rona, or Halo, and is attributed to the refraction of the rays of light in passing through the vesiculæ of a thin

vapour.

These Coronæ are sometimes accompanied by Parhelia or Mock-suns, which latter are found, by the reflection of the sunbeams, in a cloud appropriately situated for that purpose. The Mock-suns appear of a bright white, and of the same size as the true sun; when many of them appear together, some of them are brighter than others. They are sometimes tinged with the colours of the rainbow, and often appear to have a fiery tail; they have been sometimes seen with two or three tails. These phenomena have been repeatedly observed in North America, where they have remained visible for several hours. They have made their appearance in England, but their visits are very rare and uncommon. According to our old chroniclers five suns were seen at once in the year 346; three also were seen in 812; three in 953, and five 1233. Lilly mentions three seen in 1644 and three in 1648. Of late years they have not been seen in England at all. A similar phenomenon sometimes attends the moon; this is called a Paraselene.

Fiery Meteors of a very wonderful and striking appearance often visit our atmosphere, but of their origin nothing is known. A meteor appeared in 1783, which was calculated to be as large as Great Britain, and from its having been seen nearly at the same instant over the whole of Europe, it was calculated to be more than 100 miles high. A meteor as large as the moon appeared in the western counties of England in 1832, its light for a short time was intense. Luminous clouds are often seen, but their origin is unknown; one in Java, in 1772, destroyed a district twenty miles round, and killed 2000 persons.

A meteor like a falling star, sometimes appears darting rapidly through the air, this is supposed to be an electrical phenomenon, as it takes place when the air is in a state of electric excitement.

Stones called Aeroliths sometimes fall from the atmosphere, concerning which there are various opinions, although it seems not improbable that they are impelled

from the lunar volcanoes. There are records of more than 300 instances of Aeroliths of all sizes, from a few ounces to some hundreds of pounds weight, falling in different parts of the earth. They strike the earth obliquely with a great force, penetrating it to a considerable depth. An Aerolith of fifty-six pounds weight fell in Yorkshire in 1795. Immense masses of iron of a meteoric nature have been found in different parts of the earth, from a portion of a mass which was found near the Cape of Good Hope, a sword was some years since manufactured and presented to Alexander the late Emperor of Russia, by Mr. Sowerby, a gentleman then well known in the scientific world, but since deceased.

One of the most beautiful meteoric appearances is the Aurora Borealis, which although rarely seen in our latitude is a constant visiter of the Arctic regions, sometimes covering the whole heavens, and eclipsing by its splendour the stars and planets. The Aurora Borealis is often accompanied with a rustling snapping noise, and its appearance has been described as terrifically grand. There have been various opinions relative to the cause of this phenomenon, but it is generally ascribed to the combustion of inflammable air by means of electricity, although from recent observations of the polar voyagers it appears to be in some way connected with the magnetism of the earth.

The Ignis Fatuus, or Jack with a Lantern, is a meteor that is often seen in marshy places, and is supposed to be of the nature of phosphuretted hydrogen gas. This meteor is never seen on hills or other elevated places, because they do not sufficiently abound with moisture to produce this gas.

When the air is put into motion through any cause it becomes Wind. The principal cause of Wind is the rarefaction of the air through heat; the rarefied air ascending, the unrarefied rushes in, to supply its place. Evaporation is another cause of Wind by producing an increase of volume in the atmosphere, and Rain is considered a third cause. Although the Wind in our climate is considered very changeable and uncertain, yet even in England there is a degree of regularity, for the easterly wind usually prevails from the Vernal Equinox to somewhat beyond

the Summer Solstice, and then the westerly for the remainder of the year. This is of course subject to exceptions. Within the tropics a very great regularity in the wind prevails, it blows at various places, for six months in one direction, and six months in the opposite direction throughout the year. The velocity of the wind varies from one mile in an hour to 100 miles; from a scarcely perceptible breath to a terrific hurricane.

A most exceedingly rapid and impetuous wind moving in a spiral manner called a Whirlwind, sometimes takes place. This usually occurs after very hot weather, and in the warmer climates, and has by some been attributed to a stream of elastic matter rushing violently out of the earth. Whirlwinds and Water-spouts most probably arise from the like cause, which is intimately connected with Electricity.

The following are the principal instruments used in meteorology. The Anemometer, which measures the force of the wind; the Atmometer,-the quantity of water evaporated in a given time; the Barometer,-the weight, or pressure of the air; the Cyanometer,-the intensity of the blue colour in the atmosphere; the Drosometer,-the quantity of dew that falls; the Eudiometer,-the pureness of the air; the Hygrometer,-the humidity of the air; the Ombrometer,-the quantity of rain that falls, and the Thermometer,—the temperature of the air.

ELECTRICITY AND GALVANISM.

Origin of Electricity-Electrics-Conductors or Non-electrics-Mode of exciting Electricity-Electric Machine and Apparatus described-Electric Battery-Electrophorus-Electrometer-Electricity identified with Lightning-Paratonneres or Conductors-Electric Fish-Galvanism or Voltaic Electricity-Voltaic Pile described-Galvanic Excitement of the Body, &c. &c.

THE origin of the science of Electricity may be traced to Thales the Milesian, who flourished about 600 years before the Christian era, and was particularly celebrated for his improvements in the different sciences. He first discovered the attractive power of amber; and as the Greek name for amber is electron, this science obtained the name of electricity.

Although it was soon discovered that other substances besides amber possess an attractive power, yet so little attention was paid to the subject, that it was not until the last century that electricity could be deemed a science.

From its having been found that only certain substances could be excited so as to produce electric effects, these substances were called electrics; and as those substances which cannot be excited have the property of transmitting the electric excitement, they received the name of conductors ; so that conductors are non-electrics, and electrics are non-conductors.*

The principal electrics are glass, resinous substances, silk, hair, feathers, baked wood, and atmospheric air. The principal conductors are the metals and fluids, living animals and vegetables, most of the earths and stones.

The usual mode of exciting electricity is by friction. The process of heating will sometimes produce electricity, but heating may be considered a species of friction.

It may be naturally asked, what is electricity? In reply, no satisfactory answer can be given. By some it is considered a fluid sui generis; by others a peculiar affection of the surfaces of bodies. Electricity is identified with lightning, but it is only from the results produced by it that its existence is known.†

As the effects of electricity appeared to differ by the excitement of different substances of glass and sealingwax, for instance-some philosophers imagined that there were two different kinds of electricity, and these they distinguished by the terms vitreous and resinous. Others supposed there to be but one kind of electricity, the difference in the effects being caused by the substance excited possessing more or less than its natural share. The former they called positive electricity, the latter negative. If a glass tube or ruler be excited by friction, it will attract light bodies, as pith or feathers; also if a stick of sealing

* Although all bodies are considered to belong to one or other of these classes, there are none that are either perfect conductors or perfect electrics; also many conductors may be made to be electrics, and many electrics to be conductors.

Sir Richard Phillips imagines electricity to be an affection of the air, or medium intervening between the surfaces of bodies.

wax be similarly excited, it will attract in a similar manner. Here different causes conspire to produce the like effects. According to the former theory, which is known by the name of the theory of Du Fay, although the two fluids exist in bodies in a state of intimate union, yet, when separated, they become repulsive with regard to themselves, and attractive of each other. Thus the friction of the glass tube will separate the fluids, and the vitreous electricity will attach itself to the glass, which becomes attractive in order to restore the equilibrium; or rather the vitreous electricity of the glass attracts the resinous of the body, and at the same time carries the body with it. According to the latter, which is called the Franklinian theory, and which assumes that there is but one kind of fluid, and that all bodies continue in an unelectrified state as long as they retain a natural share of it; but, when the equilibrium is disturbed, as when the electric is excited by friction, the electricity becomes conveyed either from the rubber to the electric, or from the electric to the rubber, according to the peculiar nature of the electric employed. In the former case, the electric is said to have a positive excitement, and will attract light bodies in order to throw off its superabundance of electricity, in the latter it is said to have a negative excitement, and will attract for the purpose of obtaining its natural share. Philosophers of the present day still continue divided as to the nature of electricity, and its mode of action, some following the theory of Du Fay, and some that of Franklin.

Although electrical authors generally state that there are two kinds of electricity, yet it appears that either kind may in some instances be produced from the same body, by varying the nature of the rubber. Thus sealingwax excited by fur becomes negatively electrified, but excited by tinfoil, it will be positively electrified.

To exhibit the most striking and important phenomena of electricity, it is necessary to have an extensive apparatus, which, in a work like the present, it is impossible to describe minutely. The principal article of the electrical apparatus is that which is usually called the Electrical Machine. A brief description of that used at the present day is here subjoined.