arcuit. 4, 5. Columnar electroscope. 6. Galvanic element. 7. Cups or cells. 8. Bunsen's 11, 12. Galvanic light. 13, 14. Decomposition of water by galvanic current. 15. Voltameter. metal experiment. 19. Tangent-bussole. 20. Multiplier. 21. Magnetic coil. 22. Law of der and strip with Morse or Graham alphabet; 26, Key; 27, Circuit complete; s, key; Electro-dynamic test. 31. Solenoid. 32, 33. Ampère's theory of magnetism. 34. Electropillars. 39, Electro-magnetic machine. 40. Induction apparatus. 41. Rumkorff's spark This is Ohm's law. By transposing the terms of the equation, we may get an expression for either of the three elements-current, pressure, or resistance, in terms of the other two. This relation holds true, and is completely accurate, in every possible case and condition of practical work. This remarkable precision and definiteness of action renders possible the creation of an extensive art of electrical testing, by which we are enabled not only to make accurate measurement of electrical apparatus, but to make determinations in other subjects through the agency of electricity. For example, when an ocean cable is injured or interrupted, the precise location of the trouble is ascertained by measuring the electrical resistance of the parts of the cable on each side of the break, or by observing the quantity of electricity which the parts of the cable will hold, etc. See Kempe's Electrical Testing. Electricity and the capacities of electrical apparatus are measured and the magnitudes of the measurements expressed in the following convenient electrical units. Ampère Volt Ohm unit of current. The amount of current at unit pressure that would flow through a circuit of unit resistance per second, or such a current as will deposit .00111815 gramme of silver per second. = unit of electric pressure. The pressure that would cause a current of one ampère to pass through a circuit of unit resistance. The value of the electromotive force of a current is called its voltage. Coulomb = Farad Joule Watt unit of electrical resistance. The ohm is a resistance equal to that of a column of mercury of 106 centimeters in length, and one square milli- * meter of cross section, at 0° C. temperature. unit of quantity. The quantity of electricity that flows per second past a cross section of a conductor conveying one ampère. = unit of electrical capacity. The capacity of a conductor that would enable it to hold one coulomb under a pressure of one volt. = unit of electric work. The work required to raise a coulomb one volt in = unit of electric power, 1 joule per second horse-power. Watts = The conversion of electrical energy into energy of other kinds for practical use, is accomplished by taking advantage of the peculiar properties of electricity in the different ways in which it can be done with especial advantage. It should be remembered that electricity is only utilized as a means of transmitting energy from one point to another, and is not a form of energy itself. It may be compared to the belt between a steam engine and a machine, which serves to transmit the power of the engine over to the machine when the power is utilized. In the same way the electric current transmits the power of an engine or any other prime mover over any distance through conductors, at the other end of which the power is utilized in the form of heat, light or mechanical energy. The relation between electricity and heat is very close, hence, the transition from electricity to heat is extremely simple. Upon this fact and principle the processes which depend upon the conversion of electricity into heat are founded. The chief example is the electric light (q. v.), which is produced by converting an electric current into intense heat by means of the resistance of the conductor at the desired point. The relation of light to heat and electricity is also known to be very close, the difference being simply a matter of different rates of vibration. The class of uses of electricity for producing mechanical power depends upon its faculty of attraction, which is now explained by the following theory: A wire through which a current of electricity is passing is found to be surrounded always with a circular region of attractive force. The attraction is found to exist in the form of rings around the wire; and lines so drawn to represent the position of these imaginary attractable objects, are called "lines of force" (see COMPOSITION OF FORCES). These imaginary lines, or the direction in which a current-carrying wire attracts, are invariably found to be at right angles to the wire. A magnet or magnetic needle placed near the wire will swing around and place itself at right angles to the wire and parallel to these lines. This shows that the direction in which magnetism acts is at right angles to the direction in which electricity acts-that is, the electric current creates, at right angles to itself, an artificial magnetism. The lines of force around a wire are found to be magnetic lines, and to have strong power of attraction, as if they were magnets laid crossways to the wire. A conclusion from this is that if we wind a quantity of wire on a cylinder of soft iron, since the axis of the cylinder will be at right angles to all of the wire, we shall find that the cylinder becomes strongly magnetic, and this effect increases in proportion to the number of turns of wire about the cylinder and the current which is passed through it. This is the electro-magnet, which, together with the solenoid (q. v.), is the foundation of most electrical apparatus, such as regulators, telegraph instruments, motors, etc. It is seen from this that the relation between electricity and magnetism is very close. According to Ampère's theory, magnetism consists in the circulation around a bar of iron of minute electric currents which throw out lines of force, and produce the attraction as above described, which in this case we happen to call magnetism. The breaking up of chemical unions by electrical action, giving rise to the arts of electro-plating, electro-chemistry, etc., remains to be considered. The subject has not as yet been extensively investigated. The effects probably depend upon the disturb ing effect which the molecular or atomatic motions known as electricity produce upon the chemical unions. The vibrations of heat are a common means of producing chemical change or separation; and the vibrations of electricity probably act in the same way. The production of electricity by the action of chemical batteries also depends upon the conversion of the energy of chemical affinity into the energy of electrical vibrations in some way similar to its easy conversion into heat. It is known also that the amount of electricity produced will in every case be proportional to the affinity of the chemicals about to combine. See titles under ELECTRIC, ELECTRO; also MAGNETO ELECTRIC MACHINES, TELEGRAPH, etc. See Gordon's Electricity and Magnetism (London); Sprague's Electricity: its Theories, Sources, and Applications (London); Fleeming Jenkin's Electricity and Magnetism (New York); Ganot's Physics; Sylvanus Thompson's Dynamo-Electric Machines (London); Kempe's Electrical Testing (London); The Electric Motor and its Applications, by Martin and Wetzior; Caillard, Electricity (1891); Brackett, Electricity in Daily Life (1891). ELECTRICITY, ANIMAL. In this article we shall notice (1) the electricity developed by the so-called electrical fishes; (2), the electric properties of muscle and nerve; and (3) the electric phenomena of membranes and glands. 1. Although the peculiar powers of the torpedo and of the gymnotus were well known to the ancients, the first scientific discovery in this department of electricity was the determination of the electrical character of the shock of the torpedo by Walsh in 1772 (“ Of the Electric Properties of the Torpedo," Philadelphia Transactions, 1773). From that date to the present time, the electric organs of certain fishes, which will be immediately mentioned, have been made the object of special study by some of our greatest anatomists and physiologists, among whom may be named John Hunter, Galvani, Rudolphi, Knox, Valentin, Pacini, Matteucci, Goodsir, and Jobert de Lamballe, who has published a special work, entitled Des Appareils Electriques des Poissons Electriques (Paris, 1858), accompanied by a magnificent volume of plates. The species of electrical fish which has been the longest known, is the raia torpedo, or electric ray, which has much the appearance of a skate. It is common in the bay of Biscay and in the Mediterranean, but is seldom met with on the shores of Britain. It grows to a considerable size, and is often above 80 lbs. in weight. It is now usually regarded as not a true ray, but as constituting a distinct genus, to which the terms torpedo and narcine have been applied by different naturalists-the latter name being derived from the Greek word narke, which was given to it by Aristotle. The electric organs or batteries are placed on each side, in the spaces between the pectoral fins, the head and gills: See TORPEDO. Each battery consists of a number (varying according to the age of the animal) of hexagonal prisms, which extend perpendicularly between the dorsal and abdominal surfaces, and present somewhat of a resemblance in shape and arrangement to the cells of a honey-comb. Four nerves, which are branches of the fifth and eighth cerebral pairs, go to each battery; and the nervous center of the electrical apparatus is, therefore, the medulla oblongata. Several species of narcine are known, all of which possess the electric property. The ordinary rays and skates possess an organ in the tail which closely resembles the electric organ of other fishes, but its function is still doubtful; and in opposition to the view of its electric nature, it may be mentioned that while Dr. Starke (to whom the discovery of this organ is due) found it in the tail of every species of true ray, both professor Goodsir and M. Robin ascertained it to be wanting in the tail of the torpedo. The gymnotus electricus, or electrical eel, is little inferior in celebrity to the torpedo. It is common in all the streams which flow into the Orinoco, and is generally procured from Surinam. It is usually 3 or 4 ft. in length, but may reach a length of 6 feet. The whole of its viscera lie close to the head, and the anal aperture is only 2 in. behind the mouth; all the rest of the body inferiorly is occupied by the electrical apparatus, which consists of four batteries-viz., two on either side, and one above the other-the uppermost or dorsal being the larger. These batteries consist of a number of piles placed horizontally in a direction from head to tail; and from this circumstance, as well as from their peculiar structure, they were compared by Redi to galvanic troughs. The number of these piles in the greater battery, is from 30 to 60; in the lesser, from 8 to 14. These batteries are supplied by about 224 pair of nerves on each side, derived from the inferior or motor roots of the spinal nerves. Humboldt, both in his Personal Narrative and in his Views of Nature, gives a graphic account of the mode in which the Indians catch wild horses through the agency of the gymnotus. Faraday made numerous observations on a specimen 40 in. in length, which was exhibited in the Adelaide gallery some years ago. He calculated that, at each medium discharge, the animal emitted as great a force as the highest charge of a Leyder battery of 15 jars, exposing 3,500 sq.in. of coated surface. The strongest shocks were obtained by touching the fish simultaneously near the head and near the tail; scarcely any shock being felt if the hands be placed one on each side of the fish, at the same distance from either extremity; the amount of the shock, as might have been expected, varying with the length of the column which produces it. The shocks have sufficient power to stun, or even to kill fish; and the same discharge produces a more powerful effect upon a large fish than it does upon a small one, since the larger animal exposes a larger conducting surface to the water, through which the electricity is passing, and, consequently, it receives a more violent shock. On one occasion, when a live fish was put into the tub, which was 46 in. in diameter, the animal was seen to coil itself into a semicircle, the fish lying across the diameter; this was the most favorable position for giving the strongest shock; an instant afterwards, the fish floated dead upon its side, and was then devoured by the gymnotus (q.v.). The shock of both the torpedo and the gymnotus gives rise to momentary currents of sufficient intensity to deflect the galvanometer, to magnetize a needle, and to decompose iodide of potassium; and from both fish sparks have been obtained. We next come to the electrical fishes of the genus malapterurus. The only fish of this genus whose electrical organs have been examined and described is the M. electricus of the Nile, called raash or thunder-fish by the Arabs. It has barbules dependent from the region of the mouth, like the common barbel; and its smooth skin is diversified with irregularly shaped spots. Its length is from 8 to 14 inches. The batteries are two in number, "separated," to adopt Prof. Goodsir's description, "but at the same time intimately connected to one another in the mesal plane along the dorsal and ventral margins of the body, so as to form a continuous layer of a gelatinous consistence closely adherent to the skin, and enclosing as in a sac the entire animal, except the head and fins." The structure of these batteries is very complicated, and we shall not attempt to explain it. In the year 1854, a new electrical fish became known to us, belonging to the same genus as the one just described. It is found in the muddy brackish water of the river Old Calabar, which empties itself into the bight of Benin. The fish has accordingly been named the malapterurus Beninensis by Mr. Andrew Murray, who has described and figured it in the Edinburgh Philosophical Journal for July, 1855. It is much smaller than the Nilotic species, and the formulæ of the number of fin-rays differ in the two species. We believe that this new species was dissected by the late Prof. Goodsir, but we are not aware that the results were ever published. See MALAPTERURUS. Our limits will not allow of our noticing the successive opinions which have been entertained regarding the action of the electric organs in fishes. There does not seem to be room for doubt that the electrical organs of fishes have been developed from muscular tissue. In order to generate an electric current it is only necessary to establish a difference of electrical pressure, and we know that muscular contraction does produce such a pressure. A gymnotus in the possession of M. d'Arsonval, of Paris, was able to give a discharge of about 2 ampères at over 100 volts pressure. The electrical organ was situated underneath the animal, the positive pole being at its head and the negative at its tail. In giving violent shocks the animal rolls itself into a circle, and completes the circuit from its head to its tail through the object attacked. The discharge is at the will of the animal, which may be touched, if not irritated, without causing a discharge. 2. The study of the electrical properties of muscle and nerve dates from the period (1786-94) in which Galvani made his great discoveries. Having first ascertained that contractions were produced by electricity in the muscles of a recently killed frog, he subsequently found that similar contractions occurred when two dissimilar metals in contact with one another were brought in contact with the nerve and muscles respectively of the frog's leg. The experiment may be readily made in the following manner: Expose the crural nerve of a recently killed frog; touch it with a strap of zinc, and at the same time touch the surface of the thigh with one end of a bit of copper wire. At the moment that the other end of the wire is brought in contact with the zinc, the limb is convulsed; but the convulsions cease when the two metals are separated from each other, though they are still in contact with the animal tissues; and they are renewed when the zinc and copper are again made to touch. At first, Galvani believed that the contractions were due to electricity evolved by the metals, but finally he concluded that it is produced by the animal textures themselves. No important step in this direction was afterwards taken till 1827, when Nobili, with his improved galvanometer (q.v.), discovered the electric current of the frog. He found that when the circuit of the nerve and muscles of the leg is closed by the instrument, a deviation of the needle, to the extent sometimes of 30°, occurs, due to a current which passes in the limb from the toes upwards, and which could be increased when several frogs were simultaneously included in the experiment. Undoubted proof was thus afforded that electricity is developed in connection with muscle and nerve. The researches of Matteucci, confirmed by the subsequent investigations of Dubois Reymond, have demonstrated the existence of what is termed the muscular current in living animals. They show that in the living animal an electrical current is perpetually circulating between the internal portion and the external surface of a muscle-a current due probably to the chemical changes which are always occurring in the animal tissues. This muscular current ceases in warm-blooded animals in a very few minutes after their death; but in cold-blooded animals, as in the frog, it continues for a much longer period. The following is perhaps the best experiment for showing the existence of the muscular current Five or six frogs are killed by dividing the spinal column just behind the head ; the lower limbs are removed, and the integuments stripped off them; the thighs are next separated from the legs at the knee-joint, and are cut across transversely. The lower halves of these prepared thighs are then placed upon a varnished board, and so arranged that the knee-joint of one limb shall be in contact with the transverse section of the next, and thus a muscular pile is formed, consisting of ten or twelve elements; the terminal pieces of this pile are each made to dip into a separate small cavity in the board, in which a little distilled water is placed. If the wires of a sensitive galvanometer be attached to a pair of platinum plates, and these plates be placed simultaneously, one into each cavity in connection with the muscular pile, a deviation of the galvanometer needle will be ob |