learr, that light flies at the rate of nearly twelve millions of miles every minute-that it moves in straight lines that its particles may be several thousands of miles distant from each other-that every visible body emits particles of light from its surface, in all directions-that the particles of light are exceedingly small; for a lighted candle will fill a cubical space of two miles every way with its rays, before it has lost the least sensible part of its substance; and millions of rays, from a thousand objects, will pass through a hole not larger than the point of a needle, and convey to the mind an idea of the form, position, and colour of every individual object—that the intensity or degree of light decreases, as the square of the distance from the luminous body increases; that is, at two yards' distance from a candle, we shall have only the fourth part of the light we should have at the distance of one yard; at three yards' distance, the ninth part; at four yards, the sixteenth part, and so on-that glass lenses may be ground into the following forms, plano-convex, plano-concave, double convex, double concave, and meniscus, that is, convex on one side, and concave on the other-that specula, or mirrors, may be ground into either a spherical, parabolical, or cylindrical form-that, by means of such mirrors and lenses, the rays of light may be so modified as to proceed either in a diverging, converging, or parallel direction, and the images of visible objects represented in a variety of new forms, positions, and magnitudes-that every ray of white light may be separated into seven primary colours: red, orange, yellow, green, blue, indigo, and violet-that the variegated colouring which appears on the face of nature is not in the objects themselves, but in the light which falls upon them that the rainbow is produced by the refraction and reflection of the solar rays in the drops of falling rain-that the rays of light are refracted, or bent out of their course, when they fall upon glass, water, and other mediums-that the light of the sun may be collected into a point or focus, and made to produce a heat more intense than that of a furnace*-that the rays from visible objects, when reflected from a concave mirror, converge to a focus, and paint an image of the objects before it, and that when they pass through a convex glass, they depict an image behind it.

• This is produced by means of lenses, or mirrors of a large diameter, called burning-glasses. By these Instruments the hardest metals, on which common fires, and even glass-house furnaces, could produce no effect, have been melted in a few seconds. M. Villette, a Frenchman, nearly a century ago, constructed a mirror, three feet eleven inches in diameter, and three feet two inches in focal distance, which melted copper ore in eight seconds, iron ore in twentyfour seconds, a fish's tooth in thirty-two seconds, cast iron in sixteen seconds, a silver sixpence in seven seconds, and tin in three seconds. mirror condensed the solar rays 17,257 times, a degree of heat which is about four hundred and ninety times greater than common fire. Mr. Parker, of London, constructed a lens three feet in diameter,

13

This

On these and other principles demonstrated by this science, the Camera Obscura, the Magic Lantern, the Phantasmagoria, the Kaleidoscope, the Heliostata, the Micrometer-Spectacles, Opera-Glasses, Prisms, single, compound, lu cernal, and solar Microscopes, reflecting and refracting Telescopes, and other optical instru ments, have been constructed by means of whic1 the natural powers of human vision have beer wonderfully increased, and our prospects nito the works of God extended far beyond what former ages could have conceived.

VI. Electricity. This name has been given to a science which explains and illustrates the operations of a very subtile fluid called the electric fluid, which appears to pervade every part of nature, and to be one of the chief agents employed in producing many of the phenomena of the material world. If a piece of amber, sealing wax, or sulphur, be rubbed with a piece of flannel, it will acquire the power of attracting small bits of paper, feathers, or other light sub stances. If a tube of glass, two or three feet in length, and an inch or two in diameter, be rubbed pretty hard, in a dark room, with a piece of dry woollen cloth, besides attracting light substances, it will emit flashes of fire, attended with a crackling noise. This luminous matter is called electricity, or the electric fluid. If a large globe or cylinder of glass be turned rapidly round, and made to rub against a cushion, streams and large sparks of bluish flame will be elicited, which will fly round the glass, attract light bodies, and produce a pungent sensation if the hand be held to it. This glass, with all its requisite apparatus, is called an electrical machine. It is found, that this fluid will pass along some bodies, and not along others. The bodies over which it passes freely are, water, and most other fluids, except oil and the aerial fluids; iron, copper, lead, and in general all the metals, semimetals, and metallic ores; which are, therefore, called conductors of electricity. But it will not pass over glass, resin, wax, sulphur, silk, baked woods, or dry woollen substances; nor through air, except by force, in sparks, to short distances. These bodies are, therefore, called non-conductors,

The following facts among others, have been ascertained respecting this wonderful agent :That all bodies with which we are acquainted possess a greater or less share of this fluid-tha. the quantity usually belonging to any body produces no sensible effects; but when any surface and six feet eight inches focus, which weighed 212 pounds. It melted twenty grains of gold in four seconds, and ten grains of platina in three seconds. The power of burning glasses is as the area of the lens directly, and the square of the focal distance in versely-or, in other words, the broader the mirror or lens, and the shorter the focal distance, the more intense is the heat produced by such instruments. A globular decanter of water makes a powerful burning-glass; and house furniture has been set on fire by incautiously exposing it to the rays of th

sun.

stances, have been inflamed-charcoal has been made to burn with a most brilliant and beautiful white flame-water has been decomposed into i's elementary parts-metals have been melted and set on fire-fragments of diamond, charcoal, and plumbago, have been dispersed, as if they had been evaporated-platina, the hardest and heaviest of the metals, has been melted as readily as wax in the flame of a candle-the sapphire, quartz, magnesia, lime, and the firmest compounds in nature, have been made to enter into fusion. Its effects on the animal system are no less surprising. When applied to a fowl or a rabbit, immediately after life is extinct, it produces the most strange and violent convulsions on the nervous and muscular system, as if the vital functions were again revived, and when applied to the human body after death, the stimulus has produced the most horrible contortions and grimaces in the muscles of the head and face, and the most rapid movements in the hands and feet. The galvanic agency enables us to account for the following among other facts:-Why porter has a different and more pleasant taste, when drunk out of a pewter vessel, than out of glass or earthenware, why a silver spoon is discoloured when used in eating eggs,-why the limbs of people, under amputation, are sometimes convulsed by the application of the instruments, why pure mercury is oxydized when amalgama ted with tin,-why works of metal, which are soldered together, soon tarnish in the places where the metals are joined, and why the cop per sheathing of ships, when fastened with iron nails, is soon corroded about the place of contact. In all these cases a galvanic circle is formed, which produces the effects. We have reason to believe, that, in combination with the discoveries which modern chymistry is daily unfolding, the agencies of this fluid will enable us to carry the arts forward towards perfection, and to trace the secret causes of some of the sublimest phenomena of nature.

VIII. Magnetism.-This department of philosophy describes the phenomena and the properties of the loadstone, or natural magnet. The natural magnet is a hard dark-coloured mineral body, and is usually found in iron mines. The following are some of its characteristic proper ties:-1. It attracts iron and steel, and all substances which contain iron in its metallic state. 2. If a magnet be suspended by a thread, or nicely poised on a pivot, or placed on a piece of wood, and set to float in a basin of water, one end will constantly point nearly towards the north pole of the earth, and the other towards the south; and hence those parts of the magnet have been called the north and south poles. 3. When the north pole of one magnet is presented near to the south pole of another, they will at wact each other; but if the north pole of one be presented to the north pole of another, or a south 39

pole to a south, they will repel each other. 4. A magnet placed in such a manner as to be entirely at liberty, inclines one of its poles to the horizon, and of course elevates the other above it. This property is called the dipping of the magnet. 5. Magnets do not point directly north and south; but in different parts of the world with a different declination eastward or westward of the north; it is also different at the same place at different times. In London, and in most places of Great Britain, the magnetic needle, at present, points about 24 degrees to the west of north. For more than 160 years it has been gradually declining from the north to the west; but seems of late to have begun its declination to the eastward. 6. Any magnet may be made to communicate the properties now mentioned to any piece of iron or steel. For example, by gently rubbing a penknife with a magnet, it will be immediately invested with the property of attracting needles, or small pieces of iron or steel. 7. Heat weakens the power of a magnet, and the gradual addition of weight increases the magnetic power. 8. The properties of the magnet are not affected either by the presence or the absence of air; and the magnetic attraction is not in the least diminished by the interposition of any bodies except iron. A magnet will equally affect the needle of a pocket compass when a thick board is placed between them as when it is removed. It has been lately discovered, that the violet rays of the solar spectrum, when condensed with a convex glass, and made to pass along a piece of steel, have the power of communicating to it the magnetic virtue.

The cause which produces these singular properties of the magnet has hitherto remained a mystery; but the knowledge of the polarity of the magnet has been applied to a most important practical purpose. By means of it, man has now acquired the dominion of the ocean, and has learned to trace his course through the pathless deep to every region of the globe. There can be little doubt that magnetism has an intimate connexion with electricity, galvanism, light, heat, and chymical action; and the discoveries which have been lately made, and the experiments which are now making by Morichini, Oersted, Abraham, Hansteen, Barlow, Beaufoy, and Scoresby, promise to throw some light on this mysterious agent, and on the phenomena of nature with which it is connected.

Such is a faint outline of some of the interesting subjects which natural philosophy embraces. Its relation to religion will appear from the following considerations:

1. Its researches have led to the invention of machines, engines, and instruments of various kinds, which augment the energies, increase the comforts, and promote the general improvement of mankind; and these objects are inseparably connected with the propagation of Christianity

through the world. If we admit, that, in future ages, the religion of the Bible will shed its benign influence over all nations-that the external condition of the human race will then be prosperous and greatly meliorated beyond what it has ever been-and, that no miraculous interposition of Deity is to be expected to bring about such desirable events-it will follow, that such objects can be accomplished only in the ordinary course of Providence, by rational investigations into the principles and powers of nature, and the application of the inventions of science to the great objects of religion and of human improvement, as I shall endeavour briefly to illustrate in the following chapter. As the destructive effects of many physical agents, in the present condition of our globe, are, doubtless, a consequence of the sin and depravity of man; we have reason to believe that, when the economy of nature shall be more extensively and minutely investigated, and the minds of men directed to apply their discoveries to philanthropic and religious objects, they will be enabled to counteract, in a great measure, those devastations and fatal effects which are now produced by several of the powers of nature. The general happiness of all ranks, which will be connected with the universal extension of Christianity, necessarily supposes that this object will be accomplished; for, were a dread of destruction from the elements of nature frequently to agitate the mind, as at present, no permanent tranquillity would be enjoyed; nor would that ancient prediction, in reference to this era, receive its full accomplishment, that "there shall be nothing to hurt or destroy in all God's holy mountain, when the earth shall be full of the knowledge of the Lord." And since miraculous interpositions are not to be expected, to what quarter can we look for those subordinate agencies by which this object is to be effected, but to the discoveries and inventions of philosophical science?

Science has already enabled us to remedy many of those evils which are the accidental effects of the operation of physical agents. For example-the discoveries of the philosopher, with respect to the nature of the electric fluid, have enabled us to construct conductors for preserving buildings from the stroke of lightning: and we have every reason to hope, that in the progress of electric, galvanic, and chymical science, more complete thunder-guards, applicable to all the situations in which a person may be exposed, will be invented. Nay, our increasing knowledge of the electric fluid, and of the chymical agents which concur in its operation, may ena ble us to dissipate thunder-storms altogether, by disturbing the electricity of the clouds by means of a series of elevated artificial conductors. This is not only possible, but has already been in some degree effected. The celebrated Euler informs us, in his "Letters to a German Princess,"

that he corresponded with a Moravian priest named Divisch, who assured him "that he had averted, during a whole summer, every thunder storm which threatened his own habitation and the neighbourhood, by means of a machine constructed on the principles of electricity—that the machinery sensibly attracted the clouds, and constrained them to descend quietly in a distillation, without any but a very distant thunder-clap.” Euler assures us that "the fact is undoubted, and confirmed by irresistible proof." Yea, not only may the destructive effects of lightning be averted by the inventions of philosophy, but its agency may be rendered subservient to human industry, and made to act as a mechanical power. This effect, too, has been partially accomplished. About the year 1811, in the village of Philipsthal, in Eastern Prussia, an attempt was made to split an immense stone into a multitude of pieces, by means of lightning. A bar of iron, in the form of a conductor, was previously fixed to the stone, and the experiment was attended with the most complete success; for, during the very first thunder-storm, the lightning burst the stone without displacing it.*

It is, therefore, probable, that in the future ages of the world, this terrific meteor, and other destructive agents, which now produce so much alarm, and so many disastrous effects, may, by the aid of philosophy, be brought under the control of man, and be made to minister to his enjoyment.

The electric fluid has also been, in many instances, successfully applied in curing palsies, rheumatisms, spasms, obstructions, and inflammation; and it is known to have a peculiar effect on the nervous system. Lightning has been known to restore the blind to a temporary enjoy. ment of sight. Mr. Campbell, of Succoth, in Dumbartonshire, who had been blind for several years, was led by his servant one evening through the streets of Glasgow, during a terrible thunderstorm. The lightning sometimes fluttered along the streets for a quarter of a minute without ceasing. While this fluttering lasted, Mr. C. saw the street distinctly, and the changes which had been made in that part by taking down one of the city gates. When the storm was over, his entire blindness returned. A still more remarkable instance is stated, along with this, under the article Thunder, in Dr. Gleig's Supp. to Ency. Brit. which was written by the late Professor Robison. It is also possible that barren deserts might be enriched with fertility, and immense portions of the desolate wastes of our globe prepared for the support and accommodation of human beings, by arresting the clouds, and drawing down their electrical virtue and their watery treasures by means of an extended series of ele vated metallic conductors. What has been now

See Monthly Magazine, vol. 32, p. 162

stated is only one instance, out of many, which might be adduced, of the extensive and beneficial effects which may be produced, in future ages, by the application of the discoveries of natural science.

2. A knowledge of natural philosophy enables us to detect pretended miracles, and to discriminate between those phenomena which are produced by the powers of nature, and the supposed effects of diabolical influence. It has been chiefly owing to ignorance of the principles of natural science, that mankind, in all ages, have been so easily imposed upon by pretenders to supernatural powers. It is owing to the same cause, that superstitious notions and vain alarms have spread their influence so extensively among the lower ranks of the population of every country. The pretended miracles by which Pagan and Popish priests endeavour to support the authority of their respective religious systems, and every species of degrading superstition, vanish into smoke, when examined by the light of modern science; and there can be no question that an enlightened missionary would, in many instances, find the principles and the instruments of natural philosophy important auxiliaries in undermining the fabric of heathen idolatry and priestcraft. They tend to dissipate a thousand idle terrors which haunt and agitate the human mind; to detect a thousand kinds of imposture by which it has been held in cruel bondage, and to prevent the perpetration of those deeds of cruelty which have uniformly marked the reign of superstition.* Had our forefathers connected a knowledge of this subject with the study of the Scriptures, they would not have brought upon themselves that indelible disgrace which now attaches to their memories, on account of their having condemned and burned at the stake hundreds of unhappy women, accused of crimes of which they could not possibly have been guilty. In NewEngland, towards the close of the 17th century, the witchcraft phrensy rose so high, that the execution of witches became a calamity more

Mr. Douglas, in his "Hints on Missions," for merly referred to, when speaking of the facilities which Christians now possess for extensive missionary exertions, suggests, that natural philosophy might be an important auxiliary to Christian missionaries. "All the ancient war weapons of victory,' excepting miracles, are at their disposal; and new instruments of still greater potency, which the science of the latter days has been accumulating for a universal revolution of the mind, are ready to be brought into action, upon a scale of overpowering magnitude. Even the single resource which is lost may yet be recompensed by equivalents, and a substitute, in many respects, may be found for miracles. The first effect of a miracle is, to rouse the attention, and to overawe opposing prejudices; the second to afford a proof of the religion of which it is a sealing Accompaniment. The first object might be gained by the natural magic of erperimental philosophy: and as to the second, the difference in the proof from miracles lies rather in its being more circuitous, than in its being less conclusive at the present day than in the times of the apostles."

dreadful than the sword or the pestilence. Not only old women, but children of ten years, were put to death; young girls were stripped naked, and the marks of witchcraft searched for upon their bodies with the most indecent curiosity; and those spots of the scurvy which age impresses upon the bodies of old men, were taken for evident signs of infernal power. So that ignorance of the laws and phenomena of nature has led even Christians to commit acts of injustico and horrid cruelty. For, let it be remembered, that it was Christian magistrates and ministers, under a pretended zeal for the honour of God, who sanctioned such cruel and unrighteous decrees. This consideration, viewed in connexion with many others, tends to show, that the Christian revelation, considered abstractly by itself, without a reference to the visible system of the universe, is not sufficient for all the purposes for which it was intended; as, on the other hand, the study of the works of nature is not sufficient of itself to lead the mind to the true knowledge of God, without the aid of the discoveries derived from the sacred oracles. For, although the Bible has been in the hands of Protestant Christians ever since the reformation, yet it is only since the light of modern science began to diffuse its influence, that the superstitions of the dark ages, and the vulgar notions respecting witchcraft, necromancy, and other species of infernal agency, began to vanish, even from the minds of Christian teachers; as is evident from the writings of many eminent divines who flourished during the 16th and 17th centuries. As the two revelations which God has given us throw a mutual lustre on each other; the one must always be considered as incomplete without the other. Both are necessary in order "to make the man of God perfect," and to enable him to prosecute, with intelligence and success, the great objects of religion; and the Christian minister who affects to despise the aids of science in the cause of religion, has yet much to learn with respect to some of the grand bearings of the Christian system.

3. The investigations of natural philosophy unfold to us the incessant agency of God, and the plans by which his wise and benevolent designs in the system of nature are accomplished. From the immeasurable globes of heaven, down to the minutest atoms, we perceive a regular chain of causes and effects, conspiring, in a thousand different modes, to accomplish the purposes of infinite wisdom and goodness. The operation of central forces and of the law of gravitation on the earth and in the heavens-the hydrostatical laws which regulate the pressure and the motion of fluids-the chymical properties of the atmosphere, its undulatory, refractive, and reflective powers-the motion of the rays of light, and the infinite variety of effects they produce--the process of evaporation-the agencies of electricity and galvanisin-the properties of the magnet,