of art. By means of the electrical fluid, models of cornmills, water-pumps, 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,

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 brasiers, 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 undergoes 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 artisan 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, 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 extensively on this subject, and his industry will, 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 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 for 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 who point the needles 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, pro

duces 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 geology 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 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

* Herschel's Prelim. Dis. on Nat. Philos.