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to recommend such an application. The method consists in putting down the shaft for a few metres without having to keep up the sides, and in continuing this work by small passes without any stoppage, as shown in vertical section by Fig. 1. A depth is sunk of three or four metres (mean llf-ft.), or even more, according to the measures, without any lining whatever; and then the first length, or section, of the movable centring is laid perfectly level from 30 cm. to 50 cm. (mean 1 ft. 7 in.) from the bottom, on a light collar of planks resting on three timbers, which divide the shaft into the ladder compartment and that for working the kibbles. The movable centring (shown by Pigs. 2 and 3), 1 m. (3 ft. 3f in.) high and 3 m. (10 ft.) in outside diameter, is formed of five segments connected by simple cleats with pins ; and the segments of each centring are formed of timbers with radial joints nailed to horizontal joists 4 cm. (16 in.) thick, following the internal contour of the concrete lining. For facilitating the putting-up and taking-down, a simple bevelled sector that can be taken up by hand is intercalated between the first and last segment; and this construction, entirely of deal, is very light and easily manipulated. Landing.— Between the movable centring and the inside of the shaft concrete is run in; and for this work, as the taking-up of the spoil often alternates with letting down the concrete, the landing is formed of two floors, each having two flaps for allowing the kibbles to pass ; and, while the lower floor is fixed, half the upper can turn up on hinges. For the spoil the upper floor is used, so as to permit of tipping the stones directly into a tub; and for letting down the concrete the upper floor is turned up on its hinges, the loading being thus effected from the lower level, thus saving loss of time. Concreting. —The concrete is let down in the kibbles that serve for sending up the spoil, the winch drawing them up and setting them down on a simple floor laid on the joists of the centring and tipping them directly into the angular space in layers of 30cm. to 35cm. (mean Ift, lin.). Each layer is punned rapidly in as vertical a direction as possible, but with slight blows for driving off the air and uniformly consolidating the concrete, this work being performed as quickly as possible for preventing joints from forming. When the first metre—say, yard—is thus concreted a second centring is put in, and the work proceeds in the manner just described, but for rendering it easier to strike the centring the carryingtimbers are placed in notches in the lower frame. At the last centring there remains a space of about 15 cm. (6 in.), which is filled very quickly and easily with the trowel; and in this case the punning must be made horizontally. The men soon become accustomed to putting up and striking the centring, which they perform very quickly ; but the first length, or section, of 1 m. (3 ft. 3-fin.), requires to be placed perfectly level. When this small pass has been concreted the excavation of another is begun after the joists have been removed, which is effected without causing difficulty or damage, the concrete being already hard as a rock ; and each length or section of concrete perfectly filling up the irregularities caused by blasting forms one piece with the shaft-sides, so that it remains suspended, as it were, without the slightest danger. The preparation of the concrete is effected on the spot and in the following manner : On a perfectly level space is spread a 25 cm. (10 in.) layer of broken stone well washed, and the concrete mortar is poured over them, the two being thoroughly mixed by means of appropriate tools. Nature of the Lining. —This monolithic lining is thus produced by intimately mixing rock materials with mortar made from slag cement, the skeleton thus consisting of the slag of forge pig broken into irregular pieces of 3 to 5 cm. (mean If in.) gauge (or, better still, and more frequently, from the sandstone obtained in driving crosscuts), and the mortar of one part by weight of cement to two parts of granulated slag, this representing in volume one of cement to four of slag. Slag cement was used because, while being better than natural and just as good as artificial cements, it is from 50 to 100 per cent, cheaper, and a mean of five samples tested at the Government station, Mechlin, gave favourable results. The concrete showed a resistance to tensile strain of 20 kilogs. per square centimetre (284 lb. per square inch) after remaining under water for a week ; and the resistance to crushing-strain may be taken as ten times greater than that to tensile strain, while the resistances obtained after a month practically correspond with those obtained after a week, with the addition of 15 per cent. • Composition of the Concrete. —One condition was imperative in the present case : the monolithic lining must prevent the passage of water, so that all the spaces had to be perfectly filled up by the cement; and the practice in such a ease is to take two parts of cement mortar to three parts of broken stone, this giving, for 2 tons of concrete, 1 ton of broken stone, 0-25 ton of cement, and 065 ton of granulated slag. Besistance of the Concrete. —As regards the resistance proper of concrete, actual tests on tensile and especially crushing strain (which is the most important) are still wanting; but it may be concluded from official tests carried out at the Liege Cannon Foundry that the concrete employed in the case under notice will afford a resistance to crushing-strain of at least 300 kilog. per square centimetre (4,2671b. per square inch). If it be considered that the advice thus given to only use good bricks up to a mean resistance of 12 kilogs. per square centimetre (171 lb. per square inch), it may be asserted that for lining shafts concrete is, with far less thickness, preferable to bricks, and that important works of lining, and also vertical and horizontal stoppings that are impossible—or, at any rate, difficult—with ordinary materials, may be carried out in concrete with a certainty of success. In the present case the question should be asked whether the thickness of 25 cm. (10 in.) given to the lining was sufficient to withstand, not so much strain as a brick lining of double the thickness, which was certain, but also a feeder which, in the case of the winding-shaft, showed itself at a depth of about 25 m. (14 fathoms). If the principles of the strength of casings or coverings be applied to this case, the limit of 2 n BI 2 tension answering to a given thickness, c, will be T=l -f —R1 R = 19-8 kilog. per square centi-