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soil of most of the river plains was a rich alluvial deposit, from 3 feet to 10 feet in depth. Nothing was wanting but water; and this might frequently be seen a few yards off running to the sea, useless, and un productive. A few charts of comparative rainfall and temperature had been prepared, which showed that, with the exception of Oran, Spain was by far the driest country. Thus, while Piedmont had a fall of 37 inches, Lombardy 38 inches, Algiers 27 inches, and Bone 25 inches, Spain had only an average of 17 inches; and in two cases, that of Madrid and Alicante, the mean annual fall was only 12 inches and 134 inches respectively. The mean rainfall of Oran was 144 inches. A comparison of the mean rainfall and temperature during the seven irrigating months from March to September, and the mean maximum temperature during June, July, and Aimust, of Lombardy, Piedmont, and Spain, showed that, while Piedmont had a mean temperature of 63°, and a mean maximum of 85°, with a rainfall of 29 inches, Seville, with a mean temperature of 78°, and a maximum of 111°, had only a rainfall of 54 inches. Madrid, with a mean temperature of 65°, and a maximum of 98°, had a rainfall of only 5 inches. Alicante and Valla dolid, though a little better than Seville and Madrid, were far inferior in rainfall, and superior in heat, to either Lombardy or Piedmont. The vital necessity of irrigation was thus very apparent. 'The earliest, and indeed almost all the, irrigation works in Spain were constructed about the year a.d. 800 or a.d. 9( 0, when that country was under the dominion of the Moors. Perhaps the system of irrigation and the whole administration of the in Valencia and Murcia were as perfect as well could be, and t . results were very surprising. It was not possible, however, within the limits of this Paper, to give more than a cursory notice of these works; but such data were collected as would assist in the description of the new canals now in course of construction by the Iberian Irrigation Company. The areas of the several large irrigated districts in Spain were then detailed, amounting together to 680 square miles. According to the published Government returns, the total amount of irrigated ground in Spain was 4,439 square miles, so that it would seem that there was an area of 3,759 squaremiles irrigated from water wheels, small canals, tanks, &c., a quantity which was believed to be excessive. Admitting, how ever, that the returns were correct, even then only 4 J per cent, of the whole cultivated land was irrigated. While the rate of population in all Spain was only 81 to the square mile, in the irrigated garden of Murcia theme were 1681 inhabitants to the square mile, and in Orihuela 767 inhabitants per square mile. The effect of irrigation was to raise the value of land ten, fifteen, or twenty times. Several illustrations of this were cited, and it was stated that, as a rule, all over Spain, good land in the valleys when unirrigated might be bought at an average price of from £6 to £10 per acre, while irrigated ground fetched from £80 to £120 per acre. In proportion to the value of the ground was the value of the water. Colonel Baird Smith gave the value of a cubic foot of water per second in Piedmont at £16 per annum, and in Lom bardy at about £15 per annum. In most of the old systems of Spanish irrigation, the water was attached to the land, and was sold with it, and the value of the water could not, therefore, be ascertained. But perhaps the fair average value of a cubic foot of water per second in Spain might be taken to be that fixed by the Government for the Henarcs Canal, viz., £375 per annum, which was not considered a high price. The projects for irrigating the Henares and the Esla valleys were of very old date; but it was only during 1859 that the concessions were granted, and in 1863 that a company was formed in London to carry out the works. The river Henares rose amongst the mountains of the Somosierra: its course was extremely steep, and very rapid, the total fall of the river, from the weir of the new canal to Alcald, a distance of 36 miles, being 407 feet, giving a mean fall of 113 feet per mile. The total length of the new canal was 28 miles. It received its water from the river at a point 16 miles above Guadalajara, just below the junction of the Sorbe and Henares, and ended at Alcala. The area of ground capable of irrigation in this valley, after deducting that due to roads, streams, towns, &c , was 27,170 acres. For this purpose the volume of water conceded by the Government was 175 cubic feet per second for the nine months from October to June inclusive, and 105 cubic feet per second for the remaining three months. From accurate measurements made near the new weir since the commencement of the works, it appeared that during the months of July, August, and Sep tember, the average quantity of water carried by the weir was 210 cubic feet per second, the lowest point which it had touched being 140 cubic feet per second. During the remainder of the year it carried an aver age of 300 or 403 cubic feet per second ; but it was liable to enormous floods, and some came down during the progress of the works, which were estimated to amount to 8,000 cubic feet per second. The weir, it was calculated, would discharge 20,01'0 cubic feet per second. The most difficult portion of the works was comprised in the first division—involving a rock cutting, 16 feet in depth, immediately after leaving the river; then a tunnel 3,171 yards in length through a high limestone cliff, followed by a deep cutting in gravel. At the 9th kilo metre the canal crossed the Madrid and Saragossa Railway , and at the 10th kilometre, a wide torrent bed. These were the ruling points in this section, and it was with reference to them that the actual height of the new weir was fixed. At the site chosen for the weir, the bed of the river was composed of compact clay rock, very impermeable, mixed with strata of excessively hard conglomerate. I hc front wall was built of rubble in hydraulic mortar, the foundation being benched into the rock. The main body of the weir w>s of hydraulic concrete; but in order to guard against filtration, a continuous line of cut stone was let into the rock in the centre of the concrete, all the stones being bedded in pure cement. The apron was entirely of cut stone, and from the top of the rubble wall to the crest, the weir was also of cut stone. The water for the canal was drawn off by five sluices, set in masonry arches, built of large blocks of rock-faced ashlar. At the entrance of the canal three sluices were fixed, for the purpose of scouring out any deposits which might accumulate in front of the gates. Immediately inside the head sluices, and forming a portion of the head works, there was an overflow weir, to provide for the discharge of any water which a sudden flood might admit into the canal during the absence of the guard. The weir was 130 yards long between the abutments, and its total cost, including all the head works and the waste weir, had been £17,343, or 50s per cubic yard, as the mean price of the total cubical contents. Details were given of the prices paid for different classes of work, and of the materials employed. One flood, which came down when the weir, was unfinished, tried it severely. The water rose 4 feet over the crest of the finished portion, completely filling up the gap, and pouring with great force on the exposed concrete hearting of the unfinished end. This flood was estimated to have a volume of more than 9,000 cubic feet per second, yet not a single stone was dis placed. The construction of the tunnel offered no engineering difficulties. About one-half of it was in a stiff, tenacious clay, the remainder being in limestone rock. It was found necessary to line the whole with brick, as the rock, though hard when first cut, crumbled under expo sure to air and water. The bricks used were made in the valley, and, after a little trouble, they were obtained of a good quality, at a cost of £2 a th< usand, delivered on the works. The whole of the brickwork was set in hydraulic mortar. As it was found, however, that the pure lime and sand set too quickly, the custom of the country was followed, and a per centage of white lime was mixed with the hydraulic, a the pro portions being 1 part of hydraulic, 1 part of white lime, and 4 parts of sand. This mortar was longer in setting than the pure mortar, and gave much better results. It could not be used where the work was liable to be immediately covered with water; but this was not the case in this tunnel. The only other works of importance on this canal were an aqueduct over the Arroyo Tejada, at the entrance of the tunnel; the bridge under the railway; and the bridge over the Arroyo Majanar. The difficulties presented by the bridge under the railway were those due simply to the work having to be carried on without disturbing the passage of the trains. This was done by shifting the line, and building one-half of the abutments at a time. The railway was carried on wrought-iron girders, sent from England. The canal was carried over the Torrent Maj an ar in a wrought-iron tube, 66 6 feet span. When put together, complete, this tube was immediately filled with water, to a depth of 5 feet, and had since been kept full. It was perfectly tight, both at the joints with the masonry, and in other parts. With a load of 93 tons of water, it sank J inch in the centre. At the side of this tube were three sluices for discharging the canal, if necessary. The average prices paid for the smaller works, the manner in which the excavations were performed, and the class of labourers employed and their pay, were then severally treated of. The sections adopted for the first division of the canal had inside and outside slopes of 14 to 1, and the banks were 6 feet -wide on the top. The depth of water in the first few divisions was 5 feet, and the velo city was 2 feet 4 inches per second. This was rather high. but. it was a matter of importance in Spain to avoid exposing the water in wide shallow channels, as with a less velocity weeds grew freely. Many of the old canals and watercourses of Spain had a mean velocity of 3 feet per second. The Esla Canal, as regarded ease of construction, was perhaps one of the best in Spain. The whole estimated cost of the works, including a weir 191 yards long, was a little under £100,000; and for this amount 32,140 acres would be perfectly irrigated at a cost of £3 2s per acre, while the cost per acre of the Henares Canal was £7 7s. The land in the Esla Valley was exceptionally rich; it was very thickly populated; and the only objection that could be made to it was its distance from any seaport. One of the most interesting questions, in the construction of an irri gation canal, was the acreage which could be irrigated with a certain disposable quantity of water, ('pinions varied very much upon this point. The amount supplied in different districts was given, and it was stated that, in Spain, the usual dotation for rice crops, was con sidered to be 2| litres per second per hectare. It had been found, by M. Ribera, from a series of experiments made near Madrid, that the quantity of water consumed in the irrigation of a nursery garden was 0 36 litre per second per hectare, and for a market garden 0’47 litre per second, in both cases the water being supplied without stint. The author had found, by experiment, based on the quantity of water ac tually employed by cultivators, also near Madrid, that 4 litre per second would irrigate one hectare every twelve days. This, it was