Page:The American Cyclopædia (1879) Volume VI.djvu/508

 500 ELECTRICITY the fish ; in the gymnotus the intensity of the shock is in proportion to the length of the fish included between the hands; actual contact with the torpedo is not essential, as it is well known by the Neapolitan fishermen that the shock is felt when the water is dashed upon it, the electric current passing up along the stream, the circuit being completed through the earth to the ventral surface of the fish ; the dorsal surface is always positive, and the ventral nega- tive. That this is the same as common elec- tricity has been shown by Matteucci and Fara- day ; it renders the needle magnetic, and de- composes chemical compounds; by it heat is evolved, and the electric spark is obtained. The exciting nerves terminate in loops, as in the muscular tissue, and they arise like motor nerves from the anterior tract of the cord ; the reception and conveyance of impressions, and the voluntary act which results in the shock, are of the same nature and follow the same course as the muscular contractions ; a division of the electric nerves at their origin arrests all voluntary shocks, but an irritation of the ends of the nerves in connection with the organ is followed by an involuntary electric discharge, just as an irritation of the end of a divided motor nerve in connection with muscle is fol- lowed by its contraction. The electric like the muscular power is exhausted by exercise, and recovered by rest ; both are increased by en- ergetic respiration and circulation, and both are exalted by the action of strychnine, which produces tetanic contraction of the muscles, and a rapid succession of involuntary elec- tric discharges. The phenomena displayed by these fishes afford no ground for the opinion that nervous influence is identical with elec- tricity ; the former is no more identical with the latter than it is with muscular contrac- tility; the contractility of the muscle resides in its fibre, and the electricity is generated in the battery of the fish ; both are brought into play through neyvous influence, but neither re- sides in or is a property of the nerves. The phenomena of heat, electricity, and phospho- rescence within the animal body depend on chemical actions, which take place in the sys- tem just as they would in the chemist's labo- ratory, modified always by the mysterious vital principle. According to Faraday, the shock of the electrical eel is equal to that of 15 Leyden jars of 3,500 square inches of surface. ELECTRICITY, the science which treats of the peculiar phenomena of attraction and re- pulsion exhibited when friction and other me- chanical forces are applied to bodies, and of certain effects which accompany chemical de- composition or other change of physical state ; or the phenomena that arise from the rela- tion which bodies may bear to terrestrial and other magnetic lines, particularly when these are undergoing change in quantity or .direc- tion. The general science includes statical and dynamical electricity, or electric force in a state of rest or of motion. The former, being usually developed by friction, at least for experimental purposes, is often called frictional electricity. The latter may be developed by chemical action, by heat, magnetism, and other forces ; but in whatever way produced, it is always in the form of currents, and exhibits a constant manifestation of power. Statical electricity may also be obtained by greatly increasing the intensity of dynamical electricity, as will be shown in the articles GALVANISM and MAGNETO-ELECTEICITY. This article will treat of frictional electricity, while dynamical electricity, so far as it relates to the development of currents by chemical action, will be treated in the article GALVANISM. That part of dynamical electricity which re- lates to the development of magnetism by elec- trical currents, and of the development of elec- trical currents by magnetism, will be treated under the heads ELECTRO-MAGNETISM and MAG- NETO-ELECTRICITY. The development of elec- tricity by heat will be treated in the article THERMO-ELECTRICITY. The word electricity is derived from the Greek ^/le/crpov, amber, a sub- stance described by Thales of Miletus six cen- turies before Christ as possessing the property, when rubbed with a piece of silk, of attracting light bodies ; this he ascribed to the presence of a soul, which when excited left the body and brought the light bodies to it. Theophrastus and Pliny mention the power of amber to at- tract straws and dry leaves, and also the posses- sion of the same property by the lapis lincurius, supposed to be the mineral tourmaline. The electricity of the torpedo was known to the an- cients, as we learn from Pliny and Aristotle ; or rather, it was known that the fish had the power of producing certain physiological effects, but their explanation, or the relation which they bore to the property of amber, was unknown. As regards the science of electricity, a record of the simple phenomena of attraction and repulsion is all that has been handed down to us by them, and but little knowledge of the subject was acquired until toward the end of the 16th century, when Dr. Gilbert of Col- chester, England, made a series of experiments on account of which he has been called the founder of the science. This title, however, can scarcely be justly applied to any one in- dividual, especially at that early day, when a few isolated facts, as yet unconnected with any mathematical law, were all that was known. Robert Boyle, while investigating other phys- ical subjects, added several substances to the list of " electrics." Otto von Guericke, about the same time or a little earlier, made discov- eries of still greater scientific value ; for instance, that of electrical induction. Sir Isaac Newton also made some important investigations in electricity, and Sir David Brewster ascribes to him the invention of the glass globe electrical machine. Stephen Gray, a member of the royal society, between the years 1720 and 1736 made several discoveries in regard to the conduction of electricity. M. Du Fay of the