The two pieces B B form the two halves of a right-angled pyramid, and are measured by multiplying the area of the end by one-third the height: therefore 7′ 0′′ x 14' 0", the slope being 2 to 1, is equal to 98' 0"; the area of the two bases then, 1′ 0′′ × 98′ 0′′ × 44′ 0′′, gives the cube quantity in the two. Measurement of shipping for tonnage

(called the new measurement') was regulated in the 5th and 6th of George IV. By this Act certain rules were established for ascertaining the tonnage of ships, as well on shore as afloat, and of vessels propelled by steam; and the account of such tonnage, whenever the same shall have been ascertained according to the rules herein prescribed, (except in the case of ships admeasured afloat,) it is enacted, shall be deemed the tonnage of such ships, and shall be repeated in every subsequent registry of such ships, unless any alteration shall have been made in their form and burthen, or unless it be discovered that the tonnage had been erroneously computed: and it is considered that the capacity of a ship is the fairest standard by which to regulate its tonnage; that internal measurements will afford the most accurate and convenient method of ascertaining that capacity, and that the adoption of such a mode of admeasurement will tend to the interests of the ship-builder and the owner.

It was enacted that the tonnage of every ship or vessel required by law to be registered shall, previous to her being registered, be measured and ascertained while her hold is clear, and according to the following rule: Divide the length of the upper deck between the after-part of the stem and the forepart of the stern-post into six equal parts. Depths: At the foremost, the middle, and the aftermost of those points of division, measure in feet and decimal parts of a foot the

depths from the under side of the upper deck to the ceiling at the limber strake. In the case of a break in the upper deck, the depths are to be measured from a line stretched in a continuation of the deck. Breadths: Divide each of those three depths into five equal parts, and measure the inside breadths at the following points: at one-fifth and at four-fifths from the upper deck of the foremost and aftermost depths, and at two-fifths and four-fifths from the upper deck of the midship depth. Length: At half the midship depth measure the length of the vessel from the after-part of the stem to the forepart of the stern-post, then to twice the midship depth add the foremost and the aftermost depths for the sum of the depths; add together the upper and lower breadths at the foremost division, three times the upper breadth and the lower breadth at the midship division, and the upper and twice the lower breadth at the after division, for the sum of the breadths; then multiply the sum of the depths by the sum of the breadths, and this product by the length, and divide the final product by three thousand five hundred, which will give the number of tons for register. If the vessel have a poop or half-deck, or a break in the upper deck, measure the inside mean length, breadth, and height of such part thereof as may be included within the bulkhead; multiply these three measurements together, and dividing the product by 924, the quotient will be the number of tons to be added to the result as above found. In order to ascertain the tonnage of open vessels, the depths are to be measured from the upper edge of the upper strake.

To ascertain the tonnage of steam vessels, was also further enacted, that in each of the several rules prescribed, when applied for the purpose of ascertaining the tonnage

of any ship or vessel propelled by steam, the tonnage due to the cubical contents of the engine-room shall be deducted from the total tonnage of the vessel as determined by the rules, and the remainder shall be deemed the true register tonnage of the said ship or vessel. The tonnage due to the cubical contents of the engine-room shall be determined in the following manner: measure the inside length of the engine-room in feet and decimal parts of a foot from the foremost to the aftermost bulk-head, then multiply the said length by the depth of the ship or vessel at the midship division, as aforesaid, and the product by the inside breadth at the same division at two-fifths of the depth from the deck taken as aforesaid, and divide the last product by 92-4, and the quotient is deemed the tonnage due to the cubical contents of the engine-room. Measurement of standing timber.— Measure from the tree ten, twenty, thirty, &c., feet, and then plant the theodolite level: direct the telescope to the bottom of the tree, and observe the degree and tenth of depression; and to the top of the tree, the degree and tenth of elevation. When the timber has been previously felled, it is customary, in measuring, to girt a string round the middle of the tree, and fold it twice, which will give the fourth part of the girt, and which is considered the true side of the square; then the length is measured from the but-end of the tree, so far up as the tree will hold half a foot girt, or, more properly speaking, quarter-girt; that is, the line six inches when twice folded. Various tables are published, to assist the timber-measurer in the performance of his duty. All timber is bought and sold by the load, and a load is estimated at forty feet of unhewn or rough timber, and fifty feet of hewn timber, which

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is supposed to weigh one ton, or twenty hundred weight. Mechanical powers are contrivances by which we are enabled to sustain a great weight or overcome a great resistance by a small force. (See Machinery.)

The

Mechanics, that branch of practical science which considers the laws of equilibrium and the motion of solid bodies; the forces by which bodies, whether animate or inanimate, may be made to act upon one another; and the means by which these forces may be increased so as to overcome those which are more powerful. The term mechanics was originally applied to the doctrine of equilibrium. It is now, however, extended to the motion and equilibrium of all bodies, whether solid, fluid, or aëriform. complete arrangement of mechanics is now made to embrace, besides, the pressure and tension of cords, the equilibrated polygon, the catenary curve, suspension bridges, the equilibrium of arches and the stability of their piers, the construction of oblique arches, the equilibrium of domes and vaults with revetments, the strength of materials, whether they be of wood or iron, dynamics, or the science of moving bodies, with hydrostatics, pneumatics, and hydraulics. Medallion, in architecture, any circular tablet on which figures are embossed; busts, &c.

Mediaval, relating to the middle ages Member, a moulding; either as a

cornice of five members, or a base of three members, and applied to the subordinate parts of a building Mensuration is the application of the

science of arithmetic to geometry, by which we are enabled to discover the magnitude and dimensions of any geometrical figures, whether solid or superficial. To enable us to express this magnitude in determinate terms, it is necessary to assume some magnitude of the same kind as the unit, and then, by

stating how many times the given magnitude contains that unit, we obtain its measure.

The different species of magnitude which have most frequently to be determined are distinguishable into six kinds, viz. 1. Length. -2. Surface.-3. Solidity, or capacity.-4. Force of gravity, commonly called weight.-5. Angles. -6. Time.

Mere, or Meer, a name frequently given, in England and the Netherlands, to inland lakes or sheets of fresh water, such as Windermere, Whittleseamere, Ugg-mere, Soham-mere, in England, and the Egmonder meer, Purmer meer, and Haarlemmer meer, &c., in the Netherlands. The term is most frequently used in the latter country, where, prior to 1440, there were more than 150 meers, of which 85 occupied an area of 177,832 acres, since drained and reclaimed, in the provinces of North and South Holland; and where also the Haarlemmer meer, covering an area of 45,230 acres, is now in course of drainage.

As the meers, in fen-lands, serve as reservoirs to hold a portion of the surplus rain-water falling on the district of which they form a part, their being dyked off and drained, where of considerable extent, has most important effects on the neighbouring lands, by contracting the area of the reservoir or catch-water basin of the district. But as these drainages generally oblige improvements in the outfalls, their result is mostly beneficial to the other lands.

The beds of the Dutch meers are from 10 to 20 feet below the level of the lowest point of the natural outfall in their districts; consequently they are always drained by mechanical means. Wind-mills have been employed to drain the land, in the Netherlands, from time immemorial; but the drainage of the meers was not com

menced until 1440, about which period wind-mills and draining machinery were considerably improved; and as late as 1840, windmills for draining purposes continued in favour with the Dutch engineers, in preference to steam engines; and at that date, 12,000 wind-mills were employed to drain the polders, in the Netherlands, and only five small steam engines, the largest not exceeding 30-horse power the average consumption of fuel was 20 lbs. of coal per horse power per hour.

In the English fens, steam had in a great measure superseded windmills for drainage purposes; but the consumption of fuel was nearly as great as in the Dutch engines.

In 1839, the Dutch States-General decreed the drainage of the Haarlemmer meer, and voted eight millions of florins for that purpose, to which two millions more were subsequently added, making the total sum of £834,000.

The Haarlemmer meer forms part of the great drainage district of Rhynland, which has an area of 305,014 English acres: prior to 1848, this area was occupied by 56,609 acres of meers and watercourses, nearly all in communication with each other, forming what is called the boezem, or catch-water basin of the district; the surface of the water being maintained at the lowest level of natural sluiceage, by sluices at Katwyk into the North Sea, and at Sparndam and Halfweg into the Y, or the southern end of the Zuyder Zee.

Above the boezem are 75,357 acres drained into it by natural level; and at depths from 2 feet 6 inches to 4 feet below it are 170 polders covering an area of 135,850 acres; and 37,198 acres, divided into 28 polders which were formerly meers, but are now drained, and whose beds are on an average 14 ft. below the level of the boezem.

The surplus rain and infiltration

waters from the 173,048 acres of polder-land are lifted into the boezem by the united action of 261 large wind-mills, with an average force of 1500-horse power.

The drainage of the Haarlemmer meer, which forms part of the boezem or basin, will deduct 45,230 acres from its area, and reduce it to 11,379 acres, or 4th part of its former size; whilst the land surface drained into it will be increased from 229,657 to 293,735 acres.

The average level of the boezem is 10 inches below the ordinary low water, and 27 inches below high-water mark in the Y or Zuyder Zee; and 7 inches above low water, and 57 inches below ordinary high water, in the North Sea.

The bed of the Haarlem Lake is 14 feet below the winter level of the boezem; and when drained, the maximum lift will be 16 feet 6 inches to 17 feet, according to the state of the wind, which raises or depresses the surface of the water in the canals very considerably.

The water contents of the Haarlemmer meer to be pumped out, including the additional quantity arising from the surplus rain and infiltration during the draining, are estimated at 800,000,000 cubic mètres or tons.

The greatest quantity of monthly drainage when the meer is pumped out is estimated at 36,000,000 tons, and the annual average surplus of rain-water, &c. at 54,000,000 tons to be lifted, on an average, 16 feet high.

The Dutch engineers were generally in favour of wind-mills, or a combination of wind-mills and steam engines, for pumping out the meer; but in 1841, the late king, William II., by the advice of a commission, decreed that steam engines only should be employed for the purpose; and in 1842, at the suggestion of two English engineers, Mr. Arthur Dean and Mr. Joseph Gibbs, it was determined to

erect, and they were directed to prepare the designs for, three steam engines upon the high-pressure, expansive, condensing principle, of the ordinary force of 350-horse power each, but capable of being worked on emergencies up to 500horse power.

The consumption of fuel was limited to 24 tbs. of coal per horse power per hour.

The three engines were named the Leeghwater,' 'Cruquius,' and 'Lynden,' after three celebrated men who had at different periods proposed plans for draining the Haarlemmer meer.

The 'Leeghwater' was the first erected, to work eleven pumps of 63 inches diameter, with 10-feet stroke in pumps and steam cylinders; and the Cruquius' and 'Lynden,' were afterwards constructed, to work eight pumps each, of 73 in. diameter, and with 10-feet stroke; each engine is calculated to lift 66 cubic mètres or tons of water per stroke.

The accompanying sketch is a representation of the interior of the Lynden' engine and enginehouse, on the upper floor: the

Cruquius' is on the same model; but the 'Leeghwater' has the inner ends of its eleven pump-beams arranged under the great cross-head, instead of over it.

Each engine has two steam cylinders, placed concentrically, the one within the other, the outer of 12 feet diameter, and the inner one of 7 feet diameter: both are secured to one bottom, and covered by one cover, but the inner cylinder does not touch the cover within 1 inch: there are two pistons, 26 inches deep, the compartments of which are fitted with cast-iron plates: the outer piston is annular, and has a packing on both sides: beneath this annular piston a constant vacuum is maintained when working: the two pistons are connected by five pis