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HISTORY OF ENGINEERING.

Book I.

at that height the heads of the piles are cut oft’ level, and the platform of the quay is coveredwith planking. The whole of these works are executed with unsquared timber, and areneither painted nor covered with pitch or tar.

On some of the quays which extend for a considerable distance into the harbour, rows ofwarehouses are constructed.

At Boston are the only graving docks which belong to the government of the United States : one is in length 341 feet, in breadth 80 feet; the depth of water is 30 feet, but thefall of the tide being only 13 feet, 17 feet are pumped out by means of a steam-enginewhenever a vessel is admitted for repair. These docks are constructed in an admirablemanner in granite, at an expense of upwards of 150,000/. each. They were executed underthe able direction of Mr. Baldwin, the government engineer.

To connect some portions of the neighbourhood of Boston as well as to form a largebasin, an embankment of earth 8000 feet in length has been thrown up, confined betweentwo stone walls; and the water contained in the basin is made to turn machinery connectedwith some manufactories.

New York , the capital of that state, is situated on the southern extremity of ManhattanIsland, at the point of confluence of the Hudson with the east river. 'Die inner bay isperhaps the finest in the world : it is completely land-locked, and affords excellent anchorage;the entrance through the narrows is very beautiful and picturesque, the shore being studdedwith trees down to the water’s edge, mixed with farms, cottages, and villas.

From New York to the Bar between Sandy Nook Point and Schryers Island, whichseparates the outer harbour from the Atlantic , is 17 miles.

The tide flows up the Hudson for 160 miles above New York as far as Troy, and thesenatural advantages have been further improved by an extensive system of canals, whichconnect with the Lakes Erie and Ontario. One omission has, however, rendered thisbeautiful harbour a source of serious evil; from there not being any sewers in the town, theharbour becomes the receptacle of every impurity, and fevers of the worst kind are the con-stant results of the effluvia.

There are screw and hydraulic docks; the latter arc worked with a Bramah ’s press,and by means of a timber platform, swung between two frames, the loaded vessels are liftedabove the water. Twenty chains or more, on each side of the timl>er platforms, pass overiron pulleys supported above, and the platform bearing the vessel rises by the injection ofwater with a cast-iron cylinder attached, which moves a horizontal beam fastened to thesuspended chains.

The cylinder and ram are surrounded by masonry, and rendered perfectly stable ; the ex-ternal diameter of the cylinder is 28 inches, its internal 12 inches, and that of the ramwhich works it 11 inches, and 10 feet in length, which has a power sufficient to raise avessel of 800 tons. The water is injected into the cylinder by a steam-engine of high pres-sure and six horse power ; when the vessel is to be lowered, it is merely necessary to letthe water escape slowly from the cylinder, and the platform gradually descends.

Philadelphia is the city and sea-port of the state so named, and is at the conflux of theDelaware and Schuylkill. Vessels of the largest burthen ascend the river as far as New-castle, but those drawing 18 or 20 feet water cannot reach Philadelphia , in consequence ofa bar a little below the city. The harbour is a vast arm of the sea, navigable for 100miles from the Atlantic .

Baltimore y a city of Maryland , is on the north side of the Patapsco river, about fourteenmiles above its entrance into the Bay of Chesapeake . The harbour is a fine expanse ofwater, and capable of containing upwards of 2000 vessels.

Charlestown in South Carolina , is built upon a point of land between the Ashley andCooper rivers ; the harbour is spacious and convenient, but the entrance has many sand-banks. The depth of water on the shallowest part of the bar at ebb-tide is 12 feet, and atflood from 17 to 18 feet; whilst in the middle channel at low water, it does not exceed 9feet. A lighthouse has been erected 80 feet in height, with a revolving light.

New Orleans is stiuated on the eastern bank of the great Mississippi , about 105 milesfrom its mouth ; the depth of water opposite the city is about 70 feet, but the ebb and flowof the tide do not extend to it.

The Canals in the United States exceed in length more than 3000 miles; wherever in-ternal navigation cannot be obtained by the removal of obstructions in the great rivers, anartificial cut is introduced ; no labour has been spared to render water conveyance com-plete. Many of the canals are carried over wide rivers on timber viaducts, and often passfor miles through dense uninhabited forests. Some are so wide and deep as to admit thepassage of steamers through them. By one the Gulf of Mexico is united to the Mississippi and St. Lawrence: a river and canal navigation extends from New York to New Orleans ,a distance of upwards of 2700 miles, 672 of which are by the Erie and Ohio canals.

The Erie Canal is one of the most important in the United States ; its entire length is363 miles ; after leaving Albany , it passes along the right banks of the Hudson and Mohawkrivers, crossing the latter at Middleton : it then continues its course for twelve miles on