Mr. Rendel had given it as his opinion, that the latter action resulted from the former, the system of trussing adopted by him at the Montrose Bridge, would appear calculated to obtain the desired end. A slight exertion of force would produce a perceptible undulation, and a certain degree of vibration would result from the natural elasticity of the materials.

Mr. Seaward remarked, that the degree of oscillation would appear to depend in some measure upon the distance at which the platform was suspended beneath the chains, and upon the distance between the points of suspension of the main chains; if the platform was rigidly held at the extremities, the motion would be vibratory, and not amounting to undulation.

Original Communication.

ON THE ENGINEERING OF THE ANCIENT

EGYPTIANS.

BY J. S. PERRING, ESQ.

No. III.

The two former papers have treated more particularly of the Hydraulic Engineering of the Egyptians; and in this branch of the varied practice of engineering they attained great proficiency. They were close and careful observers of nature; and hydraulic engineering derives all its information from, and depends for its success, solely on natural operations. The peculiar features of the country also, as before observed, made its study of first-rate national importance.

The observation, that in a river, whose waters are charged with earthy particles, the effect of a few stones or other impediment breaking the force of the stream, and causing an eddy or still water behind, was to cause the accumulation of soil by deposit, may be supposed to have led to the formation of jetties or breakwaters at certain distances along the river throughout Nubia, where the space in the valley was confined. By these the limited soil, on the banks of the stream, was increased; and, when so increased, protected from the scour of the current.

These jetties are still remaining, and serve the same purpose; and an engineer, on contemplating their utility, may be cheered with the idea, that some of his own works may perchance, after the lapse of forty centuries, continue to serve the same benificent purpose for which they were formed. Between these jetties the water always flows in the same channel, and they also serve to form a shelter for the small vessels of the country.

The number of natural harbours on the coast of the Red Sea, and the small amount of Egyptian trade on the Mediterranean, made the formation of artificial harbours on the coast unnecessary. The mechanical skill of the Ancient Egyptians is shewn by the ease with which they managed large masses of stone, and placed them either upright as obelisks, or raised them to great heights for the architraves and roof-blocks of their temples. Indeed, much of the peculiar character of their monuments may be ascribed to this skill, and made the use of the arch unnecessary. Though the arch seems to have been in common use among them, for ordinary buildings, it would appear that they considered it merely as an expedient, and aware of its selfdestroying properties, preferred covering spaces by single blocks

of stone.

The invention of the arch has been a subject of much discussion; some authors, tracing all our knowledge from the Greeks, have ascribed to them the honor of the invention; but it does not occur in any of their buildings previous to Alexander. But, as the Greek connection with Egypt commenced at that period, there seems to us but little doubt but that they borrowed the idea from thence.

A slight outline of the history of the arch, as derived from Egyptian monuments, will not be uninteresting. The sculptures on the walls of the tombs of Beni Hassan, executed in the reign of Osirtesen I., (about the era of Joseph,) afford ample proof that the arch was used in the construction of their granaries and houses, and that its invention had been perfected. But this must have taken place between the building of the pyramids and this era, for we have negative proof, that at the early period of the erection of these monuments, they were not acquainted with its use. For though at no period do they seem to have used the arch in situations where its own pressure might have the effect of thrusting out and destroying its abutments,—that is, in any erections, yet there are many places in the pyramids, where either the mass was sufficient to prevent any fear of such result, or where the springing might have been from the solid rock. But, in their edifices, they resorted to other methods whenever it was necessary to cover a space; thus, the principal apartment of the Great Pyramid of Ghizet is covered with large flat blocks of granite; but where great strength was required, they

either covered the space with inclined blocks of stone of great magnitude, meeting in the centre and forming pointed roofs, or each course of stones, above a certain height, was made to project 3 or 4 inches over the one below it, until the opposite sides nearly met, and were then covered by flat blocks; but in no instance do we see any thing involving the principle of the arch. Thus we may fairly conclude, that when the pyramids were erected, the arch was unknown; but it seems to have been in common use in the reign of Osirtesen, and therefore, the invention must have been made and perfected betwen 2100 and 1700 B.C.; but, as there are no buildings now met with in Egypt of the intermediate period, we are unable to trace the progress of this important invention.

After that, we meet with several instances of it :-the roof of a tomb at Thebes, discovered by Sir Gardner Wilkinson, is formed, like many others near it, of crude bricks, built as a regular arch, and bears the name of Ammeoph I., who reigned about 1540 years before our era; and near the Mennorium are many arches of the same material, evidently belonging to the reign of the great Sesostris, or 1350 B.C. But the oldest stone arch in existence, whose age is positively known, is but little older than Tirhaka, about 700 B.Ĉ., and is in the portico of one of the pyramids of Meroe. In all their edifices of stone, in Egypt, (being the temples of their gods, and built for eternal duration,) the Egyptians seem to have carefully avoided the arch, as aware that it carried with it the elements of its own destruction.

The chief object of an Egyptian architect was stability; hence all weights and pressure were vertical; and though the sides of the walls were often inclined, the beds of the stones composing them were always horizontal; and so careful were they to avoid any chance of rupture, that the architrave was not allowed, in columnar buildings, to press immediately on the capital of a column, but an intermediate member was introduced, of a cubical shape, but often decorated, which being immediately over the centre of the column, was supported by it, and carried the superincumbent weight clear of the ornamental portion of the column.

Using large blocks and keeping the pressure vertical, the Egyptians did not consider it necessary to use any strong adhesive cement; hence they paid but little attention to the composition of their mortars, but generally bound together the stones of a course with cramps or dogs of bronze or wood.

There is an impression, that Egyptian architecture is grotesque, and delights in odd forms and combinations ;-this is at variance with the truth; its grand features are severity of form and simplicity of shape, more or less removed from but always allied to its original type, the pyramid; and its ornaments directly imitated.

from natural productions around it. Thus it is essentially grand and imposing, more from simplicity than real magnitude. It carries with it an air of repose, arising from the absence of any finely proportioned part or balance of pressure that was necessary to sustain the edifice; but, as Gare observes, to form a proper judgment, we ought to view the monuments of Egypt in connection with the scale of the country. We ought to see them surrounded by these immense deserts, which presenting no character but monotony and extent, still possess that of grandeur. In the midst of such localities, it was necessary that the effect of the monuments should be in harmony with them;-all subdivisons would have appeared mean. These columns of an enormous diameter, those door-ways beyond all usual size, and the lofty propyla, are perfectly in unison with the places which surround them.

The conveyance of an obelisk from the quarry, and still more arduous task of raising it on its pedestal, were no doubt celebrated with pomp and ceremony; and yet it is singular that we do not find any sculptures illustrative of the methods whereby they were effected.

Obelisks were always of single stones, from the granite quarries of Essouan; the distance from Thebes, where they abounded, being 138 miles, and from Heliopolis 800; but, as Sir Gardner Wilkinson remarks, "the power to move the mass was the same, whatever might be the distance; and the mechanical skill which transported it five, or even one, would suffice for any number

of miles."

One of these monuments, weighing about 246 tons, has been removed from Thebes, by a celebrated and scientific French engineer, M. Lebas, and re-erected in Paris. His very ingenious method of lowering and raising it, is above all praise, but requires illustration to explain it properly.* But it is singular, that upon some sculptures on the neighbouring temple of Karnack, where the Egyptian Army are represented as engaged in clearing a passage through a forest, they are lowering the large trees in precisely the same manner; and it may therefore be concluded that they extended the application of this very simple and efficient principle to the raising of their obelisks.

From a passage in Pliny,† it would appear that these immense masses were transported to their destination by water, -as he speaks of an obelisk having been moved in the following manner:- "A canal was dug from the river to the place where the obelisk lay, and two boats were placed side by side, and filled with pieces of stone, of the same material as the obelisk. These

* Vide M. Lebas's Memoir on the subject.

Pliny Bk. 36, c. 9.

pieces were in the shape of a brick, and a foot in length, so that the proportion between the quantity of matter in the obelisk and that held by the boats, could be determined. The two boats were loaded to twice the weight of the obelisk, in order that they might go under it, its two ends resting on the two sides of the canal. Then, as the pieces of stone were taken out, the boats of course rose together, and at last supported the obelisk, and carried it off."

Herodotus also mentions a Monolith, brought from Elephantine to Sais by boatmen, and therefore, his account confirms that of Pliny, that these huge masses were conveyed by water.

It would be out of place here to particularize each Monolith of which history makes mention; the one above alluded to by Herodotus, is said by him to have occupied 2000 men for three years; but as it appears to have been conveyed by water, it is probable that they were not the whole of that period engaged in the task, but rather that it occupied them during three seasons of three successive years, while the water was high enough to float the enormous mass.

Herodotus also informs us, that in moving it near the temple, it was managed by levers; but we do not glean, to a certainty, from his account, whether it was canted over or conveyed on a sledge, though the former would appear to have been the method used, as he speaks of a man having been crushed beneath it. In modern India, stones are often moved by being made up with timber, or formed of a cylindrical shape, and then rolled over to their destination; and, by the form of some masses near Heliopolis, it seems likely that the same method was sometimes used by the Egyptians.

But the most usual method, when the stone had received its shape, was by sledge, drawn by oxen when the mass was small, and by men when of a large size; and it would appear that great bodies of men were thus employed. In a grotto, discovered by the Baron Minuitoli, near El Bersheh, is a representation of a colossus on a sledge, which a number of men are employed in dragging with ropes. Judging by the proportion of the statue to the objects around, it appears to have weighed about 120 tons, and the number of men shewn dragging the sledge are 172, an insufficient force; but it is probable that the artist had no intention of representing a determinate number, or, for the sake of effect, he may have increased the dimensions of the colossus. The sledge is straight below, but curved up a little in front; and to this part are attached four ropes, at which the men are drawing, and a person standing on the front of the sledge pours on the ground or platform, whereon the sledge is

* Vide Bk. II. 175.