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right or left, for throwing light upon the object placed over the hole i, which may be laid upon a slip of thin glass. The object-glass AB, fig. 2, is placed at u, fig. 3. The glass CD is placed opposite W, fig. 3, and the eye-glass EF opposite V.

Such are the essential parts of a compound microscope. Any common mechanic may construct one for himself by attending to the following directions: The object-glass AB, fig. 2, may be about 1, 3, or 1 inch focal distance, and the aperture, or hole which lets in the light from the object, should not exceed 1-10th of an inch, otherwise it will cause a glare, which will produce an indistinct image of the object. The amplifying glass CD may be 2% inches focal distance, and 1% inch in diameter. This glass is not essentially necessary, but it serves to enlarge the field of view, and to render it more distinct near the border. The eye-glass EF should be about 1 inch focus, and about 3 inch in diameter. With respect to the distances at which they should be placed from each other, the glass CD may be placed at about 5 or 6 inches from AB, and the glass EF about 2 inches, or 1; inch from CD. The object-glass shoule be a double convex—the eye-glasses may be plano-conver; that is, plane on the one side and convex on the other, with the plane sides turned next the eye; but double convexes will do, if these cannot be procured. The tubes which contain the glasses may be made of pasteboard, and the stage, pillars, and box, of wood. The glasses may be procured for about 4 shillings; and if the individual fit them into the tubes, and perform all the other operations req'iisite, the expense of all the other materials will not exceed other four shillings. Suppose, now, that the object-glass AB is , inch focal distance, and the image GH is formed at the distance of 6 inches from it, this image will be larger than the object, nearly in the proportion of 6 to , or 12 times. Suppose the glass EF, considered in connexion with CD, to possess a magnifying power equal to 5 times, then the whole magnifying power will be 5x 12, or 60 times. The object, therefore, will be magnified 60 times in length and in breadth, and, consequently, the surface will be magnified 3600 times, which is the square of 60. With such a microscope, the animalculae in water, the circulation of the blood in frogs and fishes, the small feathers which compose the dust on butterflies' wings, and all the most interesting appearances of the minute parts of animals and vegetables,

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Besides the discoveries in the heavens and in the minute parts of creation, to which the study of the science of optics has led,—its principles are capable of being directed to many important purposes in human life and society. By means of large burning mirrors and lenses the rays of the sun have been condensed, so as to increase

their intensity more than seventeen thousand times, and to produce a heat more than four hundred times greater than that of our common fires, which would serve for the combustion and fusion of numerous substances, which are insusible in the greatest heat that can be produced in our common furnaces. The property of a convex lens, by which rays proceeding from its focus are refracted into parallel directions, has enabled us to throw, from light-houses, a strong light to great distances at sea. The large polyzonal, or built up lenses, contrived by Sir D. Brewster, which may be made of any magnitude, and the elegant lamp of Lieutenant Drummond,-the one producing the most intense light yet known, and the other conveying it undispersed to great distances,—promise to introduce improvements hitherto unthought of, and to diversify the nocturnal scenery both of sea and land. For, in the progress of extensive national improvements, they might be made subservient, in connexion with carburetted hydrogen gas, in enlivening and decorating the rural scene, in the absence of the sun, and in guiding the benighted traveller in all his journeyings. For, when we consider the improvements, in almost every department of the social state, which have been lately carried forward, it is surely not too much to expect, that, in the course of a century hence, our highways, villages, hamlets, and even some of our moors and mountains, shall be lighted up with gas lamps, connected with mirrors and lenses, analogous to those which illuminate our cities and towns, and which direct the mariner, when approaching our shores. The following figure shows the manner in which a large lens throws a light to great distances. Let AB, fig. 4, represent one of Sir D.

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Even the sciences of Electricity and Galvanism might, in some instances, be rendered subservient to the operations of art. By means of the electrical fluid, models of corn-mills, waterpumps, and orreries, showing the diurnal motion of the earth, and the age and phases of the moon, have been set in motion; and there can be no question, that, in the hands of genius, it might be directed to accomplish much more important effects. Even the lightning of the clouds, which is only the electrical fluid acting on an ample scale, has been guided by the hand of art, to perform ohanical operations, by

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splitting large stones into shivers. This has been effected in the following manner. Suppose AB to represent a stone or portion of a rock. which is intended to be split into a number of pieces. Into the midst of this stone a long rod of iron, or conductor CD, is inserted, which terminates in a point. When a thunder-cloud, as EF, passes over the stone, within its striking

distance of the earth, the lightning from the cloud strikes the upper part of the pointed conductor, and is conducted downwards to the heart of the stone, which either rends it in different places, or splits it at once into a multitude of fragments. This experiment, which appears to have been first made in Prussia in 1811, was attended with complete success, during the first storm that passed over, after the bar of iron was inserted in the stone. To braziers, tinsmiths, coppersmiths, and other workers in metals, a knowledge of Galvanism might suggest a variety of useful hints, especially where it is an object of importance to secure any piece of metallic workmanship from rust. It is sound that when metals are pure and kept separate from each other, they remain for a long time untarnished; but when alloyed, or placed in contact with other metals, they soon undergo oxidation. Coins composed of one metal are found more durable than those composed of two; and the copper sheathing of ships which is fastened with iron nails soon undergoes corrosion. These effects are now exolained on the principles of galvanism. When two metallic substances of different kinds are connected by moisture, they form what is called a galvanic circle; and, therefore, when one kind of metal is placed in contact with another, if either water or the moisture of the atmosphere adheres to them, a galvanic circle is formed, and oxidation is produced. On this ground the late Sir Humphrey Davy suggested the propriety of fastening the upper sheathing of ships with copper instead of iron nails. The same principle may be rendered of extensive application, and may afford many useful hints to every artizan employed in working and combining metals.

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A knowledge of magnetism might also, in many cases, be directed to useful practical applications. This mysterious power, in connexion with its polarity, has already enabled the miner and surveyor to traverse the remotest corners of the largest mines, and to trace their way back in safety through all the windings of those subterraneous apartments, and has directed the navigator to steer his course with certainty, through the pathless ocean, to his “desired haven.” Throughout all the regions of the globe the magnetic power extends its influence; and it is now found to have an intimate connexion with heat, electricity, and galvanism. Of late years, it has been ascertained that iron with its oxides and alloys are not the only substances susceptible of magnetic influence. The magnetism of nickel, though inferior to that of iron, is found to be considerable; and that of cobalt and titanium is quite perceptible. Nay, the recent discoveries of Arago have shown, “that there is no substance but which, under proper circumstances, is capable of exhibiting unequivocal signs of the magnetic virtue.” In consequence of a recent discovery of M. Oersted, “we are now enabled to communicate, at and during pleasure, to a coiled wire, of any metal indifferently, all the properties of a magnet—its attraction, repulsion, and polarity, and that even in a more intense degree than was previously thought to be possible in the best natural magnets.” This discovery tends to enlarge our views of the range of magneuc influence, and to lead us to the conclusion that its powers may hereafter be applied to purposes of which at present we can have no conception. Although the polarity of the magnet has been of incalculable service to mankind, particularly in promoting navigation and enlarging our knowledge of the globe, yet we have no reason to believe that this is the only practical purpose to which its powers may be applied, or the only reason why the Creator has so widely diffused its influence in the system of nature; since, in his diversified operations in the material world, he so frequently produces a variety of effects from one and the same cause. It remains with

man to prosecute his observations still more extensively on this subject, and his industry wil., doubtless, be rewarded with the discovery of new relations, laws, and combinations, which may be susceptible of the most important practi. cal applications in the arts which minister to the comfort and convenience of mankind. Even in its present state, the attractive property of magnetism is capable of being applied as a mechanical power, in certain pieces of machinery, although its application in this way has never yet been attempted on an extensive scale. The following fact shows how its attractive power has lately been applied to the prolongation of life, and the warding off of incurable disease, in the case of a useful class of our fellow men. “In needle manufactories the workmen are constantly exposed to excessively minute particles of steel which fly from the grindstones, and mix, though imperceptible to the eye, as the finest dust in the air, and are inhaled with their breath. The effect, though imper. ceptible, on a short exposure, yet being constantly repeated from day to day, produces a constitutional irritation, dependent on the tonic properties of the steel, which is sure to terminate in pulmonary consumption; insomuch, that persons employed in this kind of work used scarcely ever to attain the age of forty years. In vain was it attempted to purify the air, before its entry into the lungs, by gauzes or linen guards; the dust was too fine and penetrating to be obstructed by such coarse expedients, till some ingenious person bethought him of that wonderful power, which every child that searches for its mother's needle with a magnet, sees in exercise. Masks of magnetized steel wire are now constructed and adapted to the faces of the workmen. By these the air is not merely strained but searched in its passage through them, and each obnoxious atom arrested and removed.” This interesting fact affords a striking proof of the useful purposes to which the powers and properties of natural substances may be applied, when the mind is directed to contemplate them in all their bearings, and to trace them to all their legitimate consequences. The attractive power of the magnet, considered not only in its relation to iron and steel, but to all other substances in which magnetical virtue is found in a greater or less degree to reside—might, therefore, in the hands of an ingenious mechanic, lead to many interesting experiments, which might pave the way for the most important practical results. The facts connected with the science of Gcotogy may likewise, in many instances, be directed to practical purposes. From the researches which, of late years, have been made in the interior of the earth, geologists are now pretty well

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acquainted with the position and alternation of its strata, and with the different fossils which may be expected to abound in any particular district. Although these researches were undertaken chiefly with a view to ascertain the changes which have happened in the structure of our globe, and to support certain theories of the earth—yet they may frequently be of use to landed proprietors. to engineers, and to speculators in mining operations, so as to direct them in their investigations, and prevent them from embarking in schemes that may ultimately blast their expectations, exhaust their resources, and lead to irretrievable ruin. The ruinous effects sometimes produced by ignorance of this subject are strikingly illustrated by the following fact:— “It is not many years since an attempt was made to establish a colliery at Bexhill, in Sussex. The appearance of thin seams and sheets of fossil wood, and wood-coal, with some other indications similar to what occur in the neighbourhood of the great coal beds in the north of England, having led to the sinking of a shaft, and the erection of machinery, on a scale of vast extent, not less than eight thousand pounds are said to have been laid out on this project, which, it is almost needless to add, proved completely abortive, as every geologist would have at once declared it must, the whole assemblage of geological facts being adverse to the existence of a regular coal bed in the Hastings' sand; while this on which Bexhill is situated, is separated from the coal strata by a series of interposed beds of such enormous thickness as to render all idea of penetrating through them absurd.—The history of mining speculations is full of similar cases, where a very moderate acquaintance with the usual order of nature, to say nothing of theoretical views, would have saved many a sanguine adventurer from utter ruin.” The study of the various branches of Natural History might also be rendered productive of utility in different departments of the arts. It is quite evident that a scientific knowledge of Botany must be highly useful to gardeners and their labourers, and to all who take an interest in horticultural and rural operations. Not only a knowledge of the classification and arrangement of plants, but also of their physiological structure and functions, of their medicinal qualities, and of the chymical properties of soils and the different manures, will be found of considerable utility to such individuals.-Zoology and Comparative Anatomy, which describe the peculiar structure and habits of animals, both foreign and domestic, will convey various portions of interesting information to shepherds, cattle-dealers, and agriculturists of every description. An acquaintance with Mineralogy, which treats of the solid and inanimate mate

* Herschel's Discourse, &c.

rials of our globe, the earthy, saline, inflammable, and metallic substances of which it is composed, must be interesting to lapidaries, jewellers, iron-sounders, and all who are employed in working various metals. To know the nature of those substances on which they are operating, the materials with which they are united in their native ores, their combination with phosphorus, sulphur, and carbon, the changes produced upon them by oxygen and the different acids, their relations to heat, and the liquids with which they may come in contact, and the various compounds into which they may be formed, will have a direct tendency not only to increase their stock of general knowledge, but to render them more skilful and intelligent in their respective professions. JMeteorology, which treats of the weather and the variable phenomena of the atmosphere, will, in many instances, be found a useful study to mariners, fishermen, travellers, and farmers, by which they may frequently be directed in their movements, and avoid many inconveniences and dangers. By carefully attending to the motions of the barometer and thermometer, and comparing them with the electrical state of the atmosphere, the direction of the winds, and the appearances of the clouds, the farmer may be warned of the continuance of rain or drought, and direct his operations accordingly, so as to protect his produce from danger. There is no application of science to the arts of more importance, and more extensive in its effects, than that of the employment of Steam for driving all kinds of machinery, and for propelling vessels along rivers and across the ocean. “It has armed,” says Mr. Jeffrey, “the feeble hand of man with a power to which no limits can be assigned—completed the dominion of mind over the most refractory qualities of matter, and laid a sure foundation for all those future miracles of mechanic power, which are to aid and reward the labours of after generations.” The first person who appears to have entertained the idea of employing steam for propelling vessels, was Mr. J. Hulls, in the year 1736. But it was not till 1807, when Mr. Fulton launched, at New-York, the first steam-boat he had constructed, that navigation by steam was introduced to general practice, which may therefore be considered as the epoch of the invention. In a few years every river and bay in the United States became the scene of steam navigation. In 1822 there were more than 350 steam vessels connected with these States, some of them of eight and nine hundred tons burden, and by this time, doubtless, they are more than doubled. In 1819 an expedition left Pittsburg, descended the Ohio in steam-boats for 1100 miles, and then ascending the rapid Missouri, proceeded to the distance of no less than two thousand five hundred miles. They have now been introduced into every country in Europe. On the principal rivers and seas connerted with the British Isles, and even in the Scottish lakes, these vessels are sweeping along in majestic pomp, against wind and tide, diversifying the scenery through which they pass, and transporting travellers and parties of pleasure to their destination, with a rapidity unexampled in former ages. On the Clyde alone more than fifty or sixty steam vessels are constantly plying. The scenery of the Rhine, the Rhone, the Elbe, the Seine, the Danube, the Wolga, the lakes of Constance and Geneva, and of many other rivers and inland seas, is now enlivened by these powerful machines, conveying goods and passengers in every direction. Even the Atlantic ocean, an extent of more than three thousand miles, has been traversed by a steamboat in twenty days; and the period, we trust, is not far distant, when the Red Sea, the Persian Gulph, the Bay of Bengal, the Indian Ocean, the Mediterranean, the Euxine, the Gulph of Mexico, and even the wide Pacific, will be traversed by these rapid vehicles, conveying riches, liberty, religion and intelligence to the islands of the ocean, and forming a bond of union among all nations. The admirable improvements in the construction of steam carriages which are now going forward, are no less worthy of attention. The rapid movements of these machines, which have been lately introduced on the Liverpool and Manchester railway, and the security and comfort with which they are attended, have excited the astonishment of every beholder. And no wonder, —since goods and passengers are now conveyed between these cities, with a velocity of nearly thirty miles an hour ! so that it may be said, with the strictest propriety, that the steam engine is the most brilliant present ever made by philosophy to mankind. The discovery of carburetted hydrogen gas, and its application to the purpose of illuminating our dwelling-houses, streets, and manufactories, may also be considered in reference to the arts. Every city, and every town of a moderate size, is now enlivened with the splendid brilliancy produced from this invisible substance ; pipes for its conveyance have been laid, of many hundred miles in extent, and diverging into numerous ramifications, and thousands of artists are emoloyed in conducting its manufacture, and forming tubes and other devices for distributing it in all directions. Now, since the inventions to which I am adverting are founded on chymical and mechanical principles, and on the discoveries of modern science, and since many thousands of mechanics are now employed in constructing the machinery connected with these inventions, and in conducting its operations both by sea and land, it is of the utmost importance, in order to their being

fully qualified for their respective departments, that they understand the scientific principles which enter into the construction of such machines and engines, the peculiar uses of every part, the manner in which the chymical agents employed operate, and the effects which, in any given circumstance, they must necessarily produce. In particular, it is indispensably necessary, that engine-men, and others employed for directing these machines, when in operation, should be acquainted with every part of their structure, and the principles on which their movements depend; for the comfort and safety of the public are dependent on the caution and skill with which they are conducted. How could any man be qualified for such an office without some portion of scientific knowledge 7 and how could travellers in such vehicles consider their lives and property secure, if they were not guided by men of intelligence and prudence 3 To the want of such caution and skill are chiefly to be attributed most of the disasters and fatal accidents, connected with such operations, which have hitherto taken place. Besides the agriculturists, manufacturers, mechanics, and artificers alluded to above, there are numerous other classes to which similar remarks will apply. In short, there is scarcely an individual, however obscure, in any department of society, but may derive practical benefit from an acquaintance with science. “The farmservant or day labourer,” says Lord Brougham, “whether in his master's employ, or tending the concerns of his own cottage, must derive great practical benefit, must be both a better servant, and a more thrifty, and, therefore, comfortable cottager, for knowing something of the nature of soils and manures, which chymistry teaches, and something of the habits of animals, and the qualities and growth of plants, which he learns from natural history and chymistry together. In truth, though a man is neither a mechanic nor a peasant, but only one having a pot to boil, he is sure to learn from science lessons which will enable him to cook his morsel better, save his fuel, and both vary his dish and improve it. The art of good and cheap cookery is intimately connected with the principles of chymical philosophy, and has received much, and will yet receive more, improvement from their application.”—Nay, even the kitchen maid, the laundry maid, and the mistress of every family, may derive many useful hints from the researches of science. The whole art of cookery is a chymica. operation, and so are the arts of washing, dressing, bleaching, and dyeing. By a knowledge of the nature and properties of the acids and other chymical substances, they would learn how to eradicate stains of ink, grease, &c. from cotton, linen, woollen, and silks, in the safest and most effectual manner, and many other processes of great utility in domestic life. Even

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