1841. When an oil well ceases to flow, it is rejuvenated by being

“shot,” which is quite contrary to the ordinary conception of prolonging life. For this purpose a dynamite cartridge is exploded at the lower end of the well, which shatters the rock, and, in opening up new channels of flow for the oil, renews the yield. Many patented inventions have been made in the field of well boring, and the discovery of coal oil in the United States in 1859 has developed a great industry and built up enormous fortunes. The amount of petroleum produced in the United States in 1896 was 60,960,361 barrels, the largest yield on record. In 1897 the amount was 60,568,081 barrels. Of less consequence than the artesian well, but finding many useful applications, is the drive well. A metal tube with a perforated lower end is driven down by hammers into the ground, and furnishes a quick and cheap source of water supply. This was invented by Col. Green in 1861, in meeting the necessities of his military camp during the civil war, and was patented by him January 14, 1868, No. 73,425. _Rock Drills._--In mining and tunneling through rock, the rock drill has been the implement of paramount importance and utility. For boring by rotary action the diamond drill is most effective. This uses bits set with diamonds which, by their extreme hardness, cut through the most refractory rock with great rapidity. It was invented by Hermann and patented by him in France, June 3, 1854. More important, however, is the compressed air rock drill, in which a piston has the drill bit directly on its piston rod and cuts by a reciprocating action. The piston is actuated by compressed air admitted alternately to its opposite sides in an automatic manner by valves. The compressed air conveyed to the drill in the tunnel or mine not only operates the drill, but helps to ventilate the tunnel. As early as 1849 Clarke and Motley, in England, invented a machine drill, and in 1851 Fowle devised a similar machine, having the drill attached directly to the piston cross head. The Hoosac and Mont Cenis tunnels greatly stimulated invention in this field, and among the notable drills of this class may be named the Burleigh, Ingersoll, and Sergeant. The Burleigh drill was brought out in 1866, and was covered by patents Nos. 52,960, 52,961 and 59,960 of that year, and 113,850 of 1871, and the Ingersoll drill, by patents No. 112,254, and No. 120,279, of 1871. [Illustration: FIG. 233.--BLOWING UP FLOOD ROCK.] _Blasting._--The discovery of nitro-glycerine in 1846, followed by its convenient commercial preparation in the form of dynamite, gave a great impetus to blasting. Notable as the largest operation of the kind in the century is the blowing up of Flood Rock, in the path of commerce between New York City and Long Island Sound. The dangerous character of this and other rocks in this vicinity gave long ago to this channel the significant name of Hell Gate. The undermining of the rocks by shafts and galleries is seen in Fig. 233, and the final blowing up of the same in a single blast was the culmination of a series of similar operations at this point tending to safer navigation. On October 10, 1885, 40,000 cartridges, containing 75,000 pounds of dynamite and 240,000 pounds of _rack-a-rock_, were, by the touching of a button and the closing of an electric circuit, simultaneously exploded. In the twinkling of an eye nine acres of solid rock were shattered into fragments by the prodigious force, and a vast upheaval of water 1,400 feet long, 800 feet wide, and 200 feet high, sprang into the air in tangled and gigantic fountains. As the termination of the most stupendous piece of engineering of the kind the world has ever seen, and with spectacular features fitting the enormous expense of $1,000,000, which the work cost, this final scene put an end to the menaces of Flood Rock, and wiped out of existence the worst dangers of Hell Gate. [Illustration: FIG. 234.--CROSS SECTION MISSISSIPPI JETTIES.] _Mississippi Jetties._--The broad bar and shallow waters at the mouth of the Mississippi involved such an obstruction to commerce that in 1872 it received the attention of Congress, resulting in the building, by Capt. Eads, of the celebrated jetties. They were begun in 1875 and finished in 1879, and cost $5,250,000. The channel obtained was 30 feet deep and 200 feet wide. Its construction involved the building across the bar and out into the Gulf of Mexico two long reaches of parallel embankments, called jetties. This was effected by sinking mattresses of willow branches bound together and weighted with stone. These were laid in four layers, and when submerged, and resting upon the bottom, were covered with a layer of loose stone, and this in turn was surmounted with a capping of concrete blocks, as seen in cross section in Fig. 234. These jetties so concentrated the flow of waters into a narrow channel as to cause its increased velocity to wash out the mud and silt and deepen the channel. The immensity of the work may be measured by the quantity of material used in its construction, which included 6,000,000 cubic yards of willow mattresses, 1,000,000 cubic yards of stone, 13,000,000 feet (board measure) of lumber, and 8,000,000 cubic yards of concrete. The mattresses were laid 35 to 50 feet wide at the bottom, which width was considerably increased by the superimposed layer of stone, and the jetties extended 2¼ miles into the sea. Their influence upon commerce is indicated by the fact that before their construction the annual grain export from New Orleans was less than half a million bushels, and in 1880, the year following their completion, it was increased to 14,000,000 bushels. [Illustration: FIG. 235.--INTERIOR CONSTRUCTION MODERN STEEL BUILDING.] _High Buildings._--A distinct feature of modern architecture is the enormously tall steel frame building known as the “sky scraper.” The increasing value of city lots first brought about the vertical extension of buildings to a greater number of stories, and the necessity for making them fireproof, coupled with the desire to avoid loss of interior space, due to thick walls at the base, made a demand for a different style of architecture. To meet this a skeleton frame of steel is bolted together in unitary structure, the floors being all carried on the steel frame, and the outer masonry walls being relatively thin, and carrying only their own weight. In Fig. 235 is shown an example of the interior structure of such a building. The vertical columns are erected upon a very firm foundation, and to them are bolted, on the floor levels, horizontal I-beams and girders, stayed by tie rods, which I-beams receive between them hollow fireproof tile to form the floor. The outer masonry walls are built around the skeleton frame, as seen in Fig. 236, and the details of connections for the floor members appear in Fig. 237. [Illustration: FIG. 236.--ENCLOSURE OF STEEL FRAME BY MASONRY.] [Illustration: FIG. 237.--DETAILS OF INTERNAL CONSTRUCTION.] The construction of iron buildings began about the middle of the century. In 1845 Peter Cooper erected the largest rolling mill at that time in the United States for making railroad iron, and at this mill wrought iron beams for fireproof buildings were first rolled. In the building of the Cooper Institute in New York City in 1857 he was the first to employ such beams with brick arches to support the floors. The unifying of the iron work into an integral skeleton frame, for relieving the side walls of the weight of the floors is, however, a comparatively recent development, and this has so raised the height of the modern office building as to cause it to impress the observer as an obelisk rather than a place of habitation. An earthquake-proof steel palace for the Crown Prince of Japan is one of the modern applications of steel in architecture. It is being built by American engineers, and is to cost $3,000,000. [Illustration: FIG. 238.--THE EIFFEL TOWER. HEIGHT, 984 FEET. TALLEST STRUCTURE IN THE WORLD.] [Illustration: FIG. 239.--WASHINGTON’S MONUMENT. HEIGHT 555 FEET, 5½ INCHES. HIGHEST MASONRY STRUCTURE IN THE WORLD.] _Eiffel Tower._--Loftiest among the high structures of the world, and significant as indicating the possibilities of iron construction, the Eiffel Tower of the Paris Exposition of 1889 was a distinct achievement in the engineering world. It is seen in Fig. 238. It is 984 feet high, and 410 feet across its foundation, and has a supporting base of four independent lattice work piers. In the top was constructed a scientific laboratory surmounted by a lantern containing a powerful electric light. The total weight of iron in the structure is about 7,000 tons, the weight of the rivets alone being 450 tons, and the total number of them 2,500,000. The level of the first story is marked by a bold frieze, on the panels of which, around all four faces, were inscribed in gigantic letters of gold the names of the famous Frenchmen of the century. The summit of the tower was reached by staircases containing 1,793 steps, and by hydraulic elevators running in four stages. The cost of this structure was nearly $1,000,000. _Washington’s Monument._--Next in height to the Eiffel Tower, and being, in fact, the tallest masonry structure in the world, this noble obelisk, by its simplicity, boldness and solidity, challenges the admiration of every visitor, and gratifies the pride of every patriot. It is seen in Fig. 239, and is 555 feet 5½ inches high, 55 feet square at the base, and 34 feet square at the top. The walls are 15 feet thick at the base, and 18 inches at the top, and its summit is reached by an internal winding staircase and a central elevator. At the height of 504 feet the walls are pierced with port holes, from which a magnificent view is had of the capital city and surrounding country. The summit is crowned with a cap of aluminum, inscribed _Laus Deo_. The foundation of rock and cement is 36 feet deep and 126 feet square, and the total cost of the monument was $1,300,000. The corner stone was laid in 1848. In 1855 the work was discontinued at the height of 152 feet, from lack of funds. In 1878 it was resumed by appropriation from Congress, and completed and dedicated in 1885, under the direction of Col. Thomas L. Casey, of the United States Corps of Engineers. _The Capitol Building._--Representing the heart of the great American Republic, and overlooking its Capital City, this grand building, shown in Fig. 240, is a poem in architecture. Massive, symmetrical and harmonious, its highest point reaches 307½ feet above the plaza on the east. It is 751 feet 4 inches long, 350 feet wide, and the walls of the building proper cover 3½ acres. Crowning the center of the building is the imposing dome of iron, surmounted by a lantern, and above this is the bronze statue of Freedom, 19 feet 6 inches high, and weighing 14,985 pounds, the latter being set in place December 2, 1863. The dome is 135 feet 5 inches in diameter at the base, and the open space of the rotunda within is 96 feet in diameter and 180 feet high. The corner stone of the original building was laid in 1793 by Washington. The first session of Congress held there was in 1800, while the building was still incomplete. The original building was finished in 1811. In 1814 it was partly burned by the British. In 1815 reconstruction was begun, and completed in 1827. In 1850 Congress passed an act authorizing the extension of the Capitol, which resulted in the building of the north and south wings, containing the present Senate Chamber and Hall of the House of Representatives. The corner stones of the extension were laid by President Fillmore in 1851, Daniel Webster being the orator of the occasion, and the wings were finished in 1867. Since this time handsome additions in the shape of marble terraces on the west front have added greatly to the beauty and apparent size of the building. [Illustration: FIG. 240.--THE UNITED STATES CAPITOL. LENGTH, 751⅓ FEET; WIDTH, 350 FEET; HEIGHT, 307½ FEET; BUILDING COVERS 3½ ACRES.] It is not possible to give anything like an adequate review of the engineering inventions and achievements of the Nineteenth Century in a single chapter, and only the most noteworthy have been mentioned. The modern life of the world, however, has been replete with the resourceful expedients of the engineer, and the ingenious instrumentalities invented by him to carry out his plans. There have been about 1,000 patents granted for bridges, about 2,500 for excavating apparatus, and about 1,500 for hydraulic engineering. In mining the safety-lamp of Sir Humphrey Davy, in 1815, has been followed by stamp mills, rock-drills, derricks, and hoisting and lowering apparatus, and lately by hydraulic mining apparatus, by which a stream of water under high pressure is made to wash away a mountain side. Apparatus for loading and unloading, pneumatic conveyors, great systems of irrigation, lighthouses, breakwaters, pile drivers, dry-docks, ship railways, road-making apparatus, fire escapes, fireproof buildings, water towers, and filtration plants have been devised, constructed and utilized. Many gigantic schemes, already begun, still await successful completion, among which may be named the draining of the Zuyder Zee, the Siberian railway, the Panama and Nicaraguan Canals, the Simplon tunnel, the new East River Bridge, and the Rapid Transit Tunnel under New York City; while a bridge or tunnel across the English Channel, a ship canal for France, connecting the Bay of Biscay with the Mediterranean, a tunnel under the Straits of Gibraltar, and a ship canal connecting the great lakes with the Gulf of Mexico, are among the possible achievements which challenge the engineer of the Twentieth Century.