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THOMS, PRINTER AND STEREOTY PER, 12, WARWICK SQUARE.

INTRODUCTION.

The value of science is best shown by its influence on the happiness and well-being of mankind. This is a truism which cannot be too often borne in mind by those who impart as well as by those who receive scientific instruction. It is a constant reference to this fact which so much enhances the real importance of our modern books of science over those of the ancient schoolmen. Deep metaphysical researches, frequently combined with an ingenious play on words, formed the prominent features in their ponderous folios; and the labour of a life-time was frequently productive of less real benefit to mankind than is now effected by the sale of a single unassuming tract really fitted to impart information. Costly domes and monkish establishments were also at one period considered as the only fanes worthy of disseminating the dogmas of scholastic science; but now its study is pursued in temples of another and far more ennobling kind. Temples dedicated to the worship of the Living God have not been considered as desecrated by being appropriated to the task of teaching man how to think rationally, as well as how to adore that great and good Being who has furnished such abundant materials for the delight and improvement of his creatures. In the course of this Introduction we purpose enquiring what are the species of scientific knowledge to which the humblest may aspire, and beyond which even the most wealthy rarely receive any essential advantage.

The structure of the universe, an acquaintance with the motions and general mechanism of the heavenly bodies, are subjects within the ken and may be rendered intelligible to the meanest capacities. The structure of the human body also, as well as its general functions, may readily be made the source of much delightful as well as profitable investigation. By combining a knowledge of optics with this branch of study, we are enabled to illustrate experimentally that most extraordinary of all natural structures—the human eye, and to show how, by the agency of certain crystalline bodies differing in their refractive power, an optical instrument may be formed which far exceeds in perfection all that the sages of ancient Greece or Romo bodied forth in optical science. This one instance may suffice to point out how important it is for the student to combine the study of nature's volume with that of the laborious deductions from experimental investigation.

Mechanical science offers at first view but few attractions to the student, and it certainly does not abound in the same moral lessons which may be acquired by a careful study of natural bistory; but even here a wide field of interesting investigation opens itself to the enquiring mind. He finds by a careful comparison of his most perfect mechanical agents with the frame-work of “nature's master-piece, man,” that they are but clumsy attempts to ARTS & SCIENCES.—Vol. I.

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imitate the every-day work of a Being who has surrounded us with examples of his own perfection, compared with which our most ingenious inventions and highest wisdom are but foolishness.

Even the mere historical enquirer may derive considerable advantage from this branch of study, as he may thus be enabled to point out the processes by which the various gigantic monuments of early superstition were erected, and to trace the history of edifices, and to fix a date for their erection, by simply referring to the mechanism of their construction.

The changes observable throughout nature result either from the mutual actions of the minute particles of bodies exerted at imperceptible distances, and producing a permanent alteration in their constitution, or from the action of separate masses, exerted at sensible distances, and producing alterations in their relative positions. In the first case, the phenomena belong to that department of experimental philosophy which is denominated chemistry. The study of the phenomena exhibited in the latter case constitutes natural philosophy, or rather that department of experimental science to which the term physics is applied.

Thus we see that the provinces of the chemist and natural philosopher are distinct. Whilst the business of the former is to ascertain and classify the primary elements of bodies, and to trace the effects and comparative degrees of agency of the forces exerted among the minute particles of matter, which are incessantly and insensibly producing permanent changes in the constitution of these bodies, that of the latter is to classify the effects and measure the intensity of those forces which are continually tending to produce changes in the relative positions of bodies as they exist in nature, without at all effecting any change in their constitution, and hence to explain the phenomena which result from different combinations and modifications of these forces.

In many cases, indeed, the same force may come within the province of each. Heat, for instance, is the object of the chemist's consideration, in as far as it is efficacious in changing the character of various substances, or in resolving compound bodies into their component elements, and uniting elementary substances into distinct compound bodies ; but it also comes within the cognizance of the natural philosopher, in as far as it is the cause of alterations in the dimensions of homogeneous bodies that may be subjected to accurate measurement or calculation.

The importance of keeping steadily in view the connection between the physical sciences may be best illustrated by comparing the ancient and modern systems of astronomy; for it was the study of terrestrial mechanics that first led to the discovery of the mechanism of the universe. And the reason why the ancient theories of astronomy were so fanciful and absurd is, that ancient philosophers went to investigate what was distant, before they made themselves acquainted with what is near, and tried to know the heavens while utterly ignorant of the earth. To show the hazard of investigating one science independently of another, we shall quote the words of Mrs. Somerville, who has written a valuable work on this subject.

“The theory of dynamics, founded upon terrestrial phenomena, is indispensable for acquiring a knowledge of the revolutions of the celestial bodies and their reciprocal influences. The motions of the satellites are affected by the forms of their primaries, and the figures of the planets themselves depend upon their rotations. The symmetry of their internal structure proves the stability of these rotatory motions, and the immutability of the length of the day, which furnishes an invariable standard of time; and the actual size of the terrestrial spheroid affords the means of ascertaining the dimensions of the solar system, and provides an invariable foundation for a system of weights and measures. The mutual attraction of the celestial bodies disturbs the fluids at their surfaces, whence the theory of the tides and the oscillations of the atmosphere. The density and elasticity of the air, varying

with every alternation of temperature, lead to the consideration of barometrical changes, the measurement of heights, and capillary attraction ; and the doctrine of sound, including the theory of music, is to be referred to the small undulations of the aërial medium. A knowledge of the action of matter upon light is requisite for tracing the curved path of its rays through the atmosphere, by which the true places of distant objects are determined, whether in the heavens or upon the earth. By this we learn the properties and nature of the sunbeam, the mode of its propagation through the ethereal fluid, or in the interior of material bodies, and the origin of colour. By the eclipses of Jupiter's satellites, the velocity of light is ascertained, and that velocity, in the aberration of the fixed stars, furnishes the only direct proof of the real motion of the earth. The effects of the invisible rays of light are immediately connected with chemical action ; and heat, forming a part of the solar ray, so essential to animated and inanimated existence, whether considered as invisible light or as a distinct quality, is too important an agent in the economy of the creation not to hold a principal place in the order of physical science, whence follows its distribution over the surface of the globe, its power on the geological convolutions of our planet, its influence on the atmosphere and on climate, and its effects on vegetable and animal life, evinced by the localities of organized beings on the earth, in the waters, and in the air. The connection of heat with the electrical phenomena, and the electricity of the atmosphere, together with all its energetic effects, its identity with magnetism, and the phenomena of terrestrial polarity, can only be understood from the theories of these invisible agents, and are probably principal causes of chemical affinities. Innumerable instances might be given in illustration of the immediate connection of the physical sciences, most of which are united more closely by the common bond of analysis, which is daily extending its empire, and will ultimately embrace almost every subject in nature in its formulæ.”

Expensive apparatus was formerly considered as essential to the study of science in any useful or tangible form; this however is as erroneous as it is to suppose that highly aristocratic establishments are essential to a well-grounded acquaintance with the principles of mathematical study. Who is there who has not heard of the unassisted labours of James Ferguson the shepherd boy? For him the figured volume of a Euclid, and the laborious investigation of a Newton, had appeared in vain, and he carved out a path of study for himself, unaided by any other light than that of his own powerful mind. His apparatus consisted of a few beads and a piece of thread; and with these he marked the relative positions of the heavenly bodies, and was enabled to show with tolerable accuracy the degrees of velocity with which they moved through space.

The useless profusion and complexity of apparatus formerly considered essential for experimental chemistry was a great obstacle to the advancement of this science in the last and preceding centuries; and it was only in the ducal palace of Magdeburg, and in the laboratories of our own Royal Society, that they were pursued with any success. paratus was first simplified by the celebrated Priestley, who showed that a few glass tubes and a Florence flask were all that was essential to discoveries of the greatest magnitude.

We may now however proceed to trace in detail the progress of some of the most important branches of science, commencing with the employment of those simple mechanical appliances which, on account of their general utility, must have evidently earliest engaged the attention of mankind. To render our view, however, intelligible to the reader, we must first examine the nature of attraction, and trace our acquaintance with that invisible yet allpervading energy, which acts alike on the vast frame of creation, guiding the planetary orbs in their course through space, and giving a form and character to the minutest drop of dew.

The great principle of attraction, in the Newtonian sense of it, seems to have been first examined by Copernicus. "As for gravity," says this distinguished philosopher, “I consider it

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as nothing more than a certain natural appetence that the Creator has impressed upon all the parts of matter, in order to their uniting or coalescing into a globular form, for their better preservation; and it is credible that the same power is also inherent in the sun, and moon, and planets, that those bodies may constantly retain that round figure in which we behold them.” Kepler calls gravity a mutual and corporeal affection between similar bodies, acting so as to produce their union; and he afterwards more positively asserts that no bodies whatever were absolutely light, but only relatively so, and consequently that all matter was subject to gravitation. Lord Bacon and Dr. Gilbert come next in order, though they added but little to our knowledge on the subject; and we must look to Newton for the first correct notions in connection with gravitation. The ancient attraction was supposed to be a kind of quality inherent in certain bodies themselves, and arising from their particular or specific forms. The Newtonian attraction is a more indefinite principle, and he states that he uses the words attraction, impulse, and propulsion to the centre, indifferently ; and cautions the reader not to imagine that by attraction he expresses the modus of the action, or the efficient cause thereof, as if there were any proper powers in the centres, which in reality are only mathematical points; or as if centres could attract. So that he considers centripetal powers as attractions, though, physically speaking, it were perhaps more just to call them impulses, and he concludes by observing that what he calls attraction “may possibly be effected by impulse, though not a common or corporeal impulse, or after some other manner unknown to us. Attraction, if considered as a quality arising from the specific forms of bodies, ought therefore, with the whole list of absurd occult qualities, to be exploded. But, when we have set these aside, there will remain innumerable phenomena of nature, and particularly the gravity or weight of bodies, or their tendency to a centre, which argue a principle of action seemingly distinct from impulse, where at least there is no sensible impulsion concerned. Nay, what is more, this action in some respects differs from all impulsion we know of, impulse being always found to act in proportion to the surfaces of bodies, whereas gravity acts according to their mass, and consequently must arise from some cause that penetrates or pervades the whole substance of the body. This unknown principle-unknown, we mean, in respect of its cause, for its phenomena and effects are most obvious—with all the species and modifications thereof, we call attruction, which is a general name under which all mutual tendencies, where no physical impulse appears, and which cannot therefore be accounted for from any known laws of nature, may be ranged."

Attraction may be divided, with respect to the law it observes, into two kinds. Firstly, that which extends to a sensible distance. Such are the attraction of gravity, found in all bodies; and the attraction of magnetism and electricity, found in particular bodies. For an account of the laws and phenomena of each, see their respective articles in this cyclopædia.

The attraction of gravity, called also among mathematicians the centripetal force, is one of the greatest and most universal principles in all nature. We see and feel it operate upon

bodies near the earth, and find by observation that the same power operates on the other planets, primary as well as secondary; and even that this is the very power by which they are all retained in their orbits, &c. And hence, as gravity is found in all the bodies that come under our observation, it is easily inferred, by one of the settled rules of philosophising, that it obtains in all others; and, as it is found to be as the quantity of matter in each body, it must be inherent in every particle, and hence every particle in nature is proved to attract every other particle.

From attraction then arises all the motion, and consequently all the mutation, in the physical world. By this heavy bodies descend, and light ones ascend; by this projectiles are directed, vapours and exhalations rise, and rains, &c., fall. By this rivers glide, the air presses, and the ocean swells, in obedience to the laws which regulate the tides.

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