Origiginally published in 1895. PREFACE: THESE Chapters on Electricity, prepared for and included in the Fourth Revised Edition of Olmsteds College Philos- ophy, are here offered in a separate volume. They are intended for use as a text-book by students in those colleges which devote but thirty or forty hours to the subject. The principles presented are those which ought to be known by every liberally educated person. The economy of space necessitated by a clear and thorough presentation within such limits, has required the omission of detailed descriptions of apparatus and of demonstrative experiments. To master these chapters will require more effort on the part of a student than to master an equal number of pages in a more extended treatise. For the same efforts, however, he will obtain a knowledge of a greater number of principles. Furthermore, he will more readily perceive the correlation between different parts of the subject. Even an ordinary comprehension of the subject signifies a knowledge of many of these mutual relations. It has been the desire of the author to present each part of the subject in its most modern dress. This desire, however, has been tempered by a consideration of the intended functions of the book. IN the present edition a few typographical errors have been corrected, and a Course in Electrical Measurements has been added. This course is written in the form of a laboratory manual in which specific directions are given to the student. The experience of the author has shown that such a manual results in a saving of time both to the instructor and the student. The enthusiasm of the student is better maintained when his results are fairly accurate and of frequent occurrence. A meagre laboratory equipment is sufficient for carrying on the course, and the accuracy of the results obtained will depend almost entirely upon the student and the instructor. Contents include: The figure rvvr to the page, PART VII.-ELECTBIC1TY AND MAGNETISM. CHAPTER I. ELECTROSTATICS. POTENTIAL. CAPACITY. Definition Common Indications of Electricity Repulsion, 351 Theories of Electricity Electric Series, 352 Conductors and Insulators Coulombs Law, 353 Potential, 354 Equipotential Surfaces, 355 Difference of Potential Unit of Potential, 356 Zero Potential Potential on a Sphere Capacity, 357 Equipotential of Connected Conductors Position of Static Charge Distribution of a Charge on the Surface, 359 Surface Density QuadrantElectrometer, 360 Problems, 361. CHAPTER II. ELECTROSTATIC INDUCTION. Gold-leaf Electroscope Phenomena, 362 Induction Precedes Attraction, 363 Quantity of the Induced Electricity Condensers, 364 Specific Inductive Capacity, 365 Leyden Jar Seat of the Charge, 367 Residual Charge Modern Theory of Condensers, 368 Hertzs Experiments, 369 Electrical Machines Electrophorus Holtz Machine, 370 Effects of Statical Discharge Lightning, 372. CHAPTER III. MAGNETISM...