from it; it enters into their composition in the proportion of from two to eighteen or twenty per cent., and perhaps at a medium we may state it in all of them at six per cent.; moreover its own ores are of all others, the most common and the most copious; in many places, particularly in the most northern climates, whole mountains of it are found, and many of them magnetic. When to this consideration we add that of the specific gravity of the globe, which has been found to be 4.5 times heavier than water, notwithstanding the immense quantity of water that covers the greater part of its surface to considerable unknown depths, and notwithstanding that the specific gravity of by far the greater part of the stones and earths it contains, does not exceed, and scarcely amounts even to three times the weight of an equal bulk of water, and that the quantity of mineral substances whose specific weight exceeds four times that of water, is almost infinitely small in comparison to the other known component parts of the globe, and finally, that the weight of most iron ores, is about four or five times that of water; all this I say considered, it is difficult to avoid concluding that the interior part of the globe consists chiefly of iron ore, disposed in one or more aggregate masses; a conclusion that is farther confirmed, on reflecting that volcanic lavas ejected from the deepest recesses with which we are acquainted, contain from fifteen to twenty or twenty-five per cent. of iron in the state most favourable to magnetic attraction.

Taking then this assertion to be as fully proved as its subject matter is capable of being ascertained, we may deduce from it the following corollaries :

1st. That as the ferruginous matter in the globe being by far the most copious, its universal attractive power is principally seated in the ferruginous part.

2nd. That as all terraqueous matter was originally in a soft state, its parts were at liberty to arrange themselves according to the laws of their mutual attraction, and in fact did coalesce and crystallize in the direction in which they were least impeded by the rotatory motion of the globe, namely, in that which extends from north to south, and principally and most perfectly in the parts least agitated by that motion, namely, those next the centre.

3rd. That this crystallization, like that of salts, might have taken place in one or more separate shoots, or as we may here call them, immense separate masses, each having its poles distinct from those of the other, those in the same direction repulsive of and distant from each other.

In consequence then of the universal law of attraction of the particles of matter to each other, these internal magnets exert a double power of attraction; the first and most general, on the particles of all bodies indiscriminately in proportion to their density, and the direct or inverse ratio of the squares of their distances, according as those bodies are found within or without the earth's surface; and the second, on bodies of their own species in proportion to their

homogenity, and to the correspondence of the arrangement of their integrant particles with that of the integrant particles of these internal magnets.

A magnet, therefore, is a mass of iron, or of iron ore, whose oxygenation does not exceed 20 per cent., or thereabouts, whose particles are arranged in a direction similar to that of the great internal central magnets of the globe. This I call the magnetic arrange

ment.

of

The particles of iron attract each other more forcibly than those any other known substance. This appears by its cohesion, hardness, elasticity, and infusibility, in each of which properties, or at least in the combination of most of them, it exceeds all other known bodies.

Hence, a magnet attracts iron when within the sphere of its action, by forcing, in virtue of its attractive power, a certain proportion of its integrant particles into a disposition and arrangement similar to that of its own. For in this case it exerts a double attractive power, that of the particles of iron to each other, which we have seen to be the greatest of all others, and that of crystallizing bodies, which we have also seen to be indefinitely great.

The crystallizing power being at once attractive and repulsive, according to the direction of the surfaces (No. 6), hence we see that one part or end of the magnet must repel that which the other has attracted, as long as the same disposition of parts remains.

The disposition of parts in a particular magnet, being similar to that which obtains in the great internal general magnet, extends in the direction of from north to south. Hence magnets, when at liberty to move with a certain degree of freedom, and iron, when a sufficient number of its particles are arranged in that direction, and has sufficient liberty to conform to it, points to those poles. Hence this property is called Polarity.

The magnetic power is greater or lesser according to the number and homogenity of the particles similarly and magnetically arranged. Hence small magnets may be more powerful than a larger, and hence a magnet will attract a magnetized needle at a greater distance than one not magnetized.

The magnetic power decreases in a certain ratio of the distance of the particles that exercise it. Hence it is strongest at the point of contact, and at the poles, as it is there most unsaturated, and weakest in the central part, which separates the two opposite poles.

When a magnet is broken into small pieces its power is nearly destroyed, because, though the poles should be all of the same kind, yet the distance of each other from the opposite pole is so small that their powers counteract, and consequently destroy each other.

If, when a needle is attracted by the south pole of a magnet, a bar of iron be placed on the north pole, the needle is still more strongly attracted, because the iron acquires also a south pole, whose force is joined to that of the magnet.

If two needles be suspended from any given pole of a magnet, they will diverge, because they both require the same polar arrangement. If a bar of iron be laid on that pole of the magnet, the divergence will diminish, because the next end of the iron will require the disposition of the opposite pole, and consequently, counteract the repulsive power of the magnet.

A magnet will not transmit its power through a bar of iron, if this be too long. Muschenbrouck limits their length to six feet, but this depends on the strength of the magnet.

The power of a magnet (every thing else being equal) depends on the numbers of its surfaces magnetically arranged, and the accuracy of that arrangement.

The arrangement is accurate when the synonimous surfaces are exactly parallel to each other, and originally conformed to and parallel with those of the great general magnet.

The magnetic attraction is strongest in the direction perpendicular to the magnetic surfaces, and weakens in proportion to the magnitude of the angle of direction with the perpendicular, and consequently, is null when at a right angle with it. Hence the magnetic power seems concentrated at the poles, and the lateral powers are the weakest, as they originate only in the oblique direction of surfaces, or from surfaces inaccurately arranged.

If the south pole of a magnet be charged with filings of iron, and then approached to a bar of iron standing erect, part of the filings will drop off, because the poles of the same name, by exciting a contrary arrangement, weaken each other; but if the filings were suspended from the north pole of the magnet, it would take up still more of the filings, as the opposite poles strengthen each other; the uppermost pole of the iron in this case, becoming magnetic by position.

If the synonimous poles of two magnets of equal powers be approached to each other, if the powers be very unequal, the stronger immediately destroys the weaker, and inducing a contrary disposition attracts instead of repelling it; if the powers be less unequal, it requires a longer time; so also, if one be softer than the other. Even if their powers be equal, yet, after some time, the softer will yield to the harder. If both be equally hard, they only weaken each other.

If a magnet be cut in two, in a direction parallel to the axis, the parts before conjoined will now repel each other, because they still retain two synonimous poles.

But if the magnet be cut in two in a direction perpendicular to the axis, the two ends before conjoined will now attract each other.

If a magnetic wire be twisted, its powers are so disordered that one side of the wire, in some places of it, will be attracted and the other side repelled by the same pole of the magnet.

The power of the magnets (cæteris parib.) is in proportion to their surfaces, or as the squares of their diameters.-See Hutton's Magnetism, p. 72.

Communication.

When iron is applied to or brought within the sphere of activity of a particular magnet, it acquires the arrangement requisite to form the heteronymous pole, and thus becomes itself in some degree magnetic in its whole length, if this length be not totally disproportioned to the power of the particular magnet.

Hence the other end of such bar of iron acquires the arrangement of the opposite pole, according to the laws of crystallization already laid down.

Iron becomes magnetic either by contact or proximity to a magnet, or by position, or by internal commotion.

If a bar of iron be placed in a vertical position, its insensible fibrillæ gradually acquire the magnetic arrangement, so that after some years it becomes a complete magnet, its lowest part becoming a north pole, that is, pointing, when free, to the north, and the upper a south pole. In the south hemisphere the under end becomes a south pole.

A bar of iron not previously magnetic, does not acquire this disposition in the slightest degree while lying in a horizontal or nearly horizontal disposition, but if one end of it be raised, it immediately acquires it in some degree, as appears by approaching a magnetic needle to either end, because in that direction it is then exposed to activity of the polar ends of the great general magnet.

But if a bar of iron be heated, though only at one end, and while hot set in a vertical or nearly a vertical position, it will acquire the magnetic power much more readily.

So also if one end of a bar of iron not magnetic be struck against the ground, it will become in some degree magnetic, the lower end becoming a north pole, &c.; and if afterwards the other end be struck in the same manner, the poles will be reversed.

Hence it is evident that any motion communicated to the integrant particles of iron, placed in a proper situation, helps them to assume the magnetic disposition already impressed upon them by the great general magnet.

If the opposite poles of two magnets of equal power be approached to each other, the power of both is increased; and if one of them be more powerful than the other, it will increase the magnetic disposition, and consequently the power of the weaker.

Soft iron, as its parts are most easily moved, receives the magnetic disposition most easily; hard iron or tempered steel more difficultly, and cast iron, as being both hard and abounding in the heterogeneous particles, most difficultly and imperfectly.

Whatever way iron is applied to a magnet the magnetic power is diffused in the direction of its length. Hence it should seem that when a bar of iron is laid on a magnet, the contiguous ends of the iron become poles of the same name with those of the magnet to which they are contiguous, and hence may be derived the power of

armed magnets, for the surfaces of the armour immediately beneath those of the magnet impress a direction opposite to their own on those of the magnet, and consequently rectify such surfaces of the magnet as may have been inaccurately directed, and thus strengthen it.

To communicate the magnetic power to iron by friction against a magnet, it is necessary that its pole should slide along the magnet several times in the same direction, for if the directions be alternately opposed, the powers received will successively destroy each other.

A synonimous pole is formed at the end at which the friction begins to that of the magnet applied, and an opposite at that at which it terminates,

Appropriation to Iron.

It has of old been observed that the magnetic phenomena were peculiar to iron, and the reasons why they are so have been already assigned, but of late some semi-metals have been observed to partake of these properties, as nickel, cobalt and manganese; this has been thought to arise from a mixture of ferruginous particles, from which they can be scarcely freed, and with respect to manganese, and in many cases of the others also, this seems to hold true; but with respect to nickel, and in some instances of the others also, the magnetic properties they discover seem to me to proceed from their great attraction to iron, particularly when their particles are duly arranged, for then they are exposed to the power of the great general magnet, which acts on them in proportion to this arrangement and their affinity to iron.

Of Inclination and Declination.

These phenomena, which are so different in different parts of the globe, and even in different seasons and hours of the day, not being as yet noted with sufficient certainty and precision, I shall, for the present, decline entering into their explanation.

On the Electricity produced by Evaporation.

(Continued from page 186.)

IN the first paragraph of page 186, we have stated that "the curiositity of philosophers concerning Volta's experiments having become subsided, we hear little more of the production of electricity by evaporation till the celebrated experiments of Messrs. Armstrong and Pattison." Since the publication of that historical sketch, we have been reminded of the following series of experiments, on this subject, by the Rev. Abraham Bennet, prior to the year 1782.

"In a treatise on electricity by M. L'Abbe Hauy," says Mr. Bennet, "I find that since M. Volta's discovery of electricity produced by

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