4.5X 8.5 the principal buildings are the bey's palace, | description. The chorobates seems to have many handsome mosques, and several large been preferred. It consisted simply of a rod barracks, one of which has room for 4,000 or plank about 20 ft. long, mounted on two men. There are Moorish schools and a col- legs, at its extremities, of equal length. The lege, a Roman Catholic church and convent, a rods or legs were secured by diagonal braces, Greek church, a theatre, and public baths and on which were marked correctly vertical lines. bazaars. The leading manufactures are woollen cloths and caps, embroidery, leather, and essences of musk, rose, and jasmine. The trade is extensive, comprising exports of oil, caps, soap, grain, wool, hides, cattle, sponges, wax, gold dust, and ivory, and imports of cotton, linen, and woollen goods, tin, lead, iron, coffee, sugar, and spices. The depth of water at Tunis is only 6 or 7 ft., and vessels lie in the gulf and discharge by lighters. In 1873, 1,272 vessels of 121,957 tons entered the port. Tunis is not far from the site of ancient Carthage, and is itself a place of great antiquity. TUNKERS. See DUNKERS. TUNNEL, a subterranean or subaqueous way, constructed for purposes of passage. In inining, the term is often applied to horizontal excavations, especially to such as are known by the designations gangway, heading, drift, and adit, used as underground roads or for the passage of water. (See ADIT.) Herodotus mentions a tunnel in the island of Samos, cut through a mountain 150 orygia (900 ft.) high. Its length was seven stadia (4,247 ft.), and its cross section 8 ft. high by 8 ft. wide. In Bootia a tunnel was constructed for the drainage of Lake Copais. When Cæsar arrived at Alexandria, he found the city almost hollow underneath from the numerous aqueducts; every private dwelling had its reservoir, supplied by subterranean conduits from the Nile. The aqueducts of the ancient Romans, and of the Peruvians and Mexicans, included remarkable tunnels. (See AQUEDUCT.) Among the many Roman aqueducts on which tunnels were built were the Aqua Claudia, of which 36 m. passed underground; the Aqua Appia, built in 312 B. C., 11,190 Roman paces in length, 11,130 being underground and arched; and the Aqua Virgo, 14,105 paces long, 12,865 underground. A tunnel was begun in 398 B. C. to tap Lake Albanus, at the instance, Livy tells us, of the oracle of Delphi. It was 6,000 ft. long, 6 ft. high, and 33 ft. wide. Fifty shafts were sunk on its line, and the work was finished within one year, though it was driven through the hardest lava. A similar work of greater magnitude was undertaken to connect Lake Fucinus (now Celano) with the river Liris (now Garigliano); 30,000 men were employed on it for ten years, and it was finished at a vast expense A. D. 52. A minute account of the modern clearing out of this work by the Neapolitan government may be found in "Blackwood's Edinburgh Magazine," vol. xxxviii., p. 657. The accuracy of the surveying in these works is astonishing when we consider the rudeness of the instruments. Among those used in levelling by the Romans were the libra aquaria and dioptra, of which we have no clear 14.9 FIG. 1. A plumb line attached at each extremity, and passing over these diagonal braces, indicated whether the instrument was level. When the wind prevented the plumb bobs from remaining stationary, a channel in the upper edge of the horizontal rod was filled with water, and if the water touched equally both extremities the level was supposed to be correct; and then the observation of the descent or elevation of the ground was made with accuracy.-Tunnelling might be classed under four general heads: 1, ancient tunnelling, to which we have just referred; 2, modern tunnelling through soft ground (clay deposit, &c.) and loose rock, requiring arching; 3, modern tunnelling through solid rock before the introduction of machinery; 4, modern tunnelling through solid rock with the aid of machinery. The art of tunnelling at the present day constitutes a profession in itself, new developments succeeding each other with great rapidity. Figs. 1 and 2 show cross sections that may be adopted in tunnelling: fig. 1 through rock tenacions enough to require no artificial support; fig. 2 where arching may be found necessary. These examples are from plans adopted in the construction of the Musconetcong tunnel, New Jersey, on the hold it in place, until the permanent brick or stone arching is built. Loose rock, as its name indicates, is rock either so seamy and broken by folding or compression, or so disintegrated, as to require an arch, generally much lighter than those necessary in soft ground. According to the method generally adopted in driving a tunnel through soft ground, the first step is, if practicable, to open out a small bottom heading or adit, for the double purpose of draining the ground above and making an opening through which to carry away the material subsequently excavated; this heading also is required for passing in the materials used in arching. Often, however, owing to long and heavy cuttings necessary in the outside approaches to a tunnel, it is deemed advisable to begin with a top heading before the bottom bench of the open cut is brought up to the face of the proposed work. If a bottom heading has been driven (and it is generally best to do so when practicable in soft ground, while the opposite rule holds in tunnelling through FIG. 8. hard rock), one of the methods of subsequent enlarging that may be used is shown in figs. 3, 4, and 5. These represent the English plan, so called, it being the one generally adopted in England. For a full description of this method of enlarging, see the " Engineering and Mining Journal," vol. xix., p. 392; also Simms's "Treatise on the Blechingly and Saltwood Tunnels." Fig. 3 shows the bottom heading driven, with a section excavated and ready for arching. The enlarging and arching of a tunnel to its full size is generally done in lengths or sections. If there is no top heading previously driven, 15 or 20 ft. of an advanced heading is excavated at the top of the proposed work (shown in figs. 3 and 4). Heavy longitudinal bars of timber are then successively put in, beginning with those numbered 3, 6, and 7. The miners gradually work down, putting in a temporary arch of timber. When this is done, and foundations have been dug for the succeeding masonry, the masons take the place of the miners, and run up an up with pieces of timber or stone. In some methods of tunnelling, it is deemed more secure to brick the timber in and leave it in place, though at a considerable cost, especially when it is necessary to bring all the heavy timber down a shaft or slope, and through a long distance underground. Shafts are often sunk, and sometimes slopes, so that the work may be attacked from several points at once. Fig. 5 shows the arch built, and is divided into two portions: that on the left shows the completed tunnel, with the ballast in place and the track laid; that on the right shows the arch in place, and the supporting timbers struck, but still undrawn. Where the ground is very treacherous, and much water is encountered, an inverted arch is often put in across the bottom of the tunnel, to withstand the pressure from below. Other methods are in vogue on the continent of Europe. A description of a new system of tunnelling by the use of iron centres, in place proposed excavation, or narrower. The heading is always the most difficult and expensive part of the work; for whether it be driven at top or bottom, the miner, in removing the remaining portion of rock, of course has much less resistance to contend against in blasting. Removing the top rock or the lower "bench is more like open-air quarrying. Longer holes can be drilled, and heavier charges of powder used. At the present day, however, most heavy tunnel work is carried on with the aid of machine drills, driven by compressed air, which, on being liberated after acting as a motor, serves to ventilate the work. Since the introduction of machinery, the rate of driving attained in tunnelling has been greatly increased. Machine drilling was born of the necessity for some more rapid method of executing certain works, deemed almost too heavy to be accomplished by ordinary means. These were, in Europe, the Mont Cenis tunnel (see CENIS, MONT), and in America, the Hoosac tunnel in Massachusetts. Various types of drills have been invented and tried abroad; among them the Sommeiller, Dubois-François, Sachs, Osterkamp, Brydon Davidson and Warrington, Azolino dell' Acqua, Ferroux, McKean, and others. Among compressors that of M. Colladon of Geneva may be particularly noted. At Mont Cenis the air pumps were worked by hydraulic power. The perforators used there were built partly from designs already presented, but improved with original modifications made by the engineers in charge, Messrs. Sommeiller, Grandis, and Grattoni. A description of the Sommeiller machines may be found in the Portefeuille économique des machines (1863). The Mont Cenis tunnel was begun by hand labor in 1857, and finished in 1871, at a total cost of about $15,000,000. The following table, from M. Opperman's Nouvelles annales de la construction (1869), shows the rate of advance in that work by hand, and the increased rate attained immediately after the first introduction of machinery down to 1865, working throughout with two headings: FIG. 7. many cases, held to be more economical than by machinery. It is certainly so, as yet, in the case of small tunnels through a comparatively soft rock, where the necessary cost of a plant of air drills and compressors would be in excess of the economy in time gained by their use. In driving a tunnel through rock, an advanced heading is first driven either at bottom or top; and this may either be of the full width of the The St. Gothard tunnel, also through the Alps, is now (1876) in progress. From a late paper on the subject by Daniel K. Clark, M. Inst. C. E., London, we obtain the following general facts concerning it. The length of the tunnel is to be 16,295 yards or 91 m. The contract prices sum up to a total estimated cost of £1,896,945. Construction was begun in the The heading is driven at the top, about 8 ft. square, dynamite being used as an explosive. Dubois-François perforators were first used, making an average advance of 6.63 lineal feet a day. They were succeeded by Ferroux's, the daily advance being raised to 10-11 ft. Subsequently the machines of two or three inventors, Dubois-François, McKean, and Ferroux, were placed and worked together on the same carriage; and it is said by M. Louis Sautter, in an official report published in the Revue industrielle, Aug. 18, 1875, that the improved McKean drill has proved to be decidedly superior to any of its competitors; its best work on competition, with 63 atmospheres of pressure, was a penetration of 12 in. a minute. While actually at work, its rate will vary from 3 to 8 in. a minute, with about 800 strokes. The power is derived from water through the agency of turbines. The cylinders or air pumps of the compressors are 18.1 in. in diameter, and the stroke is limited to 174 in., in order that the mean speed of piston may not exceed 266 ft., or 90 revolutions a minute, the turbine making 390 turns. The compressed air is cooled on Dr. Colladon's system; every piece that is in contact with the air when undergoing compression being cooled by currents of cold water, passed through air-tight envelopes. It is calculated that at the present rates of advance the St. Gothard tunnel may be finished during the summer of 1879, or within seven years from the date of M. Favre's contract.-In America, both North and South, many tunnels have been built, the modern ones being mostly driven since the introduction of railroads. Until the building of the Hoosac tunnel in Massachusetts, all tunnelling through rock in the United States was done by hand labor, by the methods above described. The project of tunnelling the Hoosac mountain was broached as early as 1825. In that year a board of commissioners, with Loammi Baldwin as engineer, was appointed to ascertain the practicability of making a canal from Boston to the Hudson, in the vicinity of the junction of the Erie canal with that river. Their report ("Massachusetts Commissioners' Report," 1826, p. 141) declares that "there was no hesitation in deciding in favor of the Deerfield and Hoosac river route," and that "there is no hesitation therefore in deciding in favor of a tunnel; but even if its expense should exceed the other mode of passing the mountain, a tunnel is preferable." Railways being shortly after in troduced, the canal project was dropped. In 1828 surveys were made for three routes to afford Massachusetts railway connection with the west, viz., by Greenfield, by Northampton, and by Springfield. The last or southern route was chosen. The work was not begun immediately, but Massachusetts never lost sight of the advantage of a direct route to the Hudson river. This was finally accomplished in 1842, by the completion of the Western railroad to Albany. In 1848 application was made for a charter for a railroad from the terminus of the Vermont and Massachusetts line, at or near Greenfield, through the valley of the Deerfield and Hoosac, to the state line, there to unite with a railroad leading to Troy. The location was filed in the clerk's office of Franklin and Berkshire counties in November, 1850. In 1854 an act was passed "to enable the Troy and Greenfield railroad company to construct the Hoosac tunnel," by which the state, on certain conditions, lent its credit to the amount of $2,000,000. The estimated cost of the proposed double-track tunnel was $1,948,557, and of the road and equipment $1,401,443; total, $3,350,000. Still the company were unable to raise the funds necessary, in addition to the state loan. In 1855 a contract was made with E. W. Serrel and co., under which some work was done; and another was made with them in 1856 for the construction of the road and tunnel for $3,500,000, they subscribing $440,000. This contract also fell through, as did one made with H. Haupt and co. in the same year, by which the railroad company agreed to pay $3,880,000 for the completion of the road and tunnel. In 1858 a contract was again made with H. Haupt and co., by which the contractors themselves agreed "to assume the labor of collecting subscriptions and of carrying on and completing the Troy and Greenfield railroad and the Hoosac tunnel." Under this contract H. Haupt and co. were to receive $2,000,000 in bonds of the state of Massachusetts, to be exclusively appropriated to work done on the tunnel; $900,000 in mortgage bonds of the company; and $1,100,000 in cash, through cash subscriptions and capital stock of the company. Under this contract the work was vigorously prosecuted up to July, 1861, when, a difference arising between the contractors and the state engineer, a certificate for the amount claimed by the former on a payment was refused, and the work was thereupon abandoned by them. In 1862 an act passed the Massachusetts legislature, providing "for the more speedy completion of the Troy and Greenfield railroad and Hoosac tunnel." Under this act a board of commissioners was appointed to examine into the matter on the part of the state. At the request of these commissioners, the Troy and Greenfield railroad company, acting under the authority of certain provisions of the act, surrendered to the commonwealth of Massachusetts, under the several mortgages held by said common wealth, the road and property of the company; such surrender having been authorized by the board of directors, by a vote passed on Aug. 18, 1862. This action was ratified by a vote of the stockholders, and on Sept. 4, 1862, the commissioners took possession of the road and its property. The commission after a full examination made a thorough report (dated Feb. 28, 1863), embracing the three following most valuable sub-reports: 1, a report of Charles E. Storrow on European tunnels; 2, a report by Benjamin H. Latrobe on the Hoosac tunnel; 3, a report by James Laurie on the Hoosac tunnel and the Troy and Greenfield railroad. In conclusion the commissioners recommended that the work should be undertaken by the commonwealth. At this point the cost and estimates were as follows: Amount advanced by the state up to the date of $1,431,447 3,218,323 652,060 67.500 275,000 Total estimated final cost of road and tunnel.. $5,719,330 At this time, according to the report of James Laurie above noted, the condition of the work proper was as follows: Whole length of the proposed tunnel, feet.... Leaving to be excavated under the mountain.. 1,850 24,416 to be subsequently blasted out with gunpowder. It is reported to have cut, on a trial made March 16, 1853, on a vertical face of rock near the proposed entrance of the tunnel, at the rate of 16 in. an hour, and under more favorable conditions at a previous trial 20 in. an hour. Various trials were made with this machine, the total distance cut by it amounting to about 10 ft., but it did not prove successful. A second machine constructed at Hartford, and known as the "Talbot tunnelling machine," also working on the principle of revolving cutters, and adapted to cut out a core 17 ft. in diameter, was tried about this time near Harlem, but proved a failure. A third machine was constructed in New York, adapted to cut a core of 8 ft.; this was adopted by Mr. Haupt during the continuance of his contract, in the early days of the tunnel, but also proved a failure. Experiments were instituted by Mr. Haupt himself, while engaged with his contract at Hoosac, toward the elaboration of a percussion drill; but in 1861 the termination of his contract for a time put an end to them. Afterward he again took up the subject, and in 1867 published a descripinvention had been perfected, the Burleigh tion of the Haupt drill. By the time this drills, which have since attained so great a reputation (see BLASTING), had been adopted and were in full use at Hoosac. They were first tried in June, 1866, under the direction of the commissioners, and even in their crude and unimproved condition were favorably noticed 4,250 in Chief Engineer Doane's report. In January, 1867, the office of chief engineer was abolished, and the engineer corps reduced to one resident engineer, W. P. Granger; Mr. Latrobe still supervising as consulting engineer. In October, 1867, owing to the accidental lighting of some naphtha at the central shaft, the head house, shaft buildings, &c., were consumed, and 13 lives were lost. Previous to this time portions of the work had been let out by contract, Messrs. Dull, Gowan, and White having the east and central shaft headings, through rock, and Mr. B. N. Farren the west end, through soft ground, including the arching of the same. Owing to the above mentioned accident, Messrs. Dull, Gowan, and White voluntarily surrendered their contract, received their pay, and abandoned the work, returning it to the hands of the commissioners. Benjamin D. Frost was appointed superintending engineer in May, 1868, and on Dec. 24 of that year a contract was effected between Messrs. Shanly brothers of Montreal and the commonwealth of Massachusetts for the final completion in full of Hoosac tunnel. The dimensions were to be: "in rock, unarched, 24 ft. wide and 20 ft. high, in the clear; where arching required, 26 ft. wide and 24 ft. high (above. the rail), in the clear." The prices bid in the contract varied in the different portions of the work, and also according to whether the work was "already begun," "to be finished," or for 20,166 The shaft here referred to was on the western slope of the mountain, 325 ft. in depth. Mr. Laurie estimated that by sinking a central shaft about 1,000 ft. deep and working therefrom (which was afterward done) the tunnel, advancing at the rates respectively of 55 ft. a month from the two end portals, and 40 ft. each way from the shaft, would be completed in 11 years from date, i. e., in 1874; this estimate being based on the supposition that the central shaft would reach bottom in four years from its commencement. Work was resumed on the tunnel under the auspices of the state in October, 1863, under the control of the same board of commissioners, who appointed Thomas Doane chief engineer in charge. The governor at the same time appointed Benjamin H. Latrobe of Baltimore state consulting engineer of Hoosac tunnel.-Mr. Laurie in his report to the commissioners says that shortly after the Troy and Greenfield railroad was chartered, the attention of inventors was turned to the subject of tunnelling machines. One was constructed at South Boston in 1851, es- | pecially for the Hoosac tunnel, which weighed | about 70 tons, and was designed to cut out a groove around the circumference of the tunnel 13 in. wide and 24 ft. in diameter, by means of revolving cutters; the central core left was |