a single individual, and which has excited a very high degree of interest in every part of Europe. We regret to add, that this magnificent structure no longer exists, and that scarcely a trace of it is to be seen upon the flanks of Mount Pilatus. Political circumstances having taken away the principal source of the demand for timber, and no other market having been found, the operation of cutting and transporting the trees necessarily ceased.

Professor Playfair, who visited this singular slide, states, that six minutes was the usual time occupied in the descent of a tree, but that in wet weather it reached the lake in three minutes.

American Road-making.

"Road-making* is a branch of engineering which has been very little cultivated in America; and it was not until the introduction of railways that the Americans entertained the idea of transporting heavy goods by any other means than those afforded by canals and slackwater navigation. Their objection to paved or Macadamized roads such as are used in Europe, is founded on the prejudicial effects exerted upon works of that description by the severe and protracted winters by which the country is visited, and also the difficulty and expense of obtaining materials suitable for their construction, and for keeping them in a state of proper repair. Stone fitted for the purposes of road-making is by no means plentiful in America; and as the number of workmen is small in proportion to the quantity of work which is generally going forward in the country, manual labor is very expensive. Under these circumstances, it is evident that roads would have been a very costly means of communication, and as they are not suitable for the transport of heavy goods, the Americans, in commencing their internal improvements, directed their whole attention to the construction of canals, as being much better adapted to supply their wants.

"The roads throughout the United States and Canada are, from these causes, not very numerous, and most of those by which I travelled were in so neglected and wretched a condition as hardly to deserve the name of highways, being quite unfit for any vehicle but an American stage, and any pilot but an American driver. In many parts of the country, the operation of cutting a track through the forests of a sufficient width to allow vehicles to pass each other, is all that has been done towards the formation of a road. The

* Stevenson's Engineering in North America.

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.

"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 quarter 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 England, 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 months 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 Americans have bestowed a little more 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 this line of road to the Mississippi at St. Louis, where, the river being 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 entitle it to the name of a 'Macadamized road.' It is, however, a wonderful improvement on the ordinary pitched pavement of the country, and the only objections

to its general introduction are the prejudicial effects produced on it 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 northern parts of Germany and also in Russia, wooden pavements are a good deal used. My friend Dr. D. B. Reid informs 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 Syracuse 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 occurred 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 shore, 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 mechanical genius was the informing soul of the besieged city; and his powerful weapons struck the astonished Romans with terror.