the action of the engines is therefore very simple: the steam being applied under the inner piston, lifts both the pistons, the great crosshead, and inner ends of pump balance-beams simultaneously, and the pump-pistons descend at the same time: by an hydraulic apparatus attached to the great cross-head, the dead weight of the pistons, &c. is arrested at the point to which it has been thrown up by the steam, and time is given for the valves of the pump-pistons to close before the down-stroke of the steampistons is made; then, the equilibrium-valve being opened, the hydraulic apparatus is liberated at the same moment, and the steam passing from beneath the small piston, above both pistons, the pressure on both sides of the small one is equalized, whilst nearly twothirds of the steam acts upon the annular piston against a vacuum, and in aid of the dead weight helps to make the down-stroke in the steam-cylinder, and the upstroke in the pumps. The use of the two cylinders enables the engine-man, by judiciously altering the expansion in the small cylinder, to command his work at all times, without stopping the engine to take out, or put in, dead weight, as would be necessary for a singleacting one-cylinder engine, where dead weight only is used for lifting the water. It has frequently occurred that the load of an engine has been added to or diminished by 10 or 12 tons in the course of half an hour, by the action of gales of wind on the surface of the meer and boezem. Each engine has two air-pumps of 40 in. diameter, and 5-feet stroke. The steam is cut off in the small cylinder at from one-fourth to two-thirds of the stroke, according to the load; and after expanding through the remainder of the stroke, it is still further expanded in the large cylinder.

The whole cost of machinery, buildings, coals, and wages, to pump out the lake, will not exceed £150,000, whereas, by wind it would have cost £308,000, being a saving of £158,000; and there will also be a further economy upon the works in the bed of the lake, amounting to £40,000 more, so that the total saving by steam over wind will be £200,000, and three years' time.

To compensate the district of Rhynland for the loss of 45,230 acres of the boezem or catch-water basin, a steam engine of 200-horse power, driving 10 large scoopwheels, has been erected at Sparndam to lift the boezem water over the tide in the Y, or base of the Zuyder Zee, where the rise is on an average only 17 inches. This engine has discharged 30,000,000 tons of water in fifteen consecutive days. When the state of the boezem permits the 'Leeghwater,' Cruquius,' and 'Lynden' engines to work freely, they discharge on an average 2,000,000 tons in twenty-four hours, and they are capable of doing this down to their full depth. In the month of June, 1849, the three engines discharged 60,000,000 tons water, and lowered the meer one foot; between the 1st of May and 1st of December they had lowered the lake 5 feet, and by the autumn of 1850, it is calculated the dry land will appear. (See Table.)

The 'Leeghwater," Cruquius' and 'Lynden' engines were contracted for jointly by the Hayle and Perran Foundry Companies, Cornwall, and were manufactured and erected

under the direction of Mr. Arthur Dean; they have all worked during nearly three months with only twelve hours' stoppage.

It may be said in this instance, the Dutch have realized the fable of the Hare and the Tortoise:'in 1840, the erection of a steam engine of 30 or 40-horse power, for drainage purposes, was thought to be a bold step, whereas, under the guidance of English engineers, they have dared, between 1840 and 1849, to erect the most gigantic steam machinery in the world.

The low lands of the Netherlands are divided into large drainage districts, which have been embanked against the inroads of the tides and river floods; and the various parts of a district are connected by what is called the boezem, or water-basin, or reservoir, formed by the rivers, lakes, meers, or waterplaces having their origin in the district, and serves to receive the water drained either naturally or artificially from the surrounding lands. The boezem is put into communication with the exterior waters of the rivers or sea by locks and sluices. All lands in a given drainage district above the level of the boezem, and draining naturally into it, are called 'boezem lands.' All lands lying below the boezem, and drained into it by machinery, are called polders. Of polders there are two kinds: the first are seldom more than 2 or 3 feet below the level of the boezem, which is embanked above the natural surface of the land: of such polders there are upwards of 1000 in the province of South Holland only; and they are kept dry by the aid of an immense number of wind-mills. Of the second class of polders there are 43 in North Holland and 43 in South Holland, as recorded in the preceding Table, and these are works of a formidable character, being, for the most part, the beds of lakes, or permanent sheets of water, varying

in depth from 5 to 20 feet below the boezem, and requiring powerful machinery to pump them out in the first instance, and to maintain them dry afterwards; and as these lakes, &c., always form part of the boezem, or reservoir, of a much larger tract of land, their drainage frequently involves the construction of immense works, and seriously affects the prosperity of the whole district in which they are situate.

The preceding Table will, as an apt illustration of the subject of draining large districts, be found important in engineering history.

By the Table it will be seen that the North Hollanders had effected the drainage of nearly all their lakes, &c., as early as 1645, and they had then recovered 98,557 acres of land forming their beds; whereas the South Hollanders had in 1645 only drained five small lakes, whose area was only 3741 acres. It must be observed that the South Holland drainages are of a much more extensive character than those of North Holland, and the difficulties to be overcome were much greater; and last, but not least, the North Hollanders were much richer than their neighbours. Of the 223,000 acres of lakes, &c., recorded in the Table, upwards of 50,000 acres were formed artificially, by dredging the peat pulp to the depth of 10 or 20 feet, to serve as fuel for domestic purposes, &c.

Meridian, in astronomy, the line drawn from the north to the south, through the zenith, nadir, and poles, which line the sun crosses at noon Merlon, the solid part of an embattled parapet, standing up between the embrasures

Merus, the plain surface between the channels of a triglyph

Mesaula, a passage, gallery, lobby; an entry or court Mestling, brass ornaments; candlesticks; sacred utensils used in Anglo-Saxon times

Metallurgy, the art of working me

tals, invented by Tubal-Cain, B. C. 3608. "And Zillah also bare TubalCain, an instructor of every artificer in brass and iron." (Gen. iv. 22.) In the earliest periods of history, mention is made of the excellence in working metals among the Egyptians. Some specimens of metal-work of an early date exist, and modern fashion has also produced some very elaborate examples.

Metals are elementary bodies capable

of combining with oxygen; and many of them, during this combination, exhibit the phenomenon of combustion. Seven metals only were formerly known; but recently a much greater number has been been added. Metals are distinguished by their great specific gravity, considerable tenacity, and hardness, opacity, and property of reflecting the greater part of the light which falls on their surface, giving rise to metallic lustre or brilliancy. Metals are the best conductors of caloric: their expansibilities are various, and are probably nearly in the order of their fusibilities. Mercury melts at so low a temperature, that it can be obtained in the solid state only at a very low temperature; others, as platina, can scarcely be melted by the most intense heat which we can excite.

Metals employed in the mechanical arts:

ANTIMONY is of a silvery white colour, brittle, and crystalline in its ordinary texture: it fuses at about 800°: its specific gravity is 6.712.

BISMUTH is a brittle, white metal, with a slight tint of red: its specific gravity is 9.822: it fuses at 476°, and always crystallizes on cooling.

COPPER is the only metal, with the exception of titanium, which has a red colour: it has much lustre, is very malleable and ductile, and

exhales a peculiar smell when warmed or rubbed: it melts at a bright red or dull white heat, or at a temperature intermediate between the fusing points of silver and gold = 1996° Fahr.: its specific gravity varies from 8.86 to 8.89,-the former being the least density of cast copper; the latter, the greatest of rolled or hammered copper.

GOLD is of a deep and peculiar yellow colour: it melts at a bright red heat, equivalent, according to Daniell, to 2016° Fahr., and when in fusion, appears of a brilliant greenish colour: its specific gravity is 19.3 it is so malleable, that it may be extended into leaves which do not exceed the 282000th of an inch in thickness, or a single grain may be extended over 56 square inches of surface.

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LEAD in colour is blueish white: it has much brilliancy, is remarkably flexible and soft, and leaves a black streak on paper. When handled, it exhales a peculiar odour: it melts at about 612°, and by the united action of heat and air, is readily converted into an oxide. Its specific gravity, when pure, is 11.445; but the lead of commerce seldom exceeds 11.35. Lead is used, in a state of comparative purity, for roofs, cisterns, pipes, vessels for sulphuric acid, &c.

MERCURY is a brilliant white metal, having much of the colour of silver. It has been known from remote ages. It is liquid at common temperatures, solid and malleable at -40° Fahr., and contracts considerably at the moment of congelation it boils and becomes vapour at about 670°: its specific gravity at 60° is 13.5. In the solid state, its density exceeds 14. The specific gravity of mercurial vapour is 6.976.

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NICKEL is a white, brilliant metal, which acts upon the magnetic needle, and is itself capable of becoming a magnet. Its magnetism is more feeble than that of iron,