Page:Encyclopædia Britannica, Ninth Edition, v. 8.djvu/15

Rh EISTOHY.] ELECTRICITY bodies, such as amber, copal, gum-lac, silk, paper, thread, and a number of other substances. The characteristic of those two electricities was, that a body with vitreous elec tricity attracted all bodies with resinous electricity, and repelled all bodies with vitreous electricity; while a body with resinous electricity attracted all bodies with vitreous electricity, and repelled all bodies with resinous electricity. Two electrified silk threads, for example, repel each other, and also two electrified woollen threads, but an electrified silk thread will attract an electrified woollen thread. Hence it is easy to determine whether any body possesses vitreous or resinous electricity. If it attracts an electrified silk thread, its electricity will be vitreous ; if it repels it, it will be resinous. Gray repeated and varied the experiments of Dufay, and made mauy new ones. Like Hawksbee aud Dr Wall, he recognized the similarity between the phenomena of electricity and those of thunder and lightning ; and he expresses a hope &quot; that there may be found out a way to collect a greater quantity of electric fire, and consequently to increase the force of that power, which, by several of these experiments, si licet magnis componere parva, seems to be of the same nature with thunder and lightning&quot; &amp;gt;_ze, The discoveries which we have now recounted began to inkier, rouse ue activity of the German and Dutch philosophers. To the electrical machine used by Newton and Hawksbee, Professor Boze of Wittenberg added the prime conductor, which at first consisted of an iron or tin tube supported by a man standing upon cakes of rosin ; but it was afterwards suspended by silken strings. Professor Winkler of Leipsic substituted a cushion in place of the hand for exciting tho revolving globe ; and Professor Gordon of Erfurt, a Scotch Benedictine monk, first used a glass cylinder, eight inches long and four broad, which he caused to revolve by means of a bow and string. By these means electrical sparks of great size and intensity were produced, and by their aid various combustible substances, both fluid and solid, were inflamed. In 1744 M. Ludolph of Berlin succeeded in tiring, by the electrical spark, the ethereal spirit of Fro- benius. Winkler did the same by a spark from his finger ; and he succeeded in inflaming French brandy and other weaker spirits after they had been heated. Gordon kindled spirits by a jet of electrified water. Dr Miles inflamed phosphorus by the electric spark ; and oil, pitch, and sealing-wax, when strongly heated, were set on fire by similar means. We refer the student for lists of the works of the philosophers just mentioned to the admirable biblio graphy given by Young, Natural Philosophy, p. 515. eyden These striking effects were all produced by the electricity , obtained immediately from an excited electric ; but a great step was now made in the science by the discovery of a method of accumulating and preserving electricity in large quantities. The author of this great invention is not dis tinctly known ; but there is reason to believe that a monk of the name of Kleist, a person of the name of Cuneus, and Professor Muschenbroeck of Leyden had each the merit of an independent inventor. The invention by which this accumulation was effected was called the Leyden Jar or Phial, because it was principally in Leyden that it was cither invented or tried. Having observed that excited electrics soon lost their electricity in the open air, and that their loss was accelerated when the atmosphere was charged with moisture or other conducting materials, Muschenbroeck conceived that the electricity of bodies might be retained by surrounding them with bodies which did not conduct it. In putting this idea to the test of experiment, he electri fied some water in a glass bottle, and a communication having been made between the water and the prime con ductor, the assistant, who was holding the bottle, on trying to disengage the communicating wire, received a sudden shock in his arms and breast, and thus established the efficacy of the Leyden jar. Sir William Watson made some important experiments sir W at this period of our history (Memoirs in Phil. Trans. Watso about 1747). He succeeded in firing gunpowder by the electric spark ; and by mixing the gunpowder with a little camphor he discharged a musket by the same power. He also fired hydrogen by the electric spark; and he kindled both spirits of wine and hydrogen by means of a drop of cold water, and even with ice. In the German experi ments the fluid or solid to be inflamed was set on fire by an electrified body ; but Sir William Watson placed the fluid in the hands of an electrified person, and set it on fire by causing a person not electrified to touch it with his finger. Sir William Watson first observed the flash of light which attends the discharge of the Leyden phial, aud it is to him that we owe the present improved form of the Leyden phial, in which it is coated both without and within with tinfoil. Dr Bevis indeed had suggested the outside coating, and at Smeaton s recommendation, he coated a pane of glass on both sides, and within an inch of the edge, with tinfoil ; but still the idea of coating the jar doubly belongs to Sir William Watson. A party of the Royal Society, with the president at their Expei head, and Sir William Watson as their chief operator, menta entered upon a series of magnificent experiments, for the ^ ie purpose of determining the velocity of the electric fluid, and the distance to which it could be conveyed. The French savans had conveyed the influence of the Leyden jar through a circuit of 12,000 feet; and in one case the basin at the Tuileries, containing about an acre of water, formed part of the circuit ; but the English philosophers made a more complete series of experiments, of which the following were the results : 1. That in all their operations, when the wires have been properly conducted, the electrical commotions from the charged phial have been very considerable only when the observers at the extremities of the wire have touched some substance readily conducting elec tricity with some part of their bodies. 2. That the electrical commotion is always felt most sensibly in those parts of the bodies of the observers which are between the conducting wires and the nearest and the most non-electric sub stance, or, in other words, so much of their bodies as comes within the electrical circuit. 3. That on these considerations we infer that the electrical power is conducted between these observers by any non-electric substances which happen to be situated between them, and contribute to form the electrical circuit. 4. That the electrical commotion has been perceptible to two or more observers at considerable distances from each other, even as far as two miles. 5. That when the observers have been shocked at the end of tws&amp;gt; miles of wire, we infer that the electrical circuit is four miles, viz. two miles of wire, and the space of two miles of the non-electric matter between the observers, whether it be water, earth, or both. 6. That the electrical commotion is equally strong, whether it is conducted by water or dry ground. 7. That if the wires between the electrifying machine and the observers are conducted on dry sticks, or other substances non electric in a slight degree only, the effects of the electrical power are much greater than when the wires in their progress touch the ground, or moist vegetables, or other substances in a great degree non-electric. 8. That by comparing the respective velocities of electricity and sound, that of electricity, in any of the distances yet experienced, is nearly instantaneous. In the following year these experiments were resumed with the view of ascertaining the absolute velocity of electricity at a certain distance, and it was found &quot; that through the whole length of a wire 12,270 feet the velocity of electricity was instantaneous.&quot; The theory of positive and negative electricity which was afterwards elaborated by Franklin, was distinctly announced by Sir W. Watson. He lays it down as a law that in elec trical operations there is an afflux of &quot; electric fluid &quot; to the globe and the conductor, and also an efflux of the same