detachment of soldiers at Unjoro under the command of Casati, his sole European companion. There were four routes, any one of which Stanley could take for his expedition: one straight through the hostile Uganda country, the second through the Masai country, a third more southerly by the shores of Lake Alexandra, and the fourth by the Congo. He chose the fourth. The steamer "Navarino" carried his merchandise and ammunition from Gravesend to the starting-point of the expedition, and thence to the mouth of the Congo, where the Belgian steamers, loaned by King Leopold, were to transport everything and everybody to within 250 miles of Wadelai, thus reducing by about three quarters of its distance the march to be made overland-an immense advantage, considering that every article has to be carried on the backs of porters from the sea to the objective point. Stanley took with him a transportable steel boat, about 30 feet long and 6 feet broad, which could be separated and easily carried by two men, and when in use could carry 22 men and 1,000 pounds of baggage. He was also provided with a modern automatic Maxim gun, which can discharge 666 bullets every minute, with a range of about 2,000 yards, and which is provided with an armor-plate as protection against assault by arrows and spears. Altogether the expedition embraced about 1,000 people. Arriving on the Congo, Stanley dispatched couriers overland to the King of Uganda, informing him of the object of the expedition, and to Tippoo Tib at Stanley Pool. He found the latter at Stanley Pool, virtually in command of the whole country, and at once completed the arrangement already mentioned. This was rather forced upon Stanley, as he found that since his absence from the country the power of the Congo Free State had been crippled at most of the outposts. The Belgians, who had everywhere been left in charge, seemed to have proved quite inefficient for the work left in their hands. Stanley Falls Station had been destroyed, and all around that neighborhood the savages were in hostile humor.

The expedition left Bolombo on May 11, and it was expected that it would arrive at the mouth of the Aruwimi the first week in June. At this point Stanley proposed leaving the Congo and pushing on overland through the unexplored territory 350 miles to Wadelai, where Emin Bey was supposed to be encamped. On Dec. 30, 1887, Dr. Schweinfurth, the explorer, wrote from Cairo to Berlin that news of the junction of Stanley with Emin had reached Cairo on Dec. 22, but without further particulars. It should be mentioned that the Egyptian Government gave £10,000 toward the purpose of the expedition, not for the rescue of Emin, but for carrying dispatches and ammunition to him.

The general feeling among experts in Central Africa exploration was that in choosing the Congo route, which has 350 miles of dan

gerous and difficult unexplored country, Stanley would find that he ran great risks. Sir John Kirk, British Consul-General to Zanzibar, said: "The Congo route by Mobangi or Biyerre is impossible. No one is able to say how many months such an expedition would take. Besides, it would be necessary to bring porters from Zanzibar, for the Congo negroes are not used to that sort of work. The Congo Free State depends even now upon Zanzibar negroes for labor." Gen. Charles P. Stone, formerly chief-of-staff of the Egyptian war establishment, expressed the opinion that "a wellorganized expedition, thoroughly prepared with such full information of the route, the obstacles, and the dangers as can be given by Dr. Junker, commanded by such a man as Stanley, who is thoroughly acquainted with these coun tries and their population, starting in a favorable season, could effect the rescue, provided Emin Pasha could hold out for the necessary time, which Dr. Junker feels he can do." If this expedition should fail, the result would be to hand over to the slave-traders a population of 6,000,000 and a province nearly as large as Europe.

ENGINEERING. Bridge at Poughkeepsie, N. Y. -Ever since the first settlement of North America the Hudson river has been one of the chief arteries of commerce. Forming with its main tributary, the Mohawk, the most direct route from the sea to the Great Lakes and through them to the West, it has for upward of two centuries been the main highway of emigration. The canoe and bateau have been successively superseded by the canal-boat, the steamer, and the railroad. It must ever remain a natural highway for traffic, but with the development of artificial as distinguished from natural highways, it has assumed a new character as an obstacle. A glance at the map will show that it divides New England from the West in a way that does not at all harmonize with the demands of modern economic engineering. For many years it has been bridged at Albany, but there remained a long stretch of 150 miles involving either an indirect course by rail, or the transshipment of freight and passengers at New York.

Several schemes for bridging the river at Peekskill, Fishkill, and Hudson have been proposed, but that at Poughkeepsie is the first that has been pushed to a successful issue. The bridge was designed about 1870. It has four piers of masonry resting upon timber caissons which are dredged to a depth of about 125 feet below high water. The dimensions of these caissons are 60 feet by 100. Twelve pockets were left open for convenience of workmen, and were filled with concrete after the caissons were sunk to their final level. The tops of the caissons proper are 20 feet below high water, and are surmounted by grillage-work 10 feet deep and closely corresponding in area with the caissons themselves. The solid masonry piers are 24 feet thick and 86

feet long, and rise 30 feet above high water, affording support for steel towers 16 feet by 60 at the base, 16 feet by 30 at the top, and 100 feet high to the lower part of the superstructure. The

tower construction is shown in the illustration, consisting, in effect, of two pyramidal structures securely braced in every direction. The cantilevers are three in number, of 548 feet each, and two connection spans of 525 feet each. It will be noticed that the two end spans and the central span give a greater clear height above the water-namely, 160 feet - while the connected spans give 130 feet, a plan which facilitated the placing of the cantilevers without staging, and therefore with less obstruction to commerce. The wind-pressures are estimated on the basis of 30 pounds per square foot of surface, including towers, spans, and area of trains. The pressure on the caisson bases is about 3 tons per square foot, and the material upon which they rest is hard gravel.

From end to end, including approaches, the structure is about 11 mile long, and it is an excellent example of the latest ideas in bridge construction.

The Tay Bridge.-Some of the ingenious devices for laying the foundations of this grand bridge were described and illustrated in the article on engineering for 1885. The year 1887 saw the completion of the whole structure, and trains were passed over it early in June. Throughout the whole course of construction the ruins of the old bridge, which fell in 1879, were utilized, and the engineers were thus enabled to dispense with

BRIDGE AT POUGHKEEPSIE.

square foot has been provided for, and every 'part of the foundation has been tested to one third more than the greatest possible load that can be placed upon it.

Bridge at Taranto, Italy.-A strait separates the old and new towns of Taranto, and connects what is known as the Little Sea (Mare Piccolo) with the Gulf of Taranto, both of classic fame and of considerable maritime importance. The bridge recently finished was constructed with a view to the ready passage of large vessels. It consists of two half-ares meeting above the middle of the strait. Each half is moved by machinery driven by two turbines of 14-horse power. The halves are raised and rotated, the lifting motion being given by four nuts worked by an endless screw, and the rotation effected through large wheels at the end of the abutment. The turbines are driven by water from a reservoir, and the

distance between abutments is 188 feet. A test-load of 280 tons was left for 24 hours upon the bridge, and caused a deflection of less than 3 inches, or about half what was allowed in the specifications. On the removal of the load, the deflection disappeared altogether.

Stiffened Suspension Bridges.-A peculiar type of suspension bridge, known as Garson's patent, has been adopted by the British authorities in India, which is believed to secure greater stability with less weight of metal, for small bridges, than any previously adopted plan. The usual plan has been to adopt side girders for small suspension bridges, but this involved too much weight and too great cost. The distribution of stress is stated as follows: Upper chain.-Stress at center equal to zero, increases toward piers until it reaches a maximum. Lower horizontal member.-Stress at abutments equal to zero, increases toward center, where it

reaches a maximum. Diagonal braces.-Stress horizontal, almost equalized, and of small amount. The bridge is hinged at the center, so that it can rise and fall with changes of temperature. The pins are of wrought-iron or steel, and are hinged at the base and connected at the summit, so that the stress on them is always axial. The stress on the foundations is purely in the nature of a vertical load. The bridges are built in Glasgow in 70-foot spans complete, and are delivered in Calcutta for $625 each, the weight being 137

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cwt.

Other notable bridges are finished or in course of construction, namely, across the Harlem river at 181st Street, New York city, across the Missouri river, near Kansas City, and the Rulo Bridge over the same river. The Hawkesbury river bridge in New South Wales is well under way in charge of American conSTIFFENED SUSPENSION tractors, and it may be said, in conclusion, that American systems of bridge construction are commanding the respectful attention of engineers the world over. Suspension Foot-Bridge at Oak Park, Ill.-Among the feats of noteworthy amateur engineering is a bridge described by the "Scientific American" as the work of amateurs, young men "just in their twenties." It crosses the Desplaines river with a central span of 125 feet. One bank of the river is a bluff, upon which a concrete tower was erected. On the other bank an elm-tree, having double trunks nearly side by side, was used, the bridge passing between them to a concrete anchorage 75 feet distant. The anchorage on the bluff side is afforded by an oak-tree, to which the cables are made fast near its base. The cables are five eighths of an inch in diameter and are four in number, two of them being merely auxiliary. The footway is about four feet wide, and the whole structure weighs only 2,750 pounds. It has borne a test-strain of fifteen men standing together upon it, and is constantly used by footpassengers as means of transit.

Dams.-The near completion of the Vyrnwy dam in Wales, for the water-supply of Liverpool, England, and the beginning of work on the great dam at Quaker Bridge, N. Y., for the supply of New York city, are among the largest engineering works of the day. In connection with them it may be well to consider the other great dams of the world, ancient and modern, for the construction of reservoirs dates back to prehistoric times, and bore a conspicuous part in the oldest civilizations. Herodotus describes the lake of Moeris as formed by the Egyptians for husbanding the surplus of the Nile floods, and within a year or

two there has been some talk of reconstructing the ancient canals and restoring the lake to its former usefulness. The same writer mentions the reservoir of Nebuchadnezzar at Sippara, which is said to have been 140 miles in circumference-a statement that must be taken with some grains of allowance. Certain it is that in Egypt, Asia, India, Ceylon, and China, vast works were executed for the retention of the surplus rain-fall of the winter months. Some of these ancient earth works and masonry have wholly disappeared, but traces of others still remain. Conspicuous among them are the reservoirs of Cummum, Kala-Weva, and Horra Bera, in Hindostan. Most of the dams are in ruins now, but have been surveyed, and evince a very creditable degree of engineering skill. The first named, though perhaps the oldest, is still serviceable. The embankment is 102 feet high, with a breadth on top of 76 feet, and a base of about 300 feet. The lake that it created, when perfect, was about 15 square miles in area. The ruins of the dam of Kala-Weva are 12 miles long, and the lake, when full, must have been 40 miles in circumference. That of Horra-Bera is from 50 to 70 feet high, between 3 and 4 miles long, and controlled a lake 8 or 10 miles long and 3 or 4 miles wide.

The advance from earthwork to masonry marks a long step toward theoretical perfection. Most of the great masonry dams have been constructed within the present century. Sections of several of them are shown on the next page in outline, resting upon a common base for ease of comparison, and having a scale in feet at the left.

The Puentes Dam, No. 5, is in Spain, and is almost identical in its elements with the Alicante dam in the same country. Its height is 164 feet, and its width 65 feet at crest. It was built about three centuries ago. The sides of the valley at Puentes were rock, but the bottom was untrustworthy, and a heavy arch of masonry was thrown across, springing from solid rock, and upon this the dam was built, the under space being filled in with walling. The locality was liable to sudden and violent floods, and probably the great width at top was provided in view of unavoidable overflows, covering the entire extent of the dam and calling for great weight, the elements of pressures not being fully understood at that time. It was not practicable to construct side overflows. A very large amount of sand and silt is brought down these streams, and to get rid of it a somewhat primitive method was adopted. Two openings were provided at the base of the dam, the upper end being stopped with loose timber, while the lower end was closed by iron doors. When the accumulation of silt necessitated flushing the dam the iron gates were opened, and workmen sent in to break out the timber screen. If they had good luck it was hoped that the silt would keep back the rush of water long enough for them

Champs between the years 1859 and 1866, and was intended partly to protect the town from freshets, and partly to afford a perennial watersupply. Its cross section is shown in the engraving. Its plan is a curve on a radius of 828 feet from a center on the down-stream side. It is founded on compact granite, a trench 3 feet deep having been quarried out to prevent slipping. The material is rubble masonry, laid in courses of 5 feet, and carried up to a height of 184 feet. At the base it is 110 feet thick, and 9 feet 8 inches at the crest. The calculations aimed for a pressure of about 95 pounds to the square inch. The dam contains about 52,000 cubic yards of masonry, and the cost of erection was $180,400. The capacity of the reservoir is 352,000,000 gallons. The reservoir discharges its surplus water through two tunnels, leading through a hill into an adjacent valley, where such power as is constant is usefully employed.

M M

dations are carried down into solid rock. Its total height is 154 feet, and the width of the crest, which carries a roadway, is 49 feet. The base is 216 feet thick. The outlet pipes, always a source of danger, are carried through a hill at some distance from the end of the dam.

Another great Spanish dam is on the river Lozoyers, and supplies water to the city of Madrid. It is known as the Villar Dam. The capacity of its reservoir is 4,400,000,000 gallons, nearly thirteen times that of Furens. It is built on a sharp curve, the radius being 440 feet, and the length of the dam, on the crest, 546 feet. A curve like this probably adds considerably to the strength of a short dam. The material is rubble masonry in hydraulic mortar, costing $402,780.

The Vyrnwy Dam, shown in section in No. 4. crosses the Vyrnwy river in North Wales. The area that will be flooded is, or was, a charming region, largely occupied by villas and country-seats, and, of course, involving a large amount of outlay in property rights. The dam will impound an area of 1,115 acres. It is 1,255 feet long, built of Cyclopean rubble set in mortar, and with the interspaces filled with cement-concrete. The individual masses weigh from 2 to 8 tons each, and it is calculated that this method of construction will give exceptional solidity to the wall. The upper face of the dam is coated with cement. The height is 146 feet, and the breadth at base 117 feet 9 inches.

A large dam is building at San Mateo, Cal.,

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Another famous structure is the Gileppe Dam at Verviers, Belgium, No. 3. It was finished in 1875, under the supervision of M. Bodson. It differs largely from the Furens section, and, indeed, from the best theories of dam-construction. This was rendered necessary by the anxiety of down-stream residents, who strongly opposed the construction of the dam, on the ground of danger. It is laid on an arc, described by a radius of 1,640 feet, with a length of 771 feet. The reservoir contains 2,701,687,000 gallons, nearly eight times as much as the reservoir at Furens. The foun

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CROTON WATER-SHED.

designed for the water-supply of San Francisco. It is 170 feet high, 176 feet thick at the base, and 20 feet wide, being in shape very much like a truncated pyramid.