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chus caused to be placed at certain distances along the high roads, after the example of the Greeks, large stones to assist the horsemen in mounting.

STONE, John Hoskins, governor of Maryland, distinguished himself in the revolution. In early life, and at an early period of the war, he was first captain in the celebrated regiment of Smallwood. At the battles of Long Island, White Plains and Princeton, he behaved with great gallantry; and, at that of Germantown, he received a wound which disabled him for the residue of his life. But he still exerted himself in the service of his country, as a member of the executive council of Maryland, until 1794, when he was chosen governor, and remained so for three years (as long a time as was allowed by the constitution). He died at Annapolis, in 1804, leaving behind him the reputation of an honest and honorable man, an intrepid soldier, and a liberal, hospitable and friendly citizen.

STRENGTH OF MATERIALS. [The following article is extracted from Arnott's Elements of Physics.] "Strength depends on the magnitude, form and position of bodies, as well as on the degree of cohesion in the material."—Of similar bodies the largest is proportionally the weakest. Suppose two blocks of stone left projecting from a rock that has been hewn, of which blocks one is twice as long, and deep, and broad, as the other. The larger one will by no means support as much more weight at its end than the other, as it is larger; and for two reasons: 1. In the larger, each particle of the surface of attachment, in helping to bear the weight of the block itself, has to support by its cohesion twice as many particles beyond it, in the double extent of projection, as a particle has to support in the shorter block; and, 2. both the additional substance, and any thing appended at the outer extremity of the larger, are acting with a double lever advantage to break it, that is, to destroy the cohesion. Hence, if any such projection be carried out very far, it will break off or fall by its own weight alone. What is thus true of a block supported at one end, is equally true of a block supported at both ends, and, indeed, of all masses, however supported, and of whatever forms. That a large body, therefore, may have proportionate strength to a smaller, it must be made still thicker and more clumsy than it is made longer; and, beyond a certain limit, no proportions whatever will keep it together, in opposition merely to the force of its own weight.

This great truth limits the size and modifies the shape of most productions of nature and of art,-of hills, trees, animals, architectural or mechanical structures,&c.

Hills. Very strong or cohesive material may form hills of sublime elevation, with very projecting cliffs and very lofty perpendicular precipices; and such are seen, accordingly, where the hard granite protrudes from the bowels of the earth, as in the Andes of America, the Alps of Europe, the Himalayas of Asia, and the Mountains of the Moon in Central Africa. But material of inferior strength exhibits more humble risings and more rounded surfaces. The gradation is so striking and constant from granite mountains down to those of chalk, or gravel, or sand, that the geologist can generally tell the substance of which a hill is composed by the peculiarities of its shape. Even in granite itself, which is the strongest of rocks, there is a limit to height and projection; and, if an instance of either, much more remarkable than now remains on earth, were by any chance to be produced again, the law which we are considering would prune the monstrosity. The grotesque figures of rocks and mountains seen in the paintings of the Chinese, or actually formed in miniature for their gardens, to express their notions of perfect sublimity and beauty, are caricatures of nature, for which originals can never have existed. Some of the smaller islands in the Eastern ocean, however, and some of the mountains of the chains seen in the voyage towards China, along the coasts of Borneo and Palawan, exhibit, perhaps, the very limits of possibility in singular shapes. In the moon, where the weight or gravity of bodies is less than on the earth, on account of her smaller size, mountains might be many times higher than on the earth; and observation proves that the lunar mountains are much higher than ours. By the action of winds, rains, currents and frost upon the mineral masses around us, there is unceasingly going on an undermining and wasting of supports, so that every now and then immense rocks, or almost hills, are torn by gravity from the station which they have held since the earth received its present form, and fall in obedience to the law now explained.

The size of vegetables, of course, is obedient to the same law. We have no trees reaching a height of 300 feet, even when perfectly perpendicular, and sheltered in forests that have been unmolested from the beginning of time; and oblique or horizontal branches are kept within very

narrow limits by the great strength required to support them. The truth that, to have proper strength, the breadth or diameter in bodies must increase more quickly than the length, is well illustrated by the contrast existing between the delicate and slender proportions of a young oak or elm, while yet in the seedsman's nursery, and its sturdy form when it has braved for centuries all the winds of heaven, and has become the monarch of the park or forest.

Animals furnish other interesting illustrations of this law. How massive and clumsy are the limbs of the elephant, the rhinoceros, the heavy ox, compared with the slender forms of the stag, antelope and greyhound! And an animal much larger than the elephant would fall to pieces from its own weight alone, unless its bones were made of much stronger materials. Many have questioned whether the mammoth, or antediluvian elephant, could have lived on dry land, or must have been amphibious, that its great body might generally be borne up by water. The whale is the largest of animals, but feels not its mighty weight because lying constantly in the liquid support of the ocean. A cat may fall with impunity where an elephant or ox would be dashed to pieces. The giants of the heathen mythology could not have existed upon this earth, for the reason which we are now considering; although on our moon, where, as already stated, weight is much less, such beings might be. In the planet Jupiter, again, which is many times larger than the earth, an ordinary man from hence would be carrying, in the simple weight of his body, a load sufficient to crush the limbs which supported him. The phrase a little compact man, points to the fact that such a one is stronger in proportion to his size than a taller man. The same law limits the height and breadth of architectural structures. In the houses of fourteen stories, which formerly stood under the castle of Edinburgh, there was danger of the superincumbent wall crushing the foundation.

Roofs. Westminster hall approaches the limit of width that is possible without very inconvenient proportions or central supports; and the domes of the churches of St. Peter, in Rome, and St. Paul, in London, are in the same predicament.

Arches of a Bridge. A stone arch much larger than those of the magnificent bridges in London, would be in danger of crushing and splintering its material.

Ships. The ribs or timbers of a boat

have scarcely a hundredth part of the bulk of the timbers of a ship ten times as long as the boat. A ship's yard of ninety feet contains, perhaps, twenty times as much wood as a yard of thirty feet, and, even then, is not so strong in proportion. If ten men may do the work of a three-hundred-ton ship, many more than three times that number will be required to manage a ship three times as large. Very large ships, such as the two built in Canada in the year 1825, which carried each nearly 10,000 tons, are weak from their size alone; and the loss of these two first specimens of gigantic magnitude will not encourage the building of others like them.

The degree in which the strength of structures is dependent on the form and position of their parts, will be illustrated by considering the two cases of longitudinal and transverse compression; and the rule for giving strength will be found to be, to cause the force tending to destroy, to act, as equally as may be, on the whole resisting mass, at the same time, and with as little mechanical advantage as possible. In longitudinal compression, as produced by a body on the top of a pillar, the weight, while the support remains straight, can only destroy the support by crushing it in opposition to the repulsion and impenetrability of all its atoms. Hence a very small pillar, if kept perfectly straight, supports a very great weight; but a pillar originally crooked, or beginning to bend, resists with only part of its strength; for the whole weight above is supported on the atoms of the concave side only, which are therefore in greater danger of being overpressed and crushed, while those on the convex side, separated from their natural helpmates, are in the opposite danger of being torn asunder. The atoms near the centre, in such a case, are almost neutral, and might be absent without the strength of the pillar being much lessened. Long pillars or supports are weaker than short ones, because they are more easily bent; and they are more easily bent because a very inconsiderable, and therefore easily effected, yielding between each two of many atoms, makes a considerable bend in the whole; while in a very short pillar, there can be no bending without a great change in the relatior of proximate atoms, and such as can be effècted only by great force. The weight or force bending any pillar may be considered as acting at the end of a long lever, reaching from the end of the pillar to its centre, against the strength resisting at

a short lever from the side to the centre. The strength, therefore, has relation to the difference between these. Shortness, then, or any stay or projection at the side of the pillar, which, by making the resisting lever longer, opposes bending, really increases the strength of a pillar. A column with ridges projecting from it is, on this account, stronger than one that is perfectly smooth. A hollow tube of metal is stronger than the same quantity of metal in a solid rod, because its substance, standing farther from the centre, resists with a longer lever. Hence pillars of castiron are generally made hollow, that they may have strength with as little metal as possible. In the most perfect weighing beams for delicate purposes, that there may be the least possible weight with the required strength, the arms, instead of being of solid metal, are hollow cones, in which the metal is not much thicker than writing paper. Masts and yards for ships have been made hollow, in accordance with the same principle. In nature's works, we have to admire numerous illustrations of the same class. The stems of many vegetables, instead of being round externally, are ribbed or angular and fluted, that they may have strength to resist bending. They are hollow, also, as in cornstalks, the elder, the bamboo of tropical climates, &c., thereby combining lightness with their strength. A person who visits the countries where the bamboo grows, cannot but admire the almost endless uses to which its straightness, lightness and hollowness, make it applicable among the inhabitants. Being found of all sizes, it has merely to be cut into pieces of the lengths required for any purpose; and nature has already been the turner, and the polisher, and the borer, &c. In many of the Eastern islands, bamboo is the chief material of the ordinary dwellings, and of the furniture, the fanciful chairs, couches, beds, &c. Flutes and other wind instruments there are merely pieces of the reed, with holes bored at the requisite distances. Conduits for water are pipes of bamboo; bottles and casks for preserving liquids are single joints of larger bamboo, with their partitions remaining; and bamboo, split into threads, is twisted into rope, &c. From the animal kingdom, also, we have illustrations of our present subject-the hollow stiffness of the quills of birds; the hollow bones of birds; the bones of animals generally, strong and hard, and often angular externally, with light cellular texture within, &c.-Transverse Pressure. When

a horizontal beam is supported at its extremities, its weight bends it down more or less in the middle, the particles on the upper side being compressed, while the parts below are distended; and the bending and tendency to break are greater, according as the beam is longer and its thickness or depth is less. The danger of breaking, in a beam so situated, is judged of, by considering the destroying force as acting by the long lever reaching from the end of the beam to the centre, and the resisting force or strength as acting only by the short lever from the side to the centre, while only a little of the substance of the beam on the under side is allowed to resist at all. This last circumstance is so remarkable, that the scratch of a pin on the under side of a plank resting as here supposed, will sometimes suffice to begin the fracture. Because the resisting lever is small in proportion as the beam is thinner, a plank bends and breaks more readily than a beam, and a beam resting on its edge bears a greater weight than if resting on its side. Where a single beam cannot be found deep enough to have the strength required in any particular case-as for supporting the roof of a house several beams are joined together, and in a great variety of ways, as is seen in house-rafters, &c., which, although consisting of three or more pieces, may be considered as one very broad beam, with those parts cut out which do not contribute much to the strength.-The arched form bears transverse pressure so admirably, because, by means of it, the force that would destroy, is made to compress all the atoms or parts at once, and nearly in the same degree. The atoms on the under side of an arch, resting against immovable abutments, must be compressed about as much as those on the upper side, and cannot therefore be torn or overcome separately. The whole substance of the arch, therefore, resists, almost like that of a straight pillar under a weight, and is nearly as strong. To be able to adapt the curve to the size of an arch, and to the nature of the material, requires in the architect a perfect acquaintance with measures, &c. An error which has been frequently committed by bridge-builders is, the neglecting to consider sufficiently the effect of the horizontal thrust of the arch on its piers. Each arch is an engine of oblique force, pushing the pier away from it. In some instances, one arch of a bridge falling, has allowed the adjoining piers to be pushed down towards it, by the thrust, no longer balanced, of the arches beyond, and the

whole structure has given way at once, like a child's bridge built of cards. It is not known at what time the arch was invented, but it was in comparatively modern times. The hint may have been taken from nature; for there are instances, in alpine countries, of natural arches, where rocks have fallen between rocks, and have there been arrested and suspended, or where burrowing water has at last formed a wide passage under masses of rock, which remain balanced, among themselves, as an arch above the stream. Nothing can surpass the strength and beauty of some modern stone bridges-those, for instance, which span the Thames as it passes through London. Iron bridges have been made with arches twice as large as those of stone, the material being more tenacious, and calculated to form a lighter whole. That of three fine arches, between the city of London and Southwark, is a noble specimen; and, compared with the bridges of half a century ago, it appears almost a fairy structure of lightness and grace. The great domes of churches, as those of St. Peter's in Rome and St. Paul's in London, have strength on the same principle as simple arches. They are, in general, strongly bound at the bottom with chains and iron bars, to counteract the horizontal thrust of the superstructure. The Gothic arch is a pointed arch, and is calculated to bear the chief weight on its summit or key-stone. Its use, therefore, is not properly to span rivers as a bridge, but to enter into the composition of varied pieces of architecture. With what effect it does this, is seen in the truly sublime Gothic structures which adorn so many parts of Europe. The following are instances, in smaller bodies, of strength obtained by the arched form: A thin watchglass bears a very hard push; a dished or arched wheel for a carriage is many times stronger to resist all kinds of shocks than a perfectly flat wheel; a full cask may fall with impunity where a strong square box would be dashed to pieces; a very thin globular flask or glass, corked and sent down many fathoms into the sea, will resist the pressure of water around it, where a square bottle, with sides of almost any thickness, would be crushed to pieces. We have an illustration, from the animal frame, of the arched form giving strength, in the cranium or skull, and particularly in the skull of man, which is the largest in proportion to its thickness: the brain required the most perfect security, and, by the arched form of the skull, this has been obtained with little weight. The

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common egg-shell is another example of the same class: what hard blows of the spoon or knife are often required to penetrate this wonderful defence provided for the dormant life! The weakness of a similar substance, which has not the arched form, is seen in a scale from a piece of freestone, which so readily crumbles between the fingers. To determine, for particular cases, the best forms of beams and joists, and of arches, domes, &c., is the business of strict calculation, and belongs, therefore, to mathematics, or the science of measures. It was a beautiful problem of this kind, which Mr. Smeaton, the English engineer, solved so perfectly in the construction of the farfamed Eddystone light-house. (See LightHouse.)

About the year

STRENGTH, FEATS OF. Doctor Brewster, in his work on Natural Magic, gives some striking instances of muscular strength, and also of the effects produced by applying the principles of the mechanical powers to the human frame, from which we extract the following:-Firmus, a native of Seleucia, who was executed by the emperor Aurelian for espousing the cause of Zenobia, was celebrated for his feats of strength. In his account of the life of Firmus, who lived in the third century, Vopiscus informs us, that he could suffer iron to be forged upon an anvil placed upon his breast. In doing this, he lay upon his back, and, resting his feet and shoulders against some support, his whole body formed an arch, as we shall afterwards more particularly explain. Until the end of the sixteenth century, the exhibition of such feats does not seem to have been common. 1703, a native of Kent, of the name of Joyce, exhibited such feats of strength in London and other parts of England, that he received the name of the second Samson. His own personal strength was very great; but he had also discovered, with out the aid of theory, various positions of the body, in which men even of common strength could perform very surprising feats. He drew against horses, and raised enormous weights; but as he actually exhibited his power in ways which evinced the enormous strength of his own muscles, all his feats were ascribed to the same cause. In the course of eight or ten years, however, his methods were. discovered, and many individuals of ordinary strength exhibited a number of his principal performances, though in a manner greatly inferior to Joyce. Some time afterwards, John Charles van Eckeberg,

a native of Harzgerode, in Anhalt, travelled through Europe, under the appellation of Samson, exhibiting very remarkable examples of his strength. This, we believe, is the same person whose feats are particularly described by doctor Desaguliers. He was a man of the middle size, and of ordinary strength; and, as doctor Desaguliers was convinced that his feats were exhibitions of skill, and not of strength, he was desirous of discovering his methods; and, with this view, he went to see him, accompanied by the marquis of Tullibardine, doctor Alexander Stuart, and doctor Pringle, and his own mechanical operator. They placed themselves round the German so as to be able to observe accurately all that he did; and their success was so great, that they were able to perform most of the feats the same evening by themselves, and almost all the rest when they had provided the proper apparatus. Doctor Desaguliers exhibited some of the experiments before the royal society, and has given such a distinct explanation of the principles on which they depend, that we shall endeavor to give a popular account of them. 1. The performer sat upon an inclined board with his feet a little higher than his hips. His feet were placed against an upright board well secured. Round his loins was placed a strong girdle with an iron ring in front. To this ring a rope was fastened. The rope passed between his legs through a hole in the upright board, against which his feet were braced, and several men or two horses, pulling on the rope, were unable to draw him out of his place. 2. He also fastened a rope to a high post, and, having passed it through an iron eye fixed in the side of the post some feet lower down, secured it to his girdle. He then planted his feet against the post near the iron eye, with his legs contracted, and, suddenly stretching out his legs, broke the rope, and fell backwards on a feather bed. 3. In imitation of Firmus, he laid himself down on the ground, and when an anvil was placed upon his breast, a man hammered with all his force a piece of iron, with a sledge-hammer, and sometimes two smiths cut in two with chisels a great cold bar of iron laid upon the anvil. At other times, a stone of huge dimensions was laid upon his belly, and broken with a blow of the great hammer. 4. The performer then placed his shoulders upon one chair, and his heels upon another, forming with his back-bone, thighs and legs, an arch. One or two men then stood upon his belly,

rising up and down while the performer breathed. A stone one and a half feet long, one foot broad, and half a foot thick, was then laid upon his belly and broken by a sledge-hammer-an operation which was performed with much less danger than when his back touched the ground. 5. His next feat was to lie down on the ground. A man being then placed on his knees, he drew his heels towards his body, and, raising his knees, he lifted up the man gradually, till, having brought his knees perpendicularly under him, he raised his own body up, and, placing his arms around the man's legs, rose with him, and set him down on some low table or eminence of the same height as his knees. This feat he sometimes performed with two men in place of one. 6. In his last, and apparently most wonderful performance, he was elevated on a frame work, and supported a heavy cannon placed upon a scale at some distance below him, which was fixed to a rope attached to his girdle. Previous to the fixing of the scale to the rope attached to his girdle, the cannon and scale rested upon rollers; but when all was ready, the rollers were knocked away, and the cannon remained supported by the strength of his loins. These feats may be briefly explained thus:-The feats No. 1, 2 and 6, depend entirely on the natural strength of the bones of the pelvis, which form a double arch, which it would require an immense force to break, by any external pressure directed to the centre of the arch; and as the legs and thighs are capable of sustaining four or five thousand pounds when they stand quite upright, the performer has no difficulty in resisting the force of two horses, or in sustaining the weight of a cannon weighing two or three thousand pounds. The feat of the anvil is certainly a very surprising one. The difficulty, however, really consists in sustaining the anvil; for when this is done, the effect of the hammering is nothing. If the anvil were a thin piece of iron, or even two or three times heavier than the hammer, the performer would be killed by a few blows; but the blows are scarcely felt when the anvil is very heavy, for the more matter the anvil has, the greater is its inertia, and it is the less liable to be struck out of its place; for when it has received by the blow the whole momentum of the hammer, its velocity will be so much less than that of the hammer as its quantity of matter is greater. When the blow, indeed, is struck, the man feels less of the weight of the anvil than he did be

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