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the art of kindling a fire, and of stirring it when kindled, depends on philosophical principles. For example, the stirring of a fire is of use, because it makes a hollow, where the air being rarefied by the adjacent heat, the surrounding air rushes into the partial vacuum, and imparting its oxygen, gives life to the fire and carries the flame along with it. On this principle the following rules are founded. 1. Never stir a fire when fresh coals are laid on, particularly when they are very small, because they immediately fall into the vacuum, and prevent the access of the oxygen of the atmosphere, which is the principle of combustion. 2. Always keep the bottom bar clear, because it is there chiefly that the air rushes in to nourish the fuel. 3. Never begin to stir at top, unless when the bottom is quite clear, and the top only wants breaking, otherwise the unkindled fuel may be pressed down in a body to the bottom, and the access of atmospheric air prevented. Illustrations, of a similar kind, of the practical applications of science, might have been given to an almost indefinite extent; but the above specimens may suffice as corroborative of the general position—that scientific knowledge would render mechanics and manufacturers of all descriptions more skilful in the prosecution of their respective employments. Some, however, may be disposed to insinuate, that it is quite enough for philosophers to ascertain principles, and to lay down rules founded upon them, for the direction of the mechanic or artizan —or, that it is only requisite that the directors and superintendents of chymical processes and mechanical operations, should be acquainted with that portion of science which is necessary for their peculiar departments. But it is easy to perceive, that a mechanic who works merely by rules, without knowing the foundation or reasons of them, is only like a child who repeats his catechism by rote, without attaching a single idea to the words he utters, or like a horse driving a thrashing machine, without deviating from the narrow circle to which he is necessarily confined. When any accident occurs, when the circumstances of the case are somewhat changed, when the same principle on which he generally proceeds requires to be applied to a new object or mode of operation, he either blunders his work, or feels himself utterly at a loss how to proceed. The least deviation from his accustomed trammels puts him out, because he has no clear and comprehensive view of the principles on which his practice depends. Hence we uniformly find, that a man of scientific acquirements will easily comprehend the plan of any new machine or architectural operation, and be able to execute it, while he who works only by square and rule, will hesitate at every step, and perceive innumeraole difficulties 2 his way. To confine artists to mere

rules, without a knowledge of the principles on which they are founded, is to degrade their intellectual nature, to reduce them to something like mere machines, to render them less useful both to themselves and to their employers, and to prevent the improvement of the liberal and mechanical arts. The following instance may be stated as a specimen of the advantages of chymical knowledge, and of the practical purposes to which it may be applied in different regions of the globe. A young Parisian, of the name of Leger went on a commercial adventure to Egypt in the year 1822: but during some of the convulsions of that unsettled country, he lost the little property with which he was intrusted, and was forced to make a precipitate retreat from Suez to Alexandria. He remained some time at Alexandria, destitute and almost hopeless. But the talent of observation, and the social habits characteristic of his countrymen, came to his aid: in a lucky moment he formed the resolution of retrieving his fortune by introducing the luxury of ice into the parched land of the Ptolemies. This common product of wintry regions is known to be as grateful to the languid natives of tropical climates as ardent spirits are to the benumbed inhabitants of the Polar circle. Having succeeded in effecting a return to his family, the enterprising Parisian was enabled by the friendly assistance of Gay Lussac and Thenard, to adopt the best means that chymistry could devise for the preservation of ice, both during the voyage, and after its arrival in a sultry latitude; and at length set out from Paris with his inventions, and arrived safely at Alexandria, in April 1823. The sovereign of Egypt, Mahommed Ali, was delighted at this novel addition to oriental luxuries; and, besides valuable presents, gave the inventor the exclusive right for five years of importing ice into his dominions. This privilege is estimated to be worth one million of francs, or nearly 50,000l. In ancient times the world was enlightened by the learning of Egypt; the greatest philosophers travelled thither, as to the fountain-head of science; but the land of Sesostres and Alexander has now become the prey of the ferocious Moslem; and whatever she enjoys of art, knowledge or civilization, she is compelled to receive from the once barbarous regions of the West.*

II. Scientific knowledge will not only render persons more skilful in their respective employments, but will enable them to make improvements in the arts, and in the physical sciences unth which they are connected.

It has frequently been affirmed that many useful inventions have been owing to chance, and that persons ignorant of science have stumbled upon them without any previous investiga

* Scots Mechan. Mag. 1825.

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formed by it, C the glass next the eye, and D the sliding board on which it was fixed, for adjusting the focus. Such appears to have been the first rude construction of a telescope.” But so long as the invention remained in this state, it was of little benefit to society. It was not before Galileo, a philosopher of Tuscany, heard of the circumstance, and entered into investigations on the refraction of light, and the properties of lenses, that this noble instrument was improved and directed to the heavens for the purpose of making astronomical discoveries; and all the subsequent improvements it has received, have been the result of reasonings, and experimental investigations, conducted by men of science. Sir Isaac Newton, in consequence of his experiments and discoveries respecting light and colours, detected the true cause of the imperfection of the common refracting telescope, and suggested the substitution of metalline specula instead of lenses, which led him to the invention of the reflecting telescope; and Mr. Dollond, in consequence of his investigations and experiments respecting the different degrees of refraction and divergency of colour produced by different kinds of glass, effected the greatest improvement that had ever been made on the reJracting telescope, by producing an image free of the imperfections caused by the blending of the prismatic colours. And we have reason to believe, that the further improvement osthis tele

scope will chiefly depend on ascertaining the true chymical composition of flint glass for achromatic purposes, and the proper mode of conducting its manufacture, which may lead to the construction of instruments of this kind, on a more extensive scale than has ever yet been attempted, and to discoveries in the celestial regions far beyond those which have hitherto been made. But such improvements can never be effected, unless by numerous experimental investigations, conducted by those whose minds are thoroughly imbued with the principles of chymical and optical science.*

One of the latest improvements on Achromatic object-glasses was made by a foreigner of the name

of Guinand, who was originally a cabinet-maker,

After acquiring a knowledge of the principles of optics, and of the mode of constructing telescopes, he applied himself particularly to ascertain the proper composition of flint-glass for achromatic purposes; and, after spending twenty or thirty years in making experiments—casting one pot of #. after another, and meeting with frequent isappointments,—he at length succeeded in obtaining glass for achromatic telescopes, of larger dimensions and of a quality superior to what could formerly be procured. Of this glass was formed the largest triple achromatic telescope ever constructed, which was lately erected in the observatory of the university at Dorpat, under the direction of M." Fraunhofer. This glass is perfectly free from veins, and has a greater dispersive power than any obtained before. The diameter of this object glass is almost ten inches, and its focal distance 15 feet. It has four eye-pieces, the lowest magnifying 17; times, and the highest 700 times. Mr. Tulley of Islington lately coustructed, of similar materials, With regard to the invention and improvement of the steam-engine—a story has been told “that an idle boy being employed to stop and open a valve, saw that he could save himself the trouble of attending and watching it, by fixing a plug upon a part of the machine which came to the place at the proper times, in consequence of the general movement.” Whether or not this story has any foundation in truth—certain it is, that all the most useful improvements in this engine have been the result of the most elaborate researches and investigations of scientific truths. The frst distinct notion of the structure and operation of this powerful machine appears to have been given by the Marquis of Worcester, in 1663, in his “Century of Inventions.” Its subsequent improvements by Savary, Blackey, Newcomen, Beighton and Fitzgerald, were the results of physical knowledge, of mechanical skill, and of the most laborious investigations. Its latest and most important improvements by

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manufactured by the same artist, a telescope whose object-glass is about seven inches diameter, and its focallength twelve feet, which is now in the possession of Dr. Pearson. The piece of flint-glass of which the concave lens was formed, cost Mr. Tulley about thirty guineas. Unfortunately for science, the ingenious artist (Guinand) is now dead, it is uncertain whether he has left any particular details of his process behind him. The possibility, however, of procuring glass for the construction of very ; achromatic telescopes is now put beyond a oubt. The unscientinc reader may acquire a generol idea of an achromatic object-glass from the following figure, where A Drepresents adouble unequally convex lens of crown glass, C B a double concave offlint glass, and EF another convex lens of crownglass. These are placed together in the manner represented in the figure, and form what is called

anachromatic object-glass, the term achromatic signifying free of colour. Sometimes only two lenses, a convex of crown, and a concave offlint-glass are combined for the same purpose. In the case of a * convex glass, the image formed is blended with the prismatic colours which come to sociat different distances from the lens, and consequently produce a comparatively indistinct image, which will not admit of a high magnifying power. But the achromatic lens, forming an image without colour, will bear a largeraperture, and a higher magnifying power, than a common refractor of the same length. so great is the difference—that an achromatic telescope of Dollond, only three feet ten inches in length, was found to equal, and even excel the famous aerial telescope of Huygens of 123 feet focal length, and the gentlemen present at the trial agreed that “the dwarf was fairly a match for the giant.” The principal obstacle to their construction on a

scale, is, the difficulty of procuring large pieces of otglass of veins, and of a properdispersive quality.

Mr. James Watt, were owing no less to the scientific knowledge which adoued his mind, than to his mechanical ingenuity. He was a man of a truly philosophical mind, eminently conversant in all branches of natural knowledge, and the pupil and intimate friend of Dr. Black, and had attended the lectures of that distinguished philosopher in the university of Glasgow. And he often acknowledged “that his first ideas on this subject were acquired by his attendance on Dr. Black's chymical lectures, and from the consideration of his theory of latent heat, and the expansibility of steam.” We may therefore rest assured, that all the suture improvements and new applications of this noble invention will be the result of physical and chymical knowledge combined with mechanical skill; and consequently, no artizan can ever expect to be instrumental in bringing the steam-engine to its highest pitch of improvement, and in directing its energies to all the purposes to which they may be applied, unless the pursuits of science occupy a considerable share of his attention. The first hint of the mariner's compass is generally supposed to have been owing to chance. Some persons may have accidentally observed, that when a small loadstone is suspended in water on a piece of wood or cork, its ends pointed towards the south and north. Such experiments seem to have been applied at first for mere amusement, and to excite astonishment in the minds of the ignorant and illiterate. But it was not till some genius possessed of science and of reflecting powers seized the hint thus given, that it was applied to the important purpose of directing the mariner in his course through the pathless ocean. And to science we are indebted for the manner of determining the declination of the needle, in all parts of the world, by means of the azimuth compass, and thus rendering it an accurate guide to the navigator in every region through which he moves. The discovery of that peculiar principle termed galvanism, was partly owing to accident. Whilst Galvani, prosessor of anatomy at Bologna, was one day employed in dissecting a frog, in a room where some of his friends were amusing themselves with electrical experiments, one of them having happened to draw a spark from the conductor, at same time that the professor touched one of the nerves of the animal, its whole body was instantly shaken by a violent convulsion. Having afterwards suspended some frogs from the iron palisades which surrounded his garden, by means of metallic hooks fixed in the spines of their backs, he observed that their muscles contracted frequently and involuntarily, as is from a shock of electricity. Such facts, presented to the view of unscientific persons, might have produced nothing more than a gaze of wonder; perhaps supernatural powers might have been resorted to in order to account for the pheno

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menn, and in a short time they might have been forgotten as a vision of the night. But such scientific minds as those of Valli, Volta, Monro, Fowler, Davy, Humboldt and Wollaston, having seized upon these facts, having contemplated them in every point of view, and instituted experiments of every description in relation to them—most astonishing discoveries in science have been brought to light—the whole aspect of chymistry has been changed, and numerous improvements introduced into the practice of the useful arts. Alkalis have been decomposed, new metallic substances discovered, the cause of the corrosion of metals ascertained, and the means determined by which it may be effectually prevented. It is a truth which the whole history of science fully corroborates, that very few important discoveries have been made by accident or by ignorant persons, whose minds were not directed to the particular object of research. On the other hand, we have every reason to believe, that there are many fects and circumstances which have passed under the inspection of untutored minds, which, had they come within the range of men of science, would have led to many useful inventions which are yet hid in the womb of futurity, and which will reward the industry of more enlightened generations. The inventions to which we have now adverted, and many others, where chance suggested the first rude hints, would, in all probability, have lain for ages in obscurity, without any real utility to mankind, had not the genius of science seized upon them, viewed them in all their bearings, and traced them to all their legitimate consequences and results. Had the telescope, the steam engine, and the mariner's compass, in their first embryo state, remained solely in the hands of ignorant empirics, they might have been reserved merely as play-things for the purpose of vulgar amusement, or exhibited by cunning impostors to aid their deceptions, or to produce a belief of their supernatural powers. But science snatched them from the hands of the ignorant and the designing, and having added the requisite improvements, bequeathed them to mankind as the means of future advancement in the paths of knowledge, and in the practice of the arts. It may be laid down as a kind of axiom, to which few exceptions will occur, that great discoveries in science and improvements in art are never to be expected but as the result of knowledge combined with unwearied investigation. This axiom might be illustrated, were it necessary, from what we know of the past history of our most useful inventions. The celebrated M. Huygens, who first discovered the means of rendering clocks exact by applying the pendulum, and rendering all its vibrations equal by the cycloid—was one of the first mathematicians and astronomers of his age. He had long kept the

object of his pursuit before his mind, he plice his mechanical ingenuity in adapting the machinery of a clock to the maintaining of the vibrations of a pendulum, and by his mathemaucal knowledge investigated the theory of its motion. By the aid of a new department of geometrical science, invented by himself, he showed how to make a pendulum swing in a cycloid, and that its vibrations in this curve are all performed in equal times, whatever be their extent. The ingenious Mr. Robert Hooke, who was the inventor of spring or pocket watches, and of several astronomical instruments for making observations both at sea and land—was eminently distinguished for his I hilosophical and mathematical acquirements. From his earliest years he discovered a genius for mechanics, and all his other knowledge was brought to bear upon his numerous inventions and contrivances.— Otto Guerieke, who invented the Air-pump, was one of the first mathematicians of his time ; and the Honourable Robert Boyle, who improved this valuable instrument, was one of the most illustrious philosophers of the age and country in which he lived.—Mr. Ferguson, the inventor of several orreries, the astronomiaal rotula, the eclipsarian, the mechanical paradox, and other astronomical machinery, had, from his earliest years, devoted the greatest part of his time to the study of mechanics, and the physical and mathematical sciences with which it is connected, as appears from the numerous popular works which he published on these subjects which are still in extensive circulation.—The late Mr. Arkwright, the inventor of the spinning jennies, devoted many years to the study of mechanics and to the improvement of his invention, till he was perfectly conversant in every thing that relates to the construction of machinery. This admirable invention, by which a pound of the finest cotton has been spun by machinery into a yarn extending more than 119 miles, was not the result of chance, but of the most unwearied study and attention in regard to every circumstance which had a bearing on the object of his pursuit: and as he had not originally received any thing like a regular scientific education, his acquirements were the result of his own application and industry.—“The new process of refining sugar, by which more money has been made in a shorter time, and with less risk and trouble, than was ever perhaps gained from an invention, was discovered by an accomplished chymist, E. Howard, brother of the Duke of Norfolk, and was the fruit of a long course of experiments, in the progress of which, known philosophical principles were constantly applied, and one or two new principles ascertained.” There are few inventions of modern times that have been more directly the result of philosophical knowledge and experiment, than the

safety-lanp, invented by that accomplished chymist, the late Sir Humphrey Davy. He instituted a series of philosophical experiments, with the express purpose of constructing, if possible, a lamp by which the miner might walk through a body of fire-lamp in his subterraneous apartments without danger of an explosion; and the success with which his investigations were attended, led to one of the most beautiful and useful inventions which distinguish the period in which we live.* Had this ingenious philosopher been ignorant of the nature and properties of carburretted hydrogen gas, of the composition of atmospheric air, of the nature of combustion, and of the general principles of chymical science, he could never have hit upon the construction of this a mirable instrument, and the useful miner would still have been left to grapple with his invisible enemy (the fire-damp) without any means of escaping from its destructive agency.f

* See Appendix, No. IX.

* It is more than probable, that fatal accidents have occurred in coal mines where these lamps have been used, owing to the ignorance and in attention of some of those artists who have been employed in forming the wire-grauze with which they are surrounded. A friend of mine, who performed a great variety of experiments with this instrument, with every combination of explosive gas, informed me, that, with a lump surrounded with wire-gauze, inanufu-turel by an artist in a town in the north of England, and upho supplied it for the use of the miners—an explosion uniformly took place when the instrument was placed in a bo!y of inflammable gas. He suspected that the apertures in the wiregauze were too large, and remonstrated with the artist on his want of accuracy; and it was not before he procured gauze with smaller apertures that his experiments succeeded; and they were attended with complete success in every future experiment, after the gauze was changed. So small was the dif. ference in the contexture of the two pieces of the gauze, that, to a common eye, it was scarcely per ceptible. It is found by experiment, that the aper. tures in the guize should not exceed one twentieth of an inch square, and that wire from one sortieth to one sixtieth of an inch diameter, is the most convenient. Had the artist all it led to, known how to perform experiments with this instrument, and tried the effects of his gauze before he sold it for the pur

se intendel, such serious bluntlers would not have been committed. Who knows but the desiciency in the gauze alluded to might have been the cause of the destruction of several lives in the pits where it was u ! for it is a certain fuct that accidents from explosions are occasionally recurring, 2ven in mines where these lamps are generally in 1se. Hence the necessity of chymical knowledge an i attention to scientific accuracy in those who are the in unusucturers of instruments of this description—on the accurate construction of which the lives an consorts of a useful body of the community in w depend. I know not whether it be custoin ury to put the safety-lamp into the hands of the miner, without first trying its efficiency for resisting the effects of explosive g uses. If it is not, it is a inost gl uring an dangerous oversight; anol there can be no question, that to the neglect of this precaution are to be attributed many of those explosions which h uve taken place in the mines where this lamp has n introduced. Besides, such neglects have a direct ten lency to detract from the merits of this noble invention, to prevent its universal adoption, and to ren ter uncertain its efficiency for warding off destructive explosions. But from use experiments alluded to above, which were per

We may farther remark, that the mechanic whose mind is enlightened with scientific knowledge, has a much greater chance of being instrumental in improving the arts, than the mere chymist or philosopher. While the mere philosopher is demonstrating principles and forming theories in his closet, and sometimes performing experiments, only on a small scale, the workman, in certain manufactories, has a daily opportunity of contemplating chymical processes and mechanical operations on an ertensive scale, and of perceiving numberless modifications and contrivances, which require to be attended to, of which the mere scientific speculator can form but a very faint and inadequate conception. Being familiar with the most minute details of every process and operation, he can perceive redundancies and defects imperceptible to other observers; and, if he has an accurate knowledge of the general principles on which his operations depend, he must be best qualified for suggesting and contriving the requisite improvements. As the mechanic is constantly handling the tools and materials with which new experiments and improvements may be made,-observing the effects of certain contrivances, and of deviations from established practice—and witnessing the chymical and mechanical actions of bodies on each other—he has more opportunities of observation in these respects, and, consequently, is more likely than any other class of soc.ety to strike out a new path which may lead to some useful invention in the arts, or discovery in the sciences.” But if his mind is not imbued with knowledge, he trudges on, like a mill-horse, in the same beaten track, and may overlook a thousand opportunities of performing experiments, and a thousand circumstances which might suggest new improvements.

In short, in so far as chance is concerned in new discoveries and improvements in the arts, the scientific mechanic has a hundred chances to one, compared with the ignorant artificer, that, in the course of his operations, he shall hit upon a new principle of improvement: his chances

of such results are even superior to those of the

most profound philosophers who never engage in

formed with the greatest care, and with every pos. sible combination of explosive gas, and frequently exhibited in private, and before large public audiences—the efficiency of this lamp for resisting the ef. sects of fire-damp is put beyond the shoulow of a doubt. It is known to be the practice of some miners, occasionally to screw of the top of their lamp, in order to enjoy the benefit of more light than what shines through the wire-gauze. Such a practice oright to be strictly prohibited, and the instrument, is possible, rendered incapable of being opened at top–a practice which may probably have been the occasion of several explosions. If the workmen in mines were carefully instructed in the general principles of rhymistry, and particularly in the nature of combustion, losions, and the qualitos of the different gases, they would not dare ud hazard such dangerous experiments, * See Appen lix No. X

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