 1 . The wires are easily heated if the persons in charge 
 are not very well acquainted with the working of this 
 generator ; it is also a disadvantage that the revolving 
 drum is more strongly heated than the electro-magnets. 
 
 2. When the generators are coupled up side by side 
 an inversion of the magnetism easily occurs, which 
 causes great disturbances and much loss of time. 
 
 3. If the lamps work irregularly, there is great spark- 
 ing at the brushes, causing rapid wear of the collector 
 and the brushes. 
 
 For these reasons more experience is necessary in 
 order to work these generators satisfactorily than with 
 the Gramme generators. 
 
 A report of an American committee on comparative 
 experiments with light-machines of various construction 
 is published in the Journal of the Franklin Institute 
 (1878, vol. 103, pp. 289-361), and the results of these 
 experiments can be seen from Table III. 
 
 The American reporters, Profs. Thomson and Houston, 
 remark, that if the results obtained by the American com- 
 
SPECIAL DETAILS. 
 
 193 
 
 I 
 
 UOq-TBO 
 
 JO azig 
 
 Intensity of 
 umination in 
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194 ELECTRIC LIGHT GENERATORS. 
 
 mittee are to be compared with the results of the English 
 experiments of 1877, the intensity of illumination of the 
 concentrated light, given in Table III., must be divided by 
 2*87, so as to equalise the difference in illuminating 
 power caused by the different position of the carbon- 
 points in the lamps. 
 
 In order to ascertain the ratio that the work expended 
 in driving the generator bears to the work done in the 
 luminous arc, the well-known French physicist Tresca, 
 carried out experiments with Gramme's dynamo-electric 
 generators, in the works of Sautter and Lemonnier in 
 Paris. The experiments on October 13th, 1875, were made 
 with a generator that could produce a light of 1850 
 Carcel lamps 13,690 candle power and, on September 
 4th of the same year, Tresca tested the efficiency of a small 
 generator capable of supplying a light of (300 Carcel 
 lamps) 2,220 candle power. 
 
 The following are the dimensions of the first generator : 
 
 Electro-magnets. 
 
 Diameter of the iron core of an electro- 
 magnet . . .- 4 . 70 mm. 
 Length of the iron core of an electro-mag- 
 net . V . , ' . . _, . 404 
 Diameter of each electro-magnet with its 
 
 wire coil % . . . * . 132 
 Diameter of the wire '." v : . . 3*3 
 Weight of the wire on each electro-magnet 24 kg. 
 
 Ring. 
 
 External diameter of the core of soft iron 195 mm. 
 Internal diameter of the core of soft iron . 157 
 Width of the soft iron core . 119 
 
 External diameter of the ring . . . 230 
 Internal diameter of the ring . . 120 
 
SPECIAL DETAILS. 
 
 195 
 
 Diameter of the wire coiling V&?\ . . 2*6 kg. 
 
 Weight of the wire coiling .;"'. " . 14'50 
 
 Conducting wires from the generator to the lamp : 
 
 Diameter . . . . . 7*8 mm. 
 
 Cross-section . . . . % . 47 sq.-mm. 
 
 Generator. 
 
 Total length, including pulley . ', . 800 mm. 
 
 Total height . . . . .". ' . 585 
 
 Total width 550 
 
 The smaller generator was simpler in its construction, 
 and had the following dimensions : 
 
 Electro-magnet. 
 
 Diameter of the iron core of an electro- 
 magnet 70 mm. 
 
 Length of the iron core of an electro-mag- 
 net 355 
 
 Diameter of the electro-magnet and its 
 
 wire coil 120 
 
 Diameter of the wire . . . 3-8 
 
 Weight of the wire on each electro-magnet 14 kg. 
 
 Ring. 
 
 External diameter of the soft iron core . 168 mm. 
 
 Internal diameter of the soft iron core . 123 
 
 Width of the soft iron core . . 101 
 
 External diameter of the ring . . . 203 
 
 Internal diameter of the ring . . . 119 ,, 
 
 Diameter of the wire . . . . 2 
 
 Weight of the wire 4-650 kg. 
 
 Conducting wires from the generator to the lamp : 
 
 Diameter ....... 2'6 mm. 
 
 Cross-section ...... 5'5 sq.-mm 
 
ELECTRIC LIGHT GENERATORS. 
 
 Generator. 
 
 Total length, including pulley 650 mm. 
 
 Total height . . . ;, . 506 
 Total width . "..' V . V . 410 
 
 The large generator supplied a regulator lamp of 
 Gramme's construction, the small one a Serrin lamp ; both 
 lamps had similar carbons of 8*1 sq.-mm. cross-section. 
 
 The distance of the lamps from the photometer was 
 measured, and at the same time a diagram was taken on 
 the dynamometer from the motor that worked the 
 generator, and the number of revolutions recorded. From 
 the data obtained the following table was constructed. 
 
 1. Large generator (16th October, 1875). 
 
 Katio of the distances of the electric lamp and of the 
 Carcel lamp from the photometer, 40 : 0*93. 
 
 Ratio of the illuminating power of the electric lamp 
 and the Carcel lamp : 40 2 : 0'93 2 =1850. 
 
 Number of 
 Trial. 
 
 Revolutions per 
 minute of the 
 Dynamometer. 
 
 Mean ordinates in 
 mm. , of the 
 diagram. 
 
 "Work in kilogr. 
 metres per 
 second. 
 
 I 
 2 
 
 3 
 4 
 
 6 
 
 238 
 
 251 
 
 248 
 244 
 241 
 244 
 
 22-50 
 18-89 
 21 74 
 16*60 
 
 I5-59 
 16-65 
 
 678-28 
 6oo'^6 
 682-82 
 
 5i3'oo 
 475'86 
 516-23 
 
 Mean 244 
 
 
 576*12 or 
 7 '68 horse-power 
 
 7-68 x 100 
 1850 
 
 Work per 100 Carcel lamps (740 candles) = 
 
 = 0*415 horse-power. 
 
 Work per Carcel lamp (per 7'4 candles), and per. 
 second = 0*31 kg.m. 
 
 2. Small generator (4th December, 1875). 
 
SPECIAL DETAILS. 
 
 197 
 
 Ratio of the distances from the photometer, 20 : 1*15. 
 Ratio of the light intensities, 20 2 : M5 2 = 302-4. 
 
 Number of 
 Trial. 
 
 Revolutions per 
 minute of the 
 Dynamometer. 
 
 Mean ordinates of 
 the diagram 
 in mm. 
 
 Work in kilogr. 
 metres per 
 second. 
 
 I 
 
 2 
 
 3 
 
 234 
 238 
 244 
 
 7-11 
 666 
 7-42 
 
 20173 
 20079 
 225-42 
 
 Mean 239 
 
 
 2io'65 or 
 2 '3 1 horse-power 
 
 Work per 100 Carcel lamps = 
 
 2-81 x 100 
 302-4 
 
 = 0-92 horse 
 
 power. 
 
 Work per Carcel lamp, and per second, = 0*69 kg.m. 
 
 The generators worked steadily, and were kept going 
 only as long as no heating was noticed. 
 
 Comparing the results obtained with the large and the 
 small generator, we see that in using the latter we re- 
 quire twice as much motive power to produce a light 
 equal to one Carcel lamp as is necessary when we 
 employ the large generator. These results agree with the 
 remark made in the previous chapter, that small machines 
 are never as advantageous as large ones. 
 
 The accuracy of this view is further confirmed by the 
 experiments of Prof. Hagenbach, carried out at the 
 Physico-Technical Institute, University of Basel. In these 
 experiments were used a Grramme generator from the 
 works of Heilmann, Ducommun and Steinlen, at Miihl- 
 hausen, a Serrin lamp, and a Bunsen photometer. For 
 the unit of light, the paraffin candle of 21-4 mm. diameter, 
 and 41-3 mm. length of flame was adopted. 
 
 The width of the generator, and the length of the 
 electro-magnet was 27 c.m. ; on the shaft there were 
 
198 
 
 ELECTRIC LIGHT GENERATORS. 
 
 two rings, each of 48 coils. The whole of the current 
 traversed the external circuit and was conducted round 
 the electro-magnet. 
 
 The resistance of the luminous arc in the lamp in 
 circuit was determined by first inserting the lamp in the 
 circuit, ascertaining the number of revolutions of the 
 armature, then removing the lamp and putting in as much 
 resistance in its place, till the original number of revo- 
 lutions and strength of current was again reached. The 
 result gave 4*75 Siemens' units, for the arc, to which 
 corresponds a total resistance of 6*63 units, during the 
 production of the light. 
 
 The following table gives the results of the measure- 
 ments for the intensity of illumination and the strength 
 of current. 
 
 Number 
 of Revolutions 
 per minute. 
 
 Intensity of 
 Illumination in 
 Standard 
 Candles. 
 
 Intensity of Cur- 
 rent in cubic 
 cm. of Gases per 
 minute. 
 
 Electromotive 
 Force in Deleuil 
 Elements. 
 
 1700 
 1800 
 1900 
 20OO 
 
 506 
 
 567 
 628 
 689 
 
 119 
 
 126 
 
 133 
 
 140 
 
 40*8 
 43'2 
 45-6 
 48-0 
 
 From this table it will be seen that with 1,800 revolu- 
 tions, an intensity of illumination was obtained of 567 
 paraffin candles, which is equal to that of 80 Carcel 
 burners ; and with a Prony brake-dynamometer it was 
 ascertained that for a speed of 1,800 revolutions per 
 minute, 90 kg. mets. of work had to be expended per 
 second. Consequently, in using the small generator 
 tested by Hagenbach, 1-1 kg. mets. of work had to be 
 expended to produce a light equal to 1 Carcel burner, 
 and, comparing the results obtained in Tresca's and 
 
SPECIAL DETAILS. 199 
 
 Hagenbach's experiments, we see that the smaller the 
 generator the more unfavourable were the results. 
 
 Work per second for 
 light = 1 Carcel Burner. 
 
 Generator to give light of 1850 Carcel Burners 0-3 kg.met. 
 
 302 0-69 
 
 5? 5) ?> 80 1*1 
 
 In his work on electric lighting, Fontaine reports on 
 experiments carried out in Gramme's laboratory with a 
 generator of new construction ; and from this work we 
 take the following data and tables. 
 
 The generator employed in the experiments was a 
 Gramme's light-machine of the normal type represented 
 in Fig. 29, which had been constructed at the works of 
 Mignon and Eouart. 
 
 The lamp was a Serrin regulator made by Breguet. 
 
 The carbons had a diameter of 13 mm., and were pre- 
 pared by Gaudoin's process. 
 
 The motor employed to work the generator was an 
 Otto gas-engine of 5 -horse power, and which was con- 
 nected with a Giroud gas-pressure regulator, introduced 
 to prevent differences in the pressure of the gas, which 
 might disturb the uniform working of the engine. 
 
 The Gramme generator was directly connected with the 
 gas-engine. 
 
 The specific resistance of the cables was 0*75, silver = 1, 
 and their cross section was 10 sq. mm. 
 
 The number of revolutions per minute of the gas- 
 engine was 160, and the expenditure of work was not 
 only calculated with reference to the number of ex- 
 plosions per minute, but in order to obtain trustworthy 
 numbers, it was measured directly after each light- 
 measurement. 
 
200 
 
 ELECTRIC LIGHT GENERATORS. 
 
 I. EFFECT OF THE NUMBER OF EEVOLUTIONS. 
 
 
 
 '-3 oi* 
 
 of 
 
 &1 
 
 o a 
 
 Intensity of Illu- 
 mination, in 
 
 Work expended, in 
 
 c 
 
 o >4 ^ 
 
 
 ?.| 
 
 o i 
 
 l.fl 
 
 IS 
 
 Carcel Burners. 
 
 kilog. metres. 
 
 ."S G O 
 G g -P< 
 
 _ o 
 
 
 rt S 
 
 j^ -4^ 
 
 
 
 
 Per 100 Units 
 
 
 ~ cu 
 
 &.S 
 
 2*1 
 
 <!} p. J 
 
 Measur- 
 
 
 
 of the mean 
 
 *o % 
 
 d 
 
 1 
 
 
 ed hori- 
 zontally. 
 
 Mean. 
 
 Total. 
 
 Intensity of 
 Illumination 
 
 &*~* ^ 
 
 700 
 
 IOO 
 
 3 
 
 1 60 
 
 320 
 
 185 
 
 57-81 
 
 130 
 
 725 
 
 IOO 
 
 3 
 
 243 
 
 486 
 
 165 
 
 33'95 
 
 220 
 
 750 
 
 IOO 
 
 3 
 
 295 
 
 59 
 
 I 9 2 
 
 3 2 '54 
 
 230 
 
 800 
 
 IOO 
 
 4 
 
 365 
 
 730 
 
 230 
 
 3I-65 
 
 2 35 
 
 850 
 
 IOO 
 
 5 
 
 488 
 
 976 
 
 282 
 
 28-89 
 
 270 
 
 900 
 
 IOO 
 
 6 
 
 576 
 
 1152 
 
 330 
 
 28-64 
 
 260 
 
 IOOO 
 
 IOO 
 
 10 
 
 646 
 
 1292 
 
 338 
 
 26*16 
 
 285 
 
 
 
 1 
 
 
 
 
 
 II. INFLUENCE OF THE DISTANCE BETWEEN THE 
 CARBON POINTS. 
 
 
 
 if 
 
 Q g 
 
 een Car- 
 , inmm. 
 
 Intensity of Illu- 
 mination, in 
 Carcel Burners. 
 
 Work expended, in 
 kilog. metres. 
 
 CO CO <. 
 MM M O 
 
 G g PH 
 
 > .3 
 
 *o 
 
 
 
 03 G 
 
 
 
 ^ | 
 
 
 
 
 Per 100 Units 
 
 2 jj 
 
 'U fl 
 
 -S'i 
 
 Measur- 
 
 
 
 of the mean 
 
 ^.S Ji 
 
 i 
 
 g 
 
 II 
 
 ed hori- 
 zontally. 
 
 Mean. 
 
 Total. 
 
 Intensity of 
 Illumination 
 
 3l 
 
 750 
 
 TOO 
 
 5 
 
 351 
 
 702 
 
 175 
 
 25- 
 
 301 
 
 75 
 
 IOO 
 
 4 
 
 321 
 
 642 
 
 186 
 
 29- 
 
 259 
 
 75 
 
 100 
 
 3 
 
 2 95 
 
 590 
 
 I 9 2 
 
 32'^ 
 
 28l 
 
 75 
 
 IOO 
 
 2 
 
 2 5 6 
 
 512 
 
 214 
 
 41*7 
 
 214 
 
 75o 
 
 IOO 
 
 I 
 
 225 
 
 45 
 
 233 
 
 51-6 
 
 145 
 
 75 
 
 IOO 
 
 O 
 
 140 
 
 280 
 
 330 
 
 117-8 
 
 63 
 
SPECIAL DETAILS. 
 
 201 
 
 III. INFLUENCE OF THE LENGTH OF THE CABLE.* 
 
 volutions 
 inute. 
 
 3 
 
 si 
 
 H 
 
 Intensity of Illu- 
 mination, in 
 Carcel Burners. 
 
 Work expended, in 
 kilog. metres. 
 
 .-si 1 
 
 si i 
 
 o S 
 
 
 -fJ "t^ 
 
 
 
 
 Per 100 Units 
 
 1 1 02 
 
 *s 
 
 tig 
 
 f2 Q 
 
 Measur- 
 
 
 
 of the mean 
 
 JS-^ 
 
 & 
 
 a 
 
 <u 
 
 cS fi 
 
 ed hori- 
 
 Mean. 
 
 Total. 
 
 Intensity of 
 
 .!i>fe 
 
 5 
 
 (3 
 
 ^ 
 
 zontally. 
 
 
 
 Illumination ^^ ^ 
 
 750 
 
 IOO 
 
 4 
 
 321 
 
 642 186 
 
 28-9 
 
 267 
 
 800 
 
 150 
 
 5 
 
 345 
 
 670 
 
 230 
 
 33'3 
 
 225 
 
 825 
 
 200 
 
 5 
 
 315 
 
 630 
 
 232 
 
 36-8 
 
 178 
 
 8 5 o 
 
 300 
 
 5 
 
 275 
 
 550 
 
 225 
 
 40-9 
 
 
 900 
 
 400 
 
 5 
 
 260 
 
 520 
 
 241 
 
 46*3 
 
 162 
 
 950 
 
 50O 
 
 5 
 
 245 
 
 49 
 
 230 
 
 46*1 
 
 160 
 
 1000 
 
 750 
 
 5 
 
 236 
 
 472 
 
 243 
 
 51-4 
 
 145 
 
 IIOO 
 
 1000 
 
 5 
 
 215 
 
 430 
 
 256 
 
 59'5 
 
 126 
 
 '350 
 
 2000 
 
 5 
 
 160 
 
 320 
 
 230 
 
 718 
 
 104 
 
 IV. INFLUENCE OF THE LENGTH OF TIME DURING WHICH 
 THE GENERATOR WAS WORKED. 
 
 volutions 
 inute. 
 
 * H C 
 
 ~- - ~ 
 
 2 OT . o g 
 
 Length 
 
 Intensity of Illu- 
 mination, in 
 Carcel Burners. 
 
 Work expended, in 
 kilog. metres. 
 
 *- 
 ||1 
 
 r S 
 
 g -g ~g 
 
 of 
 
 1 
 
 Per 100 Units 
 
 
 * 
 
 "80.3 ^2 
 
 Working. 
 
 Measur- 
 
 
 of the mean 
 
 ^^^ 
 
 . P^ 
 
 
 
 ed hori- 
 
 Mean. 
 
 Total. Intensity of 
 
 
 
 & 
 
 ^ 02*J 
 
 
 zontally. 
 
 
 Illumination 
 
 ^ * 
 
 75 
 
 IOO 
 
 2 
 
 Starting. 
 
 199 
 
 398 
 
 214 
 
 537 
 
 ^39 
 
 750 
 
 IOO 
 
 4 
 
 15 mm. 
 
 180 
 
 380 
 
 183 
 
 50-8 
 
 147 
 
 760 
 
 IOO 
 
 4 
 
 30 
 
 175 
 
 350 
 
 194 
 
 55'4 
 
 T 35 
 
 75 
 
 IOO 
 
 4 
 
 i hour. 
 
 181 
 
 362 
 
 191 
 
 53' 
 
 142 
 
 75 
 
 IOO 
 
 4 
 
 2 ,, 
 
 191 
 
 382 
 
 I 9 2 
 
 50-2 
 
 149 
 
 75 
 
 IOO 
 
 4 
 
 3 > 
 
 190 
 
 380 
 
 190 
 
 So' 
 
 150 
 
 * In all the experiments the cross section of the cable was 10 sq. mm. 
 
202 ELECTRIC LIGHT GENERATORS. 
 
 For measuring the intensity of illumination, a Foucault 
 photometer was employed. 
 
 The tables, pages 200 and 201, contain the results of 
 the experiments. 
 
 The last column in Table I. shows that a light of 285 
 Carcel burners (1,909 standard candles) was obtained per 
 horse-power, which is a far more favourable result than 
 any given by other experimentalists. 
 
 Table II. shows the effect of the distance between the 
 carbons; the length of the cable and the number of 
 revolutions being constant. For practical purposes, how- 
 ever, the distances given are not all applicable, for if the 
 distance between the points of the carbons was 5 mm., the 
 light burnt very unsteadily, and it was only the results 
 obtained with a distance of 3 mm. that were of practical 
 value. 
 
 Table III. shows the influence due to the length of the 
 conducting wires on the expenditure of work (and on the 
 intensity of the light.) 
 
 From Table IV. it can be ascertained what is the 
 ratio between the current when the dynamo is started, 
 to the current when equilibrium is established. 
 
 According to Fontaine, the result shows that, using 
 a Serrin lamp the most satisfactory results are obtained 
 with the Gramme generator (normal Type) working at the 
 speed of 750 revolutions, with the carbon points 3 mm. 
 apart and the cable having a length of 100 mm. 
 
 The mean intensity of illumination (of the diffused 
 light) is then equal to 590 Carcel burners for an expendi- 
 ture of work of 192 kgr. met. (2'55-horse power), and 
 this corresponds to 32*5 kgr. met. per 100 Carcel 
 burners. 
 
CHAPTER IX. 
 
 VARIOUS APPLICATIONS OF ELECTRIC GENERATORS. 
 
 No other application of electric machines has been so 
 successful as their employment for lighting; but in 
 other ways these machines have proved of great value ; 
 and in various industries their introduction in place of the 
 batteries formerly used has brought about so complete a 
 revolution that we can predict with certainty, that these 
 generators are not only destined to supplant almost all 
 other methods of producing currents, but also that in- 
 numerable applications will still be found. 
 
 Electric generators for plating and electrotyping pur- 
 poses, for instance, render excellent service, and, in them, 
 we not only have apparatus that is more cleanly and con- 
 venient, supplying electrical energy more cheaply than 
 galvanic batteries, but, what is far more important, the 
 current remains perfectly constant and uniform. It was 
 only by employing electric generators, that it became 
 possible to execute the delicate and artistic pieces of 
 galvano-plastic workmanship as are, for instance, supplied 
 by the firm of Christofle & Co., in Paris ; or, that the 
 coating of very oxidizable metals with other metals could 
 be effected on the present scale. Since the invention o^ 
 electric generators, gilding, silvering, nickeling and 
 tinning have become so universal that it is only 
 in few branches of the trade that easily oxidized 
 metals are employed without an artificial coating, and 
 
204 ELECTRIC GENERATORS. 
 
 these coatings are not only an important advance from 
 an artistic point of view, but the durability of all articles 
 made of common metals is greatly enhanced. 
 
 With regard to the construction of generators intended 
 for galvano-plastic purposes, we have to remember that, 
 unlike the light-generators, they have to produce 
 currents of comparatively low intensity, but of large 
 quantity. In plating and typing machines therefore, 
 constructors have endeavoured to employ coils of very 
 thick wire. In principle, generators with electro-magnets, 
 which receive their current from an exciting machine, 
 would probably be the best for galvano-plastic purposes, 
 for with these generators there would be no fear of an 
 inversion of the current from the polarisation of the 
 electrodes ; at present, however, dynamo-electric genera- 
 tors are chiefly used, modified in construction, or con- 
 nected with special current interrupters, to prevent a 
 change of polarity of the field-magnets. 
 
 In order to understand this, we must remember that 
 if the field -magnets of the generator are inserted in the 
 same circuit with the galvano-plastic apparatus (as is, in 
 fact, the case if the dynamo-electric principle is alone 
 employed), a current of opposite direction, which has 
 been generated in the galvano-plastic bath by the polarisa- 
 tion of the electrodes, will traverse the coils of the 
 electro-magnets when the generator is brought to a stand- 
 still. This current then suffices to impart a small amount 
 of residual magnetism to the iron cores, converting the 
 former south and north poles into north and south poles 
 respectively. If we again set the generator in motion, 
 this polarity will start the new current, and accordingly, 
 a current will enter the galvano-plastic apparatus, which 
 will have a direction opposite to that of the original 
 
VARIOUS APPARATUS. 205 
 
 current, and which will, of course, re-dissolve the deposit, 
 and destroy the previous work. 
 
 This evil can only be remedied by not alone employing 
 the dynamo-electric principle in the generators, but by 
 conducting a portion only of the current through the 
 galvano-plastic baths, whilst the other portion is used to 
 excite the field-magnets ; or the return of the opposite 
 current can be prevented by the use of a current inter- 
 rupter, an apparatus that interrupts the connection of the 
 conducting wires between the galvano-plastic bath and 
 the generator, at the moment when the latter stops, or 
 when the current generated by it can no longer keep 
 back the opposing current. Many such current inter- 
 rupters have been constructed. 
 
 The current interrupter employed by Gramme con- 
 sists of a balanced piece of iron which has a counter- 
 weight. It connects the brushes which bear on the 
 collector with the electro-magnets. As long as the 
 armature of the generator rotates with a certain speed, 
 the magnetism of the electro-magnets is strong enough 
 to hold the piece of iron by the power of attraction. As 
 soon, however, as the speed slackens, and the current 
 accordingly becomes weaker, the magnetism of the elec- 
 tro-magnets is diminished, the piece of iron falls off, and 
 the circuit is interrupted between the electro-magnets and 
 the galvano-plastic apparatus which is connected with the 
 brushes ; no polarising current can, therefore, reach the 
 magnetising coils of the machine. 
 
 Western's circuit closer is rather more complicated. 
 It consists of a small iron column, which carries a spindle 
 in a horizontal collar, and on the spindle is a disk pro- 
 vided with two radial grooves. In each groove of this 
 disk there is a metallic slide-block, and when the gene- 
 
206 ELECTRIC GENERATORS. 
 
 rator is not working (the disk rotates simultaneously 
 with the armature) this block is pressed towards the 
 centre by a spiral-spring, where it rests on a metallic 
 nave, which is insulated from the disk. A metallic spring, 
 connected with one of the conducting wires, bears on the 
 nave, whilst the slide-blocks are connected with the other 
 conducting wire. When, therefore, the generator is at a 
 standstill, the slide-blocks and the nave are in metallic 
 contact, and these remain so, as long as the rate of 
 rotation is not great and the current is but weak ; in this 
 case, therefore, the latter will flow through the short 
 circuit established by the current-closer. However, if 
 the speed of rotation of the armature and, therefore, also 
 of the disk increases, the two slide-blocks are driven 
 towards the circumference by the centrifugal force, and 
 are pulled away from the metal nave. The current must, 
 therefore, now flow through the galvanoplastic apparatus 
 and the coils of the electro-magnets, that is, it must 
 traverse the larger circuit. From what we have said, it 
 will be seen that, while Gramme prevents polarising 
 currents entering the coils of the electro-magnets of the 
 machines, when the speed slackens, by interrupting the 
 circuit, Weston attains the same result by establishing a 
 shunt-circuit which is selected by the current, on account 
 of its smaller resistance, as soon as the metallic contacts 
 allow it. 
 
 Mohring's current interrupter is only a modification 
 of the Weston current closer. 
 
 In Mohring's generator, the disk of the current-closer, 
 which has three slide-blocks, is connected with the col- 
 lector. These slide-blocks bear against the rim of the 
 disk only when the generator attains a certain speed, thus 
 producing metallic connection between the parts of the 
 
VARIOUS APPLICATIONS. 207 
 
 collector ; but, when the generator revolves slower, the 
 slide-blocks are not in contact with the rim, and the 
 circuit is thus interrupted. 
 
 Besides the current closers and interrupters we have 
 described, there are others that have done good service, 
 but a description is superfluous, as the principle will be 
 understood from what has been said, and the construction 
 can, of course, be varied in numerous ways. 
 
 If magneto-electric generators are employed for 
 galvano-plastic purposes, wliose field-magnets are not in 
 the same circuit as the galvano-plastic bath, no pre- 
 cautionary apparatus is necessary for preventing polarising 
 currents from entering the generator. 
 
 The application of dynamos for obtaining pure metals 
 on a large scale was mentioned when we were describing 
 Siemens' generators ; we also called attention to the ap- 
 plication of electric machines to the preparation of ozone, 
 and from the results obtained we may conclude that in 
 time the employment of electric generators in the various 
 branches of industry will attain great importance. 
 
 Another application of the electric current worth men- 
 tioning, and which only became possible through the in- 
 vention of electric generators, is the melting of very 
 refractory metals. 
 
 The extremely high temperature necessary to melt 
 platinum and iridium, formerly made the working of 
 these metals very difficult and expensive, whereas by 
 means of the great heat which powerful electric currents 
 can produce, it is comparatively easy now to work them* 
 as well as to carry out those chemical reactions, and de- 
 compositions which require a specially high temperature. 
 
 Sir William Siemens, of London, deserves the merit of 
 having constructed a suitable apparatus for melting re- 
 
208 ELECTRIC GENERATORS. 
 
 fractory metals by means of the electric current. The 
 Siemens smelting apparatus consists of a crucible made of 
 graphite, or some other refractory material, which is 
 placed in a metal vessel. The crucible, does not, how- 
 ever, touch the inside of the metallic vessel, but is 
 separated by a layer of pounded wood, charcoal, or some 
 other bad conductor of heat. The positive electrode, a 
 bar of gas-carbon, projects through the bottom of the 
 crucible into the interior, whilst the other electrode, re- 
 presented by a rod of compressed carbon, passes through 
 the cover of the crucible. Both electrodes are kept at a 
 suitable distance from each other by an automatic regu- 
 lator, of simple construction, and the electric arc thus 
 remains uniform. When a dynamo was employed, which 
 absorbed 4 horse-power in its working, and produced a 
 current of 36 amperes, Siemens found that a crucible 
 20 c.m. in depth was rendered white hot in less than a 
 quarter of an hour ; and that in the next quarter of an 
 hour a kilogramme of steel could be caused to melt. The 
 subsequent meltings were carried out even more rapidly. 
 
 Electric generators are now used most successfully in 
 telegraphy. The first experiments were carried out in 
 India, in the autumn of 1879, by L. Schwendler, who con- 
 ducted a portion of the powerful current of a dynamo, 
 used in the telegraph workshops of the Alipore govern- 
 ment for lighting, through the 850 miles of telegraphic 
 wire between Agra and Calcutta, and with it he was able 
 to transmit a number of telegrams without change being 
 noticed in the brightness of the electric light, for the 
 portion of the current conducted away was only about *004 
 of the total current. 
 
 Encouraged by this favourable result, Schwendler sup- 
 plied all the wires of the Calcutta telegraph office with 
 
USES IN TELEGRAPHY. 209 
 
 branch currents from a dynamo, and the result was most 
 satisfactory. In other places, too, electric generators have 
 proved of use in telegraphy. 
 
 L. Kohlfiirst, of Prague, employed a small magneto- 
 electric machine for the same purpose, and with it he 
 worked three Morse printing telegraphs. Very satis- 
 factory results too were obtained with electric generators 
 at the Central Station of the Western Union Telegraph 
 Company, in New York. They did not, as in Schwend- 
 ler's experiments, use only one generator, from which the 
 various currents were branched off; but a number ot 
 Siemens generators, whose electro-magnets were excited 
 by the current from a dynamo, were coupled up, and 
 the necessary currents were thus produced. 
 
 The result was so favourable that the Western Union 
 Telegraph Company now solely employ electric generators 
 for telegraphic purposes, instead of batteries. The current 
 of these machines supplies the 360 wires issuing from the 
 principal station, and also the cables of the Gold and 
 Stock Telegraph Company. 
 
 The generators occupy only a tenth of the space for- 
 merly taken up by the batteries, and one engineer is able 
 to look after the whole of them. 
 
 The company believes that through the introduction of 
 electric machines the working expenses will be reduced 
 50 per cent. 
 
 We have already mentioned the employment in physical 
 laboratories and for medical purposes of the smaller 
 electric generators, worked by hand or foot, and with re- 
 gard to these we need only add that as soon as the 
 expense of their construction is diminished, they will 
 quite possibly definitely replace galvanic batteries. 
 
 The most interesting application of electric machines, 
 
2io OTHER APPLICATIONS. 
 
 and that which has the greatest future, is their applica- 
 tion to the transmission of power. 
 
 As regards this application we shall in the present 
 volume confine ourselves to a few general statements. 
 The principle of the electrical transmission of energy 
 is that by transmitting the motion of a steam-engine, 
 or any other motor, to an electric generator a current 
 is produced, and by means of conducting wires this 
 current is then conducted to a second electric generator, 
 where it is again converted into mechanical work. In 
 this way the work done by a steam-engine can be trans- 
 mitted to any distance. It is true that as yet we have not 
 succeeded in effecting this transmission economically, and 
 that, with generators as constructed at present only about 
 50 per cent, of the work done at one station is obtained 
 again at the other station. When, therefore, the motive 
 power has to be provided by an expensive method, the 
 electric transmission of energy rarely pays. 
 
 At first, it was supposed that the transmission of an 
 immense amount of energy, such as that of the Niagara 
 Falls, would necessitate an inordinately thick cable. Prof. 
 Perry, of London, however, explained in a lecture, given 
 at the Society of Arts, on March 24, 1881, that with a 
 suitable arrangement of the generators employed, and 
 with sufficient insulation, the whole energy of the Niagara 
 Falls might be transmitted to New York through a tele- 
 graph wire. 
 
 Amongst the applications which have as yet been made 
 of the electrical transmission of energy, are the working 
 of agricultural machines by means of stationary motors at 
 a great distance, as for instance, in the experiments of 
 Chretien and Felix, at Sermaize ; the electrical railways 
 of Siemens-Halske, electrical lifts, &c. The time is not 
 
POWER TRANSMISSION. 211 
 
 far off when it will be possible to transmit energy from 
 large central stations, in the form of the electric current 
 to all the houses of a town. There the inhabitants 
 will then be able to convert it into light, heat, or me- 
 chanical energy as they like, and to employ it for all 
 possible purposes. There is no doubt but that in. time 
 magneto and dynamo-electric generators are destined in 
 many cases to replace steam motors. 
 
212 CONSTRUCTION OF ELECTRO-MAGNETS. 
 
 APPENDICES. 
 
 CHAPTER X. 
 
 FORMULAE FOR THE CONSTRUCTION OF ELECTRO-MAGNETS. 
 
 ALTHOUGH in this book we have assumed that the reader 
 has a general knowledge of the theory of magnetism, and 
 although it is outside our scope to enter fully on theo- 
 retical questions, still it appears desirable that, in a 
 manual on electric generators, the formulae should be 
 given that relate to the construction of the most im- 
 portant parts of these generators, the electro-magnets. 
 Accordingly, as a supplement to Chapter VII., we give 
 some equations by which, according to Du Moncel, the 
 best conditions for the maximum intensity of the mag- 
 netic moment, and of the attractive power, can be easily 
 found. 
 Let 
 
 a = the thickness of the magnetising coiling ; 
 
 6 = the total length of the two coils, or of the two 
 limbs of the magnet ; 
 
 c = the internal diameter of the coils, which practically 
 is assumed as the diameter of the magnetic core ; 
 
 g = the diameter of the wire and insulating material ; 
 
 A = the attractive power of the horseshoe magnet ; 
 
 E = the electromotive force of the current ; 
 
 M = the magnetic moment ; 
 
 H = the length of wire on the exciting coil ; 
 
TURNS OF WIRE. 213 
 
 / = the strength of current in the whole circuit ; 
 t = the number of turns of wire on the limbs of the 
 
 magnet ; 
 R = the resistance of the external circuit. 
 
 In this case we can denote the number of turns of wire 
 
 in each layer by , and the number of layers in each 
 y 
 
 ., , a 
 coil by . 
 
 y 
 
 The number of turns of wire will, accordingly, be ob- 
 tained from the equation 
 
 b a ba ,,. 
 
 t X = -^T. (1) 
 
 9 9 tf 
 
 Further, the length of a turn, in the layer which lies 
 directly on the core, is 
 
 2 
 and the length of a turn in the outermost layer is 
 
 c + 2a - g m 
 - 2 ~~ ' 
 
 consequently the total length of the wire in each of these 
 two layers is 
 
 9 9 
 
 Now, as the layers between these two form an arith- 
 metical progression, the first and last terms of which are 
 given by the two preceding expressions, and as the 
 
 number of terms is equal to , we find the total length 
 
 y 
 of the wire in the exciting helix from the equation 
 
 TT _ b 2ir(c + g + c + 2a p} a _ TT b a (a + c) , 
 
 ~ ~~ ~ 
 
2i 4 CONSTRUCTION OF ELECTRO-MAGNETS. 
 
 The values of t and H are therefore functions of those 
 for a, 6, c and g ; and having measured the thickness of 
 the insulated wire, and the thickness and length of the 
 coil, and having counted the number of turns in the 
 coil, we can easily calculate the length and number of 
 the turns wound on a magnetic core, if we divide the 
 length of the coil by the number of turns, and determine 
 the difference between the external and internal diameter 
 of the coil. Similarly, we can, if necessary, find the values 
 for a and g from the above equation, or establish other 
 expressions for A and H. 
 
 The electro-magnetic force of the magnet is found by 
 taking into account the laws of Jacobi, Dub, and Muller, 
 who have determined that the actual strength of a mag- 
 net or, according to the physical term, its magnetic 
 moment, M is equal to the strength of the current 
 flowing through the magnetising helix, multiplied by 
 the number of turns of wire, and that its power of attrac- 
 tion, A, is equal to the square of the magnetic moment. 
 
 From this we get the formulae 
 
 Et EH* 
 
 ~ R + H a = (R + HV ' 
 
 Now, if in these formulae we substitute the values for 
 t and H previously found, we obtain the equations 
 
 M 
 
 M = Q j- 7 - r and 
 
 + TT 6 a (a + c) 
 
 -He 
 
 These equations show that we can obtain maximum 
 values of strength for M and A in various ways, accord- 
 ingly as we change the value for a, 6, c or g. The prin- 
 
MAGNETIC MOMENT AND ATTRACTION. 215 
 
 cipal conditions on which these maxima depend are : 
 1, The resistance of the coil ; 2, The ratio of its diameter 
 to the diameter of the core ; 3, The dimensions of the 
 magnet itself. 
 
 In practice, it will always be desirable to find an ex- 
 pression for R, which expression will be a function of the 
 resistance of the magnetising coil. This is arrived at in 
 the following way. 
 
 First of all we divide g, which denotes the diameter of 
 the wire and its insulation by a coefficient, /, in order to 
 obtain the diameter of the bare wire, as it is that alone 
 which comes into consideration when we calculate the 
 resistance. (In practice, this coefficient may be taken 
 as 1*6 for very fine wires, and as 1*4 for medium wires.) 
 
 The diameter of the bare wire is therefore -^- ; and if by 
 
 q we denote the ratio of the efficiency of conductor R to 
 that of conductor H (including the constants, referring 
 to conductivity per unit of cross-section, which is 
 
 0-000016), we obtain ^JT~ as the reduced value for R. 
 
 Because, with the increase in thickness (-^-) of the 
 
 wire, not only the resistance of a coil of constant diameter, 
 but also the length of its wire, is diminished two 
 values which vary at the same rate the resistance, H, 
 of the coil will be inversely proportional to g*, instead 
 
 of to <7 2 , but the quantity, -^^~ 9 will remain inversely 
 
 proportional to # 2 , so that for the nominators of M and A 
 we get the following expressions : 
 
 +46a(q + c)/ 2 ; rqRg* 4 b a (a + i)/ 2 "! 
 /V L /V 
 
216 CONSTRUCTION OF ELECTRO-MAGNETS. 
 
 The values for M and A themselves are : 
 
 C ' ' (3) 
 
 A = 
 
 Having thus determined the values for M and J., the 
 question arises as to what are the conditions for obtaining 
 maximum values for A and M. We shall first con- 
 sider 
 
 I. The dependence of the maximum values of A and 
 M on the resistance of the magnetising coil. 
 
 This dependence would have to be ascertained if we 
 were desirous of employing an electro-magnet of given 
 dimensions, and wished to select such a thickness of wire 
 as would enable us to obtain a maximum for the values 
 A and M, when the resistance of the external circuit 
 is given ; or if, with a given external resistance, we 
 wished to employ a particular kind of wire for the 
 magnetising coil, and wished to calculate the dimen- 
 sions of the latter, with which M and A would obtain 
 their maximum values. In the first case, the variable 
 is </, or the diameter of the wire ; in the second case, it is 
 the thickness of the coil. 
 
 If we now take into consideration that, in the formulae 
 
 (3), the diameter of the wire is not g, but -^4-, in which 
 
 expression / denotes a constant, we see that the calcula- 
 tion is not so simple as it would seem to be at first sight. 
 The physicists who first occupied themselves with this 
 question had assumed that they might neglect / entirely 
 in the calculation, and might put g for the diameter of 
 the wire and its insulation. Even when the value for / 
 was taken into account as, for instance, in the formulas 
 
MAXIMA. 217 
 
 (3) it was supposed that this value could not be ex- 
 pressed by a constant when the value of g varied, and in 
 consequence the final results obtained were different. 
 
 Considering the question from the simplest point of 
 view, we see that the maximum values for M and A are 
 obtained when 
 
 q Kg* _ TT b a (a + c) 
 
 7*~ ~g*~ 
 
 that is, when R = H ; or, in other words, the most ad- 
 vantageous diameter of the wire will be that which makes 
 the resistance of the magnetising coil equal to that of the 
 external resistance. 
 
 If we take the thickness of the insulating covering into 
 consideration, the coil that will render the best service will 
 be that of which the resistance is to the resistance of the 
 external circuit as the diameter of the bare wire is to the 
 diameter of the insulated wire. 
 
 Another law which can be deduced from these formula 
 is : 
 
 Of different magnetising coils that have wires of the 
 same diameter, but contain different numbers of turns, 
 the most efficient will be that in which the resistance is 
 to the resistance of the external circuit as the thickness 
 of the coiling and of the iron core is to the thickness of 
 the coil alone. 
 
 II. Dependence of the maximum strength of A and M 
 on the ratio of the thickness of the magnetising coil to 
 the thickness of the iron core. 
 
 As the strength of an electro-magnet increases with the 
 dimensions of the core, and as the resistance of the 
 exciting coil also increases proportionally to these dimen- 
 sions, we must, of course, ultimately reach a maximum for 
 the magnetic intensity ; and it is i 
 
2i8 CONSTRUCTION OF ELECTRO-MAGNETS. 
 
 struction of electro-magnets, to know the law with regard 
 to this maximum. 
 
 This law is obtained from the following equations, 
 
 g*EV^ g*E*c 
 
 ' TTT&O + C) ' - [\^ba(a + c)] 2 
 
 where X is a coefficient, with which the length of the wire 
 in the coil must be multiplied in order to obtain a maxi- 
 mum in the circuit ; and if the values of A and M are 
 ascertained with regard to c and have been equated, it will 
 be seen that maximum values are obtained for them, when 
 a = c, that is, when the thickness of the exciting coil is 
 equal to the diameter of the iron core. 
 
 The calculation for the maximum of A and of M is now 
 very simple, since, under the conditions found for the 
 maximum, the expression for the length of the wire in the 
 
 magnetising coil becomes % , and if we express the 
 
 length b of the magnets as a function of the diameter c, 
 by multiplying the latter by m, which experiments shew 
 to be equal to 12, for the two branches of the magnet, we 
 obtain the expression 
 
 2?r c 3 m 75-4 x c 8 
 
 in which the values of c and g occur. For the number of 
 turns t, we then get 
 
 12 c 2 
 
 Now, we see that A and M are maximum values when 
 R = JET, a = c, b = cm, and it follows that as g is not 
 known we must find a value for R, that is a function of g, 
 and this we get from the value of 
 
 TT 2ir c 3 m 
 n. = * 
 9' 
 
LENGTH OF CORE. 219 
 
 which is equal to R, and we write 
 
 From this it follows that 
 
 <^=/^ 2 -^; (6) 
 
 and, finally, because - is a constant, which is composed 
 of known numbers and is 0*00020106, we get the equation 
 
 ff = rf f/^ x 0-00020106. (7) 
 
 III. The dependence of the maximum strength of M 
 and A on the length of the iron core. 
 
 From what has been said, it appears that it is important 
 for the calculation, that the length of the magnetic core 
 be expressed as a function of its diameter, but it is still a 
 question whether the iron core may be lengthened 
 indefinitely or whether we can also determine a maximum 
 value for this length. 
 
 Since according to Miiller's law, the values of A and M 
 are proportional to the square root of the diameter, we 
 can find no maximum values in these cases, as long as b 
 varies ; but if we express b as a function of the diameter 
 c, the power of attraction becomes proportional to c m */ c 
 or to cf ; if we now take into consideration all the condi- 
 tions found so far for the maximum strength, we get 
 
 " \R g* + 2,r c*ri}* 
 
 in which equation R is represented by a certain length of 
 wire of the coil. 
 
 From this equation we then further obtain 
 
220 CONSTRUCTION OF ELECTRO-MAGNETS. 
 
 In other words : we can increase the dimensions of the 
 iron core till the resistance of the magnetising coil is eleven 
 times as great as the resistance of the external circuit. 
 
 In that case we get -p a 
 
 m = 11^-% 
 
 27TC 3 
 
 and from this we see that m is eleven times as great as 
 the ratio of the resistance R of the external circuit, to 
 that of the coil, for which latter in this case we have the 
 
 2?r c 3 
 expression g . Now, because in order to obtain the 
 
 maximum intensities for A and M 9 the two resistances, as 
 we have seen, ought to be equal, it follows that their 
 ratio is equal to 1, and m in consequence =11. Practi- 
 cally, however, we must assume m to be = 12, on account 
 of the magnetic poles usually having rather larger dia- 
 meters than the core, the wires, too, as a rule, not being 
 directly wound on to the iron, and on account of similar 
 minor causes, on which the deviations from theory depend. 
 From the preceding formulae, some important conse- 
 quences may be deduced : 
 
 1. For equal circuit resistance, the diameter of the 
 electro-magnets under maximum conditions should be 
 proportional to the electromotive forces employed. 
 
 2. For equal electromotive forces, the diameter should 
 be in inverse ratio of the square root of the resistance of 
 the circuit, comprising that of the generator. 
 
 3. For equal diameters, the electromotive forces should 
 be proportional to the square roots of the resistance of the 
 circuits. 
 
 4. For a given electro -magnetic force, and with electro- 
 magnets under their conditions of maximum, the electro- 
 motive force of the generators should be proportional to 
 the square roots of the resistance of the circuits. 
 
CO-EFFICIENT K. 221 
 
 If it be considered that the expression I 2 ft of , which 
 represents this force, may be converted by successive 
 
 substitutions in the values of J, of , and of c, into -j~ x -j* 
 
 ! / 
 a formulae in which Q is a constant equal to 2228 (if the 
 
 electromotive force be taken in unity of a DanielFs 
 element, and the resistance in metres of telegraph wire), 
 there is attained for the same attractive force the ratios 
 
 El- R% E V~R 
 T = 77 or ~~ ~ 7 * ln va l ues K an( i ** there 
 
 come in the numbers n and n r of elements employed, 
 these numbers may be easily calculated, knowing the 
 values of the constants e and p of the elements employed, 
 
 ne ^ n p*+ r j .j. , i LJ 
 
 for -7. = . r =, and if the accentuated quantities 
 ^rc'p' + r' 
 
 refer to those of a known typical electro-magnet, the 
 value of n may be 'easily deduced. 
 
 If, in the problem to be solved, the attractive force of 
 the electro-magnet is expressed as a weight P, and 
 modifying this value by a co-effcient J5T, which represents 
 
 F' 
 the ratio -p-, deduced from data from the typical electro- 
 
 magnet, there may be taken for the value of this con- 
 
 0*002297 
 stant for attraction at 1 millimetre, nfi85 ? or sa ^ 
 
 0*00008555. It may be remarked that the quantity F 
 in this ratio represents, for the typical electro-magnet, 
 the formula P t 2 cf or its equivalent ; and it will result 
 from putting ne% Q __ p .,. 
 
 7* ' 
 
 ne = 
 
222 CONSTRUCTION OF ELECTRO-MAGNETS. 
 
 and if the two constants Q and K be combined, 
 
 n ** = ( 0-0225 l/vjn-*\*. 
 
 n p -f r \ ) 
 
 Eepresenting by M the parenthetic quantity, which 
 may be easily calculated, 
 
 If instead of a simple circuit, there were a? derivations 
 from the same pole of the battery, and on [these deriva- 
 tions are interposed electro-magnets of equal resistance 
 and dimensions, the quantity of current on each derivation 
 would be 
 
 iE hE 
 
 -. or 
 
 2 x p 9 
 h 
 
 where i is the number of series of h cells in parallel 
 circuit ; and the values of i, h, or n will be the same as 
 in the more simple case, but multiplied by x. 
 
 As a numerical example of the preceding formulae, 
 suppose, in an electro-magnet, it be desired to have an 
 attractive force of 273 grammes, at 1 millimetre distance 
 from the armature, on a circuit of 50 kilometres resist- 
 ance, say 500 ohms, with a bichromate of potash sand 
 battery. In this battery the value of the electromotive 
 force, e, of each element is 2 (that of a Daniell being 1), 
 and the resistance, p, about 1,000 metres of telegraph 
 wire, say 10 ohms. According to the formulae 
 
 A = 0-0225 %/ 1-37* x 273 2 = 0-09 ; 
 and 
 
 ^=0-0081 x^ 
 
SHUNT CIRCUIT MAGNETS. 223 
 
 whence 
 
 c = x 0-173 = 0-01553 metres. 
 
 V 61,125 
 
 This gives for the length of each bobbin 0*0932 metre ; 
 for the diameter of the wire, with its covering, 0*39 
 millimetre, and without, 0-28 millimetre ; for length 
 1,861 metres ; number of turns, 19,078 ; for quantity of 
 current (not amperes, of course), 0-0001859 ; for value of 
 
 c^, 0-001935. Squaring the values of /and , and mul- 
 
 tiplying by ci", there is obtained 0-024378, which repre- 
 sents the electro-magnetic force, and this value, com- 
 pared with that of the typical electro-magnet (experi- 
 mented with by Du Moncel), which is 0-002297, gives 
 the ratio 10-6, nearly that of the two weights 273 and 
 26-85, representing the attractive forces in grammes. 
 
 Conditions for Maximum on Shunt Circuits. 
 The preceding deductions suppose that the permanent 
 state of electric propagation is established, that the 
 reactive effect of the extra current from the electro-mag- 
 net does not occur, that the iron of the electro-magnet is 
 magnetically saturated, and that the exterior circuit, R, 
 is perfectly insulated. When these conditions do not 
 exist, Hughes' experiments have shown that the resistance 
 of the helix must be considerably reduced. 
 
 To consider the most simple case, that of a single de- 
 rivation u established on a circuit of resistance Z, with 
 a common resistance R in the battery circuit, the at- 
 tractive force A of the electro-magnet interposed on I 
 will be 
 
 __ E* u* I 2 
 -[R(u + l + H) + u(l + H)]*' 
 
 and if, for t and H, be substituted their true values, 
 
224 CONSTRUCTION OF ELECTRO-MAGNETS. 
 
 drawn from the equations previously given, there is ob- 
 tained in relation to g, considered as variable 
 
 qg* (, Ru \ _ TT b a (a + c) ' 
 
 J* \ L " R + u) z ~-^~ 
 
 an equation consequently corresponding to the conditions 
 of maximum. 
 
 In varying the thickness of the helix, the quantity g 
 remaining constant, these conditions of maximum are 
 represented by 
 
 Now, in the first of these equations, the second mem- 
 ber represents the resistance of the wire of the helix, and 
 the first member is the total resistance of the external 
 circuit, expressed in units of the same order as those 
 used in the evaluation of the length of the helix wire. 
 But this total resistance is taken in inverse sense, because 
 that which is under consideration is really represented by 
 
 R + -, . In this case, the total resistance should be 
 
 I + u 
 
 supposed as if the part common to the two derived cur- 
 rents were represented by the shunt circuit , and as if 
 the part really common, R, were only a simple shunt 
 circuit. 
 
 In the second equation, the first member represents, as 
 before, the total resistance of the circuit taken in in- 
 verse sense ; but this total resistance, as the resistance R 
 of an insulated line, should be considered as being smaller 
 
 than that of the helix in the ratio of 1 to 1 -t- -, to satisfy 
 
 CL 
 
 the conditions of maximum relatively to the variable a. 
 
 Definitively, it may be deduced that the laws of electro- 
 magnetic maxima, on circuits to which shunt-circuits are 
 
VALUES OF K. 225 
 
 attached, are the same as for simple circuits, but only 
 by supposing that the resistance R, on which they are 
 based, is represented by the total resistance of the ex- 
 ternal circuit with its shunts, and by admitting that this 
 total resistance is considered as if the battery were sub- 
 stituted for the electro-magnet in the circuit. And as 
 the total resistance of a circuit from which shunt-circuits 
 are taken is less than its own resistance, the helix should 
 have less resistance than this latter. 
 
 If E in the preceding formulae is expressed by the 
 electromotive force of a Daniell element taken as unity, 
 and if R is evaluated in metres of telegraph wire, K = 
 0*172175, and the figure obtained represents fractions of 
 a unit. 
 
 When referring the values of K and R to the British 
 Association unit that is to say, to the volt and ohm 
 K = 0-015957. 
 
 In conclusion we would call attention to the fact, already 
 mentioned in a previous chapter, that other things being 
 equal, the strength of M and A also depends on the 
 quality of the iron employed. 
 
226 MEASURING INSTRUMENTS. 
 
 CHAPTER XI. 
 
 INSTRUMENTS FOR MEASUREMENTS IN CONNECTION WITH 
 ELECTRIC GENERATORS. 
 
 BELIEVING that a short description of a few of the most 
 useful instruments for carrying out measurements in 
 connection with electric generators will form a welcome 
 supplement to our book, we have selected the dynamo- 
 meter, the am-meter and the volt-meter, of Professors 
 Ayrton and Perry. 
 
 By this selection we do not mean to imply that the 
 instruments named are those only useful; for, amongst 
 others, the electro-dynamometer and the torsion galvano- 
 meter of Siemens, as well as the ampere-meter and 
 volt-meter of Marcel Deprez are also excellent instruments. 
 
 Ayrton and Perry's dynamometer. The Ayrton and 
 Perry dynamometer is constructed as follows : 
 
 A cross-shaped piece JOT, Fig. 51, is wedged on to the 
 shaft W of the motor that drives the electric generator, 
 and the four ends of this cross-piece R are connected, by 
 strong spiral springs, with a pulley which transmits the 
 power. When the transmission is made by means of 
 belts, S represents a belt-pulley slipped loosely over the 
 shaft ; whereas if the shaft, to which the work has to be 
 transmitted, lies in the continuation of the shaft W 9 S is 
 firmly fastened to it. 
 
 Now, if W is turned in the direction of the arrow, the 
 motion is transmitted to S by means of the springs ; and 
 the larger the amount of work transmitted the more are 
 
DYNAMOMETER. 
 
 227 
 
 the springs extended, thus causing the relative positions 
 of K and S to be changed. 
 
 At G a small bar ABC is attached to S. From Fig. 
 5 la it will be seen that this bar is supported against a 
 point in the plane of rotation, and from Fig. 51 c that it is 
 supported against a point perpendicularly to this plane, 
 and is connected with a continuation of one of the pieces 
 R by a small bar BB'. Now if, during the rotation, 8 
 
 Fig. 51. 
 
 lags a little behind W, A will approach the shaft, and 
 the greater the amount of work transmitted the greater 
 will be this approach ; so that the positions 05 shown in 
 Fig. 516, indicate various degrees of this approach. 
 
 In order to make the position of the bar ABC visible to 
 the eye, during the rotation of the machine, a small bright 
 button is attached at A. When the rotation is rapid this 
 describes a luminous circle, and the radius of this circle, 
 which is a factor in the measure of the work transmitted, 
 
228 MEASURING INSTRUMENTS. 
 
 can be read off from a scale placed on a level with the 
 shaft. 
 
 If the number of revolutions, which is important as the 
 other factor in the measurement, is known, it is easy to 
 calculate the amount of work transmitted. 
 
 A great advantage of this dynamometer is that it 
 occupies only a comparatively small radial space, and, 
 according to the inventors, it costs little more than a 
 
 Fig. 52. 
 
 flange-coupling usually employed in connecting two 
 shafts. 
 
 Ayrton and Perry's am-meter and Volt-meter. The 
 commutator am-meter is an aperiodic galvanometer, 
 obtaining its name from the circumstance that the 
 strength of current can be read off from the scale directly 
 in "amperes." Am-meter is an abbreviation of ampere- 
 meter. It is connected with a commutator, which allows 
 of the 60 convolutions of wire of the instrument being 
 coupled up either one following the other, or as ten 
 
AM -METERS AND VOLT-METERS. 229 
 
 abreast. In the latter case the resistance of the circuit is 
 only T of the resistance in the first case. 
 
 The following is the construction of the apparatus, 
 which is shown in Fig. 52. 
 
 A small magnetic needle, connected with a light alumi- 
 nium pointer, moves in the strong field of a powerful 
 horse-shoe magnet ; the coils of wire are arranged in such 
 a way that the deflections of the needle, and, therefore, of 
 the pointer, are proportional to the strength of current. 
 
 In order to gauge or to graduate this galvanometer, 
 the commutator is turned so that the 60 turns of wire are 
 connected in series, and a cell, of which the electro- 
 motive force, E, is known, is then connected with the 
 binding-screws B and PS; the position of the pointer is 
 then read off; call it S. By removing a plug, shown on 
 the left in the figure, we insert a resistance of one ohm, 
 which is connected with this circuit, and take a second 
 reading; call this second reading 6r 2 . The resistance of 
 the instrument, together with that of the cell and of the 
 conducting wires is, then 
 
 and the strength of current necessary for the first deflec- 
 tion is 
 
 E (Q l - 2 ) 
 s - ~ - - amperes. 
 
 Cr 2 
 
 We accordingly find strength of current in amperes, 
 which corresponds to a deflection of any number of 
 degrees, by multiplying the reading by 
 
 E (Q l - G 2 
 
230 MEASURING INSTRUMENTS. 
 
 when the convolutions of wire in the am-meter are 
 coupled up for intensity ; or by 
 
 10 E G - g 
 
 when the convolutions are coupled up for quantity. 
 
 If for instance in graduating we use a Leclanche cell 
 (large pattern) of which the electromotive force is 1*26 
 volts, and the first reading gives us 6*2, whilst after 
 inserting the resistance of 1 ohm the pointer indicates 
 
 4*25 
 4*25, then the resistance is - = 1'53 ohms, and 
 
 O*O ~" 4*^O 
 
 the strength of current for the deflection of 6*5 is 
 
 1*26 
 
 - = 0*83 amperes ; accordingly, to deflect the pointer 
 
 l*Oo 
 
 0*82 
 
 one degree, a current equal to --= = O125 amperes is 
 
 0*0 
 
 necessary, when the convolutions of wire are coupled up 
 by the commutator, one following the other, and equal to 
 1*25 amperes when they are coupled up, parallel or abreast. 
 
 Some of the Ayrton and Perry instruments are so 
 constructed that, when the wire turns are coupled up 
 abreast, one degree of the scale measures 1 ampere ; 
 whilst in others 1 degree means 2 amperes, in some even 
 5 amperes. With the latter instruments currents of 
 more than 200 amperes can be measured. 
 
 Although the greater sensitiveness of the commutator 
 am-meter, when arranged with its coils in parallel circuit 
 by the action of the commutator, was originally only 
 designed by the inventors for the purpose of graduating 
 the instrument, it is now taken advantage of for deter- 
 mining small strengths of current of 0*5 to 2 amperes that 
 occur in measurements with single incandescent lamps. 
 
 The commutator- volt-meter is a modification of the 
 
COMM UTA TOR- VOLT-METER. 231 
 
 instrument just described ; the resistance of the coils of 
 wire is 400 ohms (each of the ten coils = 40 ohms), when 
 coupled up in series, and 4 ohms when coupled up 
 abreast ; whereas in the am-meter the resistance is only 0*3 
 when the coils of wire are coupled up in series, and 0*005 
 when coupled up abreast. Some of the volt-meters now 
 constructed have a resistance of 200 ohms per coil, and 
 accordingly when coupled up abreast, the parallel re- 
 sistance is 20, and when in series, the resistance is 2,000 
 ohms. 
 
 Whilst the am-meter is graduated when the coils of 
 wire are in series, and is usually employed in practice 
 with the coils arranged parallel, the volt-meter is graduated 
 with the coils parallel, and is used coupled up in series. 
 In some instruments one degree corresponds to one volt, 
 in others to five volts, so that by a complete deflection of 
 45 in the 5 volt instrument, the needle indicates an 
 electromotive force of 225 volts. 
 
 But, as the am-meter can be employed, if necessary, 
 with the coils of wire in series (when, for instance, we wish 
 to measure currents of comparatively small quantity that 
 occur with single incandescent lamps), we can also in 
 exceptional cases employ the volt-meter with the coils of 
 wire coupled up parallel ; as for example, when we wish to 
 measure electromotive forces of only 2 to 3 volts, as with 
 accumulators. 
 
 In order to graduate the volt-meter, we couple up the 
 coils of wire parallel, by means of the commutator, and 
 then conduct a current through them from a cell whose 
 electromotive force, E, is known. We take a reading of 
 the deflection, and then remove the plug seen at the left 
 hand of the figure. This inserts a resistance, equal to 4 
 ohms in this instrument. We then take a second reading. 
 
232 MEASURING INSTRUMENTS. 
 
 The electromotive force corresponding to one degree is 
 10 <ff, - ff a ) 
 
 -orer 
 
 when the turns of wire are coupled up parallel, and 
 
 when they are coupled up in series (the usual arrangement 
 of the coils of wire in the instrument). 
 
 The construction of the am-meter and volt-meter is such 
 that in the am-meter the artificial resistance can be in- 
 serted only when the coils of wire are coupled up in series 
 by the commutator ; whilst in the volt-meter this inser- 
 tion is possible only when the coils of wire are connected 
 parallel. In this way damage to the resistance coil by 
 fusion is avoided. In order to protect the galvanometer 
 coils of the instrument against fusion which might 
 easily occur when the instruments are arranged for mea- 
 suring currents of small quantity in the one case, or low 
 intensity in the other each instrument is provided with 
 three binding-screws, marked B, (P $), and P,in the figure 
 which will represent either a commutator am-meter or a 
 commutator volt-meter, as both have exactly the same 
 form. 
 
 In the am-meters of the latest construction, P can be 
 used only for thick wires, and B only for thin wires, whilst 
 (P S) is alone suitable for both kinds of wire ; conse- 
 quently the wires of an electric generator can only be 
 connected with (P S) and P, and not with B ; and as a 
 current can only flow between (P S) and 5, when the 
 coils of wire in the instrument are coupled up parallel, it 
 will be interrupted in the case where the coils of wire 
 would be accidentally coupled up in series ; in this way the 
 
SIMPLE AM -METER. 233 
 
 instrument is kept from injury by fusion of the wires, or 
 by the needle being too strongly deflected. 
 
 Similar precautions are taken in the construction of the 
 volt-meter. 
 
 The coiling of the wire of these instruments is such that 
 the needle is deflected towards that binding screw which 
 is in connection with the positive pole. 
 
 Am-meter and volt-meter without commutator. In 
 large establishments using electric lighting where many 
 am-meters and volt-meters are constantly employed, it is 
 of course unnecessary that each instrument should have 
 its own arrangement for graduation. It is sufficient to 
 have a few of the instruments with commutators, and the 
 others can then be compared with these ; accordingly 
 am-meters and volt-meters without commutators are con- 
 structed. 
 
 All these measuring instruments by Profs. Ayrton and 
 Perry are constructed in such a way that the magnetic 
 needle and the pointer swing on pivots, the axis passing 
 through the centre of gravity, so that the deflection of the 
 needle, and of the pointer, will be the same for any position 
 of the instrument. The construction of the pivots is 
 similar to that in watches ; it is so fine that the friction 
 is not increased by giving the instrument a slanting posi- 
 tion. The permanent magnets of the instruments are 
 sufficiently strong that the deflections of the needle are 
 not easily affected by the proximity of electric machines. 
 
 One disadvantage which has been felt in the use of the 
 instrument described is that the magnetism of the per- 
 manent magnets becomes in time modified by the electric 
 currents. This would not be of importance if the instru- 
 ment were always graduated with a Daniell cell; but 
 Daniell cells are not always to be obtained at places where 
 
234 MEASURING INSTRUMENTS. 
 
 the am-meters and volt-meters are employed, and the fact 
 that graduation is necessary is prejudicial to the value of 
 the instruments. 
 
 To prevent the weakening of the magnetism of the per- 
 manent magnets, the inventors have added a keeper to be 
 put on when the instruments are not in use ; later, how- 
 ever, the employment of permanent magnets has been 
 given up and, am-meters and volt-meters with springs 
 made. In these instruments the needle is not controlled 
 by the pole of a magnet, but by a flat or cylindrical spiral 
 spring, and the soft iron needle makes an angle with the 
 axis of the galvanometer coil, which is less than 90 when 
 the instrument is at rest (an angle of 90 would disturb 
 the aperiodic character of the instrument). The inventors 
 have determined by a large number of experiments and by 
 calculation, what angle the needle must make with the 
 axis of the galvanometer coil (when the pointer is at 0) in 
 order to obtain the best results. 
 
 When these new instruments are well made, deflections 
 up to 45 can be obtained, which are directly proportional 
 to the current ; and the instruments of this construction 
 have the advantage that they can be used for alternating 
 currents, and by a simple adjustment of the spring (by 
 turning a small pointer moving over a scale), we can set 
 the large pointer in such a way that in the am-meter it 
 does not quit the zero position until the current has at- 
 tained a certain strength, and in the volt-meter until it 
 has attained a certain electromotive force. 
 
 This method, which permits of the spring being adjusted, 
 and the degree of adjustment read off the scale, con- 
 siderably increases the sensitiveness of the instrument. 
 Let us assume for instance that with a particular in- 
 strument we have to measure currents of about 30 am- 
 
SPRING VOLT-METERS. 
 
 235 
 
 peres or of a strength varying from 25 to 35 amperes. In 
 this case we do not adjust the needle so that weaker 
 currents will deflect it, but so that the pointer quits the 
 zero position only with a current of 25 amperes. If the 
 instrument were so adjusted that the deflection com- 
 menced with a current of 1 ampere, the 45 degrees would 
 be distributed to 35 amperes ; assuming 35 amperes to be 
 
 Fig. 53. 
 
 the maximum of the currents to be employed : in other 
 words, each increase of 1 ampere in the strength of 
 current would deflect the needle 1'3 degrees further 
 whereas if the deflection of the pointer is made to com- 
 mence with 25 amperes, the 45 degrees are distributed to 
 10 amperes ; or 45 to each ampere. The sensitiveness 
 of the instrument is, therefore, nearly four times greater 
 than in the first case. 
 
2 3 6 MEASURING INSTRUMENTS. 
 
 Instruments allowing of still more accurate measure- 
 ments are the 
 
 Am-meter and volt-meter with cog-wheel and gear. 
 In this instrument there is a very fine cog-wheel W (Fig. 
 53) in the axis of the magnetic needle, and the teeth of 
 this engage in the gearing P on the axis of the pointer. 
 By this arrangement the deflection of the pointer is made 
 ten times that of the magnetic needle, and if the con- 
 struction of the instrument is such that up to 36 degrees 
 the deflections of the needle are proportional to the 
 strength of current, 360 of the pointer's deflection will 
 have this proportionality. Besides this, the axis of the 
 needle, as well as that of the pointer, is connected with a 
 very sensitive spiral spring S and S r respectively. These 
 springs can either be used simultaneously in carrying out 
 the adjustment, or only one of them may be allowed to 
 act ; S f can be freed from the gearing by means by the 
 lever A and screw H. 
 
 When the springs are equally strong, we can increase 
 the sensitiveness of the instrument exactly a hundredfold 
 by turning this screw, ZT, and freeing S'. This sensitive- 
 ness may be adjusted to a greater or less degree by bring- 
 ing the strength of the spirals into certain relations. 
 
 To each spring there is attached a small pointer, allow- 
 ing of such an adjustment of the instrument that a com- 
 paratively few units of current in the one case or of 
 electro motive force in the other, can be distributed over 
 the 360 degrees deflection of the principal pointer. This 
 is, for instance, desirable when small variations of a 
 tolerably uniform current have to be measured ; and by 
 means of this construction of the am-meter and volt-meter, 
 we obtain instruments that, although intended for large 
 c urrents, or of high electromotive force, are as accurate and 
 
ELECTRICAL MEASUREMENTS. 237 
 
 sensitive as the more delicate instruments specially made 
 for measuring weak currents and low electromotive forces. 
 Another instrument for measurements in connection 
 with electric machines is the horse-power measurer, or 
 ergometer, the scale of which is graduated for readings 
 
 Q Volts Amp. 
 
 of horse-power, or ^ ; and, therefore, simul- 
 taneously measures the strength and electromotive force 
 of the current. We shall not, however, describe this in- 
 strument, although it is very useful in some cases, nor 
 the ohm-meter, for measuring resistance in ohms, because 
 the apparatus described are quite sufficient for all the 
 measurements that usually occur in practice. And we 
 shall conclude this section by stating a few physical 
 equations for finding the principal values in the measure- 
 ments usually to be carried out. 
 
 Equations occurring with measurements in con- 
 nection with electric generators. In order to calculate 
 the work done in the various parts of an electric machine, 
 as well as in the external circuit, the equations given by 
 Dr. A. Jobler, of Zurich, may be used with advantage. 
 
 Let T be the resistance of the armature, W that of the 
 electro-magnets, and w the resistance of the external 
 circuit, in which, for instance, a number of electric lamps 
 of unknown resistance are inserted. The resistance of 
 the latter will usually be sufficiently great that the re- 
 sistance of the conducting wires may be neglected. In 
 Fig. 54, the resistances are denoted by the abscissae, and 
 the potential by the ordinates ; the slope of the straight 
 line (/) (d) or J", accordingly represents the quantity of 
 current C ; a and b denote the terminals of the armature 
 coil ; a and c those of the generator ; and a and (d) 
 correspond to the same pole of the generator. 
 
MEASURING INSTRUMENTS. 
 C 
 
 e 
 
 o 
 
 wmmmm 
 
 a. 
 
 x V 
 
 . IT. V, 
 
ELECTRICAL MEASUREMENTS. 239 
 
 In the expressions for the various differences of 
 potential, F is assumed to be equal to o, and V v , for 
 instance, denotes the difference of potential between the 
 armature terminals, whilst v v denotes that between 
 the poles of the generator, and F represents the total 
 electromotive force. 
 
 From Fig. 54 6, we can then deduce the following 
 geometrical relations : 
 
 v u n V i/n , , < T\ n 
 
 = =r a = Q = (slope of J) = (7. 
 
 ^ W -t- w w 
 
 r + W + w 
 
 V-v 
 
 W+w 
 
 v v w 
 
 9 
 
 r+ F+ W 
 
 }__r+W+w, 
 
 o)- (2) 
 
 TT7" \ ' 
 
 D/ /}/! V. 
 
 rr T *v 
 
 W 
 
 
 F - 7 F - v 
 r W 
 
 = slope of / = C. 
 
 (3) 
 
 V -v W 
 
 W(v-v ) 
 
 (4) 
 
 V VQ ~~ W ' 
 
 V-v ' 
 
 The work E, in horse-power, done in the above circuit, 
 is obtained from the equation 
 
 C* (r + W + w) __ _J _ 
 9-81 x 75 735-75 
 
 and, as according to equation (1), v v = (7w, we get 
 
 [C7(r+TT) + (t;-t; )]C7 
 9-81 x 75 
 
 The work ^ lost in the wires, and the work e 2 ? obtained 
 in the external circuit, can then easily be found by the 
 aid of the equations 
 
 6l = (7 2 (r + F) 
 
240 MEASURING INSTRUMENTS. 
 
 The above formulae, however, can only be used when 
 the electro-magnet of the generator, in connection with 
 which the measurements are being taken, is inserted in 
 the main circuit ; other formulas are necessary for 
 generators in which the magnet is inserted in a shunt 
 circuit. 
 
 The diagrams, Fig. 54, d, e, /, will serve to determine 
 the formulae for such generators. Here, too, r denotes 
 the resistance of the armature, W that of the electro- 
 magnets, w the resistance of the external circuit, and 
 VVQ the difference of potential between the terminals 
 of the armature. 
 
 From the diagrams we then get 
 
 = (slope of j') = C"; 
 
 = C r+ V. 
 
 The reduced resistance of the electro-magnet coils and 
 of the external circuit is 
 
 w W 
 
 If this value is taken on the axis of the abscissae, 
 we easily get G and V (Fig. 54 /). 
 
 The work, in horse-power, of the current, is then dis- 
 tributed as follows : 
 
 Total work : 
 
 r * ( wW\ 
 
 ' ) 
 
 9-81 x 75 735-75 
 
 Work in the armature coils : 
 
ELECTRICAL WORK. 241 
 
 Work in the coils of the electro-magnet ; 
 
 l ~ 9-81 x 75 "' 9-81 x 75 
 Work in the outer circuit ; 
 
 
 J 
 
 9-81 x 75 9-81 x 75 
 
 With the help of these formulae and of Frohlich's 
 equations given in Chapter V., almost all measurements 
 can be carried out that occur in practice in connection 
 with magneto- and dynamo-electric generators. 
 
CHAPTER XII. 
 
 LATEST CONSTRUCTIONS OF GENERATORS. 
 
 JABLOCHKOFF'S new generator, termed the " The Elliptic," 
 is an attempt to advance in the construction of electric 
 generators by reducing the mass of the magnetic parts 
 liable to a change of polarity. 
 
 As shown in Fig. 55, the generator consists of two 
 coils, one of which is immovable and is placed in a 
 vertical plane. The other moves on a horizontal spindle 
 to which it is inclined. 
 
 At the same time, the plane of the vertical immovable 
 coil is not . placed perpendicularly to the axis of rotation 
 of the movable coil, but makes an angle with it, which is 
 determined by experiment, and is dependent on the con- 
 ditions under which the machine is to work. 
 
 The fixed coil is wound on a copper frame, the movable 
 one on an iron bobbin, which is converted into a short 
 electro-magnet, by the action of the current which 
 traverses the coil. The poles of this electro-magnet are 
 thus composed of two circular disks. The spindle carries 
 a commutator, on which the wire brushes bear. This 
 commutator is arranged in such a way that, during the 
 revolution of the spindle, the magnet is traversed by a 
 current never changing in direction, so that it always 
 keeps the same polarity. In the fixed coil, however, 
 which contains no iron, the current changes its direction 
 with every semi-revolution of the spindle. 
 
 This machine can be used as a generator and as an 
 
JABLOCHKOFFS MOTOR. s43 
 
 electro-motor. As a motor, its action depends on the 
 mutual attraction and repulsion of a movable electro- 
 magnet in a fixed solenoid, traversed by alternating 
 current. 
 
 Jablochkoff has proposed various modifications in the 
 construction of his new machine. He> for instance, makes 
 a coil, which is wound on soft iron, rotate between the 
 
 Fig. 55. 
 
 poles of two electro-magnets. The plane of this coil makes 
 a certain angle with the aiis of rotation. The arrange- 
 ment is such that first one and then the other flange of 
 the rotating coil arrives opposite the poles of the fixed 
 electro-magnets. In consequence of the change of 
 polarity, alternating currents are generated in the coil. 
 
 In another construction, the rotating coil is fixed on 
 the spindle in an inclined position. It rotates inside a 
 
244 LATEST CONSTRUCTIONS. 
 
 coil also in an inclined position, and is surrounded by an 
 iron ring. The poles of this ring are, in the latter case, 
 induced by the flanges of the rotating coil. 
 
 These generators are remarkable for their simplicity of 
 construction, and in this probably no machine surpasses 
 them. 
 
 In his patent, Jabloohkoff claims the invention of a 
 dynamo-electric or electro -dynamic machine in which an 
 electro -magnetic coil, fixed on a shaft in an inclined posi- 
 tion, moves in the magnetic field in such a way that, with 
 each revolution alternately, opposite poles face each other. 
 
 At present the efficiency of these generators, however, 
 appears in practice to be low. 
 
 In Gordon's alternating current generator we have 
 the second colossal machine. A large number of those 
 electrical engineers who have in view the erection of 
 large central stations, from which electrical energy is to 
 be supplied to whole quarters of a town for the purpose of 
 illumination and for the transmission of energy, believe 
 that this is best attained by putting up generators of 
 gigantic dimensions. The first generator which seems to 
 answer this purpose was built by Edison ; 120 horse- 
 power is necessary to work this generator, and about 1 ,000 
 incandescent (Edison) lamps, of 16 candle power each, 
 can be supplied by it. 
 
 As regards size, Edison is surpassed by the alternating 
 current generator constructed by Gordon, with the assist- 
 ance of Messrs. Clifford and Lucas. 
 
 In outward appearance, Gordon's generator resembles 
 the first electro-motor constructed by Jacoby. In both, 
 a disk carrying electro-magnets revolves in a vertical 
 plane between two fixed disks which carry double this 
 number of electro-magnets, arranged in a circle. The 
 
. GORDON'S MACHINE. - 245 
 
 ratio of the induced portions to inducing portions is the 
 same in both cases, 
 
 6 64 
 12 == 128* 
 
 This generator (Fig. 56), including the base, has a 
 length of four metres. Its essential parts, the inducing 
 portions and the armature, have a circular area of 2' 3 
 metres diameter, and weigh 18,000 kgr. 
 
 The armature consists of two iron rings fixed at a 
 certain distance from each other \ Cross-pieces secured by 
 nuts keep both rings in their relative positions. Each 
 of the two armatures carries sixty-four bobbins, whose 
 cores are composed of sheet iron rolled up in the same 
 way as the coils and fastened to the rings by nuts. 
 
 The diameter of the armature wires is mm., which 
 corresponds to a conductor of 22 sq. cm. cross-section 
 when all the bobbins are coupled up parallel; there, 
 accordingly is no fear of heating and its consequences, 
 even with considerable currents. 
 
 With a generator of such size the employment of a 
 commutator and of brushes for taking up the induced 
 currents is best avoided, as the sparks, formed at the 
 places where both Come in contact, would be a great 
 drawback. 
 
 This too, is one reason why Gordon has decided not to 
 allow the bobbins of the armature to rotate as usual, but 
 to fix them on both sides of the inducing magnets. In 
 this generator the inducing bobbins or magnets form the 
 revolving part. Accordingly the inducing field moves 
 parallel to the surfaces of the armature bobbins. 
 
 The inductor (that is, the disk with the field-magnets) 
 consists of two iron disks, connected with each other by 
 corresponding castings, fixed on a shaft at their centre. 
 
246 LATEST CONSTRUCTIONS. 
 
 At the circumference of the disks there are thirty-two 
 electro-magnets, whose cylindrical iron cores pass through 
 
 the disks and show similiar surfaces on both sides. These 
 lie flush with the free surfaces of the coils, and are pro- 
 vided with flattened pole-pieces of soft iron. The exciting 
 current is supplied by one or two Burgin generators, and 
 is conducted into the coils of the magnets by means of 
 
GORDON'S MACHINE. 247 
 
 two brushes which bear on two insulated brass rings 
 attached to the shaft. 
 
 The employment of only half as many inducing 
 magnets as of armature magnets, is an improvement which 
 Gordon arrived at from experiment. In employing equal 
 numbers of bobbins on both armature and inductor, he 
 found that the induced current of a bobbin was consider- 
 ably diminished by the neighbouring bobbins to such 
 an extent that the intensity of the lamps inserted in the 
 circuit appears to have been reduced 20 30 per cent. 
 If, however, only half the number of inducing bobbins is 
 put on the same circumference, the separate bobbins are 
 at greater distances from each other, only half the 
 armature bobbins are acted on at one time, and the 
 mutual disturbance of their reaction is almost completely 
 avoided, because between two active armature bobbins 
 there is one momentarily at rest. Two circuits are 
 generally built up from the alternate armature bobbins. 
 
 With the inductor disk making 140 revolutions per 
 minute, and with a current of 19 amperes, at an e.m.f. 
 of 88 volts, made to traverse its coils, there is obtained 
 in each of the armature coils, a current of 27*5 amperes ; 
 with 200 revolutions, and coupling up the bobbins parallel, 
 a total current of 5,000 amperes is obtained. 
 
 At the beginning of 1883, the large workshops of the 
 Maintenance Co. in Greenwich, were illuminated by this 
 generator alone, the 128 bobbins having been coupled up 
 in four series of 32 ; 1,300 Swan lamps (of 20-candle 
 power), distributed over a circuit 21 km. in length, were 
 in action, although only half of the current was used, 
 which the generator was able to produce. 
 
 According to this it seems that the electrical illumination 
 of towns, extensive workshops, &c., by means of large 
 
248 LATEST CONSTRUCTIONS. 
 
 central stations, is not only possible but also gives satis- 
 factory results from an economic point of view. 
 
 For the lighting of towns, Mr. Gordon has published 
 the following estimate of : 
 
 PLANT TO SUPPLY ELECTRICITY SIMULTANEOUSLY TO 60,000 
 LAMPS OF 20-CANDLE POWER EACH, EQUAL TO 85,000 
 OF 14 CANDLES. CAPITAL EXPENDITURE, 220,000. 
 
 Annual Expenditure, Lamps burning 2,000 hrs.per ann. 
 
 Depreciation and repairs . . . 8,000 
 
 Slack coal, at lls 7,100 
 
 Water, at 6d. per 1,000 gallons . . 7,100 
 
 Oil, &c 850 
 
 Wages and superintendence (63 persons) 5,390 
 
 Kent, rates and taxes 1,000 
 
 Office expenses 500 
 
 Directors' fees 1,000 
 
 Kenewal of incandescent lamps . . 12,000 
 
 10 per cent, of dividend on capital . 22,000 
 
 Total required revenue . . 64,940 
 85,000 14-candle gas burners burn, in 2,000 hours, 
 850,000,000 cubic feet, which would produce 65,000 at 
 Is. 6d. per 1,000 cubic feet. 
 
 * 
 
 PLANT TO SUPPLY ELECTRICITY SIMULTANEOULY TO 10,000 
 LAMPS OF 20-CANDLE POWER EACH, EQUAL TO 14,000 
 OF 14 CANDLES. CAPITAL EXPENDITURE, 50,000. 
 
 Annual Expenditure, lamps burning 2,000 hrs. per ann, 
 Depreciation and repairs , . . 1,500 
 Slack coal, at lls. .... . 1,230 
 
 Water, at 6d. per 1,000. gallons . . 1,230 
 Oil, &c. . . . 150 
 
GORDON'S ESTIMATE. 249 
 
 Wages and superintendence (30 persons) 2,968 
 
 Rent, rates and taxes . . . . 250 
 
 Office expenses 250 
 
 Directors' fees . . . ^ 350 
 
 Renewal of incandescent lamps . . 2,000 
 
 10 per cent, dividend on capital . . 5,000 
 
 Total required revenue . . 14,928 
 
 14,000 14-candle gas burners burn, in 2,000 hours, 
 140,000,000 cubic feet, which would produce 15,000 at 
 2s. Ifd. per 1,000 cubic feet. 
 
 Gas in London is 3s. 2d. per 1,000 feet. 
 
 It is not expected that each lamp erected will average 
 2,000 hours per annum, but that 2,000 hours is the 
 average consumption of the maximum number alight at 
 one time. Thus, if a house has thirty lamps, but not 
 more than eighteen alight at once, the average consump- 
 tion of that house will be 18 + 2,000 = 36,000 lamp hours 
 per annum. 
 
 Amongst the machines proposed and used for the 
 supply of the electric current to a large number of in- 
 candescent lamps, the most prominent recently has been 
 the Ferranti alternating current generator, which needs 
 a separate dynamo machine to excite its field-magnets. 
 Like the magnets of the Wilde and Siemens machines, 
 the electro magnets form two crowns, with opposing poles. 
 The difference lies mainly in the armature, which, like 
 that of Siemens, has no iron cores in the coils. It is built 
 up of copper strip, folded or bent over the eight teeth of 
 a wheel having these cogs or teeth very large* These 
 eight loops (half of which are shown in Fig. 57), move 
 between sixteen electro-magnet poles on each side ; so 
 that, as in Gordon's dynamo, self-induction is obviated. 
 
250 
 
 LATEST CONSTRUCTIONS. 
 Fig. 57. 
 
 Fig. 58. 
 
FERRANTI MACHINE. 251 
 
 Fig. 58 is a general view of this machine. Professor 
 Sylvanus Thompson accredits the invention of this zigzag 
 armature to Sir W. Thomson, who proposed originally 
 that copper strips should be wound between project- 
 ing teeth on a wooden wheel. The framework of the 
 machine is cast in two halves, which are bolted together. 
 The armature strip, arranged in three parallel circuits, is 
 held in place by bolts passing through a star-shaped hub 
 on the shaft of the machine. In the 1,000-light 
 machine, each strip makes ten turns round the zigzags, 
 making in all thirty layers, insulated from each other by 
 strips of vulcanised fibre. The armature is thirty inches 
 in diameter, about one half inch wide, and weighs only 
 ninety-six pounds. It revolves at a speed of 1,400 revo- 
 lutions. The entire machine weighs one and a half tons. 
 
 A very large alternating-current machine has been 
 constructed by Messrs. Ganz, of Buda-Pesth, and it is 
 capable of furnishing current for 1,200 Swan lamps, each 
 of twenty-candle power. This generator, which somewhat 
 resembles Gordon's, is the invention of Messrs. Mechwart 
 and Zippernowsky. Thirty-six field-magnet bobbins are 
 set concentrically on an iron frame, which serves as the 
 fly-wheel of the high-pressure compound engine used to 
 drive the machine and its exciter, and are rotated within 
 an outer circle of thirty- six flat armature bobbins, which 
 are coreless. Any one of the coils, either of the armature 
 or field-magnets, can be removed from the side of the 
 machine for repairs without interfering with the construc- 
 tion otherwise. 
 
 The Hopkinson-Edison generator is stated to be a 
 very considerable improvement on the earlier Edison 
 machines, due to Dr. John Hopkirison, F.R.S. Some of 
 these improvements are in the field-magnets, some in the 
 
252 LATEST CONSTRUCTIONS. 
 
 armature. Multiple field-magnets have been substituted 
 by a magnet consisting of an equal mass of iron, in one 
 solid piece, of much greater area of cross-section and 
 somewhat shorter length. Each magnet arm (there 
 being now only two to a machine) is attached solidly to 
 each pole-piece, and the two are united, at the opposite 
 end to that to which the pole-pieces are fastened, by a very 
 heavy yoke. In the armature a very important change has 
 been made ; the iron disks of the core were, in the earlier 
 machines, held together by six longitudinal bolts passing 
 through holes in the core-plates, and secured by nuts 
 to end-plates. These bolts are now abolished, and the 
 plates are held together by large washers running on 
 screw threads cut on the shaft or axle of the armature. 
 The central space in each plate has been much reduced, 
 thus giving greater mass of iron to the interior of the 
 armature, and providing greater cross-section for mag- 
 netic induction. By these improvements, although the 
 total weight of the machine is the same, a generator that 
 formerly provided current for 150 lamps can now supply 
 250 lamps. A generator of this size has an armature ten 
 inches in diameter, having a resistance (cold) of 0-02 
 ohm, that of the magnet coils being 17 ohms. Much of 
 the increase of efficiency that these new machines show is 
 due to the fact that, in the older construction the bolts 
 and their attached end-plates afforded a closed circuit, in 
 which idle currents were constantly running wastefully 
 round, with consequent heating and loss. The older 
 form of machine, as tested at the Munich Exhibition, 
 was found to give an efficiency of 87 per cent, in the 
 ratio of external electric work to total electric work ; 
 but its commercial efficiency, or the ratio of external 
 electric work to the mechanical work imparted to the 
 
MOR DRY'S DYNAMO. 253 
 
 belt-pulley, was at most 58'7 per cent. An improved 
 machine, as tested by Mr. Sprague, affording current to 
 200 lamps, gave an electrical efficiency of more than 
 94 per. cent., and a commercial efficiency of 85 per cent. 
 
 The Gulcher machine has also been much improved, 
 and has been " compounded," or made self-regulating, by 
 winding the field-magnets, so as to secure a constant 
 potential at the terminals. In the four-pole Giilclier 
 dynamo, there are eight magnet cores ; and each of these 
 receives a shunt coil of fine wire, and outside this a main 
 coil of stout wire. The eight fine wire coils are joined 
 up in series, and the eight main-circuit coils are put 
 parallel. A 6.5 volt machine thus wound gave, with a 
 current of 1 ampere, 61*5 volts; 64 volts at 105 amperes, 
 and 63*5 volts at 130 amperes. 
 
 The Victoria (Schuckert-Mordey) Dynamo Machine. 
 This machine is an improved form of the Schuckert 
 machine. The directions in which the principal improve- 
 ments have been made are : 
 
 (a.) With a given size of armature, the useful work 
 obtained is increased 100 to 150 per cent, without in- 
 crease of speed ; in fact, with a decrease of speed. The 
 commercial efficiency is also greatly increased. 
 
 (6.) The internal loss of energy is reduced by diminish- 
 ing the armature resistance, by decreasing self-induction 
 in the armatures, by the entire elimination of a very con- 
 siderable opposing electro-motive force (which, in the 
 Schuckert machine, was the cause of much trouble and 
 waste), and by more economical construction of the field- 
 magnets. 
 
 (c.) Eddy (so-called Foucault) currents are reduced to 
 a minimum by suitable lamination, and by insulation of 
 the iron plates or rings of the armature. 
 
254 LATEST CONSTRUCTIONS. 
 
 In the Schuckert machine the plates were connected by 
 brass rivets in such a way that considerable heat was 
 caused by these currents, which also had other hurtful 
 and wasteful effects, such as, by induction, diminishing 
 the armature " activity " or output. 
 
 (c.) Improved shape of pole-pieces, and increase in 
 their number. 
 
 (e.) The method of connecting the armature, by means 
 of which the brushes are never more than two in 
 number. 
 
 Reduction of Sparking at the Commutator. 
 With reference to the opposing electromotive force men- 
 tioned under 6, a very important improvement has here 
 been made in dynamo-electric machines of this type ; and 
 Mr. Mordey made the discovery of its existence in the 
 Schuckert machine in the autumn of 1882, and this 
 discovery led him to the improvements he has since been 
 able to make in this machine. The discovery of this 
 contrary or opposing electromotive force resulted from a 
 very simple method of examining armature potentials 
 devised by Mr. Mordey. One of the brushes of the 
 machine both being set in their proper places is con- 
 nected by a wire to one terminal of a volt-meter ; the other 
 terminal of the volt-meter is joined by a wire to a small 
 metallic brush or spring, which can be pressed against the 
 rotating collector at any desired part of its circumference. 
 Professor Sylvanus Thompson suggested that the readings 
 taken from the volt-meter when the small brush was in 
 different positions, should be plotted out round a circle 
 corresponding to the circumference of the collector. If 
 the magnetic field in which the armature rotated were 
 xiniform, this curve would be a true %< sinusoid," or curve 
 of sires. The steepness of the slope of the curve, at 
 
ISEXBECK'S EXPERIMENTS. 255 
 
 different points enables judgment to be made of the 
 relative idleness or activity of coils in different parts of 
 the field. 
 
 To understand how this wasteful opposing electromotive 
 force arises, it is necessary to refer to some experiments of 
 a very' remarkable character made by Dr. Isenbeck, and 
 described by him in the " Electrotechnische Zeitung " for 
 August, 1883. Dr. Isenbeck sought to investigate the 
 influence exerted by pole-pieces of different form on the 
 inductive actions in the coils of a Gramme ring. Isenbeck 
 constructed a very simple apparatus, of a circular frame 
 of wood placed between the poles of two small permanent 
 magnets, similarly as the ring of the Gamme machine is 
 placed. On the frame, or ring, which is centred, is placed 
 a single coil of fine wire. The coil can be slid to any 
 desired position on the ring, and the ends are put into 
 connection with a galvanometer. By vibrating the ring, 
 through a small arc, synchronously with the period of 
 swing of the needle of the galvanometer, the latter is set 
 in motion by the induced currents, and the deflection of 
 the needle shows the relative amount of induction in the 
 particular part of the field where the coil is situated. 
 The arc through which the ring and coil move is limited 
 to 7 5'. Pole-pieces of soft iron, bent to arcs of 160 
 were constructed to fit upon the poles of the magnets. 
 In some of the experiments a disc of iron, or a magnet, 
 was placed within the ring. 
 
 This little apparatus has done more in Dr. Isenbeck's 
 hands to elucidate the actions occurring in dynamo- 
 machines than any other previous investigation: Using 
 a wooden ring and magnets without pole-pieces, a remark- 
 able inversion in the inductive action was observed to 
 take place at about 25 from the poles. When vibrated 
 
256 LATEST CONSTRUCTIONS. 
 
 in the neutral line, there was no induction in the coil ; 
 but as the coil was moved into successive positions nearer 
 to the poles induction increased. But the most powerful 
 inductive effects were found to be confined to a narrow 
 region within about 12 on each side of the pole. Beyond 
 these points false inductions occurred, giving rise to 
 electromotive forces opposing those generated in the 
 positions close to the poles. These inverse inductions 
 were found to be increased when an iron disk, or an 
 internal opposing magnet pole, was within the ring ; a 
 reinforcing magnet slightly reduced these opposing elec- 
 tromotive forces. 
 
 This apparatus has enabled Dr. Isenbeck to answer the 
 question why these detrimental inductions arise in the 
 ring. He finds, by difficult calculation, the number of 
 lines of force that will be cut at the various points in the 
 path of the ring ; but Professor Sylvanus Thompson has 
 shown, in a most simple manner, how these inversions 
 may be accounted for. If any of the drawings are taken 
 that illustrate the distribution of the lines of force in a 
 magnetic field between two magnet poles, and a single 
 coil be considered to be passing, like a Gramme coil, 
 through the field, it will be 'observed that at 0, a certain 
 number of lines of force thread themselves through the 
 coil. As the coil moves round towards the south pole 
 (say) the number increases, then becomes stationary ; and 
 this is followed by a very rapid decrease, and at 90, 
 immediately under the pole, the coiling of the coil is edge 
 on to the direct lines of force, and none pass through the 
 coil from one face to the other. Immediately after passing 
 this point, the lines of force crowd into the other face of 
 the coil, and increase in number as the coil approaches a 
 point midway between the pole it is leaving and the 
 
THOMSON'S EXPERIMENTS. 
 
 257 
 
 opposite neutral point to that from which, it started. 
 Thus it is evident that these inversions will occur always 
 in a Gramme ring passing through a weak field, the lines 
 of force in which are curved. If these lines are nearly 
 straight that is, directed with greater intensity these 
 false inductions are reduced. 
 
 When an iron core or ring is substituted for the wooden 
 ring, the useful induction is greater ; but there is still 
 very slight inversion at about 25 Q from the pole. 
 
 The use of iron pole-pieces has the effect of entirely 
 removing these inversions, if the pole-pieces extend over 
 the ring through a sufficiently large arc. 
 
 Professor Sylvanus Thomson has also pointed to the 
 general assumption that the Gramme ring was an improve- 
 ment on that of Pacinotti. He finds that a properly con- 
 structed Pacinotti ring has an advantage which may be 
 measured by the numbers of the following table, the first 
 column of which shows the relative position of the coil in 
 its circular passage : 
 
 
 Gramme. 
 Wooden Ring. 
 
 Gramme. 
 Iron Ring. 
 
 Pacinotti. 
 Iron Toothed Ring. 
 
 o 15 
 
 5 
 
 2 5 
 
 30 
 
 15- 30 
 
 IO 
 
 60 
 
 70 
 
 3o- 45 
 
 
 
 I2O 
 
 140 
 
 45- 60 
 
 45 
 
 195 
 
 320 
 
 60 - 75 
 
 40 
 
 2OO 
 
 380 
 
 75- 90 
 
 30 
 
 22O 
 
 360 
 
 All these points have been very carefully considered in 
 the Mordey-Schuckert machine, fig. 59. It will be seen 
 that the pole-pieces are constructed of iron shoes, that are 
 quite narrow, not covering more than 30 of angular 
 breadth of the circumference of the armature, although 
 they embrace the ring through its whole depth. The pole- 
 
 3 
 
2 5 8 
 
 LATEST CONSTRUCTIONS. 
 
NORDEY'S DYNAMO. 
 
 259 
 
 pieces are of cast iron, cast upon the cylindrical cores of 
 soft iron which receive the coils. The armature of this 
 machine is built up of rings cut from sheet charcoal iron, 
 and Mr. Mordey has taken great pains to secure that there 
 are no electrical circuits made in the bolting together of 
 
 Fig. 60. 
 
 these cores, each plate being both electrically and magne- 
 tically insulated from the adjacent plates. Also a very 
 important improvement in these machines has been in the 
 reduction of the number of brushes. Formerly, in multi- 
 polar machines there were as many brushes as poles. Mr. 
 Mordey has reduced the number to two, by the device of 
 
260 
 
 LATEST CONSTRUCTIONS. 
 
 connecting together those segments of the armature coils 
 that occupy similar positions with respect to the poles, and 
 of connecting together those bars of the collector that are 
 at the same potential. There are sixty sections in the 
 ring, and consequently fifteen segments of the collector 
 
 Fig. 61. 
 
 from one brush to the other. The factor of conversion of 
 this machine, according to the Anglo-American Corpora- 
 tion's published statements, is 96*15 per cent., and the 
 electrical efficiency, 85-68 per cent. 
 
 Elphinstone- Vincent Generator. Another machine to 
 which highly skilled attention has been given is the 
 
CROMPTON' S DYNAMO. 261 
 
 Elphin stone-Vincent. The exterior of this machine is 
 shown in Fig. 60 ; and the internal construction will be 
 clear from Fig. 61. The sections of the armature are 
 wound on a mould as parallelograms, which are then fixed 
 upon the outer cylindrical surface of a papier-mache 
 cylinder, mounted so as to rotate between powerful field 
 magnets and internal field magnets. The latter magnets 
 reinforce the former. The parallelograms of wire are so 
 arranged as to leave the shorter ends of the parallelogram 
 to lie outside the ends of the polar surfaces of the field 
 magnets ; this admits of bringing the longer sides of the 
 parallelograms lying on the drum very close to the poles 
 of the field magnets. The segments of the collector are 
 internally cross connected, as in the Mordey machine, by 
 which arrangement only two brushes are required. 
 
 Crompton-Burgin Generator. Probably the dynamo 
 that has met with the largest practical demand is the 
 Biirgin machine, as modified by Messrs. K. E. Crompton 
 and Co. As described, the armature of the original machine 
 consisted of several rings set side by side on one shaft, 
 these rings being wound on a square or on a hexagonal 
 frame carrying four or six coils. These were placed in a 
 regular screw or helical order. Mr. Crompton increased 
 the number of rings, alternating the position of the coils, 
 instead of arranging them in helical order. The weight of 
 iron in the armature was then increased. A subsequent 
 change was to make the rings broader and fewer in 
 number, four larger rings, with a collector containing 
 twenty-four segments, being substituted for the ten 
 smaller rings, with their sixty segments. 
 
 Kecently Mr. Crompton and Mr. Kapp have again 
 changed the form and arrangement of the armature, which 
 is now a single ring of cylindrical or elongated Gramme 
 
262 LATEST CONSTRUCTIONS. 
 
 shape, with its coils wound on an iron core constructed of 
 very thin soft iron toothed disks, the wire being put 
 between the teeth, as in a Pacinotti ring. The following 
 are stated to be the dimensions of this machine : Weight, 
 22 cwt. ; length, 3 ft. 4 in. ; height, 12 in. ; width, 2 ft. 
 The armature is 17 in. long and 8 in. in diameter. At 1,000 
 revolutions the machine gives 145 volts and 110 amperes. 
 Besides these machines, are many others more or less 
 known ; but a sufficient number of typical machines have 
 been described to enable the reader to classify for himself. 
 
CHAPTEE XIII. 
 
 CLAUSIUS' THEORY OF THE DYNAMO MACHINE. 
 
 WHILST this book was in the press, a very valuable paper, 
 of the highest mathematical order, appeared in " Wiede- 
 mann's Annalen " (vol. 20, 1883, pp. 353-390), from the 
 pen of the eminent electrician and physicist, Professor 
 K. J. E. Clausius. As this theoretical discussion is of a 
 very practical kind, and as it goes farther than any pre- 
 vious inquiry into the laws relating to dynamo-electric 
 generators, this book would be incomplete without due 
 reference to the paper ; and an abstract, as far as pos- 
 sible in the terms of the author, is given in the following 
 pages. 
 
 1. Essential constituents of the dynamo-electric ma- 
 chine. Dynamo machines, as hitherto constructed, have 
 outwardly many forms, but in principle they deviate little 
 from one another, and Professor Clausius believes that 
 amongst the continuous current machines the forms of 
 Grramme and Siemens are to be regarded as types. Even 
 these are so similar to one another in their effect that they, 
 so far as concerns the origin of the basic formulae, need 
 not be separately studied. 
 
 To the essential constituents belongs, in the first place, 
 a fixed electro-magnet with large polar surfaces, or a 
 combination of several fixed electro-magnets, whose simi- 
 lar poles are united by iron pieces into a common polar 
 surface. Between the polar surfaces of the fixed electro- 
 
264 CLAUSIUS' THEORY. 
 
 magnet there is a space occupied by the rotating electro- 
 magnet, the two constituents of which, the winding and 
 the iron core, may be separately studied. The former, for 
 which rotation is necessary, is termed the rotary helix ; 
 and the latter, the rotation of which is not essential, its 
 iron core. The rotating helix is in many divisions, and 
 these are in conductive connection, so that the end of 
 one and the beginning of the following division are always 
 connected together, and with a metal strip. These metal 
 strips are so fixed next to one another as together to 
 form a cylinder, which rotates with the helix, and upon 
 which rub or glide the two contact-brushes that form the 
 beginning and the end of that conducting part which is 
 wound around the fixed electro-magnets, and including 
 the external conductor. The rotating helix, in each of 
 its positions, is divided into two halves by the electric 
 currents which go from the one contact-brush and meet 
 again in the other contact-brush. 
 
 The iron core of the rotating helix is magnetised in a 
 double manner. It forms between the poles of the fixed 
 electro-magnet a connecting armature, but which is not in 
 contact, and obtains therefore a magnetisation of such a 
 kind that to every pole of the fixed electro-magnet is 
 directed an opposite pole of the iron core. To express this 
 briefly, it may be said that the axis of magnetisation pro- 
 duced in the iron core has the opposite direction to the 
 axis of the fixed electro-magnet. On the other hand, the 
 iron core is magnetised by the electric current flowing 
 through the windings of the rotating helix from the one 
 contact-brush to the other. The contact-brushes are so 
 placed that the axis of the magnetisation produced by 
 this cause is vertical to that axis produced by the first. 
 From the junction of these effects a magnetisation results 
 
LAW OF INDUCTION. 265 
 
 whose axis has an irregular direction between these direc- 
 tions. When the iron core is revolved, its poles maintain 
 a fixed position in space, whilst they change continually 
 their position in the iron core. 
 
 The inductive effect occurring in the helix during its 
 rotation is threefold. In the first place, the fixed electro- 
 magnet acts inductively on the rotating helix. In the 
 second, there is the inductive polar effect due to the 
 magnetisation of the iron core by the convolutions of the 
 helix itself. Thirdly, the convolutions interact induc- 
 tively the one upon the other to some slight extent. 
 
 2. Law of Induction. The rotating helix, and the 
 helices of the fixed magnets consist of many convolutions, 
 and these lie so close together that for every single convo- 
 lution, and every joined group of convolutions, it is indif- 
 ferent whether it be considered as having its end con- 
 nected with its own beginning, instead of with the begin- 
 ning of the following convolution or group. The helices 
 may therefore be regarded as a system of closed circuits. 
 The magnetisation of the mass of iron may be considered 
 due to the existence of innumerable small closed electri- 
 cal circuits in its mass, so that there only remain to be 
 studied the effects of closed electrical currents upon closed 
 electrical circuits. The representation of the law of induc- 
 tion becomes very simple. Let any system of closed cur- 
 rents be given, flowing in the circuits s, s 1? s 2 , &c., and 
 having quantities i, i 19 i' 2 , &c., and, further, a closed cir- 
 cuit <r, in which flows the unit current. Understanding 
 by d s any element of some one of the circuits s, s 1? S 2 , 
 &c., and by d a an element of the circuit <r, and desig- 
 nating by (s or) the angle between the directions of both 
 elements, and their reciprocal distance by r, the electro- 
 dynamic potential W of the given current system in the 
 
266 CLAUSIUS' THEORY. 
 
 circuit 0-, and of unit quantity, is represented by the 
 equation 
 
 / 1 \ AIT rr * c s ( <r ) 7 7 
 
 (1.) W ==// - - d s d cr, 
 
 where the one integration is over the series of circuits 
 s, s 15 s 2 , &c., and the other over the circuit <r. In this 
 expression for TPthe current quantities are supposed taken 
 in electro-dynamic or electro-magnetic absolute measures. 
 If electro-static measures are adopted, the expression 
 must be divided by K 2 where K is the critical velocity of 
 electricity, about 30 meridian quadrants. 
 
 When any one movement of the circuit, and at the 
 same time an alteration of the current quantities i, i l9 i v 
 &c., occur, the induced electromotive force e in the circuit 
 a is estimated by the equation 
 
 e = ~ 
 
 in which t is time. 
 
 3. Application of the equation to the rotating helix. 
 Whilst the foregoing equation is applied to the electro- 
 motive force induced in the rotating helix, in consequence 
 of its movement, there may be studied some one of the 
 divisions into which the helix is divided as representing 
 the circuit or. Following this division of the circuit 
 during an entire revolution, there occurs a series of changes 
 until the circuit assumes its first position ; so that the 
 final value of W is equal to its initial value. But the 
 direction in which the electromotive force is to be calcu- 
 lated as positive does not hold good in the whole helix to 
 an equal degree, there being a difference in the two 
 halves, as is perceived when it is considered that the cur- 
 rent flows from one contact-brush through the two halves 
 to the other contact-brush. Thus, also, for every single 
 
RECIPROCAL ACTIONS. 267 
 
 division of the helix the direction regarded as positive 
 changes at every half-revolution. As the induced effect 
 during both halves of the revolution is equal, it is neces- 
 sary to consider only one-half revolution. At the begin- 
 ning of this half-revolution, for the time ' , W may have 
 the value W' 9 and at the end, or at the time t f + $r (where 
 r signifies the rotation-time), W may have the value W", 
 then the mean electromotive force (2) is obtained from 
 
 t + ^T 
 
 (3.) ~ I edt=- 
 2 r ^ 
 
 dt 
 
 From this expression for a single division of the helix, that 
 for the whole helix may be obtained by multiplication by 
 the number of divisions. To determine this number it 
 must be remarked that the induced force on both halves 
 of the rotating helix is not to be taken as a sum, since 
 these halves are not in sequence, but lie parallel to one 
 another. E 19 or the whole electromotive force becomes, 
 
 (4.) = (TP - W"). 
 
 If, instead of the rotation time r, the number of revolu- 
 tions in the unit of time v is used, 
 
 (5.) v =-L, 
 
 and (4) becomes 
 
 (6.) E l =n(W - W")v. 
 
 4. Retro-action of the moving circuit on the fixed. 
 In the previous paragraph there has only been studied the 
 electromotive force due to the magnetisation of the iron core 
 and the current in the fixed circuit. It may now be asked 
 whether the existing current in the moved circuit induces 
 an electromotive force in the fixed circuit. Professor 
 
268 CLAUSIUS' THEORY. 
 
 Clausius again selects for examination a single division of 
 the moved circuit, also designated by <r. The current 
 flowing through it is represented by j, and twice changes 
 its direction in each revolution. The fixed circuit is 
 supposed to be traversed by the unit current, and causes 
 the electro-dynamic potential of a upon s, represented by 
 G, and by an expression of similar form to equation (1), 
 
 frj cos (s <r} , , 
 G = II - 2, I dsdv. 
 
 With the help of this quantity the induced electromotive 
 force c in the fixed circuit, at the time , can be deter- 
 mined by the following equation, corresponding to (2) : 
 
 d Q 
 
 f =di- 
 
 To determine from this the mean electromotive force there 
 must be an integration for the time, and the integral 
 divided by the time. As the positive direction of the 
 electromotive force is unchanged, the integration may be 
 extended over the whole time of rotation r, 
 
 t 
 
 where Q,' is the initial, and Q,'' the final, values of a 
 rotation. Now, after an entire rotation, the position of 
 the division of the circuit, as also the direction of the 
 current, are the same as at the commencement of the 
 revolution ; from which it follows that Q" equals G', and, 
 consequently, the above expression is equal to nil. This 
 holds good for all the divisions of the moved conductor ; 
 hence the result that in the fixed circuit no electromotive 
 force is induced. 
 
 5. Inductive influence of the moved circuit upon itself. 
 In this respect it is to be observed that the circuit involved, 
 
WORK PERFORMED. 269 
 
 namely, the rotating helix, is only wholly moved so that 
 every two parts maintain unchanged their relative positions. 
 It therefore follows that motion does not set up any 
 reciprocal induction. There requires thus to be taken into 
 account only the change or reversal of current as productive 
 of induction effects. This subject has already been treated 
 by Joubert and by Maxwell ; and Professor Clausius agrees 
 with their views and explanations, although not with the 
 method of calculation. Professor Clausius determines that 
 in consequence of the position of the contact-brushes, and 
 of the movement of the helix, the induced electromotive 
 forces on both sides are not produced complete, but that 
 there remains a surplus on one side, which, like the 
 electromotive force from the self-induction, is opposed to 
 the direction of the current. The evaluation of this 
 difference depends on the construction of the machine, 
 and Professor Clausius is content with an expression in- 
 cluding an undetermined factor, and with an explanatory 
 remark, his reasoning leading to the equation 
 
 (8.) E = n(W - W")v - piv, 
 
 where p, the only quantity remaining unexplained, 
 represents the undetermined factor. 
 
 6. Work performed by the electromotive and pon- 
 deromotive forces. In order to express the work per- 
 formed in the unit of time by the previously determined 
 electromotive force E, this quantity must be multiplied 
 by the quantity of current i which flows through both 
 halves of the rotating helix. Therefrom 
 
 (9.) Ei = n(W - W")iv- pi*v. 
 
 This work can be compared with another work. The 
 winding through which the current is passing is affected 
 by the other current systems, to which also the magnets 
 
270 CLAUSIUS' THEORY. 
 
 belong, or by a " ponderomotive " force, and its work is 
 determined to be in unit time 
 
 (10.) T=n(W" W')iv. 
 
 If this work be compared with that of (9) the electro- 
 motive force, it differs from the latter by the term pi^v. 
 And there can be written 
 
 (11.) Ei= - T- P i*v. 
 
 7. Estimation of the magnetism of the electro-mag- 
 nets in dynamo- electric machines. To give the previous 
 theoretical results more approximate forms for further 
 calculation, there must be expressions constructed for the 
 strength of the electro-magnets. In the fixed electro- 
 magnets, the magnetic moment is not proportional to the 
 quantity of the current, but follows another law. With 
 smaller quantities of current it increases nearly propor- 
 tionally to the quantity ; with greater quantity of current 
 it increases more slowly and approaches a limit. Frohlich 
 employs an equation, of which the following is an unes- 
 sential modification : 
 
 (12.) M = ^-. 
 I + a^' 
 
 where M is the magnetic moment, and A a, constants. 
 Professor Clausius does not believe that this represents 
 the proportion in the best manner, but its adoption is 
 advisable on account of its simplicity. 
 
 With very small quantities of current the " permanent " 
 magnetism of the iron of the electro-magnets from pre- 
 vious magnetisation must be taken into consideration. 
 But this, except in special points concerned with the 
 starting of the current, is of no importance. 
 
 It is, however, necessary to study the magnetisation of 
 the iron core of the rotating helix, which presents compli- 
 
ESTIMATION OF MAGNETISM. 271 
 
 cations because it originates, as has been observed, from 
 two magnetising forces, that of the fixed magnet and that 
 of the current flowing through the helix. The first force 
 is proportional to the magnetic moment M of the fixed 
 magnet, and would produce a corresponding momentum 
 in the core, if it operated alone, and, as influenced by i, 
 the current flowing through the fixed magnet is repre- 
 sented by 
 
 CM 
 1 + yM 
 
 where C and y are constants. The second force is vertical 
 to the first, but may be represented, in substituting N for 
 M and considered as acting alone, by 
 
 GN 
 1 + yN' 
 
 The quantity N must manifestly be proportional to the 
 quantity of current i passing in the rotating helix, so that 
 
 (13.) N = Bi 
 
 where B is a constant for each machine. The resultant 
 of the two forces M and N acting together will be 
 
 p __ 
 
 = 1 + y V M* + iY 2 ' 
 
 but as the radical term in the denominator is incon- 
 venient, it may be modified by substituting for the radical 
 a quantity proportional to the current-strength, and 
 without lessening the degree of accuracy 
 
 (14.) P -^ ***+** 
 
 where ]3 is a new constant determined for each machine. 
 The axis of this magnetic moment P has the same 
 
272 CLAUSIUS* THEORY. 
 
 direction as the other resultants. If these axes make 
 
 angles and -_ -- 0, may be determined from the 
 
 equations 
 
 M N 
 
 cos * = ; sm = ' 
 
 By these equations the magnetic moment P can be resolved 
 into two components : 
 
 I : (16 ,{ P '- P "-Tf]p< 
 
 (P, , P ,in f , j-j-jj, 
 
 8. Work of the ponderomotive and electromotive 
 forces in the case where the iron core of the rotary 
 helix is at rest. After the available magnetic moments 
 are expressed, the work done by the ponderomotive force 
 can be determined. When the iron core of the rotating 
 helix is fixed, the helix is subject to a double force, that 
 of the fixed magnet operating from without and that of 
 the magnetic iron core operating from within. The pon- 
 deromotive force which the fixed electro-magnet exercises 
 upon the current-energised rotating helix, is proportional 
 to the magnetic moment M of the fixed electro-magnet, 
 and as well to the magnetic moment of the current-ener- 
 gised helix, and to the previously noticed quantity N. 
 The work due to the ponderomotive force is 
 
 -hMNv. 
 
 where - h is a constant indicating the negative character 
 of this force. The other ponderomotive force which the 
 rotating helix experiences from its magnetic iron core is 
 also proportional to the quantity N 9 and further depends 
 upon the magnetic moment of the iron core. In thi d 
 
WORKS PERFORMED. 273 
 
 magnetic moment must be distinguished the two Com- 
 ponents previously cited. The Component P 2 has no 
 working moment on the rotating helix. The component 
 Pj, whose axis is vertical tp the axis of N, gives a moment 
 proportional to PJ. Therefore this latter ponderomotive 
 force is represented by 
 
 By addition, can be obtained the whole ponderomotive 
 force during work performed in the unit of time 
 (17,) T= -hMNv ^-KNP^. 
 
 From this work of the ponderomotive force the work of 
 the electromotive force is immediately derived with the 
 help of equation (11), 
 
 (18.) Ei = hMNv + kNP 1 v-pi*v. 
 Substituting the foregoing values for P 1 
 
 9. Work of the ponderomotive and electromotive 
 forces for the case where the iron core participates in 
 the rotation of the helix. In this case, although the indi- 
 vidual convolutions of the helix maintain, during the 
 common movement, their positions relatively to the parts 
 of the iron, their positions relatively to the poles are 
 continuously changed. With slow rotation it may be 
 assumed that the poles of the iron core have the same 
 position in space, and the same strength as in an iron core 
 at rest. With quicker rotation this is certainly not the 
 case, and there occur deviations according to the position 
 and strength of the poles. If it be assumed that in the 
 
 T 
 
274 CLAUSIUS' THEORY. 
 
 rotating iron core the poles have the same position in 
 space and the same strength as in an iron core at rest, 
 equations (18) and (20) will apply. As to the work per- 
 formed by the ponderomotive force the conditions are not 
 so simple, but Professor Clausius makes intercomparison 
 by assuming that the iron core only is rotary whilst the 
 helix is maintained fixed. If now the iron core is made 
 magnetic by the common effect of the fixed electro -magnet 
 and the current passing in the helix, motion in the core 
 will not occur, as might be concluded, showing that the 
 rotary moment exercised by the fixed electro-magnet upon 
 the iron core is equal to the rotary moment exercised by 
 the iron core upon the helix, and is similarly directed. 
 Consequently, the works have the same value when the 
 iron core rotates with the helix as when the iron core is 
 at rest. 
 
 10. Modification of the previous results under quick 
 rotation. The results with quick rotation are affected by 
 the sluggishness of the iron in reference to changes of its 
 magnetic condition, so that the poles in the rotating iron 
 core have a somewhat different position in space and 
 somewhat different strength. This condition has not 
 hitherto, Professor Clausius believes, been taken into 
 account. That which next concerns the position of the 
 poles, and therefore the direction of the magnetic axis is 
 (section 7) the angle formed by the magnetic axis of the 
 iron core with the counter direction of the axis of the fixed 
 electro-magnet, determined by the equations (15). If the 
 iron core is rotated quickly it may be assumed that the 
 magnetic axis is displaced through a small angle in the 
 direction of the rotation, and that the angle is proportional 
 to the velocity of rotation. If 1 represents the angle 
 which the altered magnetic axis of the iron core forms 
 
MODIFICATIONS. 275 
 
 with the counter direction of the axis of the fixed electro- 
 magnet, there may be written 
 
 (21.) 0' = 0+ V , 
 
 where is a small constant. 
 
 As to the strength of the poles, this must be somewhat 
 less in a rotating iron core than in an iron core at rest. 
 Clausius thinks no serious error will be committed if it be 
 assumed that the altered magnetic moment is as great as 
 that of the changed axial direction of the components of 
 P in equation (14). Consequently, the existing magnetic 
 moment of the rotating iron core may be put as 
 
 (22.) P r = Pco$iv. 
 
 Professor Clausius then derives by similar reasoning as 
 previously the components 
 
 (33.) 
 
 The magnetic sluggishness of the rotating iron core 
 has, under all circumstances, prejudicial effect upon the 
 capacity for work of the machine. This influence is some- 
 what diminished by giving to the contact-brushes another 
 position for quicker rotation. Besides the retarding effect 
 of the magnetic sluggishness of the iron core, there may 
 be also the induction of currents in the mass of the iron 
 core itself. These currents, as well as other inductive 
 effects of a more remote character, are removable by 
 separating the iron core into parts ; or instead of employ- 
 ing a massive iron ring, by substituting a ring composed 
 of iron wires. Where these currents are found in impor- 
 tant measure, their effect is doubled. In the first place, 
 the currents themselves have a magnetic moment ; also 
 
276 CLAUSIUS* THEORY. 
 
 they exercise a magnetic effect upon the iron, and alter 
 the magnetism of the iron core. Their magnetic moment 
 is expressed by the product TJ v V M* + N*, where TJ is a 
 small constant. This product, multiplied by D (a constant 
 corresponding to and substituted for G\ and made the 
 numerator of the fraction in equation (14), will give the 
 magnetic moment corresponding to P. As both of these 
 moments have the same axial direction, they may be added, 
 and the moment 
 
 T, v v M* + N* i +YTTR' obtained - 
 
 The value of the components of the entire existing 
 magnetic moments in the iron core may be put 
 
 (p." = 
 
 For brevity, e' being introduced with the signification 
 
 (25.) ' = 6 + -, 
 the equations become 
 
 ( P i" - i-Ap (M-t'vN)~ wN, 
 (26.) \ *f*. 
 
 J' = ^r.(N~t'vM) + nvM, 
 
 and are more general than (23). For those machines in 
 which these induced currents in the iron are too unim- 
 portant for consideration, it is only required to put r\ = o, 
 and consequently e = <', to obtain equation (23). 
 
 11. Application of the foregoing values to determine 
 the work done by the ponderomotive force and by the 
 electromotive force.- -Keturning to equations (17) and 
 
DETERMINATION OF CURRENT. 277 
 
 (18), and substituting for the quantities P 1 and P 2 , the 
 adjusted values P/' and P 2 " 
 
 (27. 
 
 Ei=hMNv + 
 Further, putting for P/' and P 2 " the values of (26) 
 
 (28.), 
 
 Into these equations finally there are to be introduced 
 the values for M and ^ as by (12) and (13) to obtain (29). 
 
 (7 \ A^^ 2 / c ' (7 
 
 ,_. 
 
 - 
 
 ^ 
 
 These equations are fundamental to all further calcula- 
 tion. 
 
 To bring these equations under convenient control, the 
 following substitutions may be made 
 
 A 
 
 a = - I = tr - 
 
 a B a 
 
 kABC 
 
 These are applied to the preceding two equations. 
 
 12. Determination of the current quantity produced 
 by a machine when no foreign electromotive force is 
 co-exerted. When the external circuit is closed and 
 
CLAUSIUS' THEORY. 
 
 contains no foreign electromotive force, E = R i, and [with 
 the substitutions (30)] II. becomes 
 
 reduced to (by dividing by i, &c.) 
 
 (39 ^) i 
 ~~ 
 
 Substituting 
 
 (33.) i = w JL. 
 
 R 4- p v + <r 
 there obtains 
 
 (34.) 1 = --.p + r--. 
 a + iV^ b + ^ 
 
 From this equation can be immediately determined the 
 quantity i of the current produced by the machine. 
 Multiplying this equation by a + i and by b + i, and 
 arranging according to the powers of i, 
 
 (35.) i 2 (pw \v w a b)i (p b + q)w + \a v w -f a 6=0, 
 and solving the quadratic equation (36.) 
 i=(p<w X flw a 
 
 Of the two signs before the root sign only the upper is 
 applicable, and the following form can be given to the 
 equation (36) 
 
 / 37 x 
 
 + 2 
 Again, substituting for simplification, 
 
 / \ \ V -- 
 
 (38.) w' = 
 
 (39.) c = q pa i- p b, 
 
STARTING OF THE MACHINE. 279 
 
 the equation assumes the following very comprehensive 
 form 
 
 (40.) i = i(pw'-a &) + V (p w' + a 6) 2 + 4^ ~w. 
 
 13. Starting of the machine. Prof. Clausius shows 
 that for equation (36), with nil values for #, there is given 
 a negative value for i, which must not be taken as mean- 
 ing that the initial equation (II.) gives unsatisfactory 
 results for small rotary velocities ; for in this case the 
 machine gives no current until a certain velocity is 
 attained, which agrees with practical observation. To 
 deal strictly with this point, there must be taken into 
 consideration the "remanent" magnetism of the iron of 
 the electro-magnets. The equation (12) for the magnetic 
 momentum of the fixed electro-magnet gives, for i = o, 
 M=o. If now, however, a certain magnetisation is already 
 present in the iron before the introduction of the current, 
 this must naturally be taken into account in the deter- 
 mination of the existing magnetisation with a weak 
 current. An approximation may be obtained by supposing 
 ju the small moment of the "remanent" magnetization, 
 and then there is to be determined the value of i, for 
 which the expression for M has the value /*. 
 
 Therefore put fj. = ~ L_ 
 
 whence it follows 
 
 where ^ is the relative value of i. And according to this 
 determination there holds for all values of i. that are less 
 than 4 19 the equation M = ^ and for all values of i greater 
 than i the equation (12) for the magnetic moment. 
 
 It may also be considered that at starting the machine 
 
2 8o CLAUSIUS' THEORY, 
 
 is a magneto-electrical machine ; and it may be asked 
 how great is the rotary velocity at which the machine, as 
 a dynamo-eleotrio machine, gives the same current as a 
 magneto-electric machine, namely, the current of quantity 
 i r To determine this value v, there must be substituted 
 in equation (40) ^ for i. Following similar steps, there 
 obtains, with accentuation of corresponding values, 
 
 (43.) (a + i^p Wi + c w l = (a + i^ (b + ^). 
 
 In this result the values of w l and w/, deduced from 
 (33) and (38), must be introduced to determine v r 
 Neglecting the factors A and o- as of no importance at low 
 velocities, the expression ultimately becomes 
 
 (44 >> , = ( + i,) (b + ,) R 
 
 p (a + i^ + c ~ (a + ij) (6 + ij p 
 
 For ordinary practical purposes the simplification may 
 be extended, by considering that the production of current 
 takes its origin with a certain rotary velocity. With this 
 view there can be determined the limit value of the 
 velocity when JLI and ^ approach zero. Representing this 
 limit value of v l by v w 
 
 abE 
 
 (45.) V - r , 
 
 p a + c a b p> 
 or according to (39), 
 
 f*m\ abR 
 
 (46.) v n = -T T . 
 
 p b + q abp 
 
 This value of v represents the number of the so-called 
 " dead" revolutions, 
 
 Prof. Clausius has given further applications .of these 
 fundamental equations to the transmission of power by 
 dynamo-electric machines, which will be found in a sub- 
 sequent volume of this series dealing with electrical- 
 motive power. 
 
Dept. Mech Eng. 
 
 INDEX. 
 
 Accumulators : The first, 104. 
 
 Piante's, 104. 
 
 The Elwell-Parker, 109. 
 
 Faure's, 111. 
 
 Sellon-Volckmar, 121. 
 
 Defects in connection with, 
 
 131. 
 
 Applications of, 135, 138. 
 
 Action : In the Siemens' Coreless 
 Armature, 72. 
 
 of Niaudet's Machine, 83. 
 
 Explanation of the Action of 
 
 the Faure Accumulator, 112. 
 
 Explanation of the Chemical 
 
 and Mechanical Action in Accu- 
 mulators, 126. 
 
 of Circuit Interrupters and 
 
 Closers, 204, 
 
 Local, 126, 
 
 Adjustment : of the Ayrton-Perry 
 Ammeter and Voltmeter, with 
 Springs, 234, 
 
 of the Ayrton-Perry Ammeter 
 
 and Voltmeter, with Cog-wheel 
 and Gear, 236. 
 
 Advantage : of Electric Machines 
 over Galvanic Batteries, 1. 
 
 of the Siemens' Cylinder Ar- 
 mature, 11. 
 
 of the De Meritens' Machine, 
 
 34. 
 
 of Lontin's Machine, 34. 
 
 of the latest pattern of the 
 
 Gramme Alternating-current Ma- 
 chine, 43. 
 
 of the Siemens-Halske Alter- 
 nating-current Machine, 44. 
 of the Siemens' Circular Dy- 
 namo, 76. 
 
 of the Copper Discs in the 
 
 Armature of Edison's Machine, 
 85. 
 
 of the Faure Accumulator, 
 
 112, 120. 
 
 Advantage, Eelative, of Different 
 Machines, 88, 94. 
 
 and disadvantages of the 
 
 Plante Element, 107. 
 
 of Increased Dimensions of 
 
 Generators, 178. 
 
 and disadvantages of Gramme 
 
 and Siemens' Generators, 90, 189. 
 
 of Electric Machines, 203. 
 
 of the Ayrton-Perry Dynamo- 
 meter, 228. 
 
 - Prof. Sylvanus Thomson on 
 
 the relative, of the Pacinotti- 
 Gramme Ring (Table), 257. 
 
 Aimant Feuillete (Laminated Mag- 
 net) of Jamin, 53. 
 
 ALLAKD, H3. 
 
 Alliance Machine : Construction of, 
 9, 29, 30. 
 
 Application of, 29. 
 
 Alternating Current : Machines, 29, 
 49. 
 
 ' Production of, 5. 
 
 Machine of the Alliance Com- 
 pany, 29. 
 
 Machine of Brush, 46. 
 
 Machine of De Meritens, 33, 
 
 88. 
 
 Application of, Machines, 88, 
 
 90. 
 
 Machine of Gramme, 39. 
 
 Machine of Holmes, 35. 
 
 Machine of Gordon, 244. 
 
 Machine of Ferranti, 249. 
 
 Machine of Lontin, 39. 
 
 Machine of Mohring and Baur, 
 
 37. 
 
 Machine, Siemens-Halske, 43. 
 
 Machine of Weston, for Gal- 
 
 vano-plastic purposes, 35. 
 
 Ammeter : Commutator, of Ayrton 
 and Perry, 228. 
 
 Ayrton-Perry's, without Com- 
 mutator, 233. 
 
282 
 
 INDEX. 
 
 Ammeter : Ayrton - Perry's, wiih 
 Springs, 234. 
 
 Ayrton- Perry's, with Cog- 
 wheel and Gear, 251. 
 
 AMPERE : Theory of Magnets, 3. 
 
 Law of Magnetic Induction, 3. 
 
 Amperian Currents, 13. 
 
 Direction of, about the S. and 
 
 N. Poles, 3. 
 
 Direction of, in the Armature 
 
 of Pixii's Machine, 4. 
 
 Anode, 106. 
 
 Apparatus : Various, 203. 
 
 Siemens', for Melting Refrac- 
 tory Metals, 207. 
 
 Appendix, Chapters X. to XIII., 
 pp. 212280. 
 
 Application : of Large Alternating- 
 current Magneto Electric Ma- 
 chines, 9. 
 
 ' of Siemens' Cylinder Arma- 
 ture, 11. 
 
 of Wilde's Machine, 22. 
 
 of the Alliance Machine, 29. 
 
 of Secondary Batteries, 135, 
 
 139. 
 
 of Electric Generators, 26, 203. 
 
 of the Electric Transmission of 
 Energy, 211. 
 
 Applicability of the various Elec- 
 tric Generators, 88, 94. 
 
 Approximation Currents, 2; 
 
 Arc : Arrangement of Lamps in 
 Multiple and Parallel, 98. 
 
 Modification of the Law of 
 
 greatest efficiency of a Machine 
 in its employment for the Elec- 
 tric, 144. 
 
 Steadiness of, -Light, 183. 
 
 Tresca's Experiments on the 
 
 relation of the work expended to 
 the work done in the, 194, 
 
 Armature: of Brush's Machine, 46, 
 48. 
 
 of the Alliance Machine, 30. 
 
 of Baur and Mohring's Ma- 
 chine, 37. 
 of Edison's Machine, 84. 
 
 of Biirgin's Dynamo, 81, 82. 
 
 of the Crompton-Biirgin Ma- 
 chine, 261. 
 
 of De Meritens' Machine, 33. 
 
 Armature of the Elphiustone-Viri- 
 cent Machine, 260. 
 
 Coreless, of the Ferranti Ma- 
 chine. 249. 
 
 of Fitzgerald's Machine, 80. 
 
 of GUlcher's Machine, 61. 
 
 of Gramme's Alternating-cur- 
 rent Machine, 39. 
 
 of Gramme's Direct-current 
 
 Collec- 
 
 Plating Machine, 50. 
 
 Gramme's Ring, and 
 
 tor, 50. 
 
 of Gordon's Machine, 245. 
 
 of Heinrich's Machine, 59. 
 
 of the Hopkinson-Edison Ma- 
 chine, 252. 
 
 of Holmes' Machine, 35. 
 
 of Jiirgensen's Machine, 60. 
 
 of Maxim's Machine, 79. 
 
 of the Mordey Machine, 259. 
 
 of Lontin's Dynamo, 80. 
 
 of Lontin's Alternating-cur- 
 rent Machine, 38. 
 
 of Niaudet's Machine, 82. 
 
 of Pixii's Machine, 4. 
 
 r- Pacinotti's Ring, 12. 
 
 of the Siemens-Halske Alt. 
 
 current Machine, 44. 
 
 of Siemens' Plating Machine, 
 
 70. 
 
 of Siemens' Circular Dynamo, 
 
 72, 76. 
 
 of Stohrer's Machine. 8. 
 
 of Wallace-Farmer's Machine, 
 
 79. 
 
 of Weston's Light Machine, 
 
 76. 
 
 of Weston's Plating Machine, 
 
 35. 
 - Cylinder, Siemens, 10. 
 
 Cylindrical, 84. 
 
 Cylindrical Ring, 57. 
 
 Flat Ring, 58. 
 
 Ring, Pacinotti, 12. 
 
 Drum, construction and theory, 
 
 62. 
 
 Construction of, 172. 
 
 Causes of heating of, and pre- 
 vention, 174. 
 
 Relative position of, and the 
 
 Field Magnets, 175. 
 Coiling of, 125. 
 
INDEX. 
 
 283 
 
 Armature : Resistance and Electro- 
 motive force of, when the Bobbins 
 are variously coupled up, 145. 
 
 Bobbins (see " Bobbins ") 
 
 Interdependence of the electro- 
 motive force and quantity of cur- 
 rent (1) on the number of convo- 
 lutions in, 147. 
 
 (2) on the rate of rotation of, 
 
 149. 
 
 Ratio between current and rate 
 
 of rotation of, 151. 
 
 Ratio of effective magnetism 
 
 in Dynamo-electric Generators to 
 rate of rotation of, 1 51 . 
 
 Ratio of wire turns in, to turns 
 
 on Field Magnets in Dynamos, 
 157. 
 
 ARON : Explanation of the action of 
 the Faure Accumulator, 112. 
 
 Arrangement : of the Field Magnets 
 in Brush's Machine, 48. 
 
 of the Field Magnets in Lon- 
 
 tin's Machine, 38. 
 
 of Field Magnets in De Meri- 
 
 tens' Machine, 34. 
 
 of the Armature Coils in the 
 
 Siemens- Halske Alternating-cur- 
 rent Machine, 44. 
 
 of the Field Magnets in 
 
 Gramme's Machine for the elec- 
 trical transmission of energy, 50. 
 
 of Field Magnets in Jiirgen- 
 
 sen's Machine, 60. 
 
 of the Field Magnets in Sie- 
 mens' Circular Dynamo, 72. 
 
 of the Field Magnets in Wal- 
 lace-Farmer's Machine, 79. 
 
 of the Field Magnets in Wes- 
 
 ton's Machine, 76. 
 
 of Field Magnets in Edison's 
 
 Machine, 86. 
 
 of Armature Bobbins, in Bur- 
 gin's Machine, 81. 
 
 Asbestos : Insulation, 71. 
 
 Attractive force of Electro-magnets, 
 221. 
 
 Automatic regulation of the position 
 of the Brushes on the Collector, 
 173. 
 
 AYRTON and PERRY'S perfected 
 Dynamo, 101. 
 
 AYRTON and PERRY'S experiments 
 with Faure Accumulators, 124. 
 
 and Perry's Dynamometer, 226. 
 
 and Perry's Ammeters and 
 
 Voltmeters, 228, 239. 
 
 Bands (see "Bars," "Strips"). 
 
 BARLOW and PLUCKNER'S value for 
 the coeff . K. in different kinds of 
 iron, for determining the mag- 
 netic moment, 169. 
 
 Bars : Copper, round the Field Mag- 
 nets of Siemens' Plating Machine, 
 70. 
 
 Copper, on the Armature of 
 
 Edison's Machine, 84. 
 
 Battery : Advantages of Electric 
 Machines over, 1. 
 
 secondary (see " Accumula- 
 tors "), 103, 104, 
 -Ritter's voltaic, with one metal, 
 
 104. 
 
 Plante's secondary, 104. 
 
 Calculation of weight of, re- 
 quired for any number of lamps, 
 122. 
 
 BAUR : Dynamo Electric Machine, 
 37. 
 
 Bed Plates : Influence of iron on 
 the magnetic lines of force in a 
 Machine, 171, 
 
 BIOT : Formula of Biot and Cou- 
 lomb, for the distribution of the 
 magnetism on the surface of a 
 Core, 167. 
 
 Bleaching Agent: Preparation of 
 Ozone as, by the aid of Electric 
 Machines, 22. 
 
 Bobbins : On the Armature of the 
 Alliance Machine, 31. 
 
 of the Armature of De Meri- 
 
 tens' Machine, 33. 
 
 Coiling of, Gramme's Alter- 
 nating-current Machine, 41. 
 
 of the Siemens'-Halske Alter- 
 nating-current Machine, 44. 
 
 Connection of, Brush's Ma- 
 chine, 48. 
 
 Number of, Siemens' Circular 
 
 Dynamo, 76. 
 
 Armature, Wallace-Farmer's 
 
 Machine, 79. 
 
284 
 
 INDEX. 
 
 Dy- 
 
 Bobbins, Armature, Lontin's 
 namo, 80. 
 
 Armature, Biirgin's Machine, 
 
 81. 
 
 Number of, Armature and In- 
 ductor of Gordon's Machine, 247. 
 
 Method of coupling up an Ar- 
 mature, to obtain the maximum 
 efficiency, 145. 
 
 BOSANQUET, R. H. : Mathematical 
 consideration of double-wound 
 Machines, 102. 
 
 BREGUET : Gramme Machine for 
 physical laboratories, 52. 
 
 BRUSH : Alternating-current Ma- 
 chine, 46, 178. 
 
 Regulation of, Machine, 47. 
 
 Commutator, 47, 
 
 Double-wound Machine of, 98. 
 
 Improved method of " form- 
 ing" Secondary Batteries, 132. 
 
 Proposal for the construction 
 
 of the plates of Accumulators, 135. 
 
 Brushes Displacement of Neutral 
 Points, and consequent disposi- 
 tion of, 173. 
 
 of Brush's Machine, 47. 
 
 of Gramme's Machine, 51. 
 
 of Siemens' Plating Machine, 
 
 70. 
 
 of Weston's Light Machine, 78. 
 
 Reduction of number of, in 
 
 Multi-polar Machines, 259. 
 
 BURGIN : Machine, 178, 
 
 & OROMPTON'S Generator, 261, 
 
 Burner: Carcel, 119. 
 
 Branch circuit, 97. 
 
 Candles: Employment of Alter- 
 nating-current Machines with 
 electric, 89. 
 
 Capacity : Increase of, in an Accu- 
 mulator, 128. 
 
 Carbons: Advantage of the unequal 
 consumption of, 88. 
 
 Influence of the distance be- 
 tween, 200. 
 
 Carcel-burner, 119. 
 
 Cathode, 106. 
 
 Cell: Elwell-Parker, 110. 
 
 one-horse power, 122. 
 
 (see "Element") 
 
 Centrifugal force : Protection of 
 Edison's Armature, 86. 
 
 Change in direction of current in 
 the coils of an Armature during 
 its revolution, 6. 
 
 Charge : Retention of, by Accumu- 
 lators, 125. 
 
 Cause of the spontaneous loss 
 
 of, by the hydrogen and oxygen 
 plates in Secondary Batteries, 127, 
 129. 
 
 Charging : of Plante's elements,106. 
 
 of Accumulators, 112, 125. 
 
 of the Elwell-Parker Accumu- 
 lator, 110. 
 
 of the Faure Accumulators, 
 
 114. 
 
 Effects of, on the durability 
 
 of the peroxide of lead coating, 
 130. 
 
 (see "Forming") 
 
 Circuit : Extra, 95. 
 
 Main and shunt, 97. 
 
 Working, 98. 
 
 Short, caused in Accumulators, 
 
 121. 
 
 External, 160. 
 
 Relation of the internal re- 
 sistance of a Machine to the re- 
 sistance of the external, 145. 
 
 Retro-action of the moving, 
 
 on the fixed, 265. 
 
 Inductive influence in itself 
 
 of the moving, 268. 
 
 CLARKE : Modification of Pixii's 
 Machine, 7. 
 
 CLAUSIUS, R. T. E. : Theory of 
 Dynamo Machine, 263, 280. 
 
 CLIFFORD & LUCAS, 244. 
 
 Coils : Change in the direction of 
 the current in the Armature, 
 during rotation, 6. 
 
 Separation of, 20. 
 
 of the Alliance Machine Arma- 
 ture, 30. 
 
 in the Giilcher Machine, 61. 
 
 Armature, of the Wallace- 
 Farmer Machine, 79. 
 
 Armature, of Biirgin's Ma- 
 chine, 81. 
 
 Arrangement of Armature, 
 
 149. 
 
INDEX. 
 
 285 
 
 Coils, Ratio of the diameter of the 
 Electro-magnet to the diameter 
 of the Coil, 217. 
 
 of Jablochkoff 'a Machine, 242. 
 
 Shunt, in Giilch'er's new Ma- 
 chine, 253. 
 
 Determination of the relative 
 
 idleness or activity of Coils in 
 different parts of the Field, 255. 
 
 (see "Coiling"). 
 
 Coiling : of Armature Coils in Lon- 
 tin's Machine, 81. 
 
 of the Armature of Biirgin's 
 
 Machine, 81. 
 
 of Armatures, 175. [84. 
 
 Armature of Edison's Machine, 
 
 Field Magnets of self-regu^ 
 
 lating Machines, 101* 
 
 -< Magnetising influence of the 
 
 Armature, on the effective mag- 
 netism of the Generator, 156. 
 
 of Armature of Pixii's Ma- 
 chine, 4. 
 
 Armature in Siemens-Halske 
 
 Alternating -current Machine, 45. 
 
 Bobbins in Gramme's Alter- 
 nating-current Machine, 41. 
 
 Gramme's Armature, 51. 
 
 Tripolar Magnets, 54. 
 
 Field Magnets of Jurgensen's 
 
 Machine, 61. 
 
 Drum Armatures, 63. 
 
 Siemens' Coreless Armature, 
 
 73. 
 
 Armature, Weston's Light 
 Machine, 77. 
 
 Maxim's Machine, 79. 
 
 Armature of the Elphinstone- 
 
 Vincent Machine, 260. 
 Collecting : Currents from the Ring 
 
 Armature, 19. 
 
 Collector : Construction of, 20. 
 Construction of Gramme's 
 
 178, 50. 
 
 Niaudet's, 83. 
 
 Schuckert's, with two, 58. 
 
 The Drum Armature, 63, 65. 
 
 Siemens' Circular Dynamo ,75. 
 
 Weston's Light Machine, 78. 
 
 Connection of the Armature- 
 
 Coils with, Maxim's Machine, 
 
 79. 
 
 Collector, Absence of, Gordon's M a- 
 chine, 245. 
 
 Connection of the Coils with, 
 
 Mordey's Machine, 259. 
 
 Edison's, for Preventing 
 
 Sparking, 176. 
 
 Commutating : Lontin's Ma- 
 chine, 38. 
 
 Commutator, Principle of, 6. 
 
 Weston's Plating Machine, 36. 
 
 Construction of, 175. 
 
 Segments of, 6. 
 
 Method of taking the Current 
 
 from, 6. 
 
 Wear of, 89. 
 
 Absence of, Gordon's Machine, 
 
 245. 
 
 rings of, Brush's Ma chine, 47. 
 
 Jablochkoff's Machine, 243. 
 
 Committee : for the Investigation 
 of the Efficiency of the Faure 
 Accumulators (Report), 113. 
 
 Trustworthiness of Reports 
 
 and Data, 93. 
 
 Commutator: ^ammeter of Ayrton 
 and Perry, 228. 
 
 * voltmeter of Ayrton and 
 
 Perry, 230. 
 
 Compounded Machines, 253. 
 
 Conical Cores of the Armature Bob- 
 bins in Lontin's Machine, 80. 
 
 Connections of Drum Armature and 
 Collector, 63, 66, 69. 
 
 with Collector in Maxim's Ma- 
 chine, 79. 
 
 Constituents : Essential, of the Dy- 
 namo, 263. 
 
 Construction : Theoretical Basis 
 for, Electric Machines, 1. 
 
 the Alliance Machine, 30. 
 
 Pixii's Machine, 4. 
 
 Field Magnets, 164. 
 
 Commutators and Collectors, 
 
 175. 
 
 Armature, 172. 
 
 Armature of Edison's Ma- 
 chine, 84. 
 
 Maxim's Current Regulator, 
 
 96. 
 
 Commutator Rings in Brush's 
 
 Machine, 47. 
 
 Siemens' cylinder Armature,10. 
 
286 
 
 INDEX. 
 
 Const ruction, Gramme's Ring Arma- 
 ture and Collector, 50. 
 
 Pacinotti's Armature, 20. 
 
 Cylindrical Ring Armature in 
 
 Fein's Machine, 57. 
 
 Core of the Armature in Jiir- 
 
 gensen's Machine, 60. 
 
 Dram Armature, 63. 
 
 Pole-pieces in Weston's Light 
 
 Machine, 77. 
 
 - Elwell-Parker Element, 109. 
 
 Faure Accumulator, 111. 
 Plante Element, 105. 
 
 Sellon- Volckmar Element, 121. 
 
 Law's Electric Machines, 140. 
 
 Different Parts of Machines, 
 
 164. 
 
 Steel Magnets, 164. 
 
 Electro-magnets (formulae), 
 
 169, 212. 
 Points to be attended to in 
 
 good, 175. 
 Machines for plating purposes, 
 
 204. 
 Circuit Interrupters and 
 
 Closers, 205. 
 Ayrton - Perry Dynamometer, 
 
 226. 
 Gordon's Machine, 244. 
 
 Ferranti's Armature, 249. 
 Contact: Pieces (see "Brushes"). 
 
 38. 
 
 Rollers, 20. 
 
 Convolutions : Interdependence of 
 the electromotive force and quan- 
 tity of current on the number of, 
 of the Armature, 147. 
 
 Cooling : Electro-magnet Cores in 
 Weston's Machine, 36. 
 
 Armature in Heinrich's Ma- 
 chine, 60. 
 
 Journals in Edison's Machine, 
 
 86. 
 Armature Core, 175. 
 
 Core: Gramme's Ring Armature, 50. 
 
 Cylindrical Ring Armature in 
 
 in Fein's Machine, 57. 
 
 (see " Iron.") 
 
 Electro-magnets in Weston's 
 
 Machine, 36. 
 
 Schuckert's flat ring Armature, 
 
 58. 
 
 Core : Armature, of Heinrich's Ma- 
 chine, 59. 
 
 Armature, of Jiirgensen's Ma- 
 chine, 60. 
 
 of Bobbins of the Alliance 
 
 Machine, 31. 
 
 of Armature of De Meritens' 
 
 Machine, 33. 
 
 of Field Magnets of Holmes' 
 
 Machine, 35. 
 
 of Brush's Machine, 46. 
 
 Fixed, of the Siemens- Halske 
 
 Machine, 60. 
 
 Iron Wire, Drum-Armature, 
 
 69. 
 
 Iron Discs, Weston's Light 
 
 Machine. 76. 
 
 Wooden, 72. 
 
 Perforated, of Armature Bob- 
 bins, 79. 
 
 of Armature Bobbins, Lontin's 
 
 Dynamo, 80. 
 
 Armature, in Biirgin's Dyna- 
 mo, 81. 
 
 Edison's Machine, 84. 
 
 Division of, into Planes, to 
 
 prevent Foucault currents, 174. 
 
 Insulated Iron-sheet or Wire, 
 
 174. 
 
 Residual magnetism in, of Field 
 
 Magnets of Plating Machines, 
 204. 
 
 Relation of the strength of 
 
 a Magnet to the length of the 
 Iron, 216. 
 
 of Bobbins in Gordon's Ma- 
 chine, 245. 
 
 Armature, in Mordey's Ma- 
 chine, 259. 
 
 Work of the Ponderomotive 
 
 and Electromotive Forcesin, 272, 
 273. 
 
 Corrugated Plates : in Accumu- 
 lators, 133. 
 
 Method of depositing lead 
 
 uniformly on, 133. 
 
 COULOMB : Law and Formula of, in 
 connection with Magnets, 165, 
 167. 
 
 Coupling, Method of, the Bobbins 
 in an Armature to obtain maxi- 
 mum efficiency, 145. 
 
INDEX. 
 
 287 
 
 Coupling : Flange, 228. 
 
 Cost: Question of, of a Machine, 
 178. 
 
 Relation of, of a Machine to 
 
 its dimensions, 179. 
 
 Crater, in carbons of lamps, 88. 
 
 CROMPTON-BURGIN Generator, 261. 
 
 Method of winding the Field 
 
 Magnets in self-regulating Ma- 
 chines, 101. 
 
 Cross-section of Pole-pieces and 
 Armature Core of Heinrich s 
 Machine, 59, 60. 
 
 of Armature in Jlirgensen's 
 
 Machine, 60. 
 
 Currents : Direction of, in the Ring 
 Armature, 13. 
 
 Amperian, their direction 
 
 about the N. and S. Poles of 
 Magnets, 3. 
 
 Change in direction of, in the 
 
 Coils of an Armature during its 
 revolution, 6. 
 
 Direction of, in Gramme's 
 
 Dynamo Electric Light Machine, 
 54. 
 
 Weston's Plating Machine, 
 
 37. 
 
 in Machine of Baur and 
 
 Mohring, 38. 
 
 Direction of, in Armature 
 Coils of Pixii's Machine, 4. 
 
 Direction of, in the opposite 
 
 halves of the Ring Armature, 15. 
 
 Pacinotti's method of collect- 
 ing the currents in the Ring Ar- 
 mature, 19. 
 
 Direction of, in Brush's Ma- 
 chine, 48. 
 
 Alternating, Machines (see 
 
 "Generators "). 
 
 Direct, Machine (see ' ' Genera- 
 tors"). 
 
 Approximation, 2. 
 
 Retrocession, 2. 
 
 Induction, 1. 
 
 Primary and secondary, 1. 
 
 Direction of, in Siemens' 
 
 Dynamo, with coreless Arma- 
 ture, 73. 
 
 Foucault, 50, 253. 
 
 Total, 51, 63. 
 
 Current : direction of, in Tripolar 
 Electro-magnets, 54. 
 
 - Direction of, in the Drum 
 Armature, 65. 
 
 -- of low intensity and large 
 quantity, 56. 
 
 - Polarisation, 56, 104. 
 -- Interrupters, 56, 204, 205. 
 -- Direction of, in Lon tin's 
 
 Dynamo, 80. 
 
 -- Variations of, in Dynamos, 91. 
 -- Action of, in a regulator lamp, 
 
 92. 
 -- Regulation, 95. 
 
 - Method of obtaining a con- 
 stant, 102. 
 
 -- Uniform, 136. 
 
 -- Production of, in Plante Ele- 
 
 ment, 106. 
 -- Discharge, 106. 
 
 - Ratio between, and rate of 
 rotation in Dynamos, 151 . 
 
 - Ratio of increase of, to the 
 effective magnetism in Dynamos, 
 151. 
 
 -- Frohlich's " current curve," 
 153. 
 
 - Instruments for 
 
 228. 
 
 measurng, 
 
 Interdependence of quantity 
 
 of, and electromotive foix-e : 
 
 (1) on the number of convolu- 
 tions of the Armature, 147. 
 
 (2) on the rate of rotation of 
 the Armature, 149. 
 
 Method of determining the, 
 
 necessary, for saturating the Core 
 of an Electro-magnet, 169. 
 
 Self-induced, in Electro-mag- 
 nets, and their retarding action 
 on the magnetisation of the iron 
 Cores, 170. 
 
 Steadying of, 170. 
 
 Inversion of, from polarisa- 
 tion, 204. 
 
 Determination of the quantity 
 produced by a Machine, 277. 
 
 Curve : Frohlich's Current, 153. 
 
 Cylinder : -armature of Siemens, 10. 
 
 -armature of Edison's Ma- 
 chine, 84. 
 
 Interruption, 177. 
 
288 
 
 INDEX. 
 
 Data in connection with the Alli- 
 ance Machine, 90, 185, 187. 
 
 Brush's Machine, 49. 
 
 Gramme's Light ditto, 55, 90, 
 
 182. 
 
 Gramme's Plating ditto, 55. 
 
 Giilcher's ditto, 61. 
 
 Siemens-Halske ditto, 68, 70, 
 
 90, 182. 
 
 Biirgin's ditto, 81, 82. 
 
 Edison's ditto, 82, 86. 
 
 Tresca's Experiments, 1.94. 
 
 Elwell- Parker Accumulator, 
 
 109. 
 
 Faure's ditto, 111, 113. 
 
 Sellon-Volckmar ditto, 122. 
 
 Marcel-Deprez 1 Machine, 168* 
 
 Gordon's ditto, 247. 
 
 Ferranti's ditto, 251. 
 
 Hopkinson-Edison, ditto, 251. 
 
 Crompton-Biirgin ditto, 262. 
 
 Efficiency of various Machines, 
 
 183. 
 
 (See "Trinity House Report".) 
 
 (See also "Working Effi- 
 ciency.") 
 
 Dead revolutions, 154. 
 
 Defects : of Pixii's Machine, 7. 
 of Alliance Machine, 33. 
 
 of Faure's Accumulator, 121. 
 
 in connection with Accumula- 
 tors, 131. 
 
 of some of the Ayrton- Perry 
 
 Ammeters and Voltmeters, 233. 
 
 and Advantages of various Ma- 
 chines, 89, 93. 
 
 (See "Disadvantages," "De- 
 ficiency.") 
 
 Deficiency of Gramme's Machines, 
 57. 
 
 of Edison's Machine, 252. 
 
 of Fein's Machine, 60. 
 
 (See "Defect," "Disadvan- 
 tages.") 
 
 Details, Special, in connection with 
 Light Machines, 183, 202. 
 
 DEPREZ, MARCEL : Initial Field, 
 100. 
 
 Method of maintaining a con- 
 stant current, 102. 
 
 Galvanometer, application, 
 
 115. 
 
 DEPREZ, MARCEL : Small Electro- 
 motor, 168. 
 
 Conclusions as to advantages 
 
 of increased dimensions of Ma- 
 chines, 181. 
 
 Development, Historical, of Mag- 
 neto and Dynamo-Electric Ma- 
 chines, 1, 28. 
 
 Dimensions : of Gramme Machine, 
 178. 
 
 Conclusions as to, of Magnets 
 
 relative to maximum efficiency, 
 220. 
 
 of Field Magnets, to be ad- 
 vantageously employed in Dy- 
 namos, 170. 
 
 Disadvantage : of the fixed Iron 
 Core in the Drum Armature of 
 Siemens' Machine, 69. 
 
 and advantages of Plante's 
 
 Elements, 107. 
 
 of Accumulators as portable 
 
 Electrical Reservoirs, 138. 
 
 and advantages of different 
 
 Light Machines, 189. 
 
 of a porous Separator in Cells, 
 
 121. 
 
 (See " Defect," "Deficiency.") 
 
 Discharge of the Faure Accumu- 
 lator (data), 114, 118. 
 
 Discovery : of the Dynamo-Electric 
 principle, 24. 
 
 Faraday's, of the law of In- 
 duction, 1. 
 
 Distance pieces, 110. 
 
 Distribution : of magnetism on the 
 surface of a Core (formula), 167. 
 
 of free magnetism, 166. 
 
 DOUGLASS, Report of Tyndall and, 
 on Light Machines, 115. 
 
 Drum Armature : Direction of cur- 
 rent in, 65. 
 
 of Siemens and Halske, 61, 
 
 66. 
 
 Siemens' Magneto-Electric 
 
 Machine with, 67. 
 
 Siemens' Dynamo with, 61 
 
 67. 
 
 with German-silver Cylinder, 
 
 68. 
 
 DUB, Law of, in connection with 
 Magnets, 214. 
 
INDEX 
 
 289 
 
 Dynamo : Principle, 22. 
 
 Discovery and application of 
 
 principle, 24. 
 
 Variations in the resistance of 
 
 the circuit, and influence on the 
 
 working of, 93. 
 
 Simplest kind of, 24. 
 
 Defects of, 88, 94. 
 
 Edison's, 84. 
 
 Fein's, 57, 
 
 - Lontin's, 80. 
 Biirgin's, 81. 
 
 Giilcher's, 61. 
 
 Maxim's, 79. 
 
 Siemens', 66, 71. 
 
 Weston's, 76. 
 
 Weston's, for galvano-plastic 
 
 purposes, 35. 
 
 - Ladd's, 26. 
 
 Baur and Mohring's, 37. 
 
 Jablochkoff's, 244. 
 
 Historical development of, 1, 
 
 28. 
 Formulae for measurements in 
 
 connection with, 237. 
 Dr. Frohlieh's measurements 
 
 in connection with, 153. 
 
 Clausius' theory of the, 263. 
 
 Employment of Accumulators 
 
 in connection with, 125. 
 
 - Physical laws bearing on the 
 construction of, 140, 151. 
 
 Employment of large Magnets 
 
 in, 170. 
 Employment of, for plating 
 
 purposes, 204. 
 Dynamometer : Application of the 
 
 Easton- Anderson, 115. 
 Ayrton-Perry's, 226. 
 
 EASTON-ANDERSON Dynamometer, 
 
 115. 
 EDISON : Dynamo Machine, 84, 178. 
 
 Hopkinson Machine, 251. 
 
 Collector for diminishing 
 
 sparking, 176. 
 Effective Magnetism, 152. 
 Relation of, to current, 155, 
 
 156. 
 
 Maximum of, 157. 
 
 Efficiency : of a Machine, 9, 140, 
 
 163. 
 
 Efficiency: of Alliance Machine, 33. 
 
 of Lontin's Machine, 39. 
 
 of Gramme's Alternating-cur- 
 rent Machine, 43. 
 
 of Brush's Machine, 49, 183. 
 
 of Breguet-Gramme Generator, 
 
 54, 
 
 of Gramme's Direct-current 
 
 Light and Plating Machines, 55, 
 182. 
 
 of Giilcher's Machines, 61, 
 
 253. 
 
 of the Siemens-Halske Drum- 
 armature Machines, 68, 70. 
 
 of Burgin's Machine, 82. 
 
 of the Marcel-Deprez Ma- 
 chine, 168. 
 
 of Gordon's Machine, 247. 
 
 of Jablochkoff's Machine, 244. 
 
 of the Hopkinson-Edison Ma- 
 chine f 25.3. 
 
 of Edison's Machine, 252. 
 
 of the Mordey Machine, 260. 
 
 Relative working of different 
 
 Machines, 89, 182, 202. 
 
 r Relation of the dimensions of 
 
 a Machine to its, 179. 
 
 of the Faure Accumulators, 
 
 120, 137. 
 
 Increase of, in the Plante 
 
 element, 106, 107. 
 
 of the Elwell-Parker Accumu- 
 lator, 110. 
 
 of the Faure Accumulator, 
 
 112, 114. 
 
 Relative, of the Faure and 
 
 Sellon-Volckinar Accumulators, 
 124. 
 
 Electrodes, 104. 
 
 Electrolyte, 110. 
 
 Electro-Magnets : Construction of, 
 169. 
 
 Employment of, as Field Mag- 
 nets, by Wilde, 21. 
 
 Double winding of, 98. 
 
 Relation of the strength of an, 
 
 to the resistance of its Coils, 216. 
 
 Formulae for the construction 
 
 of, 212. 
 
 Determination of the strength 
 
 of current necessary for satu- 
 rating the Core of, 169. - 
 
2QO 
 
 INDEX. 
 
 for 
 
 Electromotive force : Method 
 maintaining a constant, 96. 
 
 and resistance of the Faure Bat- 
 tery, 117. 
 
 Relation of, to the work done, 
 141. 
 
 Relation of, to an opposing 
 Electromotive force, 142, 144. 
 
 of the Armature, when the 
 
 Bobbins are coupled up in series, 
 or for quantity, 145. 
 
 Inter-dependence of, and quan- 
 tity of current, (1) on the number 
 of convolutions of the Armature, 
 147. 
 
 (2) on the rate of rotation of 
 
 the Armature, 149. 
 
 (3) on the intensity of the 
 
 magnetic field in which the Ar- 
 mature moves, 150. 
 
 Dependence of, on the shape 
 of the Pole- pieces, 171. 
 
 of large Machines relatively to 
 
 that of small Machines, 179. 
 
 =- Relation of the dimensions of 
 
 an Electro-magnet to, employed, 
 220. 
 
 -. Discovery of an opposing, in 
 
 Machines of the Schuckert type, 
 254. 
 
 Clausius' theory of the Dy- 
 namo, 269, 277. 
 
 Electrotyping, 203. 
 
 ELIAS: Determination of the co- 
 efficient in Haker's formula, 
 165. 
 
 Method of forming powerful 
 
 Steel Magnets, 167. 
 
 Elliptic : Jablochkoffs Machine, 
 243. 
 
 ELPHINSTONE- VINCENT Machine, 
 260. 
 
 ELWELL-PARKER'S. Accumulator, 
 109. 
 
 Ergometer, 237. 
 
 Exciting : the Field Magnets of a 
 Dynamo, 25. 
 
 Employment of an, Machine, 
 
 with Lontin's Alternating-cur- 
 rent Machine, 38. 
 
 Field Magnets of Gramme's 
 Alternating-current Machine, 39. 
 
 Exciting : Field Magnets of Brush's 
 Machine, 49. 
 
 Field Magnets of Gordon's 
 
 Machine, 246. 
 
 Experiments : Tyndal & Douglass, 
 183. 
 
 with light Machines, by an 
 
 American Committee, 192. 
 
 Tresca, on the ratio of the 
 
 work expended in driving the 
 Generator, to the work done in 
 the Luminous Arc, 194. 
 
 by Professor Hagenbach, on 
 
 the ratio to the illuminating 
 power to the work expended, 
 198. 
 
 ditto, report by Fontaine 
 
 (data), 199. 
 
 on the efficiency of the Faure 
 
 Accumulator, 113. 
 
 by Hughes, on Electro-Mag- 
 nets, 223. 
 
 Explanation : Dr. Aron's, of the 
 action in the Faure Accumulator, 
 112. 
 
 Brush's, of the action in Ac- 
 cumulators, 126 
 
 External circuit, 160. 
 
 Extra circuit, 95. 
 
 FARADAY : Researches on the phe- 
 nomena of induction, 1. 
 
 FARMER and WALLACE'S Machine, 
 79. 
 
 FERRANTI'S Machine, 249. 
 
 Field : Magnetic, 21, 93. 
 
 Intensity of the magnetic, 175. 
 
 Initial, 100. 
 
 Avoidance of edges and cor- 
 ners in Pole-pieces, if a uniform 
 field is desired, 171. 
 
 .Number of wire turns on the 
 
 Magnets of Dynamos, 151. 
 
 Intensity of the magnetic, and 
 
 its influence on the Electromotive 
 force of the Machine, 151. 
 
 Magnets of Holmes' Machine, 
 
 35. 
 
 Employment of Electro-mag- 
 nets as Magnets, 21. 
 
 Magnets of de Meritens' Ma- 
 chine, 34. 
 
INDEX. 
 
 291 
 
 Field : Exciting the, Magnets, 22, 28. 
 Magnets of Weston's Plating 
 
 Machine, 35. 
 Magnets of Weston's Light 
 
 Machine, 76. 
 
 Magnets of the Alliance Ma- 
 chine, 31. 
 
 Magnets in a shunt-circuit, 
 97. 
 Double-wound, Magnets, 98. 
 
 Magnets of Siemens small Al- 
 ternating-current Machine, 10. 
 
 Magnets of Baur and Mohring's 
 
 Machine, 37. 
 
 Magnets of Lontin's Alter- 
 nating-current Machine, 38. 
 
 Tripolar Magnets of Gramme's 
 
 Direct-current Machines, 54, 57. 
 
 - Magnets of Gramme's Alter- 
 nating-current Machine, 39. 
 
 Magnets of Gramme's Genera- 
 tor for the electrical transmission 
 of energy, 56. 
 
 Magnets of the Siemens- 
 
 Halske Alternating-current Ma- 
 chine, 43. 
 
 Magnets of Brush's Machine, 
 
 48. 
 
 Magnets of Fitzgerald's Ma- 
 chine, 60. 
 
 Magnets, Coiling of, Jiirgen- 
 
 sen's Machine, 60, 61. 
 
 Magnets, V-shaped, of the 
 
 Siemens-Halske magneto-electric 
 Drum-armature Machine, 67. 
 
 Magnets of Siemens' Plating 
 
 Machine, 70. 
 
 Magnets of Farmer's Machine, 
 
 79. 
 
 Magnets of Niaudet's Machine, 
 
 82. 
 
 Magnets of Gordon's Machine, 
 number of, 285. 
 
 Magnets of the Mechwart and 
 
 Zippernowsky Machine, 251. 
 
 Magnet of Edison's Machine, 
 
 86. 
 
 Magnets of the Hopkinson- 
 
 Edison Machine, 252. 
 
 Magnets, strength of, 91. 
 
 Magnets, construction of, 164, 
 
 198. 
 
 Field Magnets, resistance of, 160, 
 161. 
 
 Magnets, advantageous dimen- 
 sions of, 170. 
 
 Magnets, relative position of 
 
 the Armature and, 175. 
 
 FITZGERALD, DESMOND F. : Direct- 
 current Machine, 60. 
 
 Fixed Poles : Influence of, on the 
 Ring-armature, 16, 255. 
 
 Flange-coupling, 228. 
 
 Flat Ring-armature, 58, 61. 
 
 - Machine, of Schuckert, 69. 
 
 FONTAINE : Report on the relation 
 of the illuminating power to the 
 work expended, 199. 
 
 Force : Attractive, of Electro-mag- 
 nets, 221, 
 
 Forming : The Plante element, 106. 
 
 Rapid process of, 108. 
 
 Faure's method of shortening 
 
 the forming process, 111. 
 
 Brush's process of, 132. 
 
 process in the case of Plates 
 
 coated with coherent lead, 1-34. 
 
 Formula : for the portative power 
 of Magnets, 165. 
 
 for the construction of Electro- 
 magnets, 212. 
 
 for the magnetic moment of 
 an Electro-magnet, 214. 
 
 for measurements in connec- 
 tion with Electric Machines, 237. 
 
 FOUCAULT currents, 253, 275. 
 
 Prevention of, in Gramme's 
 Armature, 50. 
 
 Prevention of, in Jiirgensen's 
 
 Machine, 61. 
 
 Prevention of, in Edison's Ar- 
 mature, 84, 251. 
 
 Avoidance of, in Pole-pieces, 
 
 171. 
 
 Prevention of, in iron Cores, 
 
 174. 
 
 FRANKENHEIM : Increase of the 
 "permanent moment" of Mag- 
 nets, 166. ; 
 
 Relation of the permanent 
 
 magnetism of an annealed steel 
 Magnet to the magnetism attain- 
 able with a given magnetic field, 
 166. 
 
2Q2 
 
 INDEX. 
 
 Free Magnetism : Jamin's experi- 
 ments on, 166. 
 
 Friction : Wearing of Collectors.and 
 Commutators, and loss of energy 
 by, 175.. 176. 
 
 FROHLICH'S, Dr. F., theory, 151, 
 270. 
 
 Current curve, 153. 
 
 FROMME and FRANKENHEIM'S ex- 
 periments, 166. 
 
 Fusion : Employment of Electric 
 machines for, of metals, 207. 
 
 Siemens' apparatus for, of re- 
 fractory metals, 207. 
 
 Galvanometer : DEPREZ, G. appli- 
 cation, 115 (see, "Ammeter," 
 " Voltmeter.") 
 
 Galvano-plastic purposes : Ma- 
 chines for (see "Plating Ma- 
 chines "). 
 
 Employment of WILDE'S Ma-. 
 
 chines for, 22. 
 
 Weston's Machine for, 35. 
 
 Baur and Mbhring Machine. 37. 
 
 Double collectors, Machines 
 
 for, 5. 
 
 Employment of Machines for,, 
 
 203. 
 
 Construction of Machines for, 
 
 204. 
 
 .GANTKEROT, 104. 
 Gases : Production of a lead coat- 
 ing on Accumulator Plates by the 
 reduction of oxide of lead with, 
 135. 
 
 Generators (see "Machines ' ). 
 GERALDY Messrs. Frank, and Hos- 
 pitalier's investigations as to 
 the efficiency of the Faure Accu- 
 mulator, 112. 
 
 GORDON'S Alternating - current 
 Machine, 244. 
 
 estimate for the lighting of 
 
 towns, 248. 
 
 Graduation of the Ayrton-Perry 
 Ammeter, 229. 
 
 ditto Voltmeter, 231. 
 
 GRAMME, 21, 50. 
 
 * System, 12. 
 
 Alternating-current Machine, 
 
 59. 
 
 GRAMME Collector, 50, 178. 
 
 Ring- Armature, 50. 
 
 Dynamos employed by Tresca 
 
 in his experiments, dimensions, 
 
 174. 
 
 Data in connection with Ma- 
 chines of, 184, 202. 
 
 Current-interrupter, 205. 
 
 Relative advantages of the, 
 
 and Pacinotti ring, 257. 
 Grids in the Sellon-Volckmar 
 
 Accumulator, 12. 
 Grooving : of the Armature -cores to 
 
 prevent overheating, 174. 
 of the Armature-core of Brush's 
 
 Machine, 46. 
 . of the Armature-core of 
 
 WESTON'S Light Machine, 76. 
 Grouping of the Coils of an 
 
 Armature, 145. 
 GULCHER'S dynamo, 61. 
 
 improved Machine, 253. 
 
 Relation of the work expended 
 
 to the intensity of illumination, 
 
 197. 
 
 MAKER'S formula for the portative 
 power of magnets, 165. 
 
 Heat: Production of, in the in- 
 terior of a Machine, 114. 
 
 Conversion of electrical energy 
 
 into, 142. 
 
 Heating ; Influence of, on the re- 
 sistance of the Armature, 149. 
 
 Prevention of, in Weston's 
 
 Machines, 36, 77. 
 
 Prevention of, in the Siemens- 
 
 Halske Drum-Armature, 68. 
 
 Causes of, in Armature-cores, 
 
 and prevention, 174, 175. 
 
 HEFNER-ALTENECK, Differential 
 lamps, 46, 90. 
 
 Drum- Armature, 61. 
 
 see Clausius' theory, 272. 
 
 HEINRICH'S Generator, 59. 
 
 Helix : Rotating, 264. 
 
 HJORTH'S Machine, 101. 
 
 HOLMES'S Alternating - current 
 Machine, 35. 
 
 HOPKINSOX-EDISOX Machine, 251. 
 
 Horse-power: Measurer, 237. 
 
 One h.p. accumulator Cell, 122. 
 
INDEX. 
 
 293 
 
 Horse-shoe : Elias method of mag- 
 netising, Magnets, 167. 
 
 shaped cross section of Hein- 
 
 rich's Armature-core, 59. 
 
 HOSPITALIER'S, Messrs. GERALD Y 
 and, investigation on the efficiency 
 of the Faure Accumulator, 
 112. 
 
 Hub of Fein's Machine, 51. 
 
 HUGHES' experiments on Electro- 
 magnets, 223. 
 
 Illuminating : Experiments and 
 data on the relation between 
 Power expended and the Work, 
 199. 
 
 Relative advantages of diffe- 
 rent Machines for, purposes, 88-. 
 
 Illumination, 183. 
 
 Intensity of, with various 
 
 Machines, 183, 202-. 
 
 Improvement : of the Edison 
 Machine, 252. 
 
 of the Schuckert Machine, 
 
 253. 
 
 Induced current strengthened, 82. 
 
 Inducing Magnets ; (see " Field- 
 magnets "). 
 
 Induction : False, 257. 
 
 Useful, 217. 
 
 Laws of, I, 265. 
 
 Increase in strength of, Cur- 
 rents, 3. 
 
 Magnetic, 4. 
 
 Self, of Field-magnets, 247, 
 
 249. 
 
 Inductive : Action of Pole pieces in 
 Brush's Machine, 48. 
 
 Action of Field-magnets, more 
 
 complete utilisation, 68. 
 
 - Action of Field Magnets in 
 Weston's Light Machine, 77. 
 
 Inversion ot'action in Gramme's 
 
 Ring-armature, 255. 
 
 Action of the Poles on 
 
 Gramme's Ring, 257. 
 
 Action of the moved circuit 
 
 upon itself (Clausius' theory), 268. 
 
 Inductor : of Gordon's Machine, 
 245. 
 
 Influence : Exposing coils of Arma- 
 ture to, of the Field Magnets, 174. 
 
 Influence (see "Clausius' Theory"), 
 268. 
 
 of the fixed Poles on the Ring 
 
 Armature, 13, 19. 
 Initial Field, 100. 
 Instruments for measurements in 
 connection with Electric Genera- 
 tors, 227, 237. 
 
 Insulation : of Commutator Rings 
 of Brush's Machine, 47. 
 
 Destruction of, 60. 
 
 Asbestos, 71. 
 
 Paper, 84. 
 
 between the iron wires or 
 
 sheets, of Cores, 174. 
 of wire in the Alliance Ma- 
 chine, 32 
 
 Integrating Dynamometer, (appli- 
 cation) 115. 
 
 Intensity : Measurement of mean 
 intensity and quantity of Electrii 
 city, 115. 
 
 of the Magnetic Field, 91, 175, 
 
 of illumination obtained with 
 
 various Machines (see "Trinity 
 House Report"), 183. 
 
 Ratio ol expenditure of work 
 
 to, of illumination, 199. 
 Internal resistance : Relation of the, 
 of a Machine to the resistance in 
 the external circuit, 145. 
 Resistance or Light Machine, 
 
 183. 
 Interrupter : Current, 37, 204. 
 
 in connection with Gramme's 
 
 Plating Machine, 56. [206. 
 
 Baur and Mohring's, 205, 
 Interruption Cylinder of Edison's 
 
 collector, 177. 
 Invention of Dynamos, 24. 
 Inversion of the direction of tha 
 current in a Machine, 204. 
 
 of the inductive action in the 
 
 Gramme Ring- Armature, 255. 
 Iridium : Fusion of, 207. 
 Iron : Wedges in Fitzerald's Ma- 
 chine, 60. 
 
 wire core of Jurgensen's Ma- 
 chine, 61. 
 
 wire drum Armature Core, 69, 
 
 Discs, core of Weston's LigUt 
 
 Machine, 76. 
 
294 
 
 INDEX. 
 
 Iron plates, Armature Core of 
 
 Edison's Machine, 84. 
 Barlow and Pluckner's values 
 
 for the co-efficient of Magnetic 
 
 moment, 169. 
 Expenditure of energy in 
 
 magnetising a piece of iron, 170. 
 Sheet Cores of Bobbins in 
 
 Gordon's Machine, 245. 
 ISENBECK : Experiments on the 
 
 influence exerted by Pole-pieces 
 
 on the inductive actions in the 
 
 Coils of a Gramme Ring, 255. 
 Discovery and explanation of 
 
 an inverse induption in Gramme's 
 
 Ring. 
 
 JABLOCHKOFF'S Machine, 243. 
 
 Relative advantages of Ma- 
 chines with regard to, candles, 
 88. 
 
 JACOBI : Law of Lenz and, 147 
 Laws of Dub and Muller, 214 
 
 JAMIN : Normal Magnet, 52. 
 
 Relative advantages of Ma- 
 chines for Electric Lighting with, 
 candles, 88. 
 
 on the co-efficient A in Biot 
 
 and Coulomb's formula for the 
 distribution of Magnetism on the 
 surface of a Core, 167. 
 
 JOUBERT : method p.f determin- 
 ing difference of potential, 115 
 
 Joubert, 113. 
 
 JOBLER : Equations for determining 
 the work in the Circuit and Ma- 
 chine, 237. 
 
 JOULE'S law, 142. 
 
 Equation, 161. 
 
 JURGENSEN'S direct current Ma/- 
 chine, 60. 
 
 KAPP: Gisbert, 82, 261. 
 Keeper, 95. 
 
 KOHLFURST : Employing Electric 
 . Machines in Telegraphy, 209. 
 
 .Ladd's dynamo, 26. 
 
 Laminated Magnet ; Gramme M a 
 chine with, 52. 
 
 Lamp : Action of current in a Regu- 
 lator, 92. 
 
 Lamps, Incandescent, employment 
 of the Ferranti Machine for a 
 large number of, 249. 
 
 Application of Maxim In- 
 candescent, 115. 
 
 Employed in Tresca's experi- 
 ments, 196. 
 
 Lead: Sheetsin Plan tes element, 104. 
 
 Perforated, sheet Electrodes, 
 
 109. 
 
 Red, employed in Accumula- 
 tors, 111, 121. 
 
 conducting power of Peroxide 
 
 of, 127, 129. 
 
 Effect of charging on the 
 
 durability of the Peroxide of, 130 
 
 Effects of the Sulphate of, 131 
 
 Employment of Plates with a 
 
 reduced, coating, 133. 
 
 Length ; influence of Cable on 
 the relation between the work 
 expended and the illuminating 
 power, 201. [213. 
 
 qf Cores of Electro-magnets, 
 
 LENZ : Law of, 147. 
 
 Light : Direction of Current in 
 Gramme, Machines, 54. 
 
 Weston's, Machine, 76. 
 
 Hagenbach's experiments with, 
 
 Machines, 197. 
 
 Tresca's experiments with, 
 
 Machines, 194. 
 
 Resistance of Machines, 144. 
 
 Theoretical Laws for the Con- 
 struction of, Machines, 145. 
 
 Details in connection with, 
 
 Machines, 182, 202. 
 
 Employment of Electric, Ma- 
 chines in h,ouses, 9, 184. 
 
 Lighting : Efficiency of Faure 
 Accumulators, 121. 
 
 Application of the Sellon- 
 
 Volckmar Accumulators, 123. 
 
 General employment of Accu- 
 mulators for, 126. 
 
 Application of Secondary Bat- 
 teries, 138. 
 
 Modification of the law of 
 
 maximum efficiency of a Genera- 
 tor when employed for, 144. 
 
 Employment of Machines for, 
 
 182, 202. 
 
INDEX. 
 
 295 
 
 Lighting : Employment of the Sie- 
 mens-Halske Alternating Cur- 
 rent Machine for, 46. 
 
 Electric, 84, 88. 
 
 Gordon's estimate for, 248. 
 
 Lines of Force : Direction of, in 
 Gramme Armature, 256. 
 
 Prevention of short circuiting 
 
 of magnetic, 172. 
 
 Liquid, for Accumulators, 104. 
 
 LONTIN : Alternating Current Ma- 
 chine, 38. 
 
 Dynamo, 80. 
 
 Loss : Explanation of Charge of Ac- 
 cumulators, 127, 129. 
 
 LUCAS : Clifford and, construction of 
 Gordon's Machine, 244. 
 
 Machines: (see "Generators"). 
 
 Magnet Construction of Steel, 
 Ib4. 
 
 Formula* for the Construction 
 
 of Electro, 212. 
 
 Strength of a, on what it 
 
 depends, 165, 166. 
 
 Haker's formula for the porta- 
 tive power of, 165. 
 
 r- Permanent moment of, 166. 
 
 Magnetic: Induction, 3. 
 
 Ampere's Law of, Induction, 
 
 3,4. 
 
 -. Field of Magneto-electric Ma- 
 chines, 93. 
 
 Retardation of the attainment 
 of the maximum Moment in Iron 
 Cores of Electro -magnet, 172. 
 
 Intensity of field, 175. 
 
 Field in Electric Machines, 
 
 151, 152. 
 
 Moment (law), 214. 
 
 Magnetisation : Maximum, of Steel 
 
 Plates, 53. 
 of the Tripolar Field Magnets, 
 
 54, 58. 
 Expenditure of energy in the, 
 
 of iron, 170. 
 Periods of change in the, of an 
 
 Iron Core, 172. 
 of Core in the Ring-armature 
 
 264. 
 
 -(^"Magnetising".) 
 Magnetising (see "Magnetisation"). 
 
 Magnetising: Influence of the Arma- 
 ture-coiling on the effective mag- 
 netism, 156. 
 
 of Steel Bars (by simple and 
 
 double touch), 164, 165. 
 
 Determination of the Moment 
 
 of different kinds of iron, 169. 
 Magnetism, 270. 
 
 Residual, 25, 88, 172. 
 
 Effective, 151, 152, 156. 
 
 Strength of, of Field Mag- 
 
 nets, 91. 
 
 Distribution of free, 166. 
 
 Distribution on the surface of 
 
 a Core (formula), 167. 
 
 Retardation in the maximum 
 
 magnetisation of an Iron Core, 
 and in the disappearance of the, 
 172. 
 Magneto-Electric Machines (see 
 
 "Machines"). 
 MALDEREN : Improvement of the 
 
 Alliance Machine, 29. 
 Massive, Advantage of, Field Mag- 
 nets, 170, 
 MASSON : Improvement of the 
 
 Alliance Machine, 29. 
 MAXIM Machine, 79. 
 
 Incandescent Lamp, 15. 
 
 Maximum : Conditions for, strength 
 of Electro-Magnets, 214. 
 
 Laws for Electro- Magnetic, on 
 
 Shunt Circuits, 223. 
 Measurements : in connection with 
 the Faure Accumulator, 119. 
 
 Instruments for taking, in 
 
 connection with Electric Ma- 
 chines, 226, 237. 
 
 Frohlich s, in connection with 
 
 Electric Machines, 153. 
 
 Jobler's formulae for, with 
 
 Electric Machines, 237. 
 in connection with Dynamo- 
 Electric Machines, 153. 
 with the Ay rton- Perry Am- 
 meter, 230. 
 
 Voltmeter, 231. 
 
 Spring Ammeter and Volt- 
 meter, 234. 
 
 (See "Data".) 
 
 MECHWART and ZIPPERNOWSKT'S 
 Machine, 251. 
 
2Q6 
 
 INDEX. 
 
 Medical purposes : Employment of 
 small Electric Machines for, 209. 
 
 MKRITENS, DE, Machine of, 33, 88. 
 
 Metals : Preparation of pure, 70, 
 207. 
 
 Employment of Electric Ma- 
 
 'chines for fusing refractory, 207. 
 
 Siemens' apparatus for fusing 
 
 refractory, 207. 
 
 MOHRING and BAUR, Dynamo of, 
 37. 
 Current interrupter, 206. 
 
 Moment : Increase of permanent, 
 166. 
 
 Law of Jacobi, Dub & Miiller, 
 
 214. 
 
 Influence of duration of the 
 
 action of a current, and the per- 
 manent of a Machine, 166. 
 
 Value of the co-efficient, in 
 
 determining the magnetic, for 
 different kinds of iron, 169. 
 
 Magnetic moment of the fixed 
 
 Electro-Magnets in Dynamos, 
 270. 
 
 MONCKL, Du, Construction of Elec- 
 tro-Magnets, 212. 
 
 MORDEY : Method of examining 
 Armature potentials, and dis- 
 covery of an opposing Electro- 
 motive force in Machines of the 
 Schuckert type, 254. 
 
 Schuckert, Machine, 253. 
 
 MORTON, Prof. HENRY ; Measure- 
 ments in connection with the 
 efficiencv of the Sellon-Volckmar 
 Accumulator, 122. 
 
 Motors : Electro (fee " Machines "). 
 - Electro, 243. 
 
 MULLER, Law of Jacobi, Dub and, 
 in connection with Magnets, 214. 
 
 Multiple Arc, Arrangement of 
 lamps in, 98. 
 
 Neutral points, 15, 65, 51. 
 
 Displacement of, and conse- 
 
 sequent position of the brushes, 
 
 173. 
 
 NIAUDET'S Machine, 82. 
 NOLLET, Inventor of the Alliance 
 
 Machine, 29. 
 Normal Magnet, 53. 
 
 OHM'S Law, 141. 
 
 Oiling, in Edison's Machine, 86. 
 
 Ozone, Employment of Electric 
 
 Generators for the preparation of, 
 
 22, 207. 
 
 PACINOTTI, Dr. ANTONIO : Ring- 
 armature, 12, 50. 
 
 Method of collecting currents 
 
 from Ring-armature, 19. 
 
 Relative advantages of, and 
 
 Gramme's Ring-armatures, 50, 
 257. 
 
 PAGET-HIGGS : Method of main- 
 taining a constant electro-motive 
 force, 98. 
 
 Need of an "Initial Field," 
 
 100. 
 
 Winding, self-regulating Ma- 
 chines, 101. 
 
 Parallel Arc, Arrangement of lamps 
 in, 98. 
 
 PARKER-ELWELL Accumulator, 109. 
 
 Peripheral currents (see " Foucuult 
 Currents "), 174. 
 
 Permanent moment of Magnets, 1 66 . 
 
 Peroxide of Lead (see " Lead "). 
 
 PERRY : Perfected Dynamo, 101. 
 
 Experiments on Faure Accu- 
 mulators, 124. 
 
 Dynamometer, 226. 
 
 on the transmission of energy, 
 
 210. 
 
 Photometric determinations in con- 
 nection with Faure Accumula- 
 tors, 119. 
 
 Pixn Machine, 3, 7. 
 
 Planes, Division of Cores into, to 
 prevent Foucault currents, 114. 
 
 PL ANTE : Secondary Battery, 105. 
 
 Process for rapid forming of 
 
 elements, 108, 109. 
 
 Plates: Perforated, for Batteries 
 109, 121. 
 
 Employment of corrugated, 
 
 for receiving chemically-depo- 
 sited lead, 133. 
 
 Employment of other metals 
 
 for supporting the peroxide of 
 lead, 134. 
 
 Plating, 203. 
 
 Gramme's, Machine, 55. 
 
INDEX. 
 
 297 
 
 Plating : Siemens', Machine, 70. 
 
 Machine of Weston, 35. 
 
 Machine of Baur and 
 
 Mohring, 37. 
 
 Machines, Construction, 204. 
 
 Current Interrupters and 
 
 Closers in connection with, Ma- 
 chines, 205. 
 
 Prevention of change in pola- 
 rity of, Machines, 204. 
 
 Platinum, Fusion of, 207. 
 
 PLUCKNER and BARLOW : Valves of 
 the coeff. K. , for various kinds of 
 iron, 166. 
 
 Polarisation: 104, 142. 
 
 Inversion of current in Plating 
 
 Machines from, 204, 
 
 Currents, 50. 
 
 Polarity : Prevention of change of 
 Field Magnets in Plating Ma- 
 chines, 204. 
 
 Pole: Pieces (see Isenbeck), 255. 
 
 Pieces, size of, 171* 257. 
 
 Distribution of the Electro- 
 motive force in the sections of 
 the Armature Coils, depends on 
 the shape of, pieces, 171. 
 
 Construction ofj pieces, to 
 
 avoid Foucault currents, 171. 
 
 Direction of the Amperian- 
 
 currents round the S. and N., 
 3. 
 
 Influence of the fixed, on the 
 
 Coils of the Ring Armature, 12, 
 19. 
 
 Travelling, in the Core of the 
 
 Ring Armature, 13. 
 
 Distance of the Armature Core 
 
 from, 175. 
 
 Pieces of the Field-magnet in 
 
 Brush's Machine, 41. 
 
 Pieces, in Breguet's Gramme 
 
 Machine, 52. 
 
 Pieces, in Gramme's Plating 
 
 Machine, 56. 
 
 Pieces, in Fein's Machine, 58. 
 
 Pieces, in Schuckert's Ma- 
 chine, 58. 
 
 Pieces, in Heinrich's Machine, 
 
 58. 
 
 Pieces, in Gulcher's Machine, 
 61. 
 
 Pole : Pieces, in the Siemens-Halske 
 Drum Armature Machine, 67. 
 
 Pieces, in Weston's Light Ma- 
 chine, 76, 77. 
 
 Pieces, in Edison's Machine, 
 
 86. 
 
 Pieces, in Mordey's Machine, 
 
 257. 
 
 Ponderomotive Force : (see " Clau- 
 sius' Theory"), 269. 
 
 Portative Power : Of Magnets, 53. 
 
 Haker's formula for, 165. 
 
 POTIER, 113. 
 
 Potential : Constant, 252. 
 
 Mordey's method of determin- 
 ing the Armature, 254. 
 
 Change of, 104. 
 
 Power : Carcel burner, 119. 
 
 Candle, 119. 
 
 (See " Portative Power ". ) 
 
 Electrical transmission of, 56, 
 
 210. 
 
 Prevention of Foucault currents 
 (see these.) 
 
 Primary current^ 2. 
 
 Principle : Of Compound- wound, 
 Self- regulating Machines, 100. 
 
 Of construction of the Com- 
 mutator, 6. 
 
 Of direct Current Machines, 
 
 20. 
 
 Dynamo- electric, 22, 24. 
 
 Pure Metals, Preparation of, 207. 
 
 Quantity : Measurement of, 115. 
 
 Interdependence of, of Current 
 
 and Electro-motive force on (1) 
 number of convolutions in the 
 Armature, 147. 
 
 (2) the rate of rotation of the 
 
 Armature, 149. 
 
 (3) the intensity of the mag- 
 netic field in which the Armature 
 moves, 151. 
 
 Rapid: "Forming" of Secondary 
 Batteries, 108, 109, 111. 
 
 Rate (see " Rotation ").' 
 
 Rectifying : Currents, 6. 
 
 Current in Siemens' circular 
 
 Dynamo, 76. 
 
 Red Lead (see "Lead"). 
 
INDEX. 
 
 Keduced Lead Coating for plates 
 for Accumulators, 133. 
 
 Reducing : Process of, Lead on the 
 plates of Accumulators, by means 
 of gases, 134. 
 
 Refractory metals : Fusion of, 207. 
 
 Siemens' apparatus for melt- 
 ing, 207. 
 
 REGNIER'S statements in connec- 
 tion with Faure Accumulators 
 criticised, 137. 
 
 Regulation : Current, 95, 97. 
 Brush's Machine, 47. 
 
 Regulator : Maxim's, 96. 
 
 Report: "Trinity House," 90,183. 
 
 Trustworthiness of, and Data, 
 
 93. 
 
 of relative efficiency of various 
 Machines, by American Commit- 
 tee, 192, 
 
 Experiments by Hagenbach, 
 
 197. 
 
 Experiments by Fontaine, 
 
 199. 
 
 Experiments with Faure Ac- 
 cumulators, 113. 
 
 of Tresca's experiments, 194. 
 
 of experiments at the School 
 
 of Military Engineering at Chat- 
 ham, 189. 
 
 Reservoirs of electrical energy (see 
 " Accumulators"), 103, 104, 136. 
 
 Residual Magnetism, 25, 88, 172, 
 204. 
 
 Resistance and Electro-motive force 
 of the Faure Battery, 117. 
 
 Increase of, in Secondary Bat- 
 teries, 129. 
 - Relative, 143. 
 
 Relation of the internal, of a 
 
 Generator to the existence of the 
 external circuit, 145, 147. 
 
 Resistance of the Armature 
 
 when the Bobbins are coupled up 
 in series or for quantity, 145. 
 Siemens' Formula for calculat- 
 ing the increase of resistance of a 
 wire with the increase of tem- 
 perature, 150. 
 
 of Armature Core, 174. 
 
 Relation of, to intensity of 
 
 Current, 383. 
 
 Resistance : Internal, of the normal 
 Siemens Light Machine and 
 Gramme Machine, 183. 
 
 Relation of, of the Coils of 
 
 an ElectroMagnet to its strength, 
 216. 
 
 Diminution of, in the Arma- 
 ture Coils of Edison's Machine, 
 85. 
 
 Retention of charge by Accumula- 
 tors, 125. 
 
 Retroaction of the moving circuit 
 on the fixed, 267. 
 
 Retrocession currents, 2. 
 
 Reversing : in charging accumu- 
 lators, 128. 
 
 Revolutions: " Dead " 154, 
 230. 
 
 Effect of the number of, on 
 
 the relation of the work spent to 
 the intensity of illumination, 
 200. 
 
 Changes in the direction of the 
 
 current in the Coils of the Arma- 
 ture during its, 6. 
 
 Ring Armature, influence of the 
 fixed Magnets on, 13, 19. 
 
 Pacinotti's, 12, 20, 50. 
 
 Gramme's, 50, 
 
 Theory of, 12. 
 
 r Commutator of Brush's Ma- 
 chine, 47. 
 
 Armature of Gramme's plating 
 
 Machine, 56. 
 
 Cylindrical, Armature, 57. 
 
 Flat, Armature, 58. 
 
 Armature of Heinrich's Ma- 
 chine, 59. 
 
 collector of Siemens' circular 
 
 Dynamo, 75. 
 
 RJTTER : Voltaic Battery with one 
 metal, 104. 
 
 Rollers, contact, 20, 69. 
 
 Rotation : Rate of, Ferranti's Ma- 
 chine, 257. 
 
 Interdependence of the Elec- 
 tromotive force and quantity of 
 current on the rate of, of the 
 Armature, 149. 
 
 Relation of the heating of the 
 
 wire of the Armature to the rate 
 of, 149. 
 
INDEX. 
 
 299 
 
 Rotation : Relation of current and 
 Effective Magnetism of a Dynamo 
 to the rate of, of the Armature, 
 91, 151. 
 
 Position of the neutral points 
 
 depending on the rate of, of the 
 Ring Armature, 173. 
 
 (see "Data," "Working"). 
 
 Saturation : Method of determining 
 the strength of current necessary 
 for, of the Core of an Electro- 
 magnet, 169. 
 
 Sawyer's Switch, 95. 
 
 SAITOH : modification of Pixii's 
 Machine, 7. 
 
 SCHUCKERT: Flat Ring Genera- 
 tors, 253, 5.8, 59. 
 
 Machine with two flat Rings. 
 
 Mordey or Victoria Machine, 
 
 253. 
 
 SCHWENDLER : Experiments on the 
 employment of Magneto-electric 
 Machines in Telegraphy, 208. 
 
 Secondary ; Batteries (see " Accu- 
 mulator"), 103. 
 
 currents (production and direc- 
 tion) 1, 3. 
 
 wire, 3. 
 
 Segments : Metallic and insulating, 
 of a Commutatqr, 6. 
 
 Segment strips of the Collector of 
 Weston's Light Machine, 78. 
 
 Self-induction, 247, 249, 253. 
 
 Sellon-Volckmar Accumulator, 121. 
 
 Series Machines, 98. 
 
 Sheet Iron: Cores of thin insulated, 
 174. 
 
 Shunt Circuit : suggested by 
 Wheatstone, 97. 
 
 value of the, 162, 206. 
 
 Condition for Electro-magnetic 
 
 Maximum on, 223. 
 Electrical work in, 240. 
 
 Shunt Coils in Gulcher's Im- 
 proved Dynamo, 253. 
 
 SIEMENS; Cylinder Armature of Dr. 
 Werner, 10. 
 
 Small Machine, 10. 
 
 -Halske Dynamos, 27. 
 
 - -Halske alternating current 
 Machines, 43. 
 
 SIEMENS-HALSKE : direct current 
 Machines, 63, 76. 
 
 Application of Wheatstone' s 
 
 Shunt-circuit, 97. 
 
 (See "Machines," "Data"). 
 
 method of winding the Field 
 
 Magnets of Self- Regulating Ma- 
 chines, 101. 
 
 Formula for calculating the in- 
 crease of the resistance of a wire 
 with rise of temperature, 150. 
 
 Sinusoid, 254. 
 
 Sluggishness, magnetic, 170. 
 
 Sparking : at the Collectors and 
 Commutators, 175. 
 
 Reduction of, 254. 
 
 Edison's Collector for the re- 
 
 duction of, 176. 
 
 Sparks, 38, 89. 
 
 Starting the Machine, 279. 
 
 Steadying Current in Dynamos by 
 employing large Field Magnets, 
 170, 
 
 Steel, Magnetising of, bars, 164. 
 
 Elias' method of forming 
 
 powerful, Magnets, 166. 
 
 STOHRER'S Machine, 8. 
 
 Stops, 'Rubber, in the Swan, Sellon- 
 Volckmar Accumulator, 121. 
 
 Storage Batteries (see " Accumula- 
 tors"), 
 
 The first (Ritter's), 104. 
 
 Strength : Increased, of Induction 
 Currents, 3, 9. 
 
 of a Magnet (see * ' Magnetic 
 
 Moment"), 165/214. 
 
 Coulomb's Law for, of geome- 
 trically similar Magnets, 165. 
 
 Instruments for measuring, of 
 
 Currents, 228, 233, 234, 236. 
 
 Strips, Copper, of Ferranti's Arma- 
 ture, 249. 
 
 Stroke, Magnetising by single or 
 double, 164. 
 
 SWAN, Sellon-Volckmar Accumula- 
 tor, 121. 
 
 Switches, of Sawyer and Siemens, 
 95. 
 
 System, Gramme, 12, 50. 
 
 Telegraph : Employment of Electric 
 Generators in the, 208. 
 
3 oo 
 
 INDEX. 
 
 Telegraph: employment of a Siemens 
 Generator by the Western Union 
 Company, 209. 
 
 Temperature, Law of the Increase 
 of the resistance of the wire with, 
 149. 
 
 Employment of Electric Ma- 
 chines for obtaining high, 207. 
 
 Siemens' Formula for calculat- 
 ing Increase of Resistance with 
 rise of, 150. 
 
 Theoretical Principles of the efficient 
 construction of Electric Machines, 
 140. 
 
 Theory : Ampere's, of Magnets, 3. 
 of the Ring Armature, 12. 
 
 of the Drum Armature, 63. 
 
 of Siemens' Coreless Armature^ 
 
 74. 
 
 Clausius', of the Dynamo, 263. 
 
 (See "Laws"). 
 
 Thomson's, in connection with 
 
 Dynamos, 157. 
 251. 
 
 THOMPSON : Prof. Sylvanus, Conclu- 
 sions respecting the Advantage of 
 increased dimensions of Electric 
 Machines, 179. 
 
 on the Magnetism of a piece of 
 
 iron, 170. 
 
 on the relative Advantages of 
 
 Pacinotti's and Gramme Machine, 
 257. 
 
 Explanation of the inversions 
 
 which occur in the Ring Arma- 
 ture, 256. 
 
 Suggestion in connection with 
 
 determining the relative activity 
 of Coils in different parts of the 
 field, 254. 
 
 THOMSON, 157. 
 
 Sir W., Suggestion for the 
 
 Copper Winding of an Armature, 
 
 Time, Influence of, during which 
 the Machine works, on the rela- 
 tion between the work expended 
 and the intensity of illumina- 
 tion, 201. 
 
 Transmission of Energy: Employ- 
 ment of Electric Machines for, 
 210. 
 TRESCA, 113, 124. 
 
 TRESCA : Experiments, 194. 
 
 Trinity House Report, 90, 183. 
 
 Tripolar Magnets, 54. 
 
 Turns of Wire on Armature and 
 Field Magnets, 147. 
 
 - (see " Coils," " Coiling"), 157. 
 
 TYNDALL and DOUGLASS on compa- 
 rative Experiments with light 
 Machines, 183. 
 
 UPPENBORN : Modification of the 
 law of the relation that the inter- 
 nal resistance of a Machine bears 
 to the external resistance, 147. 
 
 Utilisation of the Armature Coils as 
 completely as possible, 60, 68. 
 
 Values : Comparative, of Generators, 
 183. 
 
 Variations in the strength of Cur- 
 rent of a Machine, 92. 
 
 VICTORIA (Schuckert-Mordey) Dy- 
 namo, 253. 
 
 VINOENT-ELPHINSTONE, Generator, 
 260. 
 
 VOLCKMAR-SELLON, Accumulator, 
 121. 
 
 Voltaic Battery, Ritter's, with 
 one metal, 104. 
 
 Voltmeter, with Spring, 234. 
 
 Commutator, 230. 
 
 without Commutator, 233. 
 
 with Cog-wheel and Gear, 236. 
 
 Wearing : of Commutators and 
 
 Collectors, 89, 175. 
 Wedges: wooden, 20. 
 
 Iron, 60. 
 
 Weight : of various parts of Ma- 
 chines, (see " Data "). 
 of Battery required for lighting 
 
 purposes, 123. 
 WESTON : Plating Machine, 35. 
 
 Light Machine, 76. 
 
 Current closer, 205. 
 
 WHEATS-TONE : Method of exciting 
 
 the Field Magnets of a Dynamo 
 
 by a Shunt Circuit, 97. 
 Dynamo Electric principle, 
 
 24. 
 WILDE : Magneto-electric Machines 
 
 of, 21. 
 
INDEX. 
 
 301 
 
 WILDE : Employment of Electro- 
 magnets as Field-magnets 21. 
 
 Winding : of Armature and Field- 
 magnets of Siemens' Plating 
 Machine, 70. 
 
 of Field-magnets in Gulcher's 
 
 improved Dynamo, 253. 
 
 Methods of, Field -magnets of 
 
 self-regulating Machines, 101. 
 
 Wire : Primary and Secondary, 3. 
 
 strands, 61. 
 
 Iron, Drum Armature Core, 
 
 69. 
 
 Branch, 79. 
 
 Turns of, (see " Coils," " Coil-. 
 
 ing")- 
 
 Iron Cores, 174. 
 
 Wooden Cores, 72. 
 
 Work : Relation of the Electro- 
 motive force of a Machine to 
 the, done, 141. 
 
 Calculation of Electrical, 
 
 116. 
 
 Work : Relation of the Electro- 
 motive force of, in a Machine to the 
 opposing Electromotive force in 
 doing Magnetic or Dynamic, 144. 
 
 Ratio pf total, useful, in a 
 
 Dynamo, 160. 
 
 Ratio of, expended in driving 
 
 a Generator to, done in the lumi- 
 nous arc, 194. 
 
 Calculation of, done in a Ma- 
 chine and the external Circuit, 237. 
 
 Unnecessary loss of, due to 
 
 badly constructed Commutators 
 and Collectors, 176. 
 
 (See " Report") 
 
 Loss of, in the Electric trans- 
 mission of energy, 210. 
 
 Measurement of, transmitted 
 
 to a Generator, 228. 
 
 (See " Clausius' Theory of the 
 
 Dynamo ".) 
 
 ZlPPERNOWSKY AND MECHWART 
 
 Machine, 251. 
 
 UHIVISSITT 
 
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