cements are slow-setting, and these do not contain - more than 22 per cent. of clay. They set under water when half their weight consists of clay. The | proportion of sand used with Roman cement should not much exceed that of the cement. When employed for external coatings of buildings it is apt to effloresce and become unsightly.

Portland Cement.-This is considered by far the most important of the stone cements. It is an artincial product, named from its resemblance to Portland Stone, but is much more largely used than Roman cement. In the manufacture of Portland cement on the banks of the Thames and the M-dway by the wet process, three parts of white chalk are mixed with one part of clay or mud from the lower reaches of these rivers. The two substates, along with water, are placed in a wash min which strong revolving knives or cutters recure the whole to a creamy slurry' or slip. The slurry then passes by gravitation to backs or reservoirs. There it is allowed to settle for some weeks, when the superfluous water is removed by decantation. The mixture is next dried on heated iron plates or on the floor of a heated chamber, an 1 then burned in kilns. Finally it is ground to a the powder. Modifications of the wet process by which the large reservoirs are dispensed with have been introduced in recent years. In other parts of the country Portland cement is manui tured by the dry process from the hard limestones of other formations than the chalk, along with elay or shale. These limestones are crushed amal, mixed in the proper proportion with clay orale, then roughly burned, and ground to powder. This powder slightly moistened is passed trgh a pug mill, and then made into bricks, we are afterwards burned in kilns and reduced to

Since Portland cement is hardly ever employed in the pure or neat state, its strength is perhaps best texted when it is mixed with an equal weight ut sand. The best cement so mixed and moulded In the state of a stiff mortar, into any convenient #tape, when tested after the lapse of seven days, during six of which it is customary to keep it perersed in water, exceeds in tensile strength 2001h per square inch, and in crushing strength, tested by 14-inch cubes, 1000 lb. for the same area. Its strength in the unmixed state is much greater. Much of the Portland cement made is, however, he more than half as strong as the best kind. Koran cement of good quality mixed to the same extent with sand as the above, and tested under the sae conditions, has on an average a tensile strength of 30 ib, and a crushing strength of 200 lb. in each case per square inch. Portland cement is slow in Betting compared with most varieties of Roman eement. Both Portland and Roman cement form kutevike morfars-that is, they set under water. No mortar will do this which contains less than iu per cent. of silica.

ful close on 1840 Portland cement was hardly known, but the use of it has extended rapidly,

aily in recent years. Its most important a: cation is in the construction of docks and Latwurs, many of which are partly or wholly ut of it, mixed with sand and broken stones, in the form of a concrete. In this state, or simply mited with sand, it is also much employed for ser purposes where strength and durability are

red Owing to the nature of some of the extensive engineering works in which Portland resent is largely used, it is plainly of great conence that its properties should be thoroughly understood. Numerous failures with it have taken The chemical investigation into the case the Aberdeen docks in 1887 distinctly showed the deleterious action of sea-water upon this sub

59

Of

stance. But it is also known that objects made of unmixed Portland cement from the works of some of the best makers will sometimes keep good for nearly twenty years, and then crumble to pieces even when not exposed out of doors at all. course explanations of these failures are forthcoming. They are generally attributed to carelessness in the manufacture of the cement, or in the selection of the materials for it. But if they occur, as they have done, with cements that have stood very well the ordinary mechanical tests, how can any cement of this kind be entirely depended upon for durability? Twenty, thirty, or even fifty years is far too short a time to test the lasting property of a building material of this nature. The use of Portland cement in pavements and for architectural ornaments is not attended with much risk, and for such purposes it is very suitable. The capital employed in the manufacture in Great Britain is probably near two millions sterling. For American cements, see ROSENDALE.

Scott's Selenic Cement consists of burnt limestone mixed with about 5 per cent. of sulphate of lime in the form of plaster of Paris, and ground to powder. The presence of the sulphate arrests the slaking action of the lime, causes the cement to set more quickly, and admits of more sand being used with it than ordinary lime does. This cement has been a good deal used for plastering, and to some extent also for mortar.

Plaster of Paris (see ALABASTER and GYPSUM ). -This material is used for cementing marble and alabaster in much the same way as mortar is in brick-work. It is also employed for uniting the separately moulded pieces of any large object cast in the same material. Sometimes it is selected for fixing metal mounts to glass.

Keene's Cement is made by saturating plaster of Paris in small lumps with alum and recaleining it. It then forms a hard plaster for the projecting portions of halls and rooms, such as pilasters, columns, and skirtings. It is capable of taking a high polish.

Parian or Keating's Cement somewhat resembles Keene's. In its manufacture borax as well as alum is added to the plaster of Paris.

Martin's Cement is another kind, with plaster of Paris for its basis, but instead of borax, carbonate of potash is added, and sometimes hydrochloric acid as well. With the exception of Scott's, these plaster of Paris cements are only used in plastering or other internal work--not for mortars.

Mastic Cement, consisting of a mixture of burnt clay or limestone in a powdered state, with boiled oil and litharge, was more in use formerly than now; but though expensive, it is an excellent material for preventing the admission of rain-water at certain joints about buildings, such as where wood and stone work come together at windows. It was also used for covering external mouldings.

Rust or Iron Cement.-Joints in iron-work, such as those for hot water pipes, are filled up with a cement of iron borings or turnings, mixed with at least 2 per cent. of sal-ammoniac. Sometimes sulphur in powder is added. The iron oxidises and forms a firm joint.

Sulphur Cement. -For jointing earthenware pipes, and occasionally for fixing bars of iron into stone, a cement is made of sulphur, resin, and brick-dust. It is a cheap but not a strong cement where metal is concerned.

Water-glass Cements.-For furnaces one kind consists of burnt and unburnt fireclay made plastic with silicate of soda or water-glass. Another cement, capable of standing a high heat, is formed of asbestos powder made into a paste with silicate of soda. The same silicate mixed with ground glass makes an acid-proof cement.

White and Red Lead Cements.-Either white lead or red lead by itself, or a mixture of both, is much in request as a cement for the joints of slate or glass cisterns, such as aquariums. These are also employed for the joints of gas-pipes, for cementing metal mounts to glass tubes, and other chemical and electrical purposes. White and red lead cements are made up with boiled linseed-oil, and sometimes gold size is added. Mixed white and red lead make a very hard and firm cement. A cement of these two substances and ground plumbago in equal parts, mixed with oil, is said to stand a great heat in steam-joints.

it.

Shell-lac Cements.-An excellent cement is made by digesting 4 oz. of the finest shell-lac in 3 oz. of methylated spirit in a warm place. It should be made into a consistency like thick syrup. This makes a firm cement for mending pieces of glass, china, ornamental stones, and ivory. It is not soluble in water. A cheaper, but still very serviceable cement can be formed by dissolving shell-lac in wood naphtha. For some purposes shell-lac itself is used as cement by simply melting Marine Glue is a mixture of shell-lac in a solution of india-rubber. It is made into thin sheets, and melted when required for use in shipbuilding, &c. Gelatin and Isinglass Cements. -Fish-glue, gelatin, or Isinglass (q.v.), made up with dilute acetic acid and other bodies into a jelly or thick liquid, produces a cement slightly varying in its nature, for mending china, glass, ivory, bone, and other substances. Foulke's cement and liquid fish-glue are cements of this class. These can be obtained in a convenient form for use in hardware or druggists' shops. They are more or less soluble in water, so that articles mended with them must be quickly washed. Cement of mixed glue and glycerine, sometimes with tannin added, is occasionally used for leather and cloth.

Armenian or Diamond Cement.-The following is the reputed formula for preparing the cement used by the Armenian jewellers for attaching diamonds, &c., without any metallic setting: 'Dissolve five or six bits of gum-mastic, each the size of a large pea, in as much rectified spirit of wine as will suffice to render it liquid; and in another vessel dissolve as much isinglass, previously a little softened in water-though none of the water must be used-in French brandy, or good rum, as will make a 2-ounce phial of very strong glue, adding two very small bits of galbanum or ammoniacum, which must be rubbed or ground till they are dissolved. Then mix the whole with a sufficient heat. Keep the glue in a phial closely stopped, and when it is to be used, set the phial in boiling water.'

Elastic Cements.-One part of caoutchouc dissolved in 3 parts of chloroform; also, 5 parts of caoutchouc in 3 parts of chloroform, with 1 part of powdered gum-mastic added. Benzole is sometimes used instead of chloroform as the solvent. Another elastic cement can be made by a mixture of guttapercha and caoutchouc dissolved in bisulphide of carbon. The solvents of these cements must not be exposed to any but a gentle heat.

Resin Cements.-There are a great number of cements partly formed of ordinary resin. One kind consists of resin 4, beeswax 1, and whiting 1 part. The proportions of these ingredients in the same order for another are 15, 1, and 4. Another is made from resin 4, and plaster of Paris 1 part. These cements are used to fix pieces of stone, glass, &c. to handles when grinding them. Resin, pitch, beeswax, and plaster of Paris or brick-dust are made up in various proportions into

cements.

Cutlers' Cement, used for fixing knives and forks

CEMETERY

in handles, is made of equal weights of resin and brick-dust melted together; or, for a superior quality, 4 parts of resin, 1 of beeswax, and 1 of brick-dust.

Copal varnish, mastic varnish, Canada balsam, and gold size are each useful occasionally for cementing substances like two pieces of glass together.

ferruginous limestone, generally compact, which is Cement-stone, a somewhat argillaceous and occasionally employed for making hydraulic mortar or cement. The Cement-stone Series is the name of a group of strata occurring in the Carboniferous System of Scotland. See CARBONIFEROUS SYSTEM.

Cemetery (from the Greek koimētērion, literally a sleeping-place) may mean any graveyard, or other place of deposit for the dead; but it has lately acquired a special meaning, applicable to those extensive ornamental burial-grounds which have recently come into use as the practice of burying within and around churches was gradually abandoned (see BURIAL). The fine burial-grounds of the Turks, extending over large tracts adorned by cedars and other trees, may have suggested the plan to western Europeans. Those round Constantinople are famous, and are dense forests of cypresses. A Moslem grave is never reopened, and a cypress is usually planted after every interment. Of western cities, Paris took the lead in this respect, and in Britain there are now no considerable towns near which there is not at least one cemetery, and the legislation mentioned under the head of BURIAL has rendered their establishment, to a certain extent, a legal necessity. There was at first a natural feeling of regret at the prospect of deserting places of deposit for the dead so hallowed by ancient use and recent associations as the church and the churchyard. On the other hand, the new places of interment began to become attractive in virtue of their trees and flowers, natural scenery, and works of monumental art. The new cemeteries are in many instances cheerful open places, and in them the place of rest for the dead has rather tended to improve than to undermine the health of the living. One of the first and most celebrated of modern European cemeteries is that of Père la Chaise (q.v.), near Paris, the arrangements of which have been generally followed in the cemeteries of London and other English cities. It was laid out in 1804, and is now within the enceinte of the city. The Campo Santo of Pisa (1228-83), the pantheon of the Pisans, has been the model of many Italian cemeteries. It is an oblong court, surrounded by lofty arcades of marble, and adorned with famous frescoes and works of art. In the centre is a mass of earth brought from the Holy Land. The Genoese Campo Santo contains an enormous wealth of sculpture. One Neapolitan cemetery (the Campo Santo Vecchio) differs widely from most others. It contains 366 deep pits, one of which is opened each day, and in it all the interments of the day take place. night a funeral service is performed, and the pit is filled with earth and lime, not to be reopened till the year after. The Sicilian catacombs are also a kind of cemetery. Kensal Green Cemetery dates from 1832; other well-known London cemeteries are those of Highgate and Woking (1855), near Guildford, 7000 acres in area, with a crematory. The Dean Cemetery at Edinburgh, and the Necropolis of Glasgow, are notable; that of Glasnevin, outside of Dublin, is the most celebrated in Ireland. English cemeteries are usually divided into two portions-one conse crated for the burials of members of the Estab lished Church, ver whose remains the funeral service is read ad one unconsecrated, for the

At

CENCI

burials of dissenters. In the United States great 1 pains are bestowed on the adornment of cemeteries. The most famous are Mount Auburn, near Boston, Greenwood in Brooklyn, and Laurel Hill, near Filadelphia. See BURIAL.

Cenci, BEATRICE, the beautiful parricide,' was the daughter of Francesco Cenci, a Roman nobleman of colossal wealth. According to Muratori CAnnales, lib. x.), Francesco was twice married, Beatrice being the youngest of twelve children by tue first wife. After his second marriage, he treated the children of his first wife in a revolting manner, and was even accused of hiring bandits to murder two of his sons on their return from Spain. The beauty of Beatrice inspired him with the horrible and incestuous desire to possess her person; with mingled lust and hate he persecuted her from day to day, until circumstances enabled him to consummate his brutality. The unfortunate girl besought the help of her relatives, and of Pope Clement VII. (Aldobrandini), but did not receive it: whereupon, in company with her step-mother and her brother, Giacomo, she planned the murder of her unnatural parent, into whose brain two hired assassins drove a large nail (9th September D. The crime was discovered, and both she and Giacomo were put to the torture; Giacomo our fessed, but Beatrice persisted in the declaration that she was innocent. All, however, were condemned and beheaded (10th September 1599). baen is Muratori's narrative. Others allege that Eatrice was the innocent victim of an infernal piot. The results, however, of Bertolotti's investiAtions (Francesco Cenci e la sua Famiglia, 1877), d on original documents and contemporary notices, go far to deprive the story of the Cenci tragedy of the romantic elements on which Shelley's powerful tragedy mainly turns. Francesco, it would appear, was profligate, but no monster: Beatrice at the time she murdered her father was not sixteen, but twenty-one years of age, was far from beautiful, and was probably the mother of an illegitimate son. And Bertolotti further shows Dat the sweet and mournful countenance which fortas one of the treasures of the Barberini Palace in Rome cannot possibly be a portrait of Beatrice by Gaido, who never painted in Rome till some R.be years after Beatrice's death. See an article in the Edinburgh Review for January 1879. Cenis. See MONT CENIS.

Cenobites. See MONACHISM.

Cenomanian, the name given by French geo| lasts to the Lower Chalk and Upper Greensand of English geologists.

Cenotaph (Gr. kenotation: kenos, empty, and fatos, a tomb), a monument which does not estain the remains of the deceased. They were sally erected for those whose bones could not found, as for those who had perished at sea. Lattery the name was applied to tombs built by a man during his lifetime for himself and the neers of his family. The memorials in Westmuster Abbey to Franklin and Gordon are ceno

Censer (Fr. encensoir, from Lat. incendo, I a vase, or other sacred vessel, used for m.ng Incense (q.v.). Censers were used in the Hebrew service of the temple. The ordinary resser, called also a thurible (Lat. thuribulum, trim thus, *frankincense'), used in Catholic ser11%, is a metallic vessel for holding burning charof brass or latten, silver, silver-plated, or eves of gold. It is shaped like a vase or cup, has a movable cover, usually perforated, and is sepe, led by chains (generally four in number) so to be swung to and fro for the readier dispersion |

of the smoke of the incense, which is thrown upon the live charcoal.

Censors, the name of two Roman officers of state of high dignity, whose duties related to the official registration of the citizens (census), the superintendence of public morals (regimen morum), and arrangements for the collection of the public revenue and the execution of public works. They were elected in the comitia centuriata, presided over by a consul. The term of office at first lasted five years, but was shortly afterwards limited to eighteen months. The censorship was regarded as the highest dignity in the state, except the dictatorship. It was a sacred and irresponsible magistracy, whose powers were vast and undefined, and whose decisions were received with solemn reverence. The census or registration was taken in the Campus Martius, in a building called Villa Publica, It was a complete catalogue of the citizens of Rome, stating in detail the age of each, the amount of his property, and the number of his children. Next the censors drew up a list of the equites, entitled to have a horse at the public expense, and made up the roll of senators, supplying the vacancies. The regimen morum was the most dreaded and absolute of their powers. It grew naturally out of the exercise of the previous duty, which compelled them to exclude unworthy persons from the lists of citizens. Gradually the superintendence of the censor extended from the public to the private life of citizens. They could inflict disgrace (ignominia) on any one whose conduct did not square with their notions of rectitude or duty. For instance, if a man neglected the cultivation of his fields, or carried on a disreputable trade, or refused to marry, or treated his family either too kindly or too harshly, or was extravagant, or guilty of bribery, cowardice, &c., he might be degraded, according to his rank, or otherwise punished. The administration of the finances of the state included the regulation of the tributum or property-tax; of the rectigalia, such as the tithes paid for the public lands, salt-works, mines, customs, &c., which were usually leased out to speculators for five years; the preparation of the state budget, &c. The office of censor continued to be filled by patricians till 351 B.C., when Censor Marcius Rutilus, a plebeian, was elected. Twelve years later it was enacted that one of the censors (there were always two) must be a plebeian. In 131 B.C. both censors for the first time were plebeians.

Censorship of Press. See PRESS.

Census means the counting of the people. The word is a Latin one, and was applied to the functions which the Roman Censors (q.v.) per. formed of periodically enumerating the people, but no records of these enumerations remain, and indeed we have but a few scattered notices of them. In Greece a census was established by Solon at Athens for the double purpose of facilitating taxation and classifying the citizens. Religious prejudice prevented any censuses being taken during the middle ages, and it was not till the 18th century that the necessity for obtaining correct information as to the population of European countries overcame this feeling. The first country to undertake a census on a scientific basis was Sweden in 1749; in France an enumeration was made in 1700, but the first reliable was not taken till 1801. In America the first census was taken in 1790, and in England in 1801. Censuses are now taken in Austria, Belgium, Italy, Norway and Sweden, Russia, Switzerland, the United States of America, India, and most of the British colonies, every ten years; in France and Germany every five years; in Spain at irreg

ular intervals, the next after that of 1860 having been in 1877. The International Statistical Congress, which consists of eminent statisticians from all countries, has done much to improve the taking of censuses, and now several countries, such as Austria, Belgium, Italy, Prussia, Russia, and Switzerland, have statistical bureaus for the purpose, amongst other things, of controlling the taking of the periodical census. In a few countries in formation as to the religion of the population, and in some cases additional particulars, are obtained, such as the census of useful domestic animals' in Norway.

or

In the United Kingdom the practice is for parliament to pass special acts directing the tak ing of each census. These acts provide that the registrars of births and deaths shall be the officers through whom the census is to be taken by enumerators, of whom at the census of 1881 there were upwards of 30,000 employed in England alone. All the registrars' districts are so subdivided that no enumerator has more houses than he can conveniently visit in one day. The enumerators have to deliver schedules at all houses, requiring particulars concerning every person who is alive at midnight preceding the census day, and on the census day to collect them. Account has also to be taken of all persons not dwelling in houses wherever found, and of persons travelling, and persons in ships, barges, &c. The enumerators are authorised to require the information necessary for the census, and persons refusing to answer wilfully giving false answers to the questions are rendered liable to penalties. The particulars to be required in each census are specified in the act directing it to be taken. The Census Act, 1880, required that the census of the following year should show the name, sex, age, rank, profession or occupation, condition as to marriage, relation to head of family, and birthplace of every living person who abode in every house on the night of Sunday the 3d of April 1881, and also whether any were blind or deaf and dumb, or imbecile or lunatic.' When the schedules have been collected they are transmitted to the census office, where the work of tabulation, which takes about two years, is carried out. The census when finished is presented to parliament in the form of several bulky volumes. Hardly any two countries agree as to the subjects on which information is demanded; thus some census schedules contain inquiries as to whether there are in the household infirm persons, blind, deaf and dumb, idiots, insane persons, persons who have been convicted of crime; how many languages are spoken by the persons entered; how many are at school; how many exercise the franchise; how many rooms and windows there are in the house, and so on. an attempt was made to obtain religious statistics of the United Kingdom; since that year the census shows the religious statistics of Ireland only.

In 1851

The census of the United States aims at giving a specially full conspectus of the condition of the people, and is illustrated by a large number of maps bearing on almost every branch of the census inquiries. Thus there are maps showing the prevalence of certain diseases; others the area occupied by various crops. The United States census of 1880 extended to 22 volumes, embracing statistics of population, agriculture, manufactures, mining, taxation, public indebtedness, with special reports on cotton-growing, petroleum, coal, coke, building. stones, iron and steel products, &c. The census of 1890 is comparatively limited in the scope of its inquiries.

Cent and Centime (Lat. centum, 'a hundred'), names of coins. The Dutch cent is a copper coin, the 100th part of the guilder (1s. 8d.);

CENTENARIAN

the United States cent is a bronze coin, the 100th part of the dollar, or nearly one halfpenny English, and the Canadian cent has the same value. The centime, the 100th part of the French franc, and of the value of th of an English penny, has been adopted in Belgium, and, under other names, in Greece, Italy, and Switzerland; and the Spanish real (24d.) also is divided into 100 centimes. The cental in the United States, legalised in 1878, is 100 lb. avoirdupois (cf. CENTNER). See DECIMAL SYSTEM.

Centaurea, a palæarctic genus of Compositæ, containing about two hundred species, all herbaceous annual and perennial, of which five or six are natives of Britain. The species most familiar, on account of its beauty, is the blue C. cyanus (see CORN-FLOWER), which is sometimes sown as an annual; while its larger perennial ally, C. montana, with white or purple ray florets, is a familiar denizen of old-fashioned gardens; C. americana is a showy lilac-purple annual (3 or 4 feet); while the oriental Sweet Sultan (C. moschata) and Yellow Sultan (C. amberboa) are also not uncommon; the latter two being often sold under the name of Amberboa. Among perennials, the large, downy C. babylonica, with yellow flowers, is often cultivated; also C. ragusina and C. candidissima, of which the silver-white pinnate leaves furnish an admired contrast to bright-coloured bedding-plants. Several species (C. calcitrapa, &c.) bear the name of Star-thistle, from their spiny involucre. Some are common wayside weeds, often troublesome in pastures, notably C. nigra, the Common or Black Knapweed, also called Horse Knot in Scotland; and the closely allied C. Scabiosa. The flowers or roots of several species were formerly used in dyeing, and the astringent roots employed by herbalists.

Cen'taurs ('bull-killers '), a wild race of men who inhabited, in early times, the forests and mountains of Thessaly, and whose chief occupation was bull-hunting. Homer, the first who mentions them, describes them merely as savage, gigantic, and covered with hair. They do not appear as monsters, half-man and half-horse, until the Pindar. The most ancient account of the Hippocentaurs, sometimes considered as distinct, but more often confounded with the Centaurs, is that

age

of

they were the offspring of Magnesian mares and Centaurus, himself the offspring of Ixion and a cloud. The Centaurs are celebrated in Greek mythology on account of their struggles with the Lapithæ (q.v.), and with Hercules. famous was Chiron, the teacher of Achilles and

The most

other heroes. In works of art the Centaurs were represented as men from the head to the loins, with the rest of the body that of a horse. It is worth mentioning that the Mexicans, who had no native horses, when they first saw the Spaniards on horseback, believed that the horse and man together made but one animal.

Centaury (Erythraea), a pretty little annual, genus of Gentianacer, with pink or rose coloured flowers. They possess the tonic and other medicinal virtues of gentian, and the Common Centaury (E. Centaurium) has especially been esteemed in medicine since the days of Dioscorides and Galen; and although no longer in the pharmacopoeia, its flower-tops are still sometimes gathered and dried by country-people in England and the Continent; while the allied Sabbatia angularis enjoys similar repute in the United States and Canada. The Yellow Centaury is Chlora perfoliata; but plants belonging to the wholly distinct composite genus Centaurea (q.v.) are also sometimes called Centaury.

Centenarian. See LONGEVITY.

CENTENARY

Centenary, consisting of a hundred (Lat. rentum), a period of a hundred years, is now usually employed to signify a commemoration of an event, as the birth (sometimes the death) of a great man. The centenary of Burns's birth was celebrated in 1859; the bi-centenary of Pope in 1888; the tercentenary of Shakespeare in 1864. The centenary of A nerican Independence was celebrated by a Centennial Exhibition in 1876; the octo-centenary of the Bologna University in 1888.

Centering, the framework upon which an arch or vault of stone, brick, or iron is supported daring its construction. The simplest form of centering is that used by masons and bricklayers

for the arches of common windows and doors.

This is merely a deal-board of the required shape, upon the curved edge of which the bricks or stones of the arch are supported until they are keyed in. In building bridges or other structures where arches of great span are to be constructed, the centering is usually made of framed timbers, or traders and iron combined. The arrangement of the timbers should be such that the strain upon each shall be mainly a thrust in the direction of its length, for if the strain were transverse, a comparatively slight force would snap it, and if a longito final pull, the whole structure would be no stronger than the joints holding the pieces of tir together. In arches of great span, a longitinal pulling strain is almost inevitable in some parts, as a beam of great length would bend to some extent under a thrusting strain. In such cases great skill and care are demanded in the dering and construction of the joints. As an arch built from the piers towards the keystone, the weight upon the haunches during construction tends to push the crown upwards, and therefore the problem of designing a framed centering involves the resistance of this tendency, as well as the supporting of the weight of the materials. Occasion ... when a very great span is required, and the acation will permit, piers are built on the bed of the river, or piles are driven into it, to support the centering directly, simplifying it, and at the same time facilitating a more rigid disposition than in centering supported only from the sides. Ale BRIDGE for descriptions and illustrations of three types of centering: (1) that for the bridge over the Dee at Chester, Vol. II., page 437, supperte directly from the bed of the river; also the centering for the Ballochmyle Bridge; (2) ined struts in pairs supported from the sides, as Rennie's centering for Waterloo Bridge, page 3) trussed wooden girders supported from Lae sides, as Rennie's centering for London Bridge,

See

to more than twelve times as many. In counting the rings the ventral surface should be looked to, for the dorsal shields often overlap. The rings are flattened from above downwards, and each bears a pair of appendages. Dorsally and ventrally the skin is hard and horny. Glands occur in various positions. (b) Appendages.-The head, which is covered by a flat shield above, bears (1) a pair of antennæ, usually of considerable length, and consisting of from twelve to over one hundred joints; (2) a pair of small, strong, toothed, and bristly mandibles; (3) a pair of under-jaws, usually with palps. The next appendages are limb-like, and are followed by a modified pair of legs, the basal pieces of which generally meet in the middle line, while the strong joints terminate in a sharp claw, at which a poison-gland opens. These appendages are obviously of use for seizing and killing the prey. The legs of the other segments are usually seven-jointed, sometimes bear spurs and glands, and are generally clawed. The last pair differ in size and form from the rest, and are turned backwards. (c) Internal Anatomy. The large brain is connected as usual with a ventral chain of ganglia. Compound eyes occur in one family, simple eyes in many, while the feelers, certain bristles, and portions of the skin are also sensory. In some cases there is a special well-defined sense-organ of undecided func tion in front of the head, or on one of the jaws, The alimentary canal is straight, and has associated with it salivary and digestive glands, and The heart is excretory (Malpighian) tubu'es. represented by a chambered dorsal vessel. Trachea or air-tubes open on the sides of the body, some times on each ring, often on alternate segments, ramify throughout the tissues, and are connected together on each side by a longitudinal stem. The reproductive organs are usually tubular, and open on the last ring of the body. A distinct penis is sometimes present.

Life and Habit.-Centipedes are darkness-loving animals, nocturnal in their food-hunting, lurking under stones or among rotten wood and the like during the day. Their powers of vision are very poorly developed, and most of the sensory work is tactile. Only in one family (Scutigerida) are there compound eyes, in most forms only simple eyes, in many none at all. The recent researches of Plateau and others have shown that these creatures can distinguish light from darkness, but do not need eyes to do this; species with eyes do not apparently get on much better than those without them; those with eyes seem to perceive bright objects reflecting much white light, and in some cases conspicuous movements, but probably in no case the forms of objects. Moving actively about at nights, feeling their way by means of their antennæ, which function as a blind man's staff, they light upon in

Le centerings.

Centigrade. See CELSIUS and THERMOMETER. Centipede, a general name for the members of 4 the orders of the class Myriapoda. Popuare sometimes called Galley-worms, aly Chilopoda. Like the Millipedes, which the most important neighbour order, the les are segmented animals bearing jointed lages, having a well-defined head furnished feezers and jaws, and breathing by means of ** or trachea.

Structure --The Centipede is like a primitive in its general structure,~(a) Externals.— body is divided into well-marked rings, but n behind the distinct head is practically and not divisible into thorax and abdomen. at bend the head a few rings appear to be Iue number of rings varies from twelve

seize and kill with their poison-bearing appendages. They are all voracious carnivorous forms, not vegetarian like the Millipedes, Some forms can run with some rapidity, and wriggle about in curious serpent-like fashion.

The

Development.-In some cases the males are said to deposit their reproductive elements in packets (spermatophores) fixed by a web to the ground. In most cases copulation probably occurs. Scolopendra is viviparous, the others lay eggs. eggs develop into larvae, which are either miniature adults (Scolopendrida and Geophilidae), or differ from the full-grown forms in having only seven pairs of legs (Scutigeridæ and Lithobiidæ ).

Classification and Forms of Interest.-The order of Centipedes is one of the three or four divisions of Myriapods (q.v.), and, like the class, generally represents a somewhat low grade of development among animals breathing by air-tubes. The most