5. The Case of a Uniform Field . 6. The Case of a Field not Uniform 7. The Case of Incomplete Circuits 8. Reconsideration of Ampère's Laws 4. Ampère's Theory of Magnetism. 5. Solenoid, and Hollow Cylindrical Magnet, Contrasted 6. Matter Placed in a Uniform Magnetic Field of Force. 7. Movements of Small Bodies in a Non-Uniform Magnetic Field 8. The 'Setting' of a Long Body in a Uniform Magnetic Field 14. Relative Magnetism or Diamagnetism 15. Is there Absolute Diamagnetism? 16. Rotation of the Plane of Polarisation in a Magnetic Field 1. General Account of Induction Phenomena 2. General Reason for Induced Currents' 3. More Exact Reasoning, in a Simple Case 4. General Expression for Induced E. M. F. 5. Induction where there is no Initial Current 9. Coefficient of Mutual Induction, or of Mutual Potential 10. Self-Induction. The Extra Current ' II. Induced Currents of Higher Orders 2. Arago's Disc and Magnetic Needle. 3. Continuous Current Collected from Barlow's Wheel 4. Induction in the Earth's Field 5. Induction Coils; General Plan . 6. Practical Difficulties to be Overcome 8. The Part Played by the Condenser. 8. Transmission of 'Power' from a Distance . 9. Electric Railways and Tram-Cars; Telpherage; &c. 10. Distribution of Potential in the Circuit of a Dynamo and Motor 11. Work done per Second upon a Dynamo as Related to the Velocity 408 408 409 409 411 412 415 Note.-In cases where the above symbols have other meanings, the context will obviate ELECTRICITY. CHAPTER I. GENERAL PHENOMENA OF MAGNETISM. § 1. Introductory.-The subjects of magnetism and electricity are in reality not two, but one; all inagnetic, electro-magnetic, and voltaic phenomena―to use terms with which most of our readers will have some acquaintance-belong to one great branch of science for which we have not yet one comprehensive name. Perhaps it might be more logical were we to give at once a general survey of all the above-named classes of phenomena before proceeding to a more detailed discussion of each. But, as in this course no previous knowledge has been assumed, it has been thought better to avoid any chance there might be of confusing the mind of the student by the presentation of a multitude of strange facts, and hence we shall first discuss the main phenomena of magnetism. A study of these will serve as a training to the beginner, and he will incidentally become acquainted with many facts and conceptions that will prove to be of great value in the study of the other branches of our science. § 2. First Phenomena observed.—Accustomed as most of us are to the use of a 'magnet,' there is still something very startling in the simple elementary experiment with a 'magnet' or a piece of lodestone. When a piece of lodestone (magnetic oxide of iron, Fe3O4, magnetised by the influence of the earth) is held above a piece of iron or steel of not too great weight, the piece of iron or steel will move up to the lodestone, against the force due to gravity. And, more remarkable still, the lodestone can convert pieces of hard steel into permanent magnets,' it being B |