evident that, in all these cases, the effects were produced by galvanic action.

Several persons may receive the galvanic shock together, by joining hands, in the same manner as in receiving the shock from a Leyden jar. Their hands should be well moistened; but, unlike electricity, the strength of the shock diminishes as it proceeds, in consequence of which, the last person feels it much less violently than the first. After receiving the shock, a slight numbness of the part exposed to it remains for some time. The shock may be also conveniently given by placing the hands or feet in salt water, and bringing wires from each end of the battery into the liquid. If any other part of the body is intended to be operated upon, a sponge moistened with salt water, and fastened to a metal plate connected with one end of the battery, may be applied to the part, and the hand or foot put into a vessel of the same liquid, connected by a wire with the other end of the battery.

The decomposition of water by galvanism is easily effected. The simplest mode of performing this experiment is, to bring the wires coming from each end of the battery into a vessel of water. A profusion of bubbles of gas will appear to be given out from each wire as far as it is immersed in the liquid. The closer the wires are brought together, so as not to touch, the more rapidly decomposition goes on. The gas produced from the wire coming from the zinc end of the battery, if the wire be of gold or platina, will be oxygen; but if the wire be of any metal more oxidable, no gas will appear, but the wire will be oxidated. The gas furnished by the wire from the copper end of the

battery, of whatever metal the wire may be, is of pure hydrogen. Both the gases are produced by the decomposition of the water.

Batteries containing 6000 or 8000 square inches of zinc and copper surface, furnish the means of performing a variety of experiments in which light and heat are abundantly extricated. Such a battery, in its highest state of energy, will make red-hot, and even fuse, a considerable length of fine steel wire, when it forms part of the circuit in making the connection between the two ends of the battery. Attach to the end of each wire of the battery a small piece of charcoal : on completing the circuit, by bringing the two pieces of charcoal into contact, a light, the most vivid that the eye can behold, immediately appears. The charcoal

should be prepared for the purpose by burning some very hard, close-grained wood in a closed vessel. The foils, or thin leaves, of gold, silver, tin, and other metals, may be consumed by the help of mercury. Let the conducting wire from one end of the battery terminate in the mercury, in a small iron dish; to the other conducting wire attach the foil or wire to be deflagrated, and, upon touching the mercury with the latter, the effect will follow. The light afforded by the combustion of different metals is of different colors. Copper or brass leaf, commonly called Dutch gold, burns with a green light; silver with a pale blue light; gold with a yellow light; and all with a slight crackling. The galvanic discharge fires gunpowder, hydrogen gas, oils, alcohol, &c.

One of the most brilliant discoveries in modern chemistry was effected by the application of galvanism.

This was the decomposition of the fixed alkalies, by Sir Humphry Davy. These alkalies-namely, soda and potass were supposed to be simple bodies; but Davy discovered them to be metallic oxides. A small piece of one of these oxides being laid upon a piece of platina connected with one end of a powerful battery, and another piece of platina, connected with the other end of the battery, being brought into contact with it, a portion of black matter is soon formed, in which are found imbedded small metallic globules. These globules are the base of the alkali, which has been deprived of its oxygen by the action of the battery. Experiments made by Davy, and other chemists, also showed that many other substances before supposed to be simple as lime, barytes, strontites, magnesia, zircon, &c.—were capable of analysis; and though silex, alumina, and others, offered great resistance to the application of galvanism, in the majority of cases the analysis was successful. In giving a theory of galvanism, we are struck with a primary question: How does galvanism differ from common electricity? This query may refer both to the nature of the phenomena themselves, and to the means employed for their production. It is in some cases difficult to draw the exact line of distinction between the two principles, and many persons doubt whether any precise distinction actually exists. For, as it is conceived that they both depend upon the same agent, having merely experienced some modification in its nature, or mode of action, we must conclude that there may be some intermediate or indeterminate state which might be referred to the one or the other with almost equal propriety.

The electricity produced by the galvanic battery is of the same nature as that given by the common electrical machine; the only difference being that the mode of producing galvanism is continuous; that is, when in any way discharged, it is immediately reproduced by the oxidation of the zinc; and hence many galvanic phenomena have been successfully imitated by a series of sparks of ordinary electricity.

MAGNETISM.

THE Word MAGNETISM, in its original and particular acceptation, is employed to denote that invisible force with which certain ores of iron, called in Greek magnes, attract pieces of iron to themselves. This property is found naturally in all the ores of oxidulated iron; but when the laws of its action are known, we may excite it artificially in metallic iron or steel by a particular process. Of the nature of the principle which produces the phenomena of magnetism, we are entirely ignorant.

Of magnets there are two kinds the natural and the artificial. The natural magnet, or loadstone, is an ore of iron, hard enough to strike fire with steel: its color is dull, generally dark gray, brown, or nearly black. The power of magnetic attraction may be communicated to iron in any state; and a bar of iron possessing it in any considerable degree is called an artificial magnet. Magnetism is an accidental property of iron, and the metal may either possess or be deprived of it without losing any of its essential characteristics as a metal. Magnetic attraction was, till lately, supposed to be exerted by ferruginous bodies alone on other ferruginous bodies, and hence the use of the magnet was resorted to as a sure means of detecting the presence