probably entirely wanting among elastic fluids, such as air, and

the gases.

Thus, a small iron wire will hold a suspended weight of many pounds, without having its particles separated; the particles of water are divided by a very small force, while those of air, are still more easily moved among each other. These different properties depend on the force of cohesion with which the several particles of these bodies are united.

When the particles of fluids are left to arrange themselves according to the laws of attraction, the bodies which they compose assume the form of a globe or ball.

Drops of water thrown on an oiled surface or on wax-globules of mercury,-hail stones,-a drop of water adhering to the end of the finger,-tears running down the cheeks, and dew drops on the leaves of plants, are all examples of this law of attraction. The manufacture of shot is also a striking illustration. The lead is melted and poured into a sieve, at the height of about two hundred feet from the ground. The stream of lead immediately after leaving the sieve, separates into round globules, which, before they reach the ground, are cooled and become solid, and thus are formed the shot used by sportsmen.

To account for the globular form in all these cases, we have only to consider that the particles of matter are mutually attracted towards a common centre, and in liquids being free to move, they arrange themselves accordingly.

In all figures except the globe, or ball, some of the particles must be nearer the centre than others. But in a body that is perfectly round, every part of the outside is exactly at the same distance from the centre. Fig. 1.

Thus the corners of a cube, or square, are at much greater distances from the centre, than the sides, while the circumference of a circle or ball is every where at the same distance from it. This difference is shown by fig. 1, and it is quite obvious, that if the particles of matter are equally attracted towards the common centre, and are free to arrange themselves, no other figure could

In what substances is cohesive attraction the strongest? In what substances is it weakest? Why are the particles of fluids more easily separated than those of solids?

possibly be formed, since then every part of the outside is equally attracted.

The sun, earth, moon, and indeed all the heavenly bodies, are illustrations of this law, and therefore were probably in so soft a state when first formed, as to allow their particles freely to arrange themselves accordingly.

Attraction of gravitation.-As the attraction of cohesion unites the particles of matter into masses or bodies, so the attraction of gravitation tends to force these masses towards each other, to form those of still greater dimensions. The term gravitation, does not here strictly refer to the weight of bodies, but to the attraction of the masses of matter towards each other, whether downwards, upwards, or horizontally. The attraction of gravitation is mutual, since all bodies not only attract other bodies, but are themselves attracted.

Fig. 2.

Two cannon balls, when suspended by long cords, so as to hang quite near each other, are found to exert a mutual attraction, so that neither of the cords is exactly perpendicular, but they approach each other, as in fig. 2.

In the same manner, the heavenly bodies, when they approach each other, are drawn out of the line of their paths, or orbits, by mutual attraction.

The force of attraction increases in proportion as bodies approach each other, and by the same law it must diminish in proportion as they recede from each other.

Attraction, in technical language, is inversely as the squares of the distances between the two bodies. That is, in proportion as the square of the distance increases, in the same proportion attraction decreases, and so the contrary. Thus, if at the distance of 2 feet, the attraction be equal to 4 pounds, at the

What form do fluids take, when their particles are left to their own arrangement? Give examples of this law. How is the globular form which liquids assume, accounted for? If the particles of a body are free to move, and are equally attracted towards the centre, what must be its figure? Why must the figure be a globe? What great natural bodies are examples of this law? What is meant by attraction of gravitation? Can one body attract another without being itself attracted? How is it proved that bodies attract each other? By what law, or rule, does the force of attraction increase?

distance of 4 feet, it will be only 1 pound; for the square of 2 is 4, and the square of 4 is 16, which is 4 times the square of 2. On the contrary, if the attraction at the distance of 6 feet be 3 pounds, at the distance of 2 feet it will be 9 times as much, or 27 pounds, because 36, the square of 6, is equal to 9 times 4, the square of 2.

The intensity of light is found to increase and diminish in the same proportion. Thus, if a board a foot square, be placed at the distance of one foot from a candle, it will be found to hide the light from another board of two feet square, at the distance of two feet from the candle. Now a board of two feet square is just four times as large as one of one foot square, and therefore the light at double the distance being spread over 4 times the surface, has only one fourth the intensity.

one; B being four times the size of A.

This experiment may be easily tried, or may be readily understood by fig. 3, where c represents the candle, A the small board, and B the large

The force of the attraction of gravitation, is in proportion to the quantity of matter the attracting body contains.

Some bodies of the same bulk contain a much greater quantity of matter than others: thus, a piece of lead contains about twelve times as much matter as a piece of cork of the same dimensions, and therefore a piece of lead of any given size, and a piece of cork twelve times as large, will attract each other equally.

Capillary Attraction. The force by which small tubes, o porous substances, raise liquids above their levels, is called capillary attraction.

If a small glass tube be placed in water, the water on the inside will be raised above the level of that on the outside of

Give an example of this rule. How is it shown that the intensity of light increases and diminishes in the same proportion as the attraction of matter? Do bodies attract in proportion to bulk, or quantity of matter? What would be the difference of attraction between a cubic inch of lead, and a cubic inch of cork? Why would there be so much difference? What is meant by capillary attraction? How is this kind of attraction illustrated with a glass tube?

me tube. The cause of this seems to be nothing more than the ordinary attraction of the particles of matter for each other. The sides of a small orifice are so near each other, as to attract the particles of the fluid on their opposite sides, and as all attraction is strongest in the direction of the greatest quantity of matter, the water is raised upwards, or in the direction of the length of the tube. On the outside of the tube, the opposite surfaces, it is obvious, cannot act on the same column of water, and therefore the influence of attraction is here hardly perceptible in raising the fluid. This seems to be the reason why the fluid rises higher on the inside than on the outside of the tube.

A great variety of porous substances are capable of this kind of attraction. If a piece of sponge or a lump of sugar be placed, so that its lowest corner touches the water, the fluid will rise up and wet the whole mass. In the same manner, the wick of a lamp will carry up the oil to supply the flame, though the flame is several inches above the level of the oil. If the end of a towel happens to be left in a basin of water, it will empty the basin of its contents. And on the same principle, when a dry wedge of wood is driven into the crevice of a rock, and afterwards moistened with water, as when the rain falls upon it, it will absorb the water, swell, and sometimes split the rock. In Germany, mill-stone quarries are worked in this manner.

Chemical attraction takes place between the particles of substances of different kinds, and unites them into one compound.

This species of attraction takes place only between the particles of certain substances, and is not, therefore, a universal property. It is also known under the name of chemical affinity, because it is said, that the particles of substances having an affinity between them, will unite, while those having no affinity for each other do not readily enter into union.

There seems, indeed, in this respect, to be very singular preferences, and dislikes, existing among the particles of matter. Thus, if a piece of marble be thrown into sulphuric acid, their particles will unite with great rapidity, and commotion,

Why does the water rise higher in the tube, than it does on the outside? Give some common illustrations of this principle. What is the effect of chemical attraction? By what other name is this kind of attraction known? What effect is produced when marble and sulphuric acid are brought together?

and there will result a compound differing in all respects from the acid or the marble. But if a piece of glass, quartz, gold, or silver, be thrown into the acid, no change is produced on either, because their particles have no affinity.

Sulphur and quicksilver, when heated together, will form a beautiful red compound, known under the name of vermilion, and which has none of the qualities of sulphur or quicksilver.

Oil and water have no affinity for each other, but potash has an attraction for both, and therefore oil and water will unite when potash is mixed with them. In this manner, the well known article called soap is formed. But the potash has a stronger attraction for an acid than it has for either the oil or the water; and therefore when soap is mixed with an acid, the potash leaves the oil, and unites with the acid, thus destroying the old compound, and at the same instant forming a new one. The same happens when soap is dissolved in any water containing an acid, as the water of the sea, and of certain wells. The potash forsakes the oil, and unites with the acid, thus leaving the oil to rise to the surface of the water. Such waters are called hard, and will not wash, because the acid renders the potash a neutral substance.

Magnetic Attraction.-There is a certain ore of iron, a piece of which, being suspended by a thread, will always turn one of its sides to the north. This is called the loadstone, or natural Magnet, and when it is brought near a piece of iron, or steel, a mutual attraction takes place, and under certain circumstances, the two bodies will come together and adhere to each other. This is called Magnetic Attraction. When a piece of steel or iron is rubbed with a Magnet, the same virtue is communicated to the steel, and it will attract other pieces of steel, and if suspended by a string, one of its ends will constantly point towards the north, while the other, of course, points towards the south. This is called an artificial Magnet. The magnetic needle is a piece of steel, first touched with the loadstone, and then suspended, so as to turn easily

What is the effect when glass and this acid are brought together? What is the reason of this difference? How may oil and water be made to unite? What is the composition thus formed called? How does an acid destroy this compound? What is the reason that hard water will not wash? What is a natural magnet? What is meant by magnetic attrac tion? What is an artificial magnet? What is a magnetic needle?