MACHINERY: A MANUAL FOR STUDENTS OF ELECTROTECHNICS. BY SILVANUS P. THOMPSON, D.Sc., B.A., F.R.S.; PRINCIPAL OF, AND PROFESSOR OF PHYSICS IN, THE CITY AND GUILDS OF LONDON TECHNICAL LATE PROFESSOR OF EXPERIMENTAL PHYSICS IN UNIVERSITY COLLEGE, BRISTOL; VICE-PRESIDENT OF THE PHYSICAL SOCIETY OF LONDON; MEMBRE DE LA SOCIÉTÉ DE PHYSIQUE DE PARIS; HONORARY MEMBER OF THE PHYSICAL SOCIETY CF FRANKFORT-ON-THE-MAIN; E. & F. N. SPON, 125, STRAND, LONDON. 1892. PREFACE TO THE FOURTH EDITION. IN this fourth edition, which has been very largely rewritten, there are several features which distinguish it from its predecessors. The great development of public electric lighting during the past five years has necessitated the construction of very large dynamos suitable for central stations. Of the established types of these machines detailed descriptions are given. A number of Plates have been added, some of them being scale-drawings of recent forms of machines. The invention of alternate-current motors of many novel types, depending on the production of multiphase alternate currents, has claimed a special chapter. A chapter has been added on the theory of armature winding. No pains have been spared to ascertain the most approved practice in the construction of armatures, commutators, and other details requiring combined mechanical and electrical knowledge and experience. A chapter has been added on dynamo design. Transmission of power by electrical means also claims a short special chapter. Some remarks on the management of dynamos have been embodied at the end of the work. It would have been impossible to do justice to the present development of the subject but for the co-operation of the electrical engineers and engineering firms who are leading the advance. For such co-operation the author's thanks are gratefully given. And in particular he tenders his acknowledgment to the following, who have specially aided him by furnishing him with drawings and statistical data: Mr. C. E. L. Brown (late of the Oerlikon Works, Zürich); Mr. Gisbert Kapp; Mr. W. B. Esson (of Messrs. Paterson and Cooper); Mr. Mordey (Brush Electric Engineering Co.); Mr. T. Parker (Electric Construction Corporation); Mr. Albion T. Snell (General Electric Traction Co.); Messrs. W. T. Goolden and Co.; Mr. S. Z. de Ferranti; Messrs. Blakey, Emmott and Co.; The Gülcher Electric Co.; Messrs. Ernest Scott and Co.; Messrs. J. H. Holmes and Co.; Messrs. Siemens Bros.; Messrs. Mather and Platt; Messrs. R. E. Crompton and Co.; Messrs. S. Schuckert and Co.; Messrs. J. G. Statter and Co. For the use of cuts the author is indebted to various of the above-named firms, and also to the publishers of the following journals: The Electrician, Electrical Review, Industries, and La Lumière Électrique. To the publishers of the Electrical Engineer (N.Y.) for Plate XIII. The author is indebted to his colleague, Professor Perry, F.R.S., for the use of some of his notes in the preparation of Chapter XV. His former chief assistant, Professor R. Mullineux Walmsley, has again kindly rendered help in reading proofs of several of the new chapters. To his late pupil, Mr. Walter Hawkings, the author is indebted for valuable help in preparing drawings, particularly those dealing with armature winding. Heavy as the task is of adequately presenting the principles and practice of a department of science which has undergone such an enormously rapid development, that task has been lightened in three directions by the circumstance that three fellow-workers in science have lately devoted themselves to expounding special branches of it. Professor Ewing, of whose researches in magnetism an all too brief account has been given in this book, has prepared a treatise on magnetism which is on the very eve of publication. Professor Fleming has already published the first half of a treatise on the Alternate Current Transformer, and the second half will soon appear. Mr. Gisbert Kapp's work on Electric Transmission of Power has already commanded a wide accept-· ance. There has been, therefore, the less necessity to extend those chapters in the author's book which deal with these topics, though they have been carefully brought up to date. Want of space has precluded the author from treating as fully as he would have desired the topic of central station machinery. This has assumed three different types in England, Germany, and America. In England, engineers have developed special forms of high-speed engine to be coupled direct to the dynamo. In Germany practice has taken the inverse course of designing huge slow-speed dynamos for attachment direct to engines of older type. Either of these methods is, in the author's opinion, preferable to the American practice of building high-speed dynamos and low-speed engines, and then connecting them by belts running over pulleys. It would be difficult to discover any scientific subject which more thoroughly illustrates the principle of action and reaction than does this of dynamo-electric machinery. In every department of the subject the essential thing to be understood is a reaction of some sort. In the rotating armature of the dynamo the very production of the current sets up an opposing drag, and the work of generating the current is done by driving the machine against this mechanical reaction. In the motor the very production of motion sets up an opposing electromotive-force which tends to stop the supply of current. In the transformer, the current which is set up by the magnetic changes in the core, tends to oppose those changes. In the self-induction coil the changes of magnetism which result from the impressed waves of current tend to destroy those waves. In the alternate-current motor the moving part tends so to move as to annul the changes of magnetic polarity which urge it round. In the classical law of magneto-electric action, formulated by Lenz, it is declared that an induced current is always such that by virtue of its |