Greenock

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GREENOCK.

FEW works, either public or private, are more worthy of inspection than Shaw's Water Works at Greenock, notwithstanding that the scheme, as a matter of speculation, has not been attended with success. All originally proposed to be done by the engineer is fully effected, and since the year 1827 the town has been amply supplied with water, both for domestic purposes, and as a means of mechanical power.

The town of Greenock, although situated on the Clyde at the foot of land rising abruptly to a very considerable elevation, was, previous to the year 1824, most scantily supplied with water; in consequence of which deficiency, the first measures were then taken to remedy the defect. A small stream, or burn, descending the brae, from a height of five hundred feet, discharged itself into the river a few miles below, forming a channel through which, no matter how great the abundance of water in rainy seasons, all was exhausted, without use or profit to the inhabitants of the vicinity; the primary object to be effected, therefore, was to augment the resources of this stream by drainage, and then to economize the water so obtained, by means of artificial lakes or reservoirs. A watercourse of about twelve feet in width, and of declination to afford as many cascades as possible, sites for water wheels for any description of mills that might be afterward built thereon, was next to be constructed. This watercourse, or aqueduct, was accordingly made and thrown open in the year 1827; the quantity of water stipulated by the joint stock company to be supplied thereby being at the rate of twelve hundred cubic feet a minute for the day of twelve hours; according to which regulation the water is consequently set on every morning, and stopped in the evening; the stream being directed during the night to replenish the reservoirs. In the mean time the aqueduct, which commences on the top of the elevated ground three or four miles from the town, is conducted by a circuit of nearly six miles round the mountain, and then directed downward, so as to gain nearly every perpendicular foot of fall; the intervening space between each cascade deviating only from the true level by as much as is barely sufficient to propel the stream onward towards the next. The cascades in the line are each about twenty yards in length, of different angles of declination, in number about fourteen or fifteen, but very few up to the present day are let; under other circumstances, had the scheme been attended with success, it was calculated that, inasmuch as an extension of drainage is capable of being accomplished, if required, to an almost unlimited extent, the water in the reservoirs might have been made equal to the supply of another line to the westward: which augmentation would have called for a quantity of two thousand four hundred cubic feet per minute; and eight years' subsequent experience has fully shown that the latter object is feasible.

On a walk in a fine evening up the brae, it is beautiful to see these mimic waterfalls as they glitter in the sun, here and there sending their smoke and spray aloft from among the flowery heather, as one proceeds from the town towards the main reservoir. The circuitous course of the aqueduct from the town to the upper level, namely, that of five hundred and twelve feet, is about a mile: the ground then continues to rise gradually as the path leads across a tract of moorland, till, on attaining the summit of the mountain, the principal lake or reservoir, called Lake Thorn in compliment to the engineer, is seen below, covering a surface of two hundred and ninety-five imperial acres, and estimated to contain upward of two hundred and eighty-four and a half millions of cubic feet of water—equal, at the rate of twelve hundred a minute, to more than five months' full supply for the mills on the line. Thence the water passes through self-acting sluices into other auxiliary reservoirs, the latter being three quarters of a mile farther removed, and from the extreme distance, namely, about four miles from the town, it is carried, as has been before stated, by a circuitous artificial course round the hill.

Notwithstanding the high elevation of Lake Thom, as the ground rises considerably around it, nature had already contributed in great measure to facilitate the drainage to which it entirely owes its existence; the chief part of its artificial formation is a dam of earth raised sixty feet above the bed of the rivulet, and about five hundred yards in length. From the middle of the dam a wooden jetty protrudes at right angles, about twenty-five yards into the lake. At the extremity of the jetty is constructed a strong screw purchase, by which the main sluice is raised. At the farther end of the dam, or embankment, are the self-acting sluices, by which the water, as soon as it has arrived at a certain level, passes away to the next reservoir. The level determined on here is forty-eight feet; on the evening in question, as I stood upon the jetty, I observed it to be, by the scale of depth, forty-six and a half feet—the reservoir next in dimensions contains forty imperial acres in extent, and fourteen and a half millions cubic feet of water.

The operation of the several self-acting sluices is really admirable, whereby the waters of a small inconsiderable stream, augmented by judicious drainage, are not only economized in the reservoirs aforesaid, but are caused, by artificial means, to perform as it were a series of evolutions, as regularly as if in obedience to the order of nature. The self-acting sluices may fairly be said to exert a power as varying and incessant as that of the stream itself, whether trickling along lazily in the drought of summer, or plunging impetuously forward in the middle of winter; and these sluices, in fact, though specimens of human art, consist merely of forces purely natural: which forces effect at all times the equilibrium required by acting one against the other. I will not attempt to detail their mechanism, otherwise than by briefly stating their modes of action.

Of these modes, those that particularly engaged my attention were two: that of the float, and of the hollow cylinder acting as a weight.

In the first instance, that of the float—this may be said to perform the office of the common ball cock, but on a larger scale. An aperture, or pit, communicating by a drain with the stream or lake, is dug in the ground. The water, when redundant, runs off by the said drain, and entering at the bottom of the pit, raises the float, which is suspended therein. The float being appended to a chain, of which the other end is fixed to the valves of the sluice, as it rises consequently acts upon the chain, so that the valves open, and the water escapes, as required.

The other mode, that of the hollow cylinder, is the same principle as the latter, though reversed in its action. The pit, the communicating drain, and the chains and valves, being as before, the desired end is attained by the descent of the weight contained in the vessel, instead of the ascent of the float. The application of the weight is an ingenious contrivance, merely the cylinder full of water; a hole at the bottom being always open, so that the weight is efficient only so long as the water runs in faster than it escapes from the aperture; on the contrary, the moment the ingress of the stream is less than its egress, the vessel, losing the weight of the water, becomes non-effective.

Besides the above-mentioned aqueduct and cascades, water for the supply of the town is derived from different sources, and from a spot more contiguous. The necessary supply for the domestic uses of the inhabitants originally estimated at the rate of two cubic feet for each individual per day, for a population of twenty-five thousand, is conveyed by a stone conduit fifteen inches square into a circular basin a quarter of a mile from the town, containing a full day's supply. The water is discharged into this basin by five spouts, proceeding from as many filters, in passing through which it is previously subjected to the process of filtration; and it is interesting to observe the ingenious expedient by which this useful operation is performed on so large a scale.

Each of the filters consists of a pit fifty feet long, twelve wide, and eight deep, containing a bed of sand five feet in thickness, through which the water passes downward. As by continual use a sediment is necessarily formed on the surface of the sand, means are adopted to cleanse the filter by changing the course of the stream, and causing it to pass upward through the sand from the bottom, thus carrying away the sediment aforesaid. A single man is able to perform this service in half an hour, standing, while the reversed current is in action, on a plank laid on the sand, during the whole time stirring the sediment incessantly with an iron rake. Each filter is constructed with a view to the above operation; and in order to preserve a clear space below, shallow drains, about six inches in depth, intersect the bottom, one lengthwise, and several others across: these drains are covered in the first instance by a layer of large stones, then others smaller, next others broken of the size required for a road, and so on gradually decreasing to that of peas. Upon this foundation rests the layer of sand aforesaid.

CASTING SHEET LEAD.

Strolling about the streets in Greenock, while waiting the arrival of the steamer, I saw some workmen occupied in a building adjoining the quay, in the simple operation of casting sheet lead. The dimensions of their frame were nineteen feet six inches in length, by six feet two inches in breadth; the surface of coarse sand being levelled by a flat iron passed over it by hand. From a trough, at the head of the frame, extending its whole breadth, the melted lead was poured by a couple of men who tilted i(, by means of chains fixed at the ends of two levers; the trough was previously filled from the caldron, with iron ladles; heat being meanwhile applied by flues from the furnace to prevent the lead from cooling under a process so slow. The newly cast sheet being rapidly levelled by a wooden bale, at that particular instant of time when its consistence suited, a chalk line was then applied, and the rough edges pared off by a common knife.

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