CHAMBERS'S INFORMATION FOR THE PEOPLE. CONDUCTED BY WILLIAM AND ROBERT CHAMBERS, EDITORS OF CHAMBERS'S NUMBER 51. NEW AND IMPROVED SERIES. NATURAL PHILOSOPHY. PRICE 1d. bodies may have the same volume, but possess very different figures. Thus, two masses of matter may have the same volume, although the one be round and the other be square. NATURAL PHILOSorur is a term of wide import, and has | a reference to all those branches of physical science which treat of existing substances, their motions, their mutual connexion, and their influence on each other. In this enlarged sense it may be considered as embrac- Matter is divisible into parts, and these parts may ing astronomy, mathematics, dynamics, hydrostatics, again be subdivided into other parts. By this is meant geology, chemistry, opties, botany, in short, a vast range divisibility or separability. To the practical subdivision of human knowledge, which for the sake of convenience of matter there seems to be no assignable limit; and is usually divided into distinct branches of science. In many of the instances of it which may be found in phiits more limited and ordinary meaning, the term applies losophical investigations almost exceed credibility. The only to inorganic substances, and the laws which regu- thinnest part of a soap-bubble, which is a thin shell of late their connexion with each other, but without alte-water and the matter of soap, does not exceed in thickration of character; and it is this most important branch of knowledge, which in reality is the basis of all others, of which we now propose treating. We shall commence with an explicit definition of the meaning of the term substances or matter, it being necessary that this be clearly understood. MATTER AND ITS PROPERTIES. Matter-or that of which all bodies are composed whose existence is made known to us by means of the senses or by the test of philosophic experiment-is possessed of various properties, some of which are essential to its existence, while others are only accidental or confingent. The essential properties of matter are Impenetrability, Extension, Figure, Divisibility, Inertia, and Attraction. Impenetrability is that quality of bodies, in virtue of which each occupies a certain portion of space, and excludes other bodies from existing in the same place at the same instant. In the usual sense, we call any hard body, such as a stone, impenetrable, because it firmly resists our efforts to pierce it. But as it is understood philosophically (although we can condense, pierce, and remove the greater number of them), all bodies are alike impenetrable, because they equally possess the property of excluding other substances from the spaces which they occupy. This, in fact, is saying no more than that two things cannot be in the same place at once, which is a self-evident truth, whether we apply it to a single particle of matter or a large mass. Every body, or portion or particle of matter, possesses a certain extension or magnitude. It is impossible to form a conception of matter, however minute may be the particle, without connecting with it the idea of its having a certain bulk, and filling a certain extent í space. In common phraseology, we express this property of bodies by the word size or volume. The next property demanding our attention is the figure of bodies. Figure or form is the result of extension, for we cannot have the idea of a body possessing length and breadth, without its having some kind of figure, however irregular. The volume of a body has no relation to its figure. Bodies which have the vame figure may possess very different volumes; and ness the 2,500,000th part of an inch. The useful arts, also, furnish many striking examples; but it is in the organised world that the most astonishing proofs of the extreme divisibility of globules, or particles of matter, are to be found. Animalcules that is, animals which are so small as to be invisible to the naked eye, and which, by means of microscopes, are seen floating in water-are in some cases so minute, that it would require a million of them to form the bulk of a grain of sand. As these animalcules possess, in every case, a perfect organisation to enable them to perform all the functions of life, the smallness of their different parts, and the extreme minuteness of the particles of matter which compose them, are too exquisite to be made the subject of calculation: the imagination is lost in the contemplation of their wonderful economy. The effluvium or odour which excites the sensation of smell, consists of an incalculable number of particles of matter floating in the atmosphere, and so minute as to be altogether invisible to the eye. These particles are not more remarkable for their inconceivably small size than for the length of time which they will remain in suspension in the atmosphere, or in connexion with some particular place. The effluvium given forth by a single grain of musk has been known to perfume a large apartment for twenty years, and yet at the expiry of that period there was no sensible diminution of the little mass of matter from which the smell had proceeded. The diffusion of particles of matter invisible to the naked eye, is also obvious in the case of the melting of a piece of sugar in our tea; the solid mass of the sugar disappears, and the particles of which it was composed are diffused in the liquid. There is a similar diffusion of particles of salt in the ocean. When we look through a glass full of sea water, we perceive that it is pure and limpid; but if we pour the water into a vessel on the fire, and boil it, we shall at length discover that, while the liquid has escaped in the form of vapour, the particles of salt it held in solution remain incrusted on the vessel. Particles of matter are never destroyed or lost, although they may disappear from our immediate observation. Under certain circumstances, the particles may again be collected into a body without change of form. Mercury, water, and many other substances, may be converted into vapour, or distilled in close vessels, without any of their particles being lost. In such cases, there is no decomposition of the substances, but only a change of form by the heat; and hence the mercury and water assume their original state again on cooling. When bodies suffer decomposition or decay, their elementary particles, in like manner, are neither destroyed nor lost, but only enter into new arrangements or combinations with other bodies. When a piece of wood is heated in a close vessel, such as a retort, we obtain water, an acid, several kinds of gas, and there remains a black, porous substance, called charcoal. The wood is thus decomposed, or destroyed, and its particles take a new arrangement, and assume new forms; but that nothing is lost is proved by the fact, that if the water, acid, gases, and charcoal, be collected and weighed, they will be found exactly as heavy as the wood was, before distillation. In the same manner, the substance of the coal burnt in our fires is not annihilated; it is only dispersed in the form of smoke, or particles of culm, gas, and ashes or dust. Bones, flesh, or any animal substance, may in the same manner be made to assume new forms, without losing a particle of the matter which they originally contained. The decay of animal or vegetable bodies in the open air, or in the ground, is only a process by which the particles of which they were composed change their places and assume new forms. The decay and decomposition of animals and vegetables beneath the surface of the earth, fertilise the soil, which nourishes the growth of plants and other vegetables; and these, in their turn, form the nutriment of animals. Thus is there a perpetual change from death to life, and from life to death, and as constant a succession in the forms and places which the particles of matter assume. Nothing is lost, and not a particle of matter is struck out of existence. The same matter of which every living animal and every vegetable was formed in the earliest ages, is still in existence. As nothing is lost or annihilated, so it is probable that nothing has been added, and that we ourselves are composed of particles of matter as old as the creation. In time, we must in our turn suffer decomposition, as all forms have done before us, and thus resign the matter of which we are composed, to form new existences. vidual be standing in the same position as formerly, the tendency which his body has to move forward-for it acquired the same motion as the carriage by which it was borne along-will cause him to fall in the opposite direction. The following is a familiar example of the inertia of matter:-Upon the tip of the finger let a card be balanced, and a piece of money-say a shilling-laid upon it. Let the card then be smartly struck, and it will fly from beneath the coin, leaving it supported upon the finger. This arises from the inertia of the metal being greater than the friction of the card which passes from beneath it. Coursing, or hare-hunting, affords a striking illustration of inertia. In that field sport, the hare seems to possess an instinctive consciousness of the existence of this law of matter. When pursued by the greyhound, it does not run in a straight line to the cover, but in a zigzag one. It doubles, that is, suddenly changes the direction of its course, and turns back at an acute angle with the direction in which it had been running. The greyhound, being unprepared to make the turn, and therefore unable to resist the tendency to persevere in the rapid motion which it has acquired, is impelled a considerable distance forward before it can check its speed and return to the pursuit. But, in the mean time, the hare has been enabled to shoot far ahead in the other direction; and although a hare is much less fleet than a greyhound, by this scientific manoeuvring it often escapes its pursuer. Those who have witnessed horseracing, may have observed that the horses shoot far past the winning-post before their speed can be arrested. This is also owing to the inertia of their bodies. We have now arrived at a most important property, attraction, which it is desirable should be carefully studied. It is a fundamental law of nature, ascertained by Sir Isaac Newton, that every atom or particle of matter has a tendency to approach or to be attracted towards another atom or particle. This forms one of the leading principles in modern natural philosophy. Experience and observation demonstrate that this power of mutual attraction pervades all material things, and, though unseen except in its results, is ever present with us is the cause of particles of matter adhering to each other, and forming solid masses-of these masses assuming in many instances a round or globular form -of the falling of bodies to, and their stability on, the Inertia means passiveness or inactivity. Thus, matter earth-and is one of the causes of the whole of the is perfectly passive in submitting to any condition in planetary bodies moving in their paths in the heavens. which it is placed, whether of rest or motion. When Attraction is of different kinds, although some of at rest, it shows an inability or reluctancy to move; these may be merely modifications of others, and has and when in motion, it shows an equal inability or re-received different names according to the circumstances luctancy to come to a state of rest. It is obvious that under which it acts. The force which keeps the para rock on the surface of the earth never changes its ticles of matter together, to form bodies, or masses, is position in respect to other things on the earth. It has called attraction of cohesion. That which inclines difof itself no power to move, and would therefore for ever ferent masses towards each other, is called gravitation, lie still, unless moved by some external force. Now, or attraction of gravitation. That which causes liquids it is just as true that inert matter has no power to bring to rise in tubes, or in very confined situations, is called itself to rest when once put in motion, as that it cannot capillary attraction. That which forces the particles put itself in motion when at rest; for having no life, of different kinds of matter to unite, is called chemical it is perfectly passive both to motion and rest, and attraction. That which causes the magnetic needle to therefore either state depends entirely upon external point constantly towards the poles of the earth, is magnetic attraction. And that which is excited by friction in certain substances, is known by the name of electrical attraction. circumstances. Many instances might be given of the tendency which matter has to remain in the condition in which it happens to have been already placed. The following are Attraction of cohesion acts only at insensible disamong the most instructive:-When the sails of a ship tances, as when the parties of bodies apparently touch are loosened to the breeze, slowly and heavily at first each other. This kind a etion y he described the vessel gets into motion, but gradually its speed in- as the quality in nature his cannes matiCohere creases, as the force by which it is impelled overcomes or stick together. It is mu stroager in some by the inertia of its mass. A great force is necessary at than in others. It is stronger in the metals then first to set a vehicle in motion; but when once this is most other substances, and in some of the cha effected, it goes onward with comparative ease, so that, stronger than in others. In general, it is most poweriu. in fact, a strong effort is necessary before it can be among the particles of solid bodies, weaker among those stopped. If a person be standing in it when it is sud- of fluids, and least of all, or almost entirely wanting, denly set a-going, his feet are pulled forward, whilst among elastic fluids, such as air and the gases. Thus, his body, obeying the law of inertia, remains where it a small iron wire will hold a suspended weight of many ras, and he accordingly falls backwards. On the other pounds, without having its particles separated; the parid, if the vehicle be suddenly stopped, and the indi-ticles 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 a body can be suspended in the air in a fluid state, they will, if not under the attractive influence of some other body, arrange themselves, by virtue of the same law, around a centre, and take a spherical or round form. Thus, a small quantity of dew suspended on the point of a thorn or leaf, becomes a globule, because in that case the attraction of the particles towards their own centre is greater than the attraction of any neighbouring body. Tears running down the cheeks, drops of rain, and hail, are all examples of this tendency in insulated fluid bodies to assume the globular form. When two perfect globules of mercury are brought into contact, they instantly unite together, and form one spherical drop. 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. Each stream of lead, immediately after leaving the sieve, separates into little globules, which, before they reach the ground, are cooled and become solid: thus is 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 consequence of this law of nature, it is considered probable that the planetary bodies, including our earth, were originally in a fluid state that, in that state, they unavoidably assumed a spherical form, and were then hardened into their present consistency. The force by which small tubes, or porous substances, raise liquids above their levels, is called capillary attraction, from capilla, the Latin word for a hair. In a wet tea-cup, or other vessel containing liquid, you may perceive the liquid at the sides rising above the level of that of the other parts of the surface; this is caused by attraction. If two glass plates be brought very near each other, so as to stand parallel with their flat sides in almost mutual contact, and then their lower end be dipped into a vessel of water, the fluid will rise up between the plates, and the height to which it rises will be greater the nearer the plates are to each other. The water rises very little on the outsides of the plates, for this attraction is insensible at even moderately small distances. If a glass tube, with an exceedingly small or capillary bore, be dipped in water, the fluid will rise in the interior of the tube; and the smaller the bore, the higher does the water ascend. 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 reck, and afterwards moistened with water, as when the rain falls upon it, it will absorb the water, swell, and sometimes split the rock. of treatises, they do not require particular notice here, and we proceed to consider the kind of attraction which seems to unite all ordinary masses and particles of matter. Reference is here made to the 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 those masses towards each other to form others of still greater dimensions. 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 in-* creases, 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 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 four times the surface, has only one-fourth the intensity. The gradual diminution of attraction as the distance increases, is exemplified in the following table. In the upper line, the distance is expressed by progressive numbers; in the lower corresponding squares the diminution of attraction is indicated by the common arithmetical fractions. It is here seen, that at the distance of 8, the attractive force is diminished to a 64th part of what it was at 1. The attractive force of matter is also in proportion to the numbers of the atoms of matter which a body contains: the attraction, therefore, does not proceed from the mere surface of a body, but from all the particles which individually compose it. 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. The attractive power of any mass acts from the centre. At all equal distances from the centre, the attractive power is equal; for instance, in a body perfectly spherical, the attraction to the centre would be the same at all parts of the surface. The distance of the centre of a sphere from its surface is called the semi-diameter of that sphere-that is, the It is this kind of attraction which is supposed to be half of its thickness. At a point as far from the surone of the causes of springs of water in the earth. The face of a sphere as its semi-diameter, its attractive water creeps up by capillary attraction through porous power is diminished to a fourth. At three distances, beds of sand, small stones, and crevices of rocks, and the attraction is a ninth; at four distances, a sixteenth; in this manner reaches the surface even at great heights. and so on. When we wish, therefore, to ascertain the The lower parts of the walls, and also the earthen relative amount of the attraction which any mass of floors of cottages, are in the same manner apt to matter exercises over another, the rule is, to inquire become damp, by the attraction of the moisture upwards how many semi-diameters of the one the other is disfrom the ground. Hence the necessity for clearing away tant from it, and then to multiply that number by itself. all wet earthy matter from the foundations of houses. The result shows how many times the attraction at this Besides these varieties of attraction, there are, as distance is less than at the surface of the former. The already said, chemical, magnetic and electric attrac-moon, for instance, is distant 240,000 miles from the tion, but as these are respectively alluded to under the heads Chemistry and Electricity in the present series earth, or as much as sixty semi-diameters of the earth; 60 multiplied by 60 gives 3600; consequently, the at traction exercised by the earth upon the moon is a 3600th part of what it would exercise upon the same mass at its own surface. If the earth were a perfectly spherical body, its attraction would be equal every where at the level of the sea. As the surface at the pole is thirteen miles nearer the centre than the surface at the equator, the attraction is stronger at the former than at the latter place: it gets proportionally weaker as we advance towards the equator, on account of the increase of distance from the centre. Hence, a mass of iron which is considered a pound weight in Britain, would be less than a pound on the coast of Guinea, and more than a pound in Greenland, for weight is only a result of attraction. If we ascend a mountain, the effect is the same as if we proceed towards the equator: we are always getting farther from the centre of attraction, and consequently weights become lighter. On the top of a hill four miles high, a ball of four thousand pounds weight would be found to be two pounds lighter. Pressure downwards, or weight, is in philosophical language termed GRAVITY, and under that head it is hereafter treated, in connexion with the phenomena of falling bodies. The attraction of bodies is mutual, and in proportion to the quantity of matter they contain. Therefore, any body, however small, exerts some degree of attraction upon the mass of the earth. Any body which comes immediately under our observation, is so small in comparison to the earth, that its attractive force is altogether unappreciable; but if the body were of great density, and of dimensions approaching to those of the earth, then we should see the earth rise to meet the body, or fall towards the body. The heavenly bodies, when they approach each other, are drawn out of the line of their paths, or orbits, by mutual attraction. It is found by experiment, that a plumb-line suspended in the neighbourhood of a mountain, is sensibly attracted towards the mountain from the true vertical line. The mutual attraction of matter is exemplified by the diminution of the weight of bodies as we penetrate into the earth. At the depth of a mile, a body weighing a pound would be found to be lighter than at the surface. This is in consequence of the attraction of the matter of the shell of the earth, which is exterior to the point, being nothing, in consequence of the attractions of its particles on this point counteracting each other; and hence the only efficient attraction on it arises merely from the smaller sphere below the point; and, therefore, the nearer the point is to the centre, the less is this internal sphere, and the less therefore is its attraction on the point. Were we to proceed to the centre of the earth, we should there find that weight altogether ceased, because the attractive power would be equal on all sides. Were there a cavity at the earth's centre, the body would hang suspended in space. The attraction of the earth's mass performs an important function, in binding the atmosphere, which is an elastic fluid, around the surface of our planet, and in causing the air to perforate every open crevice and pore in the superficial substances of the globe. The attractive force, in this respect, produces what is called atmospheric pressure, the air being pulled or pressed down by a force equivalent to about 15 lbs. on the square inch, at the level of the sea, and diminishes in proportion to the distance above that common level. THE REPULSIVE QUALITY IN MATTER—HEAT. While attraction tends to unite and compress the particles of matter, there is another and equally universal principle, known in familiar language by the appellation of heat, the tendency of which is to keep the particles of matter at a certain degree of expansion. Heat is often, in scientific works, named caloric, from the Latin word for heat. Heat pervades all things, but some in greater degrees than others. Even ice has been found to contain a certain portion of heat. In fact, there is no such thing in nature as positive cold. The things which seem cold to us, are only under a low gree of heat. The absolute nature of this universal principle is unknown. We only know it by its effects, and the sensations it produces. Some have conjectured that it is a fluid; others think it is a quality or affection of matter, resulting from electrical action. From its producing no sensible difference in the weight of any substance, it has been called an imponderable body. When the heat of any particular substance, as ice, stone, or wood, is not sensible to us, it is called latent (that is, concealed) heat. We may very readily detect its presence in a piece of wood or metal by rubbing or friction. If a button, for instance, be rubbed on a table, it will soon become too hot to be held by the fingers. In like manner, the axle of any carriage-wheel soon becomes hot, unless the friction is prevented by grease. Heat, in its extreme form, becomes fire. Thus, if an ungreased wheel be rapidly turned for a long time on its axle, so much heat will be excited that both wheel and axle will burst into a flame. The effects of powerful friction are known to savage nations, among whom it is common to produce fire by rubbing two sticks together. Two pieces of flint struck together, or a flint struck hard upon a piece of iron, evolve sparks of fire. By such means, many important purposes are served; for instance the discharge of fire-arms. Fire can also be evolved from the common atmosphere, by compressing a quantity of it suddenly in a tube, at the bottom of which a piece of tinder has been placed. The evolution of heat by these means, and other circumstances, lead to the conclusion that heat is an element mixed up with the atoms of matter, which it serves to keep at a lesser or greater distance from each other. Thus, as we squeeze the pores of a sponge together, and disengage the liquid which they held in cohesion, so, when squeezing or rubbing a portion of matter, do we disengage the heat which it retained amongst its component atoms. In all cases of the development of heat by pressure, hammering, and friction, the cause is the squeezing together of atoms which had been kept asunder by the latent fluid, and which fluid must, as a matter of necessity, come forth and make itself sensibly felt or seen. Heat, then, is a principle of repulsion in nature, and in this capacity its uses are as obvious as those of terrestrial gravitation, to which it apparently acts as a counterpoise. The force of attraction is so powerful, that, unless for a counteracting principle of repulsion, all bodies would hasten into close contact; there would be no air, no water, no vegetable or animal life; all would be an uniform dead solid mass, and the earth itself might perhaps be reduced to a small portion of its present bulk. Heat, by pervading all things, modifies attraction, and, according to circumstances, regulates the density or solidity of bodies. Hence we possess in nature a beautiful variety of substances, some solid and hard, like stone and marble; others soft, or of the jelly form; a third class liquid, like water; and a fourth kind aëriform, or gaseous. Heat expands most bodies in proportion as it is increased in quantity, and they become solid in proportion as it is withdrawn. Water may thus be either expanded into the form of vapour or steam, or hardened into ice. When withdrawn, the process of cooling is said to take place; cold being simply a state of abstraction or comparative absence of heat. Heat is diffused or communicated by conduction and radiation. When it passes slowly from one portion of matter to another in contact with it, it is said to be conducted; and the process, in scientific language, is termed the conduction of caloric. Metals are the best conductors, then liquids, and lastly, gases. Gold, silver, and copper, are the best conductors among solids; glass, bricks, and many stony substances, are very bad conductors; and porous spongy substances, as charcoal, hair, and fur, are the worst. Clothing is generally made of bad conductors, that the heat of the body may not be conducted quickly to the surrounding air. Furnaces, where great heat is required, are built with porous bricks, which are very effectual in preventing the |