nd of the cylinder.
The Haupt drill is supported on four adjustable legs, and is sufficiently light to be moved by two men, and is operated by a single man with 2-horse power of steam; at 30 to 40 pounds pressure it drills a 1 3/8-inch hole in hard limestone, at the rate of 5 inches per minute.
Compressed air may be used, and the machine has the usual horizontal, angular, and vertical adjustments.
Shelburne's submarine rock-drill, employed for removing the obstructions at Hellgate, is supported on a semi-spheroidal hollow cast-iron base, having three steel feet, which insure its stability on the rock.
The drill frame is conical in shape, and is made of wrought-iron, the drill-shaft passing through an opening in its top. The drill is operated by two engines within a water-tight chamber, and supplied with steam from the boiler of a steam-tug; its head is provided with diamond points, performing its work altogether by rotation.
Live steam is supplied by a rubber pipe
ig. 6021 illustrates some of the operations for the removal of the submarine obstacles to navigation which formerly rendered that part of the East River known as Hellgate so dangerous to navigation in Long Island Sound.
The principal of these were Pot Rock, on which the British frigate Hussar was wrecked at the close of the Revolvast interests involved, until 1868.
In the previous year, it was asserted, in a memorial to Congress, that the losses occasioned by the various obstructions in Hellgate amounted to from $1,500,000 to $2,000,000 a year.
In 1868, an appropriation of $85,000 was made for their removal.
Proposals for undertaking the work varied frich the displaced rock might fall and the fragments be afterward removed by grappling, if necessary.
Fig 6021 shows a longitudinal section of Grant heading at Hellgate.
The openings of other tunnels are seen to the left.
Fig. 6023 is a section of East River at Hallett's Point, and of one heading of the excavation, showing a
o more British troops were coming, and said openly that he himself was on his way to North Carolina.
But the work of defence was not given up by the Americans; under the
Chap. LVIII.} 1776. Feb. harmonizing influence of the continental committee, Lee and the New York committee held friendly conferences; the whole people showed a wonderful alacrity; and men and boys of all ages toiled with the greatest zeal and pleasure.
To control the commerce of the Sound, a fortification was raised at Hellgate; on a height west of Trinity church, a battery was erected fronting the North River; that part of the old fort which faced Broadway was torn down; Lee and Lord Stirling, crossing to Long Island, marked out the ground for an intrenched camp, extending from the Wallabout to Gowanus Bay, and spacious enough to hold four thousand men; the connection between Long Island and New York was secured by a battery of forty guns at the foot of Wall street, and another of twenty guns a little further to