earth, metallic substances, salt, &c., caleined and vitrefied.

The last great eruption of Etna, was in 1669; and the progress of the lava was at the rate of a furlong a day it destroyed, in forty days, the habitations of 27,000 persons; and of 20,000 inhabitants of the city of Catanea, only 3,000 escaped.

The other great volcanoes in Europe are, Vesuvius, and Hecla; but there are two or three hundred in different parts of the world.

XXIII. Magnetism.

649. The power of certain ores of iron to attract pieces of iron, was known by the Greeks; but accident led an Italian to discover, that if suspended on a centre, and allowed to turn in any direction, one end would constantly point northward, and, of course, the other southward.

This ore of iron was called loadstone; and it soon became evident, that the property of distinguishing the north and south, was of the highest utility to ships at sea.

550. In the course of time, it was discovered, that loudstone communicated its property o. turning northward to all pieces of iron and steel; and that these could communicate it to others, in a degree of strength proportioned to the number of magnets employed in transferring the property.

Natural magnets are not therefore now used; but needles are first made of the most convenient

shape, and the magnetic property communicated to them, by contact with other natural, or artificial, magnts.

551. The two poles or points of the magnetic needle have different properties, the south poles of magnets attracting the north poles of others; and the same poles acting repulsively towards each other; i. e. a north pole repels a north pole, and a south, a south pole.

A white heat destroys the polarity; and so will strokes of the hammer. But it will be acquired, by iron-bars that long stand upright, or that are heated red-hot, and left to cool in a polar direction.

552. If a magnet be laid on white paper, and some steel-dust be suffered to fall gently upon it, the dust will arrange itself on the paper in regular curves, under the influence of the magnetic attraction.

If the magnetic bar be bent round into the form of a horse-shoe, its poles in that position will attract and operate in a higher degree than when used separately; and the strength of all magnets is increased by thus keeping their powers in action.

553. Magnets do not point exactly north and south; but in different parts of the world, with a different inclination eastward or westward of the north; and different in each place, at dif ferent times.

To thou In London, at this time, the needle points 26 degrees to the west of the north; or, rather more westerly than north-north-west; and the incli

nation has increased to the west from due north, for 100 years past,

Nor does the needle lie parallel, or flat, in any place; but the north point is turned upward or downward, and in London at this time it dips 72 degrees.

Oba. --The cause of the phenomenon of magnetism has, hitherto, bailed the investigations of philosophers ; and the more we think of them, the greater becomes our embarrassment; but some accidental discovery will effect more than all reasoning; and till that occur, we must be content to class this, among the many unaccountable wonders of nature,

XXIV. Mathematics.'

554. Mathematics, or the mathematical sciences, are divided into

1. Para mathematics; containing arithmetic and geometry, which treat only of number and magnitude,

2. Mined mathematies; which treat of the properties of quantity applied to matter, as astronomy, geography, &c.

3. Speculative mathematics; which contemplate the proportions, relations, &e. of bodies, 4. Practical mathematics or their applica tion to the practical uses of life,

555. Geometry is an ancient, perfect, ank beautiful science; which enables us to determine the relations and proportions of superficies. and solids.

Superficies consist of figures of three sides, called triangles; of four sides, called quadran

gles, squares, parallelograms, and trapeziums; of five sides, called pentagons; of six sides, called hexagons; and of many sides, called polygons.

Superficies also are circles, ovals, or ellipses; sectors of circles, or parts cut out from the centre; and segments of circles, cut off by a strait line, called a chord

The above cut represents a Pentagon or Polygon of five sides, inscribed within a circle.

556. Solids are cubes regular and irregular; spheres; cylinders; cones; pyramids; and spheroids, or elliptical spheres.

A Cone cut obliquely to the base, forms an ellipsis; perpendicularly through the side, an hyperbola; and parallel to the side, a parabola. Angles are the corners, formed by the meeting of two lines.

A right angle is, when the lines are perpendicular to each other; an acute angle is less than a right angle; and an obtuse angle is greater than a right angle.

557. Parallel lines are those, which are equis distant; diagonals are those which cross figures from one angle to another.

Tangents are lines that only touch a circle in one point.

Every etrele is equal to 360 degrees; the three angles of every triangle, are equal to 180 degrees; the angles of every quadrangle, are equal to 360 degrees.

558. By means of a scale and a pair of compasses, all kinds of figures may be readily drawn