tions may be counted. The celebrated Echo at Woodstock, in Oxfordshire, repeats the same Sound 50 Times. A pleasing but surprising Effect is produced in the Whispering Gallery of Saint Paul's Cathedral, when the Door is closed with great Force; but we are not able to state what Number of Repetitions are given by this ARTIFICIAL ECHO.

Every Person must have remarked that Bells are often heard as if they were in a Situation different from their real one; on the left for instance, when they are really on the right; this arises from the direct Sound being interscepted by some Obstacle, so that the Ear can only hear the Sound reflected, as an Echo, from some other Body.-The Effect of Sound here described, revives in us, the Recollection of some of our earliest Observations, made on the Ringing of CHURCH BELLS.

ACOUSTICS also embraces the Beautiful and Delightful Science of Music, in all its Departments; and we may also add, that Sounds, Echoes, and Music, have always attracted the particular Attention of Philosophic Minds, from the Earliest Ages down to the PRESENT TIMES.

THE SCIENCE OF ELECTRICITY, which now ranks as one of the most important Branches of Natural Philosophy; and which embraces so many Subjects of Inquiry, exceedingly curious in themselves, and highly interesting, from their Relations with every Department of Nature, is almost wholly of modern Creation.

The Ancients were, indeed, acquainted with a few detached Facts, depending on the Agency of Electricity; such as the attractive Power which Amber acquires by being rubbed; the benumbing shocks which are experienced, on touching the Torpedo, or electrical Eel; the Appearance of those Sparks or Streams of Light, which, on some Occasions, are seen to issue from the human Body, &c., &c. But, no suspicion was entertained by them, that these Phenomena had any Connexion with each other; and far less was it imagined that they were the Effects of a Power, pervading all material Bodies, and extensively concerned in all the Operations of Nature.

The various Phenomena produced by this UNKNOWN NATURAL POWER; the Laws, Hypothesis, Experiments, &c., &c., by which its Operations are explained and illustrated; form together, what is now denominated, "THE SCIENCE OF ELECTRICITY."

THE PHENOMENA exhibited by this all pervading agent, are among the most terrific, awful, sublime, and beautiful in Nature. Witness the fierce tornado, the overpowering whirlwind, the destructive thunder storm, and the singular and splendid appearances of the falling stars and the aurora borealis.-It was reserved for the illustrious Franklin, to prove by the most simple and decisive of Experiments, the identity of the Electric Fluid and Lightning. By means of a kite, which he sent up, during a Thunder Storm, he, as it were, piercing the skies, and causing them to reveal their secrets, succeeded in procuring sparks, shocks, &c., in abundance.

After Franklin first caused inquiry into this subject, many Philosophers directed their attention towards it; and the Experiments of some were attended with splendid results. In the Experiments of M. De Romas, the streams of fire which issued from the end of the kite-string, were ten feet in length, an inch in diameter; and attended with a noise like that of Thunder.

Experiments of this nature, require the utmost caution and circumspection to prevent disasterous consequences. We have unfortunately on record, an instance, which for want of sufficient care and foresight, was attended with fatal results. Professor Richman, of Petersburg, a highly talented man, had erected a large iron rod, with other apparatus for the purpose of procuring lightning. A thunder storm coming on, while he was in the streets, he hastened home, accompanied by his engraver Sokolow, to witness the effects upon the rod. He had unfortunately neglected to place some conductor connected with the ground, sufficiently near his insulated iron rod, to convey away any redundunce of the electric fluid; and while examining some part of the apparatus, a flash of lightning, from the rod, struck him on the head, and killed him on the spot; and thus immolated the first victim to Electrical Science. The engraver Sokolow, was thrown down by the shock; but more fortunate than his companion, escaped without material injury.

Among the more modern Experimenters, in Atmospherical Electricity, we may mention William Sturgeon, Esq., Editor of the Annals of Electricity; Andrew Crosse, Esq., of Broomfield, near Taunton; and W. H. Weekes, Esq., of Sandwich, in Kent. The latter Gentleman has recently met with most splendid results; and is likely, by a continuance of his experiments, to throw considerable light upon some of the obscure points in this very interesting branch of ELECTRICAL SCIENCE. THE ELECTRICAL FLUID pervades all bodies in Nature. Under ordinary circumstances, however, it is not observable; but it may be rendered so by various methods. If for instance a body, such as glass, be rubbed with a silk handkerchief, the equilibrium of the fluid is disturbed by the friction; and the glass acquiring more than its natural share, is from thence said to be positively electrified; while the handkerchief having parted with a portion of its natural electricity to the glass, is said to be negatively electrified.

Some bodies freely admit the passage of the electric fluid, and are called conductors. Of this class are all metals, living creatures, water, moist wood, &c.; but the metals are the best conductors. Other bodies, which resist the passage of the electric fluid, are called non-conductors. Shell Lac, Glass, and rosins are of this class; also Caoutchouc, or India Rubber, dried paper, &c.; but shell lac and glass are the best.

The fundamental law of this science, is that like electricities repel, and unlike attract. Thus if two vicinal bodies, freely capable of motion, be electrified positively; they will immediately repel each other. The same effect will take place if the two bodies be electrified negatively. But if one be positive and the other negative, attraction will be the Result.

GALVANISM is a Science which treats of the Generation and continued Production of a peculiar Modification of the Electric Fluid; and of all the Phenomena, which, under certain Circumstances, it displays.

The Galvanic Fluid is produced, whenever two Pieces of different Metals; as Platinum and Zinc, Silver and Zinc, or Copper and Zinc, are brought into Contact, and immersed in an acid Solution.

The Fundamental Principles of this Science, (like many others in Philosophy,) were accidentally discovered, about the Year 1790, by Dr. Galvani, Professor of Anatomy at Bologna; and whence we derive its

Name, "GALVANISM."-Signior Volta, made great Improvements in this very curious and interesting Science; and hence, it is somtimes called "VOLTAISM."

The Current of Galvanism, among other very singular properties, has, in a variety of cases, the power to produce Chemical Decomposition, or of resolving a compound body into its elements. Thus if a current of electricity be transmitted through water, the oxygen of the water will be evolved at the point at which the electricity enters the water, and the hydrogen at the other.-Most binary combinations are thus easily decomposed, by a voltaic current of sufficient strength. It was by the application of this principle, that Sir Humphrey Davy was enabled, with such brilliant success, to decompose the alkalics and earths, which before had been regarded as simple bodies; and thus to give a most powerful impulse to Chemical Science.

In many instances, the electrical current will overcome the powerful chemical affinity of alkalies and acids; and, singular as it may appear, an acid under the influence of this current, may be transmitted through an alkaline solution, or an alkali through an acid solution, without the slightest change; though otherwise, the most energetic chemical action would be the result.

Many improvements have recently been made in the construction of Galvanic Batteries. Experimenters have directed their attention, to diminish, as much as possible, the bulk of the apparatus; and, at the same time, to increase the efficacy and duration of the current.—A battery which would furnish a constant current, for a considerable period of time, was a desideratum which has been well supplied by the battery of Professor Daniel.

The most powerful battery yet invented, is the arrangement of Mr. Groves. This Gentleman employs plates of Platinum foil, and amalgamated zinc; concentrated nitric acid being in contact with the platinum plates, and dilute sulphuric acid, with the zinc.--Some batteries of this kind will heat red hot, twenty or thirty feet of good sized platinum wire; and effect the decomposition of water, with astonishing rapidity.

Mr. Smee has introduced a battery, composed of amalgamated zinc plates, and plates of silver foil, coated with platinum; the whole acted upon by dilute sulphuric acid. This battery will maintain a powerful current for a great length of time; and is much used in the process of the ELECTROTYPE.

We may also mention the cast iron battery of Mr. Sturgeon, as being at the same time cheap, and effective. It is composed of vessels of cast iron, with plates of amalgamated zinc. For a particular description of this battery, see "Annals of Electricity," Vol. 5, Page 66.

MAGNETISM treats of the Properties of all those Bodies called Magnets, or Loadstones; the Methods of making Artificial Magnets; and all the Phenomena of Magnetic Attraction, Repulsion, Polarity, Direction, &c.

The Natural Magnet or Loadstone, is an Iron Ore, or a Ferruginous Stone, of various Forms, Sizes, and Colours; and is generally found in Iron Mines, in different Parts of the World.

It is endowed with the peculiar Property of attracting Iron; of pointing itself in a certain Direction; and of communicating the same pro

perty to Bars of Iron and Steel, which then become Artificial Magnets, from which others may be produced, of still greater Power or Intensity. We know by the Works of Plato and Aristotle, that the Ancients were acquainted with the attractive and repulsive Powers of the Magnet; but it does not appear that they knew of its directive Property, which is, of all others, the most useful and interesting; and which has been beneficially applied in the Construction of that Valuable Instrument, "THE MARINER'S CAMPASS," the Magnetic Needle of which always points towards the North; but not always, and in every Place, precisely in the same Direction.

THE VARIATION of the COMPASS is a wonderful Phenomenon; and its Cause has never yet been clearly demonstrated. This Variation differs in different Countries; and also varies at different Times, in the same Country.

At London, in 1580, the Variation was 11 degrees and 15 minutes East; in 1658, the direction of the Needle was due North and South; and in 1818, the Variation was 24 degrees West. This appears to be

the maximum Deviation westerly, from the true Meridian; for since that Time, the Variation has diminished, being at present, about 24 degrees West. We may also observe, that in 1804, when the Variation was 24 degrees and 8 minutes West, at London; it was only 22 degrees and 15 minutes, at Paris.

It appears from Experience, that the Magnetic Needle, may be greatly affected by several Natural Causes; as the Aurora Borealis, Earthquakes, Volcanic Eruptions, Lightning, &c., &c.-These Phenomena often cause great Agitation in the Needle; either deranging it suddenly, or disturbing its general Regularity.

Lightning often materially deranges the Needle; and it has been known, sometimes, to reverse its Poles; and, the Mariners mistaking the South for the North, have run upon Shoals or Rocks, and suffered Shipwreck.—The large Quantites of Iron, employed in the Construction and Equipment of Vessels, also exert a considerable Action on the Magnetic Needle; and at Woolwich, Professors Barlow and Christie, have made many Observations, in Order to determine and correct the Errors which must arise from this SOURCE.

THE INCLINATION, or DIP of the Magnetie Needle, is its Deviation from its horizontal Position. This Property of the Needle, was accidentally discovered by Robert Norman, a Compass Maker at Ratcliffe, about the Year 1580.-It was his Custom to finish and hang the Needles of his Compasses, before he touched them; and he always found that after they were magnetized, their North Ends dipped or inclined towards the Earth; and in Order to ascertain the Quantity of this Inclination, he invented an Instrument, called "THE DIPPING Needle."

In Northern Latitudes, the North Point of the Needle, is depressed, and the South Point elevated; but in Southern Latitudes, the South Point is depressed, and the North Point elevated; and at, or near the Equator, the Needle assumes a horizontal Position.

The Dip of the Needle does not vary materially at the same Place; but differs considerably in different Latitudes; and near the North Pole the Needle is almost vertical, or nearly in the Direction of a Plumb Line.

At London, in 1775, Mr. Cavendish found the Dip, or the Angle which the Needle made with the Horizon, to be 72 degrees and 30 minutes; and in 1805, Mr. Gilpin, by his Observations, made it 70 degrees and 20 minutes; but in Latitude 80 degrees North, the Dip of the Needle is 88 degrees below the Horizon, according to Captain Parry's Observations, in his attempt to discover a North West Passage into the PACIFIC OCEAN.

THE TERM ELECTRO-MAGNETISM, is derived from the Union of the two Words, Electricity and Magnetism; and is the Name given to that Science, which treats of the mutual Action which exists between them, and of the various Phenomena that are produced by their united Influence.

A strong conviction had long existed generally, in the Minds of Philosophers, of the Identity subsisting between the Electric and the Magnetic Fluids; and in 1820, Professor Ersted succeeded in making Electricity act as Magnetism, in a sure and a permanent Manner; and thus established the Basis of the Science, on a solid and lasting FOUNDATION.

Becquerel, Ampere, Jacobi, Lenz, Faraday, Barlow, Sturgeon, Marsh, and many others, have made numerous Experiments, and great Improvements in the Science of ELECTRO-MAGNETISM.

The Weight that may be sustained by a Good Electro-Magnet and a Powerful Battery, is very astonishing; and far exceeds any Weight that can be supported by either Natural or Artificial Magnets.

The following Gentlemen have made Electro-Magnets of various Forms, Weights, and Sizes; and of Course, differing in their Powers, as may be seen by the Numbers placed opposite to their Names, and which denote the Weights that the different Magnets sustained, in Pounds Avoirdupois.

Mr. Roberts's Magnet is the most powerful that has ever been constructed, either by the ordinary Modes of magnetizing Steel Bars, or by the Voltaic Current; the Weight it sustained being reduced, is 1 ton, 6 cwt., 2 qrs., 10 lb.

For further Information on this interesting Subject, we refer our Readers to Sturgeon's Annals of Electricity, Magnetism, and Chemistry, Vol. V., Page 193; and Vol. VI., Pages 166, 231, and 431; in which Work they will find Abundance of Matter for their Improvement and Gratification.

THERMO-ELECTRICITY is one of the most important Consequences of the Discovery of Electro-Magnetism; and affords us the Means of detecting the Presence of Electricity, where it was never supposed to exist.

This is accomplished simply by two Pieces of Metal of unequal Temperatures, the Ends of which are connected in a particular Manner,