ELEMENTARY LESSONS ON ELECTRICITY & MAGNETISM Part First CHAPTER I FRICTIONAL ELECTRICITY LESSON I.- Electric Attraction and Repulsion 1. Electricity. Electricity is the name given to an invisible agent known to us only by the effects which it produces and by various manifestations called electrical. These manifestations, at first obscure and even mysterious, are now well understood; though little is yet known of the precise nature of electricity itself. It is neither matter nor energy; yet it apparently can be associated or combined with matter; and energy can be spent in moving it. Indeed its great importance to mankind arises from the circumstance that by its means energy spent in generating electric forces in one part of a system can be made to reappear as electric heat or light or work at some other part of the system; such transfer of energy taking place even to very great distances at an enor mous speed. Electricity is apparently as indestructible as matter or as energy. It can neither be created nor destroyed, but it can be transformed in its relations to matter and to energy, and it can be moved from one place to another. In many ways its behaviour resembles that of an incompressible liquid; in other ways that of a highly attenuated and weightless gas. It appears to exist distributed nearly uniformly throughout all space. Many persons (including the author) are disposed to consider it as identical with the luminiferous ether. If it be not the same thing, there is an intimate relation between the two. That this must be so, is a necessary result of the great discovery of Maxwell-the greatest scientific discovery of the nineteenth century—that light itself is an electric phenomenon, and that the light-waves are merely electric, or, as he put it, electromagnetic waves. The name electricity is also given to that branch of science which deals with electric phenomena and theories. The phenomena, and the science which deals with them, fall under four heads. The manifestations of electricity when standing still are different from those of electricity moving or flowing along: hence we have to consider separately the properties of (i.) statical charges, and those of (ii.) currents. Further, electricity whirling round or in circulation possesses properties which were independently discovered under the name of (iii.) magnetism. Lastly, electricity when in a state of rapid vibration manifests new properties not possessed in any of the previous states, and causes the propagation of (iv.) waves. These four branches of the science of electricity are, however, closely connected. The object of the present work is to give the reader a general view of the main facts and their simple relations to one another. In these first lessons we begin with charges of electricity, their production by friction, by influence, and by various other means, and shall study them mainly by the manifestations of attraction and repulsion to which they give rise. After that we go on to magnetism and |
