cal and magnetic action. Some philosophers maintain that all these effects are producd by different states of the same electric fluid; (see Franklin.) Others believe that two electric fluids exist; one of them always disturbed when the other is, and each acting in opposition to the other at all times. (See Du Fay.)

"ELECTRICAL INDUCTION. The power possessed by an excited body in influencing other bodies in the vicinity of it, without touching them.

"ELECTRICITY. A science which explains the laws which govern the excitation, distribution, and other phenomena of a peculiar element, called the electric fluid. Electricity, in its more limited acceptation, explains the electric effects produced upon various bodies by friction or pressure only. In its general meaning, it includes also, the explanation of those departments of science, called galvanism, electro-magnetism, and thermo-electricity. That effect, resulting from friction alone, constituting a branch only of a general subject, and which, for distinction sake, is called common, free, or frictional electricity.

"ELECTRICITY. Disguised, is when the electric fluid is accumulated upon the surface of a body, and yet has but little tendency to fly off, in consequence of that body being under the influence of another electrified body, which is near to it and insulated. The lower plate of the electrophorus is an example of disguised electricity. "ELECTRICITY, States of. When the electric fluid in any body is so disturbed as to become apparent, one part of that body has the fluid in a redundant state; in the other part, it is deficient, or contains less than the quantity natural to it. The former, is called accumulated or positive electricity; and the latter, negative. Upon the supposition of two fluids, the former, is the vitrious; the latter, the resinous fluid. Free or common electricity is popularly divided into atmospheric, animal, chemical, mechanical, and medical, according to its effects, and the particular phenomena it explains.

"ELECTRIC LIGHT, Brush, Star, Spark. The spark or stream of brightness seen when a considerable quantity of the electric fluid passes through any imperfect conductor. If it pass into the air from a point electrified positively, it resembles a brush, as B. If from a negative point, a star, A. If it pass in a considerable quantity, and with rapidity, from one conductor to another, through the air, it will put on the appearance of a spark, more or less zigzag, c, and be attended by a snapping noise.

B

"ELECTRICAL MACHINE. Any instrument adapted to collect a considerable quantity of the electric fluid, as produced by friction. The principal electrical machines now in use are of two forms; in

one, a cylinder of glass is to be excited; in the other, a plate of glass, (see Cylinder and Plate.) In either case, there are one or more cushions which rub against the glass; and a prime conductor, (see Conductor,) to collect and retain the electric fluid given off by the glass.

"ELECTRICAL NON-CONDUCTORS. (see Electrics.)

"ELECTRIC POLES, OR ELECTRODES. The two opposite ends of a charged electric or galvanic apparatus. When the word pole is used, we distinguish them by the terms positive and negative; but employing the term electrodes, the positive is called the anode or platinode; the negative, the cathode or zincode.

"ELECTRIC SHOCK. The rapid passage of a quantity of the electric fluid through any substance, which occasioning a disruption of some bodies, and a convulsion to others, renders the term appropriate.

"ELECTRO-CHEMICAL ACTION. The chemical changes that take place owing to the interference or agency of an electric current. "ELECTRO-CHEMICAL EQUIVALENTS, are the same, and coincide with the ordinary chemical equivalents.

"ELECTRO-CHEMISTRY. That division of electricity, which treats of the chemical effects produced by the passage of an electric current through a chemical compound.

"ELECTRODES. The poles of a galvanic battery. That pole in which the electric fluid enters, is called the negative pole, or electrode. "ELECTRO-DYNAMIC CYLINDER. (See Ampere.)

"ELECTRO-DYNAMICS. That division of the science of electromagnetism, which explains the laws of all rotations, vibrations, and other motions occasioned by the mutual action of the magnetic and electric fluids.

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ELECTRO-GASOMETER. A small apparatus for collecting and measuring the amount of gas, resulting from the decomposition of water by electricity. (See Bachhoffner, Clarke, &c.)

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'ELECTROLYTES. All substances susceptible of direct decomposition by a passage of the electric fluid through them, as water.

"ELEOTROLYTIC ACTION, or ELECTROLYSIS. Galvanic action considered in reference to chemical decomposition.

"ELECTRO-MAGNET. A bar of iron which assumes temporary magnetic properties, in consequence of a current of electricity being made to pass through it. It is made by twisting around the bar of iron, whether straight or shaped like a horse-shoe, a wire covered with silk or cotton, or other non-conducting material, and passing a current from one pole of a galvanic battery to the other, along the coil of wire. The circulation of the fluid through the wire, will render the bar of iron within it a temporary but powerful magnet, capable of sustaining a considerable weight. It loses this power the moment the connection with the battery is broken. In the cut, A

is the electro-magnet; в and c, the weight raised; N and P, the wires from the poles of the battery.

P

"ELECTRO-MAGNETIC APPARATUS. (See Ampere, Callan, Bachhoffner, Clarke, Barlow, Sturgeon, Faraday, Marsh, &c.) "ELECTRO-MAGNETIC COIL. (See Callan.) "ELECTRO-MAGNETIC COIL MACHINE. (See Coil.) "ELECTRO-MAGNETIC HELIX. (See Helix.)

"ELECTRO-MAGNETIC MACHINE, or ENGINE. A machine by which the effects of electro-magnetism may be noticed or ascertained. "ELECTRO-MAGNETIC MULTIPLIER. The original name of the galvanometer, an instrument for measuring the intensity of an electric current. The original instrument was merely a mariner's compass, with a covered wire coiled five or six times round it. When an electric current is made to pass along the wire, the compass-needle is driven out of its usual polar direction, the north end being turned east or west, according to the direction of the current. The following is another, but not a more powerful form of the instru

ment:

A B are mercury cups, to hold the wires from the pole of the battery; c the magnetic needle, with a graduated card beneath it, and the coil of wire around it.

"ELECTROMOTIVE FORCE. Volta supposed that when two metals were in contact, a certain force was in operation, tending to effect a transfer of electricity from the one metal to the other. To this force he gave the name of electromotive.

"ELECTRO-MAGNETIC SPHERE. (See Barlow and Sturgeon.) "ELECTRO-MAGNETISM. The science which explains the action of the electric fluid and the magnet upon each other.

"ELECTROMETER. An instrument to measure the quantity and quality of the electric fluid disturbed during any experiment or process. Some electrometers act upon the principle of electrical attraction or

repulsion, certain parts of them becoming divergent in proportion to the intensity of the disturbance of the fluid within them, such as Coulomb's electrometer, the quadrant electrometer, &c. Others depend for their action upon the circumstance that the electric fluid acquires momentum in proportion to its concentration, as in the balance electrometer, the medical electrometer, &c. (See Balance, Coulomb, Lane, Medical, &c.)

"ELECTRO-MICROMETER. Any instrument adapted to measure very minute quantities of electricity; synonymous with condenser. "ELECTRO-MOMENTUM. The power exerted by an electric current when suddenly turned out of its direct course; or, when made to pass from a good conductor to one which is less perfect.

"ELECTROMOTIVE. The power of motion conferred upon magnets, &c., by electrical action.

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ELECTRON, OF ELECTRUM. The former is the Greek, the latter the Latin name for amber, which being rubbed, shows the property of attracting light substances; from which word and circumstance we derive the word electricity. Glass, and also gold, or an alloy like gold, was by the ancients likewise called electrum.

"ELECTRO-NEGATIVE and ELECTRO-POSITIVE. Those bodies which, when submitted to the action of a galvanic current, are apparently attracted to the anode, or positive pole of the battery, are called electro-positive, or cathions. Those attracted to the cathode, are electro-negative, or anïons; they being supposed to be in a contrary electrical state to the pole to which they are attracted.

"ELECTROPHORUS. A simple instrument, which, when once excited, retains it electrical energy, which it is ready to give out continually for a long period. It consists of two plates; the lower one may be a plate of tin, ten or twelve inches in diameter, with the edges turned up, so as to hold the following composition when poured hot into it, forming a cake when cold, of about one-eight, or from that to a quarter of an inch thick. The composition is, pitch 1 part; asphaltum 4 parts; and bees'-wax 1 part; or pitch, rosin, and bees'wax in the above proportions. The upper plate may be of wood, covered completely with tin foil, and having a glass handle to lift it by. It is two or three inches less in diameter than the lower stand. When to be used, the instrument is to be warmed, the resinous plate rubbed with a piece of warm flannel, and the upper plate put upon it, its glass handle being previously dried. Lifting up the upper plate by the handle the edge of it will give a spark; touch the upper plate with the finger, and put it down again on the other; upon lifting it a second time, it will give another spark, and so on for a considerable period. The upper plate has often a wire with two pith balls attached to it.

"ELECTRO-PULSATIONS. Electric currents or shocks, which pass in such rapid succession between the two sides of a charged Leyden jar, or between the poles of a galvanic battery, that the shocks are not to be individually distinguished.

"ELECTROSCOPE. Any instrument to indicate the disturbance of the electric fluids; but not of sufficient accuracy to show the precise amount of that disturbance, such as Bennet's gold-leaf electroscope and Saussure's pith ball ditto.

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ELECTROTYPE. A method of taking reverse fac-similes of medals, coins, copper-plates, seals, &c., by means of the power which voltaic electricity has of decomposing metallic salts. A piece of zinc is soldered at one end of a wire, and the medal, seal, &c. (if a seal, or other non-metallic body, it must be previously covered with blacklead), at the other end, and then the medal immersed in a saturated solution of copper, and the zinc end in acidulated water, there being some membrane or other porous substance between the two solutions. This being altogether a galvanic circle, decomposition of the sulphate of copper will take place, and metallic copper be deposited on the medal; after some hours the deposit will be thick enough to remove, and will be found an exact reverse impression of the medal. following cut shows three forms of apparatus :

The

In No. 1, A is a jelly pot. F a porous tube within it. c is the wire, with a bar of zinc inside the tube F, and the lower end bent, holding the medal D upon it. E is a shelf surrounding the tube F, to hold crystals of sulphate of copper. No. 2 is a square wooden box, with a division of plaster of Paris across it. No. 3 is a glass jar, holding a copper-plate to be copied, and also another copperplate; when these are connected with the poles of a galvanic battery, one of the copper-plates will be dissolved and deposited on the other."

So also under magnetism, galvanism, thermo-electricity, the list of words are equally extensive, and their meanings well defined. In short, the industry and talent which is every where shown in this cheap and valuable volume, merits the strongest encouragement. It sets the example of simplicity combined with scientific accuracy, and shows equally the unassuming character and yet extensive reading and profound knowledge of the author.

The Ninth Annual Report of the Royal Cornwall Polytechnic Society. London: Simpkin and Marshall, Stationers' Hall Court; and Weale, 59, High Holborn.

THE Royal Cornwall Polytechnic Society, whose annual reports we have regularly noticed for several years past, is still progressing