roots of the felled trees are often not removed; and in marshes, where the ground is wet and soft, the trees themselves are cut in lengths of about ten or twelve feet, and laid close to each other across the road, to prevent vehicles from sinking, forming what is called in America a Corduroy road,' over which the coach advances by a series of leaps and starts, particularly trying to those accustomed to the comforts of European travelling.

6

"On the road leading from Pittsburg on the Ohio to the town of Erie on the lake of that name, I saw all the varieties of forest road-making in great perfection. Sometimes our way lay for miles through extensive marshes, which we crossed by corduroy roads; at others the coach stuck fast in mud, from which it could be extricated only by the combined efforts of the coachman and passengers; and at one place we travelled for upwards of a quar. ter of a mile through a forest flooded with water, which stood to the height of several feet on many of the trees, and occasionally covered the naves of the coach-wheels. The distance of the route from Pittsburg to Erie is 128 miles, which was accomplished in forty-six hours, being at the very slow rate of about two miles and three quarters an hour, although the conveyance by which I trav elled carried the mail, and stopped only for breakfast, dinner, and tea, but there was considerable delay caused by the coach being once upset and several times' mired.'

"The best roads in the United States are those of New Engand, where, in the year 1796, the first American turnpike act was granted. These roads are made of gravel; a material which, by the way, is much used for road-making in Ireland. The surface of the New England roads is very smooth; but as no attention has been paid to forming or draining them, it is only for a few meaths during summer that they possess any superiority, or are, in fact, at all tolerable. In Virginia and all the states lying to the south, as well as throughout the whole country to the westward of the Alleghany mountains, the roads, I believe, are, generally speaking, of the same description as the one already mentioned between Pittsburg and Erie, affording very little comfort or facility to those who have the misfortune to be obliged to travel upon them.

"But on the construction of one or two lines of road, the Ameri. cans have bestowed a little inore attention. The most remarkable of them is that called the 'National Road,' stretching across the country from Baltimore to the state of Illinois, a distance of no less than seven hundred miles, an arduous and extensive work, which was constructed at the expense of the government of the United States. The narrow tract of land from which it was necessary to remove the timber and brushwood for the passage of the road,

measures eighty feet in breadth; but the breadth of the road itself is only thirty feet. The line of the National Road' commences at Baltimore, passes through part of the state of Maryland, and entering that of Pennsylvania, crosses the range of the Alleghany mountains, after which it passes through the states of Virginia, Ohio, and Indiana, to Illinois. It is in contemplation to produce his line of road to the Mississippi at St. Louis, where, the river peing crossed by a ferry-boat stationed at that place, the road is ultimately to be extended into the state of Missouri, which lies to the west of the Mississippi.

"The Macadamized road,' as it is called, leading from Albany to Troy, is another line which has been formed at some cost, and with some degree of care. This road, as its name implies, is constructed with stone broken, according to Macadam's principle. It is six miles in length, and has been formed of a sufficient breadth to allow three carriages to stand abreast on it at once. It belongs to an incorporated company, who are said to have expended about £20,000 in constructing and upholding it.

"Some interesting experiments have lately been set on foot at New York, for the purpose of obtaining a permanent and durable city road, for streets over which there is a great thoroughfare. The place chosen for the trial was the Broadway, in which the traffic is constant and extensive.

"The specimen of road-making first put to the test was a species of causewaying or pitching; but the materials employed are round water-worn stones, of small size; and their only recommendation for such a work appears to be their great abundance in the neighborhood of the town. The most of the streets in New York, and indeed in all the American towns, are paved with stones of this description; but, owing to their small size and round form, they easily yield to the pressure of carriages passing over them, and produce the large ruts and holes for which American thoroughfares are famed. To form a smooth and durable pavement, the pitching-stones should have a considerable depth, and their opposite sides ought to be as nearly parallel as possible, or, in other words, the stones should have very little taper. The footpaths in most of the towns are paved with bricks set on edge, and bedded in sand, similar to the clinkers,' or small hard-burned bricks so generally used for road-making in Holland.

"The second specimen was formed with broken stones, but the materials, owing chiefly, no doubt, to the high rate of wages, are not broken sufficiently small to entitie it to the name of a‘Macadamized road.' It is, however, a wonderful improvement on the ordinary pitched pavement of the cour ry, and the only objections

to its general introduction are the prejudicial effects produced on i by the very intense frost with which the country is visited, and the expense of keeping it in repair.

"The third specimen is rather of an original description. It consists of a species of tesselated pavement, formed of hexagonal billets of pine wood measuring six inches on each side, and twelve inches in depth arranged as shown in the annexed

cut, in which the larger diagram is a view of part of the surface of the pavement, and the smaller, one of the billets of wood of which it is composed, shown on a larger scale. From the manner in which the timber is arranged, the pressure falls on it parallel to the direction in which its fibres lie, so that the tendency to wear is very small. The blocks are coated with pitch or tar, and are set in sand, forming a smooth surface for carriages, which pass easily and noiselessly over it. There can be no doubt of the suitableness of wood for forming a roadway; and such an improvement is certainly much wanted in all American towns, and in none of them more than in New York. Some, however, have expressed a fear that great difficulty would be experienced in keeping pavements constructed in this manner in a clean state, and that during damp weather a vapor might arise from the timber, which, if it were brought into general use, would prove hurtful to the salubrity of large towns.

"In the no. thern parts of Germany and also in Russia, wooden pavements are a good deal used. My friend Dr. D. B. Reid in. forms me, that at St. Petersburg a wooden causeway has been tried with considerable success. The billets of wood are hexagonal, and are arranged in the manner represented in the diagram of the American pavement. At first they were simply imbedded in the ground, but a great improvement has been introduced by placing them on a flooring of planks laid horizontally, so as to prevent them from sinking unequally. This has not, so far as I know been done in America."

Archimedes.

This celebrated philosopher of antiquity was a native of Syra use in Sicily, and is supposed to have been born about two hundred and eighty years before the commencement of the Christian

era.

In proof of Archimedes' knowledge of the doctrines of specific gravities, a singular fact is related in Vitruvius. Hiero, king of Syracuse, suspecting that in making a golden crown which he had ordered, the workmen had stolen part of the gold, and substituted in its stead an equal weight of silver, he applied to Archimedes, entreating him to exercise his ingenuity in detecting the fraud. Contemplating the subject one day as he was in the bath, it occurrea to him that he displaced a quantity of water equal to the bulk of his own body. Quitting the bath with that eager and impetuous delight which a new discovery naturally excites in an inquisitive mind, he ran naked into the street, crying, Eureka! Eureka! [I have found it out! I have found it out!] Procuring a mass of gold, and another of silver, each of equal weight with the crown, he observed the quantity of fluid which each displaced, successively, upon being inserted in the same vessel full of water; he then observed how much water was displaced by the crown; and, upon comparing this quantity with each of the former, soon learned the proportions of silver and gold in the crown

In mechanics and optics the inventive powers of Archimedes were astonishing. He said, with apparent, but only apparent, extravagance, "Give me a place to stand upon, and I will move the earth; for he perfectly understood the doctrine of the lever, and well knew, that, theoretically, the greatest weight may be moved by the smallest power. To show Hiero the wonderful effect of mechanic powers, he is said, by the help of ropes and pulleys, to have drawn towards him, with perfect ease, a galley which lay on shole, manned and loaded. But the grand proofs of his skill were given during the siege of Syracuse by Marcellus. Whether the vessels of the besiegers approached near the walls of the city, or kept at a considerable distance, Archimedes found means to annoy them. When they ventured closely under the rampart raised on the side towards the sea, he, by means of long and vast beams, probably hung in the form of a lever, struck with prodigious force upon the galleys, and sunk them: or by means of grappling hooks at the remote extremity of other levers, he caught up the vessels into the air, and dashed them to pieces against the walls or the projecting rocks. When the enemy kept at a greater distance, Archimedes made use of machines, by which he threw from behind the walls stones in vast masses, or great numbers, which shattered and demolished the ships or the machines employed in the siege. This mathematical Briareus, as Marcellus jestingly called him, employed his hundred arms with astonishing effect. His me. chanical genius was the informing soul of the besieged city; and his powerful weapons struck the astonished Romans with terror

One, in particular, consisting of a mirror, by which he concentra. ted the rays of the sun upon the besieging vessels and set them or fire, must have produced an extraordinary impression upon those who suffered from it, seeing that it was of so wonderful a character as to be thought a fiction by subsequent ages, until its reality was proved by the repetiton of the experiment. Buffon contrived and made a burning-glass, composed of about four hundred glass olanes, each six inches square, so placed as to form a concave mirror, capable of melting silver at the distance of fifty feet, and tead and tin at the distance of one hundred and twenty feet, and of setting fire to wood at the distance of two hundred feet; and the story of Archimedes' instrument for burning ships at a great disance was no longer ridiculed.

Eminent as Archimedes was for his skill and invention in me. chanics, his chief excellence, perhaps, lay in the rare talent which ae possessed of investigating abstract truths, and in inventing conclusive demonstrations in the higher branches of pure geometry. If we are to credit the representation of Plutarch, he looked upon mechanic inventions as far inferior in value to those intellectual speculations which terminate in simple truth, and carry with them irresistible conviction. Of his success in these lucubrations, the world is still in possession of admirable proofs in the geometrical treatises which he left behind him. Of the unremitting ardor with which he devoted himself to mathematical studies, and the deep attention with which he pursued them, his memoirs afford striking and interesting examples. It is related of him, that he was often so totally absorbed in mathematical speculations, as to neglect his meals and the care of his person. At the bath he would frequently draw geometrical figures in the ashes, or, when according to the custom he was anointed, upon his own body. He was so much

delighted with the discovery of the ratio between the sphere and the containing cylinder, that, passing over all his mechanic inventions, as a memorial of this discovery, he requested his friends to place upon his tomb a cylinder, containing a sphere, with an inscription expressing the proportion which the containing solid bears to the contained.

No sincere admirer of scientific merit will read without painful regret, that when Syracuse, after all the defence which philosophy had afforded it, was taken by storm, and given up to the sword, not withstanding the liberal exception which Marcellus had made in favor of Archimedes, by giving orders that his house and his person should be held sacred, at a moment when this great man was so intent upon some mathematical speculation as not to perceive that the city was taken, and even when, according to Cicero, he