THE

CABINET OF ARTS.

CHAP. I.

NATURAL PHILOSOPHY,

OF NATURAL KNOWLEDGE.

WHEN we consider the immense variety of objects which present themselves to the eye, it must appear, at first sight, impossible to acquire even a general knowledge of their qualities and properties. The longest life, with the most vigorous mind, and the most persevering industry, would be wholly unequal to the task of examining even the individual objects of all kinds with which a single man is surrounded. Hence it arises that, by a natural law of the human mind, we are always attempting to arrange the objects of our inquiries into certain classes, according to certain common properties which they seem to possess. These are divided into other classes, with additional marks of distinction; and these are again subdivided into other sets, until we at last come down to the individual object. By this process the mind is assisted in its inquiries, and the communication of knowledge is rendered easy and useful. The study of all the objects of our senses may be divided into two branches, namely, Natural History, and Natural Philosophy. The first of these branches is occupied in arranging objects, and describing them in such a way that they may be easily and accurately distinguished from one another. It may be considered as a descriptive view of the material world, in a state of rest or inactivity, without taking into account the motions or actions of bodies upon one another. This is the first step in the progress of knowledge, and it constitutes Natural History. But the operations of nature are seldom at rest: change succeeds change; new combinations of objects are formed, and new productions make their appearance. The primary planets revolve round the sun as their centre; the secondary planets or moons perform similar revolutions round their primaries. The air of No 1.

B

the atmosphere presses on the surface of the earth, with a certain force. A stone when unsupported falls to the ground, in a line pointed towards the centre of the globe. Water deprived of a certain portion of its heat becomes solid in the form of ice: but if combined with a greater portion of heat than what is necessary to keep it fluid, water is converted into vapour, ascends into the atmosphere, is there again robbed of its extra heat, and returns to the earth in the form of rain; or if still more heat be taken away, it appears as snow or hail. A seed is placed in the ground, and if heat moisture and air be applied, it shoots and springs up: with the addition of light, if the operation be continued, it becomes a new plant, puts forth leaves and flowers, and produces seeds similar to that first placed in the ground. Now to determine what are these changes, to observe the laws by which such changes are effected, and to ascertain the measure and quantity of the effect produced, all this belongs to that branch of knowledge which is included under the general term Natural Philosophy, also called Physics. But of these changes and motions some are obvious to our senses, others entirely escape our observation. We see a stone fall to the earth, and experience tells us that it falls with a force proportioned to its weight, and the height from which it fell. The change or motion which takes place, when water puts on a solid form, when a fluid undergoes the process of formentation, or when a combustible body is burnt, all this is totally imperceptible by our senses. These changes and motions are too minute to be subject to our observation. The effect is produced before us, but of the process by which it is produced we are wholly ignorant. Thus Natural Philosophy is divided into two branches: the objects of the first are the sensible changes or motions observable in the material world, and the consideration of these objects is, strictly and properly speaking, Natural Philosophy or Physics: the second branch, which is employed in discovering the laws and ascertaining the effects of the insensible changes or motions of bodies, constitutes the science of Chemistry.

SECT. I.

MECHANIC POWERS.

The science of Natural Philosophy may be classed under seven ge neral heads, according to the nature of the subjects; proceeding from the grosser to the more refined substances failing under the cognisance of our senses. 1. Mechanics, from mechanè, art, contrivance, ingenuity; meanings here confined to the employment of solid bodies in mutual action, for the uses of mankind: the word machine, borrowed from the

• Fhesice is a term formed from the Greek word Physis signifying nature in general: hence physics express the study of all natural objects, and a physician is a person who has made a roficiency is that stody. In this comprehensive sense the term is employed in all countries where the Greek name is retained, excepting among ourselves, where, by a very improper restric tion of its meaning, a physician siguities only a person instructed and employed in one branch (certainty of the highest importance) of n: tural knowledge, that of the mature, cause and cure of the diseases of the human body. iwattention to this distinction occasions much confusion lu come undern works, translated from the languages of southern Europe, the French, the Spanish, and the haitau, in which the several names formed from physis signify not a curer of disecos, Got a natural piiksepter.

French, expresses equally the origin and the import of the term. 2. Hydrostatics, from hydor water and statizein to weigh. 3. Pneumatics, from pneuma spirit, breath, air, wind. 4. Acoustics, from acouein, to hear. 5. Optics, from optesthai, to see. 6. Electricity, from electron, amber. 7. Magnetism, from magnes, the lode-stone. To the Greek language we are indebted for all these terms, and for by far the greater number of all others, employed not only in ancient but in modern science.

OF MATTER AND ITS PROPERTIES.

Whatever acts upon our senses, either directly or by its perceptible effects, is termed matter. All sorts of matter possess these characteristic properties, viz, solidity or impenetrability, divisibility, and mobility : Certain kinds of bodies possess other qualities which are not common to all. By solidity in the present case we do not mean a state opposite to fluidity, but that property which all bodies possess, of not permitting any other substance to occupy the same place with them, at the same time. If a piece of stone or wood, &c. occupy a certain space, before you can put another in the same space, the stone or wood must be removed. Even fluids although they readily give way to pressure, when they have room to move about, yet if confined within certain bounds, will resist the entrance of another body, just as a solid would do. If a strong pipe be partly filled with water, and a wooden rod exactly fitting the pipe be introduced into it; when it touches the water it will stop, and no pressure, however strong, will make it occupy any part of the space filled by the water. Should the same experiment be made with a pipe empty as it is called, that is with nothing in it but common air, the rod may be pushed down a considerable way, but cannot be made to touch the bottom of the pipe; for although the air may be compressed into a very small space, yet when that space is filled no power can force the rod any lower down.

Solidity or impenetrability signifies, in common language, the property of bodies by which they resist separation into parts. Divisibility is that quality by which matter is capable of separation into parts that may be removed from one another. This divisibility is manifest in bodies of a sensible bulk; for they may be divided into halves, quarters, eighths, sixteenths, &c. without end, as however minute any part may be, still that part may be supposed to be again divided into halves, quarters, &c. The actual division of matter can be carried on to an amazing extent. A single grain weight of gold is hammered out by the goldbeaters, until it be so thin and broad as to cover 50 square inches. Each square inch may be cut into 200 slips, and each slip into 200 parts, each of which will still be visible to the naked eye: consequently a square inch contains 40,000 visible parts, which multiplied by 50 the number of inches into which the grain of gold is hammered, will give two millions of parts, which may be seen by the eye alone. But an instance still more striking is found in the manufacture of gold-lace. In this operation a bar of silver is gilded and then drawn out into wire, by passing it successively through holes of different sizes in steel plates. By these means the surface of gilded wire is prodigiously augmented, notwithstanding which the gold preserves an entire uniform appearance, without void spaces, even when examined with magnifying glasses.

It has been reckoned that sixteen ounces of gold, which in the form of a cube or die, would not measure one inch and a quarter a side, would completely gild a quantity of silver wire, sufficient to go round the globe of the earth, or about twenty-five thousand English miles. Mobility is that property by which matter is capable of being taken from one part of space and transported to another. Space is an abstract term to express the place occupied by material bodies, which, in proportion to the greater or less space they fill, are said to be more or less extended. Matter possesses another property called inertia, that is inertness, or inactivity, by which it would always continue in the state in which it is placed, whether of motion or of rest, unless prevented by some external force. That matter at rest can begin to move of itself, no one will suppose: but it is not so evident that, when once set in motion, it would continue that motion for ever, if not prevented. It is natural to imagine that all material bodies have a tendency to pass from a state of motion to a state of rest, because we see all motions upon this earth gradually decay, and at last wholly cease. This, however, is occasioned by the interruption given to the motion by the resistance of the air, the friction of one body against another, &c. for if these are diminished the motion will continue the longer, and if they were entirely removed it would continue for ever.

Motion. Philosophers are induced at times to give explanations of terms already so simple and so well understood as to be incapable of any farther elucidation. This is the case with the term motion, which has been defined to be a change of place, or the act by which a body is made to occupy different parts of space, at different successive points of time. In bodies around us we are sensible of two kinds of motion, the one when an entire body is moved from one place to another, as when a stone falls from the hand to the ground, when a bird flies across the air, when a ship sails upon the ocean. Another kind of motion, not less real, although not so evident to our senses, is that of the parts of bodies among themselves. By this imperceptible motion plants and animals increase in stature, and the various changes of natural substances are produced. The gradual changes occurring in all bodies, in the course of time, show that the parts are continually acting upon one another; and perhaps in even the most solid bodies no particles are absolutely at rest, but all in perpetual action and motion. Motion can

be communicated by one body to another: instances of this are perpetually passing before our eyes, and yet how this is done we are still totally ignorant; the fact is, however, so certain, that upon it the whole science of mechanics is founded. In considering motion several circumstances must be attended to. 1. The force producing the motion: 2. The quantity of matter in the moving body: 3. The velocity and direction of the motion: 4. The space moved over by the moving body: 5. The time employed in moving over this space: 6. The force with which it strikes another body opposed to it. The moving powers generally employed in giving motion to bodies are the action of men or other animals, wind, water, gravity or weight, the pressure of the air, and the elasticity of fluids and other bodies. The velocity of motion is measured by the space moved over in a certain time, or by the time employed in moving over a certain space. Hence the shorter the time and the greater the space moved over in it, the greater is the velocity on the contrary, the longer the time and the smaller the space

moved over in it, the less is the velocity. If a body move over a thousand feet in ten minutes, we say its velocity is that of a hundred feet in a minute. If we would compare the velocity of two bodies A and B, of which A moves 64 yards in 8 minutes, and B moves 144 yards in 12 minutes, dividing each space by its time, we have the velocity of A to that of B as 8 to 12.

A body in motion must every instant tend to some particular point. If its tendency be always toward the same point, the motion will be rectilineal or in a straight line: but if the point of tendency be continu ally changing, the motion will be curvilineal. When a body is acted upon by one force or by more, all tending one way, its motion will be in the direction of the moving force or forces: thus if a man by a rope draw a boat to him, the boat will move in the direction of the rope. But if two powers, tending different ways, act upon a body, it will not move in the direction of either, but in one between the two. The consideration of this composition or resolution of motion is of the utmost importance in mechanics. If, for instance, a ship, in a current of the sea setting due east, at the rate of three miles in an hour, be acted upon by the wind blowing due north, at an equal rate of three miles in the hour; it is evident that the ship will sail neither north nor east, but in a direction compounded of these two; and as the two moving forces are of equal power, the ship's course must be equally distant between north and east, that is to say, in the direction of north-east. The space moved over by the ship in one hour, will in this particular case, be the diagonal of a square of 3 miles a side, or 4.24 miles.

Motion is said to be accelerated when its velocity is continually increasing, and uniformly accelerated when the velocity is equally increased in equal times. Motion is said to be retarded when the velocity is continually diminishing, and uniformly retarded when the velocity is equally diminished in equal times. The regularly increasing velocity with which a body falls to the ground, is an example of accelerated motion, being caused by the constant action of the principle of gravity, by which all bodies on the earth have a tendency to move towards its centre. By various accurate experiments it has been found that a body falling freely will descend 16 feet 1 inch (or in round numbers 16 feet) in one second of time. At the end of this time the body will have acquired a velocity twice that of the 1st second, which added to the velocity of the 1st, will give a velocity three times as great as that in the first period. At the end of the 3d period the body will have gained a velocity four times the original, which in addition to that of the preceding second, will produce a velocity equal to five times that acquired in the first period. By this progress, the velocities in each successive second of time will increase in the proportion of the numbers 1, 3, 5, 7, 9, 11, 13, 15, &c.; so that the velocity at the end of the 3d instant will be 5 times that of the 1st; at the end of the 5th instant 9 times, at the end of the 8th instant 15 times, &c. Hence if a body fall through a space of 16 feet in the 1st second of its motion, at the end of the 2d, it will fall through 3 times 16 or 48 feet more, that is 64 feet from the point where it began to fall; at the end of the 3d, it will have fallen through 5 times 16 or 80 and with 64 in all 144 feet from the point where the fall began; and so on progressively. Of the nature of accelerated motion some notion may be formed from the