most dangerous of any, as it often decomposes so quickly as to kindle the coal-slack. Its composition is, in 100 parts,

45.07 iron

53.35 sulphur

0.58 manganese

99.00 white pyrites.

Yellow sulphuret of iron, yellow pyrites. This variety becomes red before the blow-pipe; and in the reducing flame it melts into a globule, which continues red-hot for a short time, and possesses, after cooling, a crystalline appearance. In nitric acid it is slowly soluble, with the precipitation of sulphur, but in no other acid. It is composed of

47.30 iron 52.70 sulphur

100.00 yellow pyrites.

Yellow pyrites is almost identical with the white pyrites, and the latter appears to be only different in containing more foreign matter : both are widely diffused among the ores of iron, and are found in massive nodules, crystals, and veins, in the coal beds, clay-slate, graywacke, greenstone, limestone, and in beds of primitive slate. It is the main material which is used for manufacturing copperas, alum, oil of vitriol, Spanish brown, and sulphur. Summer, a horizontal beam or girder Sump, in mining, a pit sunk in the engine-shaft below the lowest workings

Sump-shaft, the engine-shaft Supercilium, the transverse antepag

ment of a doorway. The word is also used to denote the small fillets or bands above and below the scotia of the Ionic base. Superficies, in geometry, the surface of any body or figure, considered as possessing two dimensions, or extension in length and breadth, but destitute of thickness: in mensuration, it is estimated as area

Supporters, in heraldry, figures standing on a scroll and placed by the side of the escutcheon, such as the lion and the unicorn in the British, and the angels in the French arms Supporters, in ship-building, the kneepieces under the cathead Surmarks, in ship-building, the stations of the ribbands and harpings which are marked on the timbers Surveying is the art of applying the principles of geometry and trigonometry to the measurement of land. The principal operations are laying down or driving base lines and triangles on either side of the base. In large surveys it is desirable to lay down these triangles by measuring each angle with an instrument called the theodolite, by which the accuracy of the measurement of the sides may be checked. The theodolite is also available in fixing the true position of points, the distances between which are immeasurable, owing to the intervention of buildings, rivers, or other obstacles. Rectangular or irregular areas of land are similarly reduced to triangles, and their exact position referred to a base line. In driving lines over land, three long poles are requisite: these are ranged in the direction of the intended line at the greatest distance at which they can be seen, either with the naked eye or with the assistance of a telescope, and driven firmly into the ground. Intermediate stakes are then fixed, by which the line is marked out. In proceeding onward to extend the line included between the front and back pole, the latter only is removed, and carried before the front pole to the greatest practicable distance, and being ranged by the two remaining poles, is there driven. Thus the middle pole becomes the back one, and is in like manner removed to the front, and there ranged and fixed: and in this manner, by successively removing the back pole, and conveying it to

the front, the line is extended as far as necessary. These poles should be as light as possible, consistent with strength, and shod with iron points, to facilitate driving. On the top of each pole a flag or disc is fixed, to render them conspicuous from a long distance. Distances are measured with a chain formed of wire links, the length of the chain being 66 feet, and formed with 100 links, each link measuring 7.92 inches. The end of each chain is marked by driving a wire pin or arrow into the ground, by counting which the number of chains measured is ascertained. The base line being thus driven and measured, it is recorded in a book, and all intersections of fences, &c. marked, and their relative distances on the base are entered. A distant point on either side of the base is then determined, and a pole erected upon it, and the distance of this point from two fixed points upon the base measured with the chain, and duly recorded. By this means, a triangle is completed, and afterwards correctly filled in with all intervening fences, &c.; and by repeated processes of this kind the survey is extended to any required distance on each side of the base. If the triangles first laid down are of great extent, they should be determined, and the position of their angles ascertained with the theodolite. This instrument consists of a pair of horizontal circular plates, the upper of which is called the vernier plate, turning freely on a centre upon the lower plate, the edge of which is chamfered off, and accurately graduated with degrees and subdivisions. By these plates and their adjusting screws, &c., horizontal angles are measured, the sight of the surveyor being aided by a powerful telescope on the upper part of the instrument, and a microscope to read off the graduations upon the vernier. An upper frame which carries the telescope

SUS

also supports a vertical arc or semicircle, which is likewise graduated, and with the aid of another microscope the elevation of any high object, as a tower, &c. (observed through the telescope) may be correctly read off. This part of the apparatus thus enables vertical angles to be measured, and by the application of trigonometry heights or distances may be thus exactly determined without the actual measurement of all the lines in each vertical triangle.

Suspension, in mechanics, as in a balance, are those points in the axis or beam where the weights are applied, or from which they are suspended

Suspension. Bridges of suspension are of several kinds and of various dimensions, consisting of several iron chains, not formed of small links, like cables, but of whole bars of iron jointed at their ends, passed over a tower, being the access to the bridge on each side of the river, while their extreme ends are firmly attached to large and ponderous stones that are sunk a great depth into the ground on each side of the stream. These masses of masonry are named abutments. The chains hang in parallel festoons over the river, between the supporting towers, and carry a number of vertical bars of iron that are attached to and hang down from them for the purpose of suspending beams of wood or iron hanging horizontally in the direction of, or obliquely to, the stream, and serving as joists to support a strong planked platform or roadway that extends across the river: frequently these roadways are paved, or at least gravelled or ballasted over for horses, carriages, and pedestrians. Extraordinary examples exist of this species of building in our own country, viz. that at Bangor, crossing the Menai Strait, by Telford, that at Hammersmith, by Tierney Clark,-Hungerford, by Brunel; but the most extraordi

nary structure is the stupendous work of Tierney Clark, uniting Pesth with Buda, in Hungary. Mr. Dredge has constructed several smaller bridges of suspension, according to his arrangement, both in England and Scotland, and Lieut.Col. Goodwyn also, in India, with some modifications of Dredge's adjustments. Suspension bridges have been constructed also with wire as a material at Fribourg, in Switzerland, and at other places. Sweep, or Tiller-Sweep, a circular

plank fitted to support the foremost end of the tiller, or handle of a rudder, much improved by conveying the tiller-rope round it, and keeping it always tight Swivel, in mechanics, something fixed

in another body so as to turn round on it; a kind of ring made to turn round in a staple or other ring. In artillery, a very small cannon, which carries a shot of about halfa-pound.

Sycamore-tree, a species of the ficus, or fig-tree, common to Europe; also called the great maple, and in Scotland and the north of England the plane-tree: its mean size is 32 feet high. It is a very clean wood, resembling the plane-tree, but much smaller. The colour of the young sycamore is silky white, and of the old, brownish white; the wood of the middle age is the intermediate in colour, and the strongest. It is used in furniture, piano-fortes, and harps, and for the superior kinds of Tunbridge ware. Sycamore may be cut into very good screws, and is used for presses, dairy utensils, &c.

Symmetry, in sculpture, &c., adaption

of parts to each other; proportion; harmony; agreement of one part with another Sympiesometer, a barometrical instru

ment in which the atmospheric pressure is indicated by the ascent of a column of oil in a short glass tube against the elastic pressure of an enclosed volume of hydrogen

gas. Its indications require correction for the changes produced by temperature on the gas. The instrument is more compact, but also more complex, than the mercurial barometer.

Synagogue, a word which primarily

signified an assembly, but, like the word church, came at length to be applied to places in which any assemblies, especially those for the worship of God, met, or were convened. Jewish synagogues were not only used for the purposes of divine worship, but also for courts of judicature. The present ordinary meaning of the term synagogue is a Jewish church. Syphering, in ship-building, lapping one edge of a plank over the edge of another for bulk-heads, making the edges of the planks and the sides of the bulk-head plain surfaces

Syphon, a bent tube, having one leg

shorter than the other. It acts from the pressure of the atmosphere being removed from the surface of a fluid, which enables it to rise above its common level, and is used for the purpose of emptying liquors from casks, &c.

Syphon. The date of the first application of the principle by which water or other fluids may be drawn from one level to another by the exhaustion of the air contained in the limb communicating with the lower level, appears to be very remote. The Egyptians certainly used it for the transvasing of wine: but the first important application of this principle to useful or general practice was in the aqueduct which conducted the springs of Mount Pila to Lyons: the date of this aqueduct is about 40 years after the commencement of the Christian

to the lower. Of these, the valley of Chaponest was 2400 feet across, measuring in a straight line across the valley; and it was about 200 feet deep. The valley of St. Foy was about 3192 feet across, by 300 feet deep; that of St. Trenée was 798 feet across, but much shallower.

The pipes of the Chaponest syphon, on leaving the upper reservoir, were 8 inches diameter and 1 inch thick: they were of lead. After running 75 feet of the descent of this dimension, they branched off into two divisions of 6 inches diameter each, in order that the pressure upon the pipes at the lower portion of the syphon might be diminished. They ran over the level bridge in the lower part of the valley of this smaller diameter, and mounted the opposite side for a height of 70 feet, when they reunited into pipes of 8 inches diameter again. The total fall of the Chaponest syphon was 150 feet, the rise on the opposite side was 130 feet, leaving a difference of level of 20 feet to compensate for the friction. The syphon of St. Foy had a difference of level, from the upper reservoirs to the straight part, of 240 feet.

The Lyons aqueduct had in its total length thirteen common straight aqueduct bridges and three syphons; it delivered very nearly 1,300,000 gallons in the twentyfour hours.

Dr. Lardner and many other writers on hydraulics have failed to notice these extraordinary works, and have expressed their surprise that the ancients were ignorant of the existence of the law by which water finds its own level. The ancients, however, appear to have wisely preferred the more economical system of carrying water in a straight trough, wherever the expense was justifiable. Water-works were, in early times, Government affairs, and the expense of their

maintenance was deliberated. The preceding cases abundantly prove that the ancients applied the wellknown law of hydrostatical balance whenever they found such a course advisable; and the details given by Vitruvius remove all doubt upon the subject. His instructions (lib. 8, c. 7) are as follows:-" When the expense of erecting a bridge is too great, a syphon may be used; but this should only be resorted to as a last expedient. The danger of bursting the pipes, and the expense of the repairs, are serious objections to this method, and in the end straight bridges are the cheapest. If, however, it be determined to employ a syphon, it should be laid with a regular curve, and all abrupt elbows avoided. To secure this, a substructure should be raised to fill in any inequalities in the valley where it is to be erected. The last length of the descending pipe and the first of the straight pipe at the level part, as also the last length of the straight pipe and the first ascending one, should be let into a solid stone, which should be carefully fixed and surrounded with ballast, properly rammed." He also gives directions for the construction of airshafts from the lower parts, which he calls columnaria,' and he expressly states that they are necessary to relax the 'vis spiritus in ventris,'-the force of the air in the curves.

Syphon-cups, in steam engines, cups placed for feeding oil to the working parts of the machinery, trimmed with cotton or worsted, the same as the axle-boxes Syringe, a small hand-pump: in its simplest form, it is provided with a piston and rod, but is destitute of valves, one simple aperture at the extremity serving for the admission and ejection of fluid: those constructed with valves, however, are available, on a smaller scale, for all the purposes of an air-pump

Systyle, a term applied to a building in which the pillars are closely placed, but not quite so close as in

the pycnostyle, the inter-columniation being only two diameters, or four modules, of the columns

TAB

TABERD (Saxon), a jerkin, or coat without sleeves; also, a herald's coat Tabernacle, a moveable fabric; among the Jews, the name of a portable temple which was constructed in the Wilderness: the term is also applied in Christian architecture to richly ornamented niches Table, in architecture, a smooth, simple member or ornament of various forms, but most usually in that of a long square Table or Tablet mouldings, horizontal bands of mouldings, such as basemouldings, strings, cornices, &c. Tables were in the Tudor age usually described as 'bordes,' and were not in any great variety: the sorts were but few, and little distinguished by workmanship; but the splendour of their coverings amply compensated for the rudeness and simplicity of the works so concealed. The most elaborate embroidery, wrought on the finest grounds, velvets and satins fringed with gold and silver, Turkey carpets, and the choicest tapestry, were used as table-covers. Table-cloths, carpets, which at earlier

periods were almost the only coverings for dining-tables and cupboards; naping was possessed by the higher orders only. In 1520, Thomas, Duke of Norfolk, bequeathed his naperie to Agnes his wife.

Tabling, in ship-building, letting one piece of timber into another, in the same manner as the beams are put together

Tablinum, an apartment of a Roman

house which was entered immediately from the atrium, and in which records were preserved in cases, and the hereditary statues placed.

TAC

Tack, in navigation, to change the course or turn about a ship during a contrary wind from the starboard to the larboard, &c. Tack, in navigation, a rope used to confine the clues of the main and fore courses forward, occasionally in a fixed position : it has a large wall-knot at one end. The word has also various other applications.

Tacks, in navigation, the foremost

lower corner of all fore and aft sails Tacking, in navigation, signifies a manœuvre by which a ship makes an oblique progression to windward in a zig-zag direction, named also 'beating to windward'

Tackle, in mining, the windlass, rope, and kibble

Tania, the band or fillet surmounting

the Doric epistylium

Taffrail, the carved work at the upper

part of the stern of a vessel, the ends of which correspond with the quarter-pieces

Tail-water, the waste water discharged from the buckets of a water-wheel in motion

Talmud, or Thalmud, a book in great veneration among the Jews, containing their doctrines and morality, of which there are two, the old, called the Talmud of Jerusalem, the other, of Babylon; the first composed by Rabbi Johanan, president of the academy of Palestine, about the 300th year of Christ : this consists of two parts, the Mishna, or the second law, containing the traditions of the Jewish doctors, collected about the year 190 by Rabbi Judah; and the Gemara, or the finishing or completing the whole, which was done by Johanan, and published both together. The Talmud of Babylon