same lens. Could such lenses be constructed of the size of 6, 8, 10 or 12 feet diameter, they would produce a degree of heat from the solar rays far surpassing what has hitherto been effected, and be capable of throwing a brilliant light to immense distances.

Fig. 6, shows the manner in which a concave mirror TU reflects the light of a lamp VW, placed in its focus, to great distances. It is in this way that the light of the Bell Rock, and other light-houses, is reflected to more than thirty or forty miles distant.

W

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 mechanical operations, by

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 found 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 un

dergoes corrosion. These effects are now explained 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. 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 magnetic 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 ev tensively 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 practical 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 me chanical 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 imperceptible, 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, there fore, 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 Goo logy 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

Herschel's Prelim. Dis. on Nat. Philos

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 neighbour hood 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-founders, 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. Meteorology, 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

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 impart ing 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 in 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 exclu sive 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 employ ments, but will enable them to make improvements in the arts, and in the physical sciences with 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.