very combustible nature, it requires to be handled with great caution; gentle pressure between the fingers is sufficient to kindle it. It burns rapidly, emitting a splendid white light, and causing an intense heat.

Iodine is a substance much resembling chlorine in some of its properties. It may be procured by drying and powdering common sea weed, and heating it with sulphuric acid: a violet coloured vapour rises, which, if received in a cool vessel, will condense on its sides, and will form scaly crystals, of a somewhat metallic lustre. These crystals are the substance: from the violet colour of its vapour it is called iodine. It has the property of forming a beautiful blue colour, when mixed with a little powdered starch, diffused through cold water hence they are used as tests of the presence of each other. Iodine stains the fingers yellow. Like chlorine, it destroys vegetable colours, though not powerfully. Iodine is used in medicine: in small doses it increases the appetite; but in large doses, or continued too long, it produces remarkable emaciation.

Chlorine was discovered in 1770. It is a substance of much importance, being, in combination with other substances, extensively used in the arts. Chlorine is a yellowish-green coloured gas, which has an astringent taste, and a disagreeable odour. It is one of the most suffocating of the gases, exciting great irritability in the wind-pipe, even when considerably diluted with air. When strongly and suddenly compressed, it emits both heat and light a character which it possesses in common with oxygen gas. Under considerable pressure it assumes the form of a limpid liquor of a bright yellow colour. Chlorine is a supporter of combustion. If a lighted taper be plunged into chlorine gas, it burns with a small red flame, and emits a large quantity of smoke. Phosphorus takes fire in it spontaneously. Several of the metals, such as tin, copper, arsenic, antimony, and zine, when introduced into chlorine in the state of powder, or in fine leaves, are suddenly inflamed. Chlorine, though formerly called an acid, possesses no acid properties. It has not a s

sour taste,

nor does it redden the blue colour of plants, which all acids do. One of the most important properties of chlorine is its bleaching power. All animal and vegetable colours are speedily removed by chlorine; and when the colour is once discharged, it can never be restored. Chlorine, however, cannot bleach unless water be present. Chlorine is useful also for the purposes of fumigation, and is used to purify the air in fever hospitals. The infection of the small-pox is also destroyed by this gas, and matter that has been submitted to its influence will no longer generate that disease.

To these simple non-metallic bodies we might add bromine, selenium, boron, fluorine (the base of fluor spar), and silicon (the base of flint.) But as they are of less importance, and as the nature of some of them is still a subject of dispute with chemists, we shall omit the consideration of them for the present.

ON ELECTRICITY.

The word Electricity denotes a peculiar state, of which all bodies are susceptible, and which is supposed to depend upon the presence of a substance called the electric fluid. Some of its phenomena were known to the ancients, particularly those attractions and repulsions which a piece of amber, after being rubbed, exhibits, with regard to hairs, feathers, and other light bodies; and it was from its power of drawing light substances to it when rubbed, that the Greeks gave amber the name elektron, which is the origin of the modern name. Thales, who lived six centuries before the Christian era, was the first who observed the electrical properties of amber; and he was so struck with the appearances, that he supposed it to be animated. Mr. Boyle is supposed to have been one of the first persons who got a glimpse of the electrical

light, or who seems to have noticed it, by rubbing a diamond in the dark. Sir Isaac Newton was the first who observed, that excited glass attracted light bodies on the side opposite to that on which it is rubbed.

If

An electric is any substance, which being excited, or rubbed by the hand, or by a woollen cloth, or other means, has the power of attracting light bodies. If a piece of sealing-wax be rubbed briskly against the sleeve of your coat, or any other woollen substance, for some time, and then held near hair, feathers, bits of paper, or other light bodies, they will be attracted; that is, they will jump up and adhere to the wax. a tube of glass, or small phial, be rubbed in a similar manner, it will answer much better. If this operation be performed in the dark, a luminous matter will be seen, which is called the electric matter or fluid; and all bodies that we are acquainted with have more or less of it in them; though it seems to lie dormant till it be put into action by rubbing. The air, and every thing, is full of this fluid, which appears in the shape of sparks; and the rubbing of the glass with the hand collects it from the air, and the glass, having now more than its natural share, parts with it to any body that may be near enough to receive it. Those bodies which we call Electrics, will not convey electricity from one body to another, and therefore they are called NONCONDUCTORS. The most remarkable are—glass, and all vitreous substances, precious stones, resins, amber, sulphur, baked wood, wax, silk, cotton, wool, hair, feathers, paper, white sugar, air, oils, metallic oxides, all dry vegetable substances, and all hard stones. Those bodies, which, when rubbed ever so much, do not exhibit electricity, are called Non-Electrics. They convey electricity from one body to another, and therefore, are denominated CONDUCTORS. Some of them conduct electricity much better than others. The principal conductors are the metals, charcoal, all fluids except dry airs and oils, most saline substances, and stony substances. Woollen and silk, when wet, will, by means of the water, conduct electricity.

When a body has more than its natural quantity of this fluid, it is said to be electrified positively, or plus; and when it has less than its natural quantity, it is said to be electrified negatively, or minus. When bodies are electrified either of these ways, they repel each other; but if some be electrified plus, and others minus, they mutually attract; or if one body be electrified plus, and the other not electrified in either way, they also attract each other.

There are some fishes which possess the extraordinary faculty of being able, at pleasure, to communicate shocks, like those of an electric battery or galvanic pile, to any animal that comes in contact with them. They are called the torpedo, the gymnotus electrious, and the silurus Indicus. The most remarkable of these is the Gymnotus Electricus or Electric Eel, which is frequently found in the marshes and stagnant pools of Guiana, and other countries of South America. The shocks they give are exceedingly severe; and Humboldt mentions a road which has been totally abandoned, because the mules, in crossing a wide ford, were, by these violent attacks, often paralysed and drowned. Even the angler on the. bank was not exempt from danger, the shock being conveyed along his wetted rod and fishing line. The Electric Eel is sometimes twenty feet long. electricity of all those fishes is exerted by them only when they please, and of course only while they are alive. After the animal has discharged its electrical matter, the next shock is weaker; and when the animal is exhausted, it has lost all the power of producing any effect for some time.

The

There is no longer any doubt that the cause of thunder is the same with that which produces the ordinary phenomena of electricity. The resemblance between them is indeed so great, that we believe thunder itself to be any other than a grander species of electricity.

cannot

GALVANISM.

Galvanism is so intimately connected with electricity, that it may be considered as a branch of that science. It was first accidentally discovered in the chemical laboratory of M. Lewis Galvani, professor of anatomy in the university of Bologna, upon the following occasion. The lady of the professor being of a delicate habit, was occasionally supported by soup made from frogs as a restorative. Some of these animals, skinned for that purpose, were lying upon a table in the laboratory of the professor, in which stood an electrical machine, One of the assistants, in experiment, by accident brought the point of the scalpel near the crural nerves of a frog recently killed, lying not far from the conductor; the muscles of the limb were instantly set in motion, being agitated with strong convulsions. By a long series of new experiments, the law of nature as far as respects the influence of this principle, was investigated, of which mere accident had at first afforded him a glimpse only. Galvani published a treatise on the subject, addressed to the Institute of Bologna, in the year 1791. On the appearance of this work, the universal attention of the philosophers of Europe was arrested. This discovery was made at a time when something more than hypothesis was necessary to satisfy the mind of the inquisitive enquirer after scientific truth. To this desire may be referred the almost innumerable experiments which were made in every district of Europe, in consequence of this publication; by which means the science became considerably enriched by the addition of a great variety of new facts, by contemporaries and successors, insomuch that it is said, the labours of Galvani, the original discoverer, bear but a comparatively small proportion to what have been since adduced for its illustration.

Galvani found that, by the mere agency of a metallic substance, where he had no reason to suspect the presence of electricity, the limbs of a recently killed