This authoritative text from the eleventh edition of the Encyclopaedia Britannica explores the science of electricity at rest, known as electrostatics. The author begins with simple experimental demonstrations using basic apparatus, such as metal tea-trays, sealing-wax, and gold-leaf electroscopes, to prove the existence of two kinds of electricity, positive and negative, and to distinguish between conductors and insulators. Through these fundamental experiments, the principles of electrostatic induction and electrical separation are clearly established.
The discussion then advances to the seat of the electric charge, tracing how the work of Benjamin Franklin, Henry Cavendish, Michael Faraday, and James Clerk Maxwell demonstrated that electrification resides not merely on the conductors themselves, but in the surrounding insulator or dielectric as a state of strain, displacement, or polarization. Mathematical definitions are introduced, explaining the absolute centimetre-gramme-second system, Coulomb's law regarding the inverse square relationship of mechanical force, and the concepts of electric force, potential difference, and equipotential surfaces.
Special attention is devoted to the laws governing the distribution of electricity at rest upon conductors. The text details three major facts: that the surface of each conductor in equilibrium is an equipotential surface, that the charge resides wholly on the surface with zero electric force in the interior, and that positive and negative electricities are always created in equal quantities. Mathematical deductions from these principles include Poisson's equation and the method of electrical images, originally introduced by Lord Kelvin to solve complex problems in electrical distribution.
The volume further examines electrical capacity, providing mathematical formulas for spheres, thin rods, ellipsoids, concentric spheres, coaxial cylinders, and parallel planes. Various methods for measuring capacity, both relative and absolute, are outlined alongside practical devices such as Leyden jars and guard plates.
Finally, the text investigates the properties of dielectrics, particularly the specific inductive capacity, or dielectric constant, established by Faraday and expanded through extensive modern measurements across solids, liquids, and gases. The phenomenon of residual charge in dielectrics is analyzed through mechanical models and analogies to elastic recovery in strained bodies, concluding with an extensive bibliography of classical treatises and scientific papers that chart the historical evolution of electrical knowledge.
