Davis's Manual of Magnetism, Price
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About Google Book Search Google’s mission is to organize the world’s information and to make it universally accessible and useful. Google Book Search helps readers discover the world’s books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web at http://books.google.com/ 1 Davis'smanualofmagnetism DanielDavis,WilliamFrancisChanning,JohnBacon ■ > The frontispiece consists of two copper-plate engravings, one printed from an engraved plate, and the other from an electrotype copy taken from it in the mode described on page 204. The engravings are introduced for the purpose of showing the accuracy of the copies obtained by this process, £f<*»^t£ J)_a V I S'S MANUAL OF MAGNETISM. INCLUDING ALSO ELECTRO-MAGNETISM, MAGNETO-ELECTRICITY, AND THERMO-ELECTRICITY. WITH A DESCRIPTION OF THE ELECTROTYPE PROCESS. FOR THE USE OF STUDENTS AND LITERARY INSTITUTIONS. WITH 100 ORIGINAL ILLUSTRATIONS. ^ -/ ^ ' s ^BOSTON: PUBLISHED BY DANIEL DAVIS, Jk. MAGNETIC AL INSTRUMENT MAKER, No. 11 Cornhill. 1842. Entered according to Act of Congress in the year 1842, by DANIEL DAVIS, Jr. In the Clerk's Office of the District Court of Massachusetts. WILLIAM s. DAMRELL, PRINTER, NO. 11 CORNHILL. PREFACE. Magnetism and Electricity have become related sciences within so short a period, and their growth has been so rapid, that many important facts which have been observed have not yet been collected in any scientific treatise, and the amount of unwritten knowledge has been constantly increasing. For this reason it has been necessary, in preparing the following work, which is intended as a companion to the apparatus manufactured by me, to give a fuller view of these sciences, and more minute descriptions of the instruments and experiments designed to illustrate them, in their relation to each other, than would otherwise have been required. This Manual, therefore, will answer the purpose of an elementary treatise on those branches of science to which it relates, and may be used as a text-book. vi PREFACE. The aid of several gentlemen scientifically ac quainted with the subject has been obtained in describing the various instruments, the experiments which may be performed with them, and the prin ciples on which they depend. The object, which has been kept in view, is in all cases simply to state the facts which have been observed, and to gener alize them only so far as the progress of discovery has fully authorized. The theories concerning mag netism and electricity in their relation to each other, which have been discussed in the scientific journals of Europe and America, must yet be regarded as hypothetical, and have been as far as possible avoided. It will be found that many of the observations recorded here, and many of the instruments de scribed, are new. Wood cuts have been introduced, wherever, from the nature of the instrument or experiment under consideration, it has been deemed advisable in order to ^nsure a clear comprehension of the subject. Boston, August, 1842. CONTENTS. INTRODUCTORY CHAPTER. Page DEFINITIONS AND EXPLANATIONS 1 PRODUCTION OF ELECTRICITY. 1. MECHANICAL OR FRICTION AL ELECTRICITY, 6 2. GALVANIC OR VOLTAIC ELECTRICITY, 7 3. THERMO-ELECTRICITY, 21 4. ANIMAL ELECTRICITY, 34 MAGNETISM. CHAPTER I. DIRECTIVE TENDENCY OF THE MAGNET. 1. IN REFERENCE TO ANOTHER MAGNET, 35 2. I\ REFERENCE TO A CURRENT OF ELECTRICITY, 43 3. IN REFERENCE TO THE EARTH, 62 viii CONTENTS. CHAPTER II. INDUCTION OF MAGNETISM. Page. 1. BY THE INFLUENCE OF A MAGNET, 61 2. BY THE INFLUENCE OF A CURRENT OF ELECTRICITY, 68 3. BY THE INFLUENCE OF THE EARTH, 122 CHAPTER III. INDUCTION OF ELECTRICITY. 1. BY THE INFLUENCE OF A CURRENT OF ELECTRICITY, 125 2. BY THE INFLUENCE OF A MAGNET 153 3. BY THE INFLUENCE OF THE EARTH, 197 THE ELECTROTYPE PROCESS. 1. ORIGIN OF THE ELECTROTYPE 193 2. PROCESSES FOR ELECTROTYPES IN COPPER, 200 3. PROCESSES FOR GILDING, SILVERING, AND PLATINATING,.. 205 INTRODUCTORY CHAPTER. DEFINITIONS AND EXPLANATIONS. 1. Magnetism. The term magnetism expresses the peculiar properties of attraction,repulsion, &c., possessed, under certain circumstances, by iron and some of its compounds, and in a feebler degree by the metals nickel and cobalt. Hammered brass is said to be sometimes magnetic. The science which treats of these proper ties is also called magnetism. Electro-Magnetism. That branch of science which relates to the development of magnetism by means of a current of electricity, is called electro-magnetism. It will be treated of in chapter I, section 2, and in chapter II, section 2. Magneto-Electricity treats of the development of electricity by the influence of magnetism, and will form the subject of chapter III, section 2. 2. The Magnet. Any body in which the magnetic phenomena manifest themselves, is called a magnet. It may be of any form, but it must be composed in whole or in part of iron, nickel, or cobalt. Natural Magnets. Certain ores of iron are found to be possessed of the magnetic properties in their natural state. These are called natural magnets, or loadstones. 1 2 DANIEL DAVIS, JK.'s MANUAL. Artificial Magnets. Bodies of whatever form or composition, in which magnetism is artificially induced, are called artificial magnets. 3. Induction of Magnetism. Whenever magnetic properties are developed in bodies not previously pos sessed of them, the process is termed the induction of magnetism. When this is effected by the influence of a magnet, it is called magnetic induction : when by a current of electricity, electro-magnetic induction. Induction of Electricity, is whenever electricity is developed by the influence of other electricity in its neighborhood, or by the influence of magnetism. In order to distinguish the inductive action of an electric current from the static induction of electricity at rest, the former is called electro-dynamic induction. The development of electricity by the influence of a magnet is termed magneto-electric induction. 4. Poles. The magnetic phenomena manifest them selves principally at the two opposite extremities of the magnet : as may be shown with regard to the attractive force by the following experiment : Exp. L — Immerse a magnet in iron filings and then withdraw it. A considerable quantity of the filings will be found to adhere to it ; being accumulated most abundantly about its ends, while few or none will be attached to its middle : thus proving the attractive force to be strongest at the extremities, and to diminish rapidly as the distance from them increases, until it becomes entirely insensible at the middle point These extremities are called the poles of the magnet 5. The earth itself is found to possess the properties of a magnet, having magnetic poles corresponding nearly in their direction with the poles of its diurnal rotation. EXPLANATIONS. 3 Now if a straight magnet be suspended so as to allow of a free horizontal motion, it will be found to place itself in a direction nearly north and south : as will be explained hereafter. The end which turns towards the north is called the north pole of the magnet, the other end its south pole.