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curator of aqueducts under the Emperor Nero. We learn from this excellent authority,1 that for about 400 years after the building of the city, water was supplied by the Tiber, or by wells and fountains; but as the population became greatly increased, the Censor, Appins Clandins, constructed an aqueduct for bringing in the water of distant springs. Other aqueducts were afterwards constructed as the wants of the city required, and it became a fashion with the great men of the time to present the city with the munificent gift of an aqueduct. In the time of Frontinus the city was supplied by nine large aqueducts; five more were added by Nerva, and the number was increased by successive emperors to twenty. They were mostly named after the rivers or lakes which supplied them, or after the emperors who caused them to be constructed. The Virgin Aqueduct, however, was so called from the circumstance of a young girl showing some veins of water to a few soldiers who were in search of a spring. On following these veins by digging, an abundant supply was procured, and, "there is a painting," says Frontinus, "in a little temple erected close by the source, representing the event."
The most remarkable aqueducts of ancient Rome were the Aqua Appia, the Old and the New Anio, the Aqua Martia, which also conveyed the waters of the Aqua Julia and the Aqua Tepula; the Aqua Virginia and the Aqua Claudia. The Aqua Appia was named in honour of the Censor, Appins Clandins, by whom it was constructed in the 442d year of Rome. Its source was in a field near the Via Pnenestina, between the sixth and the eighth mile-stones: it made a circuit of 780 paces to the left, and then proceeded by a deep subterranean channel of more than eleven miles, and entered the city at the Appian way by the Porta Capena, and delivered the main body of its waters into the Campus Martins. The Old and New Anio conveyed to Rome the waters of that river. The former began above the Tiber at the 30th milestone, and consisted mostly of a winding channel of 43 miles. The latter took a higher level, running a length of 7,543 paces above ground, and then through a subterranean passage, a length of 54,267 paces. The Aqua Martia rose from a spring 33 miles from Rome; it made a circuit of 3 miles, and afterwards forming a vault of 16 feet diameter, ran 38 miles along a series of arcades at an elevation of 70 feet. Openings were perforated at certain places, for the discharge of the collected air, and at different parts of its course were deep cisterns, in which the water deposited its solid contents. The water of this aqueduct was celebrated for its clear green colour, and was praised by Pliny for its coomess and salubrity. The triple aqueduct of the Aqua Martia consisted of three stories or conduits, placed one
(1) An excellent edition of this author is that published by Rondelet, with the Latin text on one side and a French translation on the opposite page. It is entitled, "Commcntaire de S. J. Frontin aur les Aquedues dc Rome. Par J. Rondelet," Paris 1820. The work is accompanied by an Atlas of 31 large copper plates. The reader who desires further information, should also consult Fabrcttus, "Dc Aquis ct Aquseductibus veteris Roma:." 4° Rom. 1680.
above the other. The uppermost conduit was the Aqua Julia, the middle one the Aqua Tepula, and the lowest the Aqua Martia. This accounts for the extraordinary height of this aqueduct, and from the ruins of it which still remain it is called // castel del Aequo Marcia. The Aqua Virginia was constructed by Agrippa : its source was a very copious spring, in the midst of a marsh 8 miles from the city, but its channel was about 12 miles, a portion of which was through a tunnel 800 paces in length. The Aqua Clandia was commenced by Nero and completed by Clandins; it rose 38 miles from Rome, and formed a subterranean stream of 36£ miles, then ran 10J miles along the surface of the ground: it was vaulted for a space of 3 miles, and was supported on arcades through 7 miles, being carried along a level sufficiently high to supply all the hills of Rome. It was constructed of hewn stone, and of such excellent workmanship, that after withstanding the attacks of time during many centuries, and the still more destructive attacks of barbarians, it was found sufficiently perfect to be restored by Sixtus V., and it furnishes the modern city with water of the best quality. This aqueduct was named Aqua Felice, in honour of Sixtus V. whose conventual name was Fra Felice, or "Brother Felix."
It will be seen that in some of these aqueducts the length of the channel was greater than that of the roadway between the city and the source of the aqueduct. This was necessary to ensure a very gentle fall for the channel; for, if the source of the water conveyed were much higher than where it was to be delivered, the pressure of water from the head would burst or blow up the covering arch or coping of the aqueduct, and thereby render the structure useless, and inundate the district over which it was attempted to convey it. Hence in order to reduce the flow of water to the proper velocity, the stream had frequently to be carried in a winding direction so as to expend
brick, and arched above to cover in the channel, so as to protect the water from impurities and evaporation. In crossing valleys the conduit was raised upon a series of arches with massive piers and of solid substantial structure, sometimes of brick, and often of hewn stone. When the height was not very great a single row of arches sufficed, but in other eases a double row was constructed as in Fig. 52. Many of these works exceed in magnitnde even those portions of our modern railroads which have been the admiration of our age. The aqueduct of New Anio, for example, consisted during 6£ miles of one continuous series of arches, many of which were upwards of 100 feet high. In the 38 miles which formed the length of the Aqua Martia, there were nearly 7,000 arches. The New Anio conduit was 63 miles 700 paces in length, of which 49 miles 200 paces formed a subterranean stream; in 9 miles 400 paces the conduit was above ground, and some of the arches 109 feet.
The following table represents the supply of water to Rome from the nine earlier aqueducts. It has been constructed from the data furnished by Frontinus:—
Some auxiliary supplies or feeders make the total length of the Roman aqueducts at that period to exceed 255 miles.
Modern Rome is also abundantly supplied with water, either by means of new aqueducts, or by the ancient structures which have been repaired.
In the cities of the provinces of the vast Roman Empire were conduits and aqueducts on as large a scale as those which supplied the capital of the empire, and in some cases larger. Our limited space will not allow us to notice more than one of these, viz. the Aqueduct of Nismes, which is, perhaps, the most remarkable Roman remain of the kind, surpassing even the aqueducts of Rome in lightness and striking boldness of design. That portion of the aqueduct which crosses the river Gardon, and hence called the Pont du Gard, (Fig. 53,) is thus noticed in Murray's Hand-Book for Travellers in France: "The sight of this noble edifice, one of the grandest monuments which the Romans have left behind them in France or any other country, would well repay for a very long detour. Like Stonehenge, it is the monument of a people's greatness, a standard by which to measure their power and intellect. It consists of 3 rows of arches, raised one above the other, each smaller than the one below it; the lowest of 6 arches, the central tier of 11, and the uppermost of 35; the whole in a simple, if not stern style of architecture, destitute of ornament. It is by its magnitnde and
the skilful fitting of its enormous blocks that it makes an impression upon the mind. It is the more striking from the utter solitude in which it stands, a rocky valley, partly covered with brushwood and greensward, with scarcely a human habitation in sight, only a few goats browsing. After the lapse of sixteen centuries, this colossal monument still spans the valley, joining hill to hill, in a nearly perfect state, only the upper part at the north extremity being broken away. The highest range of arches carries a small canal about 5 feet high and 2 feet wide, shaped like the letter U, just large enough for a man to creep through, still retaining a thick lining of Roman cement. It is covered with stone slabs, along which it is possible to walk from one end to the other, and to overlook the valley of the Gardon. The arches of the middle tier are formed of 3 distinct ribs or bands, apparently unconnected. The height of the Pont du Gard is 180 feet, and the length of the highest arcade 873 feet. Its use was to convey to the town of Nismes the water of two springs 25 miles distant, the Airan rising near St. Quentin, and the Ure near Uzes. It forms only a small portion of the conduit constructed for this purpose, whose course, partly raised on low arches, some of which exist on the north of the Pont du Gard, partly cut in the rock round the shoulders of the hills, may be traced at the village of St. Maximin near Uzes, and above that of Vers, to the Pont du Gard; thence, by St. Bonnet and Sernhac, to the hill of the Tour Magne and Bassin des Thermes at Nismes. The conveyance of this small stream was the sole object and use of this gigantic structure, an end which would now be attained by a few iron water-pipes. Its date and builder are alike lost in oblivion, but it is attributed to M. Agrippa, son-in-law of Augustus, B.C. 19. The quarry whence the stone was obtained is a little way down the Gardon, on its left bank. The bridge by which the road crosses the Gardon on a level with the lower tier of arches, and formed by merely widening them, is a modern addition to the ancient structure, having been erected in 1743 by the States of Languedoc."
The Pont du Gard above described occupied about a medinm position in the acqueduct, which was nearly 30 miles in length, forming in its course the figure of a horse-shoe. The channel way was of stone throughout. The bottom of the interior had a curved form, being an arc of a circle; the sides were vertical, and the top was covered with a flagging of cut stone, except where the channel ran underground, in which case it was covered by an arch of stone. The interior face of the walls and bottom of the conduit was covered with a coating of plaster 2 inches thick, composed of quick lime, fine sand and brick nearly pulverized. This coating has now a tenacity equal to the hardest stone. The size of the channel way is 4 feet wide, and 5|- feet high, except where it was covered by an arch, in which case it was 7£ feet high in interior dimensions. The descent was 1 foot in 2,500, or 2 V« feet per mile. The water formed a deposit of lime on the sides of the channel, until nearly half the channel was closed, this deposit being 11 inches thick on each side. This aqueduct appears to have been in use for more than 4 centuries, and now, after the lapse of 14 centuries, it is in such good preservation that it could be restored without any very considerable outlay.
In modern times the French have imitated the Bomans in the construction of aqueducts. The aqueduct for conveying water from Versailles to Marli was built by Louis XIV. at great expense. The famous aqueduct bridge of Maintenon was erected for conveying the waters of the river Euro to Versailles. This magnificent structure is 4,400 feet in length, or nearly I of a mile, and is upwards of 200 feet high; it consists of 242 arcades, each divided into 3 rows, making in all 726 arches of about 50 feet span.
It is frequently stated, that had the Romans been aware of the principle that water seeks the level of its source after encountering depressions in its conduit, they might have spared themselves the immense labour and cost of constructing their colossal aqueducts, by forming an inverted syphon of pipes across valleys. It might as reasonably be argued that the modern French and Americans were ignorant of this principle, because they have preferred the stone conduit to the system of pipes. The fact is, that the Romans were fully aware of the principle in question, as is proved by the remains of many of their works, but they preferred a system of stone channels, not only on account of the greater permanence and durability of the work, but also on account of the greater abundance of the supply of water which this method secured, and its greater purity. In considering the best method of supplying the city of New York with water from the Crolon river, situated at a distance of 38 miles from that city, it was caleulated that a system of iron pipes would be more costly than an enclosed stone channel, and far less durable. An open canal was also objectionable on account of the loss of water by filtration through the banks, and by evaporation. Another objection to the open canal was the difficulty of preserving the water from receiving the wash of the country through which it passed, and of preventing injurious matters from being thrown into it and rendering it impure; impurities might also be contracted in passing through different earths; frost would also interfere with the supply. When we find an enterprising and intelligent nation like the Americans adopting the system of the ancient Romans, it is difficult to suppose that the same reasons did not in both cases lead to the adoption of the same method. When the system of sewage and water supply of modern London shall exceed that of ancient Rome, we shall then, and not till then, be in a condition to accuse the old masters of the world of ignorance.
In the magnitnde of our metal castings for pipes, the moderns are certainly superior to the ancients, and in some cases a system of iron pipes has been used to supply a city with water. Such is the case
at Edinburgh, which is supplied by the Crawley Spring from the rising ground on the south base of one of the Pentland Hills. The distance is scarcely 7 miles from Edinburgh in a straight line, but it is 8f miles by the line of pipes. The spring is 564 feet above the level of the sea, and 360 feet above the level of the reservoir in Princes Street. The original issue of the spring is augmented by a drain carried about half a mile above the spring, up the valley in which the spring is situated. The soil of the valley is of gravel 40 feet deep, forming a vast natural filter, through which the water from the high grounds on each side percolates. The water is thus rendered very pure, and being all intercepted by the drain, is conducted with the original discharge of the spring into a reservoir or water-house, from which the pipes take their rise, and continue in one connected train to the city. For the first 3 miles the pipes are from 18 to 20 inches in diameter, and afterwards 15 inches. As they approach the city they are carried through a tunnel under Hcriot's Green, and another under the Castle Hill through the solid rock. By means of a reservoir, branch-pipes and service-pipes, the water is supplied to each house or floor of a house. Air-cocks are placed at intervals all along the main pipes, to let off the accumulated air, which is done by hand every three or four days. The average supply of water by this aqueduct is 180 or 200 cubic feet per minute, and it is stated that double this quantity could be easily supplied. The water is said to be of the finest quality; it issues from a deep source and at a great altitnde, so that it is fresh and cool even in the heat of summer. In thls respect the supply of Edinburgh is far superior to that of most other towns of the same magnitude. The elevated nature of the country about the city affords facilities for distributing the water without the aid of machinery.
Aqueduct bridges were first used in this country for the canals constructed by the Duke of Bridgewater, under the direction of Brindley. The first and largest was the aqueduct at Barton Bridge, for conveying the canal across the Irwell, 39 feet above the surface of the river. It consists of three arches, the middle one 63 feet span, admitting under it the largest barges which navigate the Irwell, with sails set. This aqueduct bridge was commenced in September 1760, and in the July of the following year, the singular spectacle was first seen in this country of vessels sailing across the course of the river, while others in the river itself were passing under them. So little were engineers acquainted with works of this kind at the time of its erection, that when, at the request of Brindley, an eminent engineer was called in to give his opinion respecting the proposed aqueduct, he said with a sneer, "I have often heard of castles in the air, but never before was shown where any one of them was to be erected."
Allusion has been already made to the construction of aqueducts on a large scale in the United States of America, by improving on the model of the ancient Romans. New York had always been badly supplied with fresh water: the quantity collected, chiefly from wells, was small and the quality bad. So loug back as the year 1798, Dr. Brown, in an official report, considered these as the chief causes of the yellow fever and other contagious diseases which so frequently ravaged the city. He shows that the well-water, although cool and pleasant to the taste by the admixture of carbonic acid, was nevertheless contaminated with the filth of men and animals, which sinks into the streets, yards and stables, and then drains through the cemeteries, before it reached the collecting pond. The water was so bad that the ships in the harbour could not use it at all, but brought their supply from other seaports. At length the citizens became fully impressed with the necessity of obtaining a plentiful
supply of pure water, by the ravages of the yellow fever in the summer of 1822, and of the cholera in 1832. After some preliminary proceedings, an Act was passed in May 1834, appointing five Water Commissioners, with powers to examine and consider all matters relative to the supply of the city of New York with a sufficient quantity of pure and wholesome water, and to adopt such plans as in their opinion would be most advisable for securing such supply. After much careful inquiry it was decided that the Croton river was the only source that could be depended on for present and future purposes, to ensure a sufficient quantity at all seasons at an elevation preclnding the use of steam or other extraneous power, and that the quality of the water was unexceptionable. The distance of the Crotou
river from New York is about 40 miles, over a country extremely broken and uneven, and following a direction for a part of this distance parallel with the Hndson river, and encountering the streams which empty into it and form deep valleys in their courses. .To convey this water to the city, it was decided to erect a close channel or conduit of masonry?
The sources of the Croton are principally in the county of Putnam, fifty miles from New York; they consist mostly of springs, which in that elevated and uneven country have formed many ponds and lakes never failing in their supply. About 20 of these lakes form the sources of the Croton river, and the magnitnde of their surface areas is about 3,800 acres. The country is sufficiently cleared to prevent any injury to the water from the decay of vegetable
matter. The river has a rapid descent, and flows over a bed of gravel and masses of broken rock, and the water is so pure that in earlier days the native Indian called it "the Clear Water."
Having ascertained the elevation in the city at which it would be desirable to distribute the water, it was only necessary then to find a point ou the Croton river wiicre a dam could be constructed, so as to turn the water into a channel gradually descending from this point through the whole length of the aqueduct to the required elevation in the city. At the spot where it was decided to construct the dam across the Croton river, the surface of the natural flow of water was about 38 feet below the elevation required as a head from which the water was to flow into the channel of the aqueduct. By going fartner up, a dam of less height would have sufficed, but in that case some important tributaries of tbe Croton would have been lost. The medinm flow of water in the Croton, where the Fountain Reservoir was formed, exceeds 50,000,000 gallons m. 24 hours, and the minimum flow after long droughts is about 27,000,000 within the same period. The dam sets the fountain back about 6 miles, thus forming the Fountain Reservoir, which covers an area of about 400 acres, forming a beautiful sheet of water in the lap of the hills, in the wild region of the Croton. It has received the name of the "Croton Lake." The country forming the valley of the river was such as to give in general bold shores to this reservoir, and in cases where there was a gentle slope or level of ground near the surface of the water, excavations were made so that the water should not be of less depth than 4£ feet. In this reservoir the water collects and settles before it flows into the aqueduct. The available capacity of this reservoir down to the level at which the water would cease to flow off into the aqueduct, is estimated at 600,000,000 gallons; so that if the number of inhabitants of New York be estimated at one third of a million, the Fountain Reservoir would contain a supply for 90 days in a season of extreme drought; in addition to which, the Reservoir in the city would afford a further supply of about 25 days, thus providing for a season of 4 months' drought. Should the population greatly increase, other streams can be turned into the upper branches of the Croton, or into the aqueduct along its course. Other reservoirs might also be constructed further up the Croton, to draw from in time of need.
From the Fountain Reservoir on the Croton to the Receiving Reservoir on the Island of New York, a distance of 38 miles, no essential change was made in the form of the channel way, except in crossing Harlem river to reach the island, and also in passing a deep valley on the island, in both which cases iron pipes were used instead of the channel way of masonry. At these points the iron pipes descended and rose again, so that when water is flowing in the channel they are completely full. The channel way of masonry is never filled entirely, so as to occasion a pressure on its interior surface. To prevent this, 6 waste weirs were constructed at suitable places, to discharge the surplus water: they were formed on one side of the channel way, so as to allow the water to flow off when it rose above a certain level.
The following figures will show the kind of work employed in constructing the channel. Fig. 54 is a section of the aqueduct, showing the form of masonry used in earth excavations. The foundation was formed with concrete, the side walls are of stone, and the bottom and sides of the interior faced with brick, and the top covered with an arch of brick. After the masonry was finished, the excavation was filled up around it, and over the top of the roofing arch, generally to the height of 3 or 4 feet, and in some crises of deep excavation up to the natural surface.