34

HISTORY OF ENGINEERING.

Book I.

siderably advanced. All the streets were set out at right angles with each other, and morethan a third of the area comprised within the walls was devoted to public purposes.

Every private dwelling had its reservoir of water provided for it, which was supplied bysubterranean conduits from the Nile ; all built of stone, with flat terraces at the top,which answered for their covering, timber being sparingly used in the construction. Thecisterns and conduits were lined with a fine cement, which remains perfect at thepresent day.

To render the harbour approachable at all times, a lighthouse was built on a rock somedistance from the eastern extremity of the Isle of Pharos, which was long consideredone of the wonders of the world, and which has given a name to all others. A mole unitedthe rock with the mainland, and Sostratus of Cnidos , who was so esteemed by PtolemyPhiladelphus that he was surnamed the friend of kings, was the engineer employedfor its construction. This pharos was in height 450 feet, and could be seen at a distanceof 100 miles. It was formed of several stories, decreasing in dimension towards the top,where fires were lighted in a species of lantern. The ground-floor was hexagonal; thesides alternately concave and convex; each a stadium in length; the second and thirdstories were of the same form: the fourth was square, with a round tower at eachangle; and the fifth circular, continued to the top, to which a winding staircaseconducted.

The whole, exquisitely wrought in stone, was surrounded entirely by a sea-wall: onentering the harbour, this wonderful structure was on the right hand, and the pro-montory of Lochias to the left, where was placed the palace or royal residence, near whichwas the island, called Antirhodus, which contained a small harbour, devoted entirely tothe reception of the royal vessels. The ancient causeway now forms the site of part of themodern town, and is in length about 4000 feet; on the easternmost side is the great har-bour, and on the western that of Eunostus, or, as it is now called, the ancient port. Hereis a basin or kibotus, which by means of a canal communicates with the Lake Mareotis,the dimensions of which Strabo says were 300 stadia in length, 100 in breadth, and thatit contained 8 islands.

Alexandria was second in importance only to Rome itself: its circumference was 15 miles,and its population estimated at 300,000 free inhabitants, besides an equal number of slavesand dependents. In its streets idleness was unknown : some were employed in blowingglass, in weaving linen, and manufacturing papyrus.

When Ccesar arrived at Alexandria, he sent to Rhodes, Syria , and Cilicia for his fleet;and upon reconnoitring the town, he found all the avenues and passes shut up by a triplewall, 40 feet in height, built of squared stone. The lower portions of the city were de-fended by lofty towers, ten stories in height. There were many timber structures of thesame height, movable on wheels, which could be drawn by horses. We also learn thathe found Alexandria almost hollow underneath, from the many aqueducts that furnishedthe private houses with water from the Nile , where, being received into cisterns, it wasallowed to throw down the earthy matter, and become perfectly clear. Ganymed, theAlexandrian general, to deprive the Romans of a supply in that part of the city of whichthey had taken possession, stopped the current through these subterraneous passageswhich led from the Nile , and turned salt-water into them, which caused great wonder aswell as inconvenience to the Romans. Cajsar, on the discovery, ordered his soldiers to findwater by digging wells, telling them that on all sea-coasts fresh springs abounded ; and thealacrity used was so great, that they arrived at fresh water in abundance the first nightafter the digging commenced.

Smelting and refining metals. The Egyptians began this process by pounding theirgolden ore, and reducing it to very small grains; they then put it into a mill, and groundit to powder; after which it was spread on boards slightly inclined: water was then madeto flow over it, which carried away the earthy particles. After the watering had beenfrequently repeated, it was rubbed by the workmen for some time between theirhands, and wiped with small sponges, until nothing was left but the gold. It was thenput into earthen pots, and mixed with certain proportions of lead, salt, tin, and barley meal:after this it was poured into other vessels, which were luted with great care and placed in arefining furnace for five days and nights; these were then taken out and suffered to cool,when the gold was found to be quite pure. They do not appear, according to Pliny , tohave used quicksilver, for the refining of either gold or silver : lead was the menstruum,and by frequent meltings the pure metal was obtained. The great quantity of gold used bythis people convinces us that the art of mining, smelting, and refining that metal was wellunderstood.

Forging metals was known in Egypt at the earliest time; most of the arms, tools forhusbandry and the mechanical arts, were usually made of copper or brass, though in thetime of Moses we find iron well known. He describes its hardness, speaks of mines, andmentions the iron furnaces, and tools for cutting stone, made of iron.

Hydraulics. In the school of Alexandria, which flourished under the patronage of the