Michael Faraday

Faraday, Michael. 1791–1867. Chemist. Author of numerous scientific works, The Chemistry of a Candle, Physical Forces, etc. See Life and Letters of, 1870, by J. Bruce Jones, Tyndall's Faraday as a Discoverer, and Life, by J. H. Gladstone. Pub. Har. Rou.

Faraday's Electrical Illustrations

The following are selected from the very able series of lectures delivered by Professor Faraday at the Royal Institution:

The Two Electricities.—After having shown by various experiments the attractions and repulsions of light substances from excited glass and from an excited tube of gutta-percha, Professor Faraday proceeds to point out the difference in the character of the electricity produced by the friction of the two substances. The opposite characters of the electricity evolved by the friction of glass and of that excited by the friction of gutta-percha and shellac are exhibited by several experiments, in which the attraction of the positive and negative electricities to each other and the neutralisation of electrical action on the combination of the two forces are distinctly observable. Though adopting the terms “positive” and “negative” in distinguishing the electricity excited by glass from that excited by gutta-percha and resinous bodies, Professor Faraday is strongly opposed to the Franklinian theory from which these terms are derived. According to Franklin's view of the nature of electrical excitement, it arises from the disturbance, by friction or other means, of the natural quantity of one electric fluid which is possessed by all bodies; an excited piece of glass having more than its natural share, which has been taken from the rubber, the latter being consequently in a minus or negative state. This theory Professor Faraday considers to be opposed to the distinct characteristic actions of the two forces; and, in his opinion, it is impossible to deprive any body of electricity, and reduce it to the minus state of Franklin's hypothesis. Taking a Zamboni's pile, he applies its two ends separately to an electrometer, to show that each end produces opposite kinds of electricity, and that the zero, or absence of electrical excitement, only exists in the centre of the pile. To prove how completely the two electricities neutralise each other, an excited rod of gutta-percha and the piece of flannel with which it has been rubbed are laid on the top of the electrometer without any sign of electricity whilst they are together; but when either is removed, the gold leaves diverge with positive and negative electricity alternately. The Professor dwells strongly on the peculiarity of the dual force of electricity, which, in respect of its duality, is unlike any other force in nature. He then contrasts its phenomena of instantaneous conduction with those of the somewhat analogous force of heat; and he illustrates by several striking experiments the peculiar property which static electricity possesses of being spread only over the surfaces of bodies. A metal ice-pail is placed on an insulated stand and electrified, and a metal ball suspended by a string is introduced, and touches the bottom and sides without having any electricity imparted to it, but on touching the outside it becomes strongly electrical. The experiment is repeated with a wooden tub with the same result; and Professor Faraday mentions the still more remarkable manner in which he has proved the surface distribution of electricity by having a small chamber constructed and covered with tinfoil, which can be insulated; and whilst torrents of electricity are being evolved from the external surface, he enters it with a galvanometer, and cannot perceive the slightest manifestation of electricity within.

The Two Threads.—A curious experiment is made with two kinds of thread used as the conducting force. From the electric machine on the table a silk thread is first carried to the indicator a yard or two off, and is shown to be a non-conductor when the glass tube is rubbed and applied to the machine (although the silk, when wetted, conducted); while a metallic thread of the same thickness, when treated in the same way, conducts the force so much as to vehemently agitate the gold leaves within the indicator.

Non-conducting Bodies.—The action that occurs in bodies which cannot conduct is the most important part of electrical science. The principle is illustrated by the attraction and repulsion of an electrified ball of gilt paper by a glass tube, between which and the ball a sheet of shellac is suspended. The nearer a ball of another description—an unelectrical insulated body—is brought to the Leyden jar when charged, the greater influence it is seen to possess over the gold leaf within the indicator, by induction, not by conduction. The questions, how electricities attract each other, what kind of electricity is drawn from the machine to the hand, how the hand was electric, are thus illustrated. To show the divers operations of this wonderful force, a tub (a bad conductor) is placed by the electric machine. When the latter is charged, a ball, having been electrified from it, is held in the tub, and rattles against its sides and bottom. On the application of the ball to the indicator, the gold leaf is shown not to move, whereas it is agitated manifestly when the same process is gone through with the exception that the ball is made to touch the outside only of the tub. Similar experiments with a ball in an ice-pail and a vessel of wire-gauze, into the latter of which is introduced a mouse, which is shown to receive no shock, and not to be frightened at all; while from the outside of the vessel electric sparks are rapidly produced. This latter demonstration proves that, as the mouse, so men and women, might be safe inside a building with proper conductors while lightning played about the exterior. The wire-gauze being turned inside out, the principle is shown to be irreversible in spite of the change—what has been the unelectrical inside of the vessel being now, when made the outside portion, capable of receiving and transmitting the power, while the original outside is now unelectrical.

Repulsion of Bodies.—A remarkable and playful experiment, by which the repulsion of bodies similarly electrified is illustrated, consists in placing a basket containing a heap of small pieces of paper on an insulated stand, and connecting it with the prime conductor of the electrical machine; when the pieces of paper rise rapidly after each other into the air, and descend on the lecture-table like a fall of snow. The effect is greatly increased when a metal disc is substituted for the basket.