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Magnus Celsius (1621–79), a professor of Astronomy school of medicine. Indeed, to Celsus, next to
and decipherer of the Helsing runes, and the nephew Hippocrates and Galen, we mainly owe our know-
of Olof Celsius (1670–1756), professor of Theology ledge of the medicine of antiquity. Celsus's works
at Upsala, author of the Hierobotanicon, and an were translated into English in 1756. Next to the
early friend and patron of the great Linnæus. first edition (1478) the most important are those
Anders became in 1730 professor of Astronomy at of Targa (1769) and Daremberg (1859). See Broca's
Upsala. Two years later he set out on a scientific Conférences historiques (1865).
tour, visiting the observatories of Nuremberg, Rome,
and Paris. After his return he published his De

Celt (Lat. celtis (?), 'a chisel'), a name by,

which the axe-heads of the early inhabitants of Observationibus pro figura telluris determinanda in

Europe are known among British and French Gallia habitis (Upsala, 1738). In 1740 he had the

archæologists. The Scandinavian archaeologists satisfaction of seeing a splendid observatory erected

use the word 'axe' and not 'celt.' Its use is now at Upsala, and here he laboured till his death, 25th April 1744. The Inscriptions of the Swedish considered pedantic, and it is fast becoming obAcademy contain many papers by Celsius on as

solete. The word is generally believed to have

originated from a misreading of Job, xix. 24, in the tronomy and physics. It is, however, as the first

Vulgate, where Celte, understood to mean 'with a constructor (1742) of the thermometer now chiefly

chisel,' was read in place of Certe, 'verily' (corused by scientific men, that he is best known. In

responding to the ‘for ever' of the English Bible). it the space between the freezing-point and the

Celte or Celtis is not elsewhere found in Latin. See boiling-point of water is divided into one hundred

Notes and Queries (1878), vol. ix. p. 463 ; vol. x. p. spaces, hence Celsius's thermometer is often called

73. the centigrade or centesimal scale. See THER

Celts are either of stone or of bronze. Stone MOMETER

celts vary in length from about 1 inch to 22 inches; Çelsus, a Platonic philosopher, but tinged with but the most common size is from 6 to 8 inches Epicureanism, who lived in the 2d century after in length, and from 2 to 3} inches in breadth. Christ, was a friend of Lucian, and wrote, about They are made of almost every kind of stone, and 176-180, during the persecution of Marcus Aurelius, show considerable diversity of shape, almost all, under the title Logos Alēthēs (“true word'), the first however, having more or less resemblance to the notable polemic against Christianity. The book mussel-shell. The ruder celts are generally of slate, itself has perished; but considerable fragments have shale, schist, or grit; the finer, of flint, porphyry, been preserved as quotations given by Origen in greenstone, syenite, or agate. Many of the finer his answer, Contra Celsum, in eight books. In the celts are beautifully shaped and highly polished. fragments, which are very interesting, as showing Some very remarkable examples of this class are in the views of a heathen philosopher in regard to the National Museum of Antiquities, Edinburgh, Christianity-Celsus, with great acuteness and wit, and one found near St Andrews, in Scotland, is but without depth or earnestness of thought, prefers described by Sir David Brewster in the Philosoagainst the new religion charges of unphilosophi- | phical Journal for 1823. The stone celt was calness and blind credulity; and especially endea fastened into a handle of horn, bone, or wood. yours to convict Christians of self-contradiction Bronze celts vary in length from about 1 inch to 8 in their spiritual doctrine contrasted with their or 10 inches, the most common length being about 6 anthropomorphic representations of Deity; in their inches. They show much greater diversity of religious arrogance contrasted with their confession shape than the stone celt. As many as four classes of sinfulness; and in their views of the necessity have been distinguished by archæologists : (1) of redemption. He also reproaches Christians with The flat wedge-shaped celt, most nearly resemtheir party divisions and ever-varying opinion, and bling the common form of the stone celt. (2) The ridicules them as worms in a corner who think flanged celt, with the side edges more or less overthey occupy the centre of the world. Celsus lapping, and a stop-ridge or elevation between the holds that the Supreme God can have no contact blade and the part which received the handle. with the material world, the creation of which is (3) The flanged-edges celt, with side greatly overthe work of inferior deities or demons. He regards lapping, with or without the stop-ridge, but with a evil as an essential property of the material world ; loop or ear upon one side. (4) The socketed celt,

There neither has been in former times, or the celt with a hollow to receive the handle, and
nor is there now, nor ever shall be, an increase or generally with a loop or ear upon one side. They
diminution of evil. The nature of the universe is are sometimes ornamented with raised lines or
ever identical, and the production of evil is not circles formed in the mould in which they were
& variable quantity. . . It is evident that those cast.
who sin by nature and by habit cannot be changed Both stone and bronze celts were probably used
in any respect either by punishment or by pardon. for many purposes, serving for chisels, adzes, and
He charges Christians with having remodelled axes, as well as for weapons of war, like the stone

The Gospel” from the "first writing” three times, hatchets of the South Sea Islanders. See under
four times, and many times. However, as Origen Flint, STONE AGE, and BRONZE AGE.
which Celsus refers is to be found in our Gospels, ancient Spain, supposed to have sprung from a
remarked, almost everything of an historical kind to

Celtibe'ri, a brave and powerful people of especially the Synoptics. See Keim, Celsus' Wahres blending of the aboriginal Iberians with Celtic Persécutions de l'Église (1878); Pélagaud, Etude invaders from Gaul.

They inhabited a large sur Celse (1878); Froude's Short Studies, vol. iv.; inland district of the peninsula, corresponding and the article on ORIGEN.

to the south-west half of Aragon, nearly the

whole of Cuença and Soria, and a great part of Celsus, AULUS CORNELIUS, a Latin physician Burgos, but the name Celtiberia had often a wider and writer, who probably flourished about 50 A.D., signification, including the country as far south as and wrote not only on medicine, but also on rhetoric, the sources of the Guadalquivir. The Celtiberi history, philosophy, the art of war,

and agriculture.

were divided into four tribes, the chief the Arevaca His style is succinct and clear, but full of Græcisms. and Lusones, and were unquestionably one of the The only great work of his which survives is the bravest and noblest peoples in the peninsula. Their De Medicina. The portions relating to surgery cavalry and infantry were equally excellent. For are exceedingly valuable, as giving an account of many years they withstood the efforts of the the opinions and observations of the Alexandrian Ronians to subdue them, and it was not till after

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the death of Sertorius (72 B.C.) that they began to lacing band might be replaced by an elongated adopt the Roman language, dress, and manners. animal form with its feet, its tail, and its top-knot The chief cities were Legobriga, the capital ; drawn out to interlace with each other, and with Bilbilis, the birthplace of Martial; and Numantia, the corresponding parts of other lacertine forms, destroyed by Scipio Africanus after a desperate ten the whole forming a diaper of quaintly expressed years' resistance, 133 B.C.

and complicated construction. The fretwork was Celtic Ornament, a peculiar development of also elaborated with much ingenuity into most the system of iron-age decoration prevalent in the complicated patterns, a special feature of the style British Isles. Its history is divided into two being its partiality for diagonal frets and patterns periods by the introduction of Christianity, which produced by combinations of oblique lines, in direct engrafted on the older style a number of new ele- contrast to the fretwork of Greek and Roman art, ments of decoration brought into the country with which was essentially rectangular. The elliptical the manuscripts of the gospels and psalters, and curves and divergent spirals of the older style, supplied new forms for the display of these ele. which had received their only expression in the ments, such as churches and crosses, shrines, bells, solid forms proper to metal-work, were found to be and crosiers. In its pre-Christian stages, ranging equally capable of adaptation to the purposes of approximately from two or three centuries before the illuminator, and by a similar process of comthe Christian era to about the end of the 6th bination and elaboration they also produced century A.D., it appears principally in connection patterns and diapers of inexhaustible variety and with the metal mountings of harness and horse- beauty. A special feature of Celtic decoration trappings, and on shields, sword-sheaths, mirrors, was its tendency to divide the surface to be armlets, and other articles of personal use and decorated into a series of panels, each of which ornament. The material is usually bronze, but

was treated as

a separate whole. The finest occasionally silver or gold. The principal charac- examples of Celtic ornament are unquestionably, teristics of the pre-Christian style are its pre

to be found in the grandly illuminated pages of ference for elliptical curves and divergent spirals; | manuscript copies of the Gospels, from the 7th its use of chased or engraved lines or dots as a to the 9th century. Of these the most famous for diaper in the spaces of the general design in the elaborate nature of their ornament and the contrast with other spaces left plain; its use of beauty of their colouring are the Book of Kells repoussé work, sometimes in very high relief, at in Trinity College, Dublin, and the Lindisfarne other times in low relief on thin plates riveted Gospels in the British Museum. Of enamelled on in their places in the general design; the metal-work in this period there may be mentioned production of peculiar patterns often in excess the Ardagh Chalice, perhaps the most elaborate ively high relief in the casting; and the employ- and beautiful of all the products of Celtic art, the ment of champ-levé enamels red, yellow, blue, Lismore Crosier, and the Monymusk Shrine. Exand green, and settings of coloured vitreous pastes. amples of filigree-work, and chasing or engraving One of the finest examples of such settings occurs in gold and silver of the highest excellence are in the decoration of an oval shield of bronze, from found in the Tara Brooch, the Ardagh Brooches, the bed of the Thames, ornamented with Celtic the Rogart Brooches, and the Hunterston Brooch, patterns in relief, enriched by twenty-seven set the Shrine of St Patrick's Bell, the Shrine of tings of red enamel, kept in their places by small St Manchan, and the Cross of Cong. The approx. cruciform ornaments of bronze riveted in the centre imate dates of the metal-work of the highest excelof each. There are to be seen in the National lence range from the 10th to the 12th century. Museums of London, Edinburgh, and Dublin For sculpture in stone it is only necessary to refer enamelled shields, sword-sheaths, and ornaments generally to the incised slabs and sculptured crosses of horse-trappings in bronze, of great beauty of Scotland and Ireland, ranging from the 9th to and excellence both of design and workmanship, the 12th centuries, the special characteristics of and other articles in bronze, silver, or gold, orna their decoration being the same as those of the mented in repoussé work or in relief, with or manuscripts and metal-work already mentioned. without enamel as an enrichment, found in many For illustrations, see BROOCH, CROSS, SCULPparts of England, Scotland, and Ireland, in pagan TURED STONES. See further Kemble's Horæ grave-mounds, in crannoys or lake-dwellings, in Ferales, edited by Latham and Franks (1863); earth-houses, in the beds of lakes and rivers, or in Anderson's Scotland in Early Christian and casual deposits under the soil for concealment. In Pagan Times (1881-83); Westwood's Palæoa work entitled Horæ F'erales, Mr Franks of the graphia Sacra Pictoria (1845), and Fac-similes of, British Museum has figured in colours many of the the Miniatures and Ornaments of Anglo-Saxon and best of these remarkable products of the earliest Irish Manuscripts (1868); O'Neill's Fine Arts known process of champ-levé enamelling, and ad- of Ancient Ireland (1863), and Sculptured Crosses duced evidence to show that it and this peculiar of Ancient Ireland (1857); Stuart's Sculptured style of Celtic ornament which accompanies it Stones of Scotland (Spalding Club, 1856 and 1867); were of indigenous origin, and at this early and Miss Stokes's Early Christian Art in Ireland period peculiar to the British Isles.

The re

(1887). markable development of Celtic ornament which

Celtis. See NETTLE-TREE. succeeded the introduction of Christianity was characterised by the association of interlaced Celts. The Celtic nations of antiquity had no work and fretwork with the elliptical curves comprehensive name. Those of the Continent were and divergent spirals which up to that time called Galli by the Romans, and less usually Celtæ. had been the principal elements of Celtic design. The Greek equivalents for these terms were Galatai To these were occasionally added a step-like or Galate, and Keltoi or Celti. But neither Greeks pattern, and diapers of the Z and I shaped patterns nor Romans regarded the British Isles as belonging sometimes seen in Chinese decoration. The inter

to the Celtic world. They were situated outside laced work was elaborated with excessive care into it, and lay over against it in the sea; still it patterns, presenting an infinite variety of combina was known to men like Julius Caesar that certain tions pleasing to the eye, and capable of being portions of Britain were inhabited by Celts in the harmoniously treated in colours. It was sense of Galli or Belgæ. times a simple ribbon-like band, which might be Celtic ethnology involves many difficult questions, plain, or divided in the middle, or divided into and we shall speak of them in this article mostly three by lines close to the margin ; or the inter- 1 according to the more palpable distinctions of speech;

.

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and in order to proceed as much as possible from the test of some of the most palpable differences that known to the unknown, we begin by classifying are known to exist between the Goidelic and the their idioms. These, whether dead or still spoken, Brythonic idioms to the remains of the Gaulish belong to the Aryan or Indo-European family of language, we find at once that it is to be ranked languages, and those of them spoken in modern times with the Brythonic dialects, and not with the divide themselves into two groups—viz. Goidelic Goidelic ones, and our Brythonic group becomes and Brythonic. (1) The Goidelic group embraces what may be more exactly described as a Gallothe dialects termed Gaelic, that is to say, Irish Brythonic one. This further suggests the question Gaelic, or Irish as it is now more frequently and whether there was no continental Celtic idiom briefly called ; Manx Gaelic, or the Gaelic dialect which partook of the characteristics of the Goidelic not yet extinct in the Isle of Man; and Scotch branch. The probability is that there was; for Gaelic, or the Gaelic spoken in the Highlands and one finds Sulpicius Severus, an ecclesiastical writer Islands of Scotland. In ordinary Scotch and English of the 4th century, distinguishing between Celtic parlance this is what is understood by the word and Gallic or Gaulish, as if both were spoken in his Gaelic when it is used without any qualification. time. (See Dialogue i. 26, in Migne's Patr. Lat. In order to resist one of the delusions to which vol. xx. col. 201 : Tu vero, inquit Postumianus, charlatans are always leading the unwary, it is vel Celtice, aut, si mavis, Gallice loquere, dumright to say that the words Gael and Gaelic have modo jam Martinum loquaris.') And the use nothing to do with Galli. Gael is the simplified of the two names Celtæ and Galli would seem English spelling of a word which is now written to point to the same inference—viz. the existin Scotch and Irish Gaelic Gaidheal, with an ence in Gaul of two Celtic peoples, the one, evanescent dh; but the most ancient form known probably, superimposed on the other, as on a vanof it was Goidel, whence the adjective Goidelic, quished population, or driving it towards the which has been resorted to by Celtic scholars as south and west. Thus, if the Celtic language applicable equally to all three Gaelic subdivisions which Sulpicius Severus distinguished from Gaulish of the Celtic group here in question. The Celtic should be ranked with the Goidelic dialects, we languages of this group are sometimes also called should have alongside of a Gallo-Brythonic group Erse, which is a term derived from the Scotch form another which might be called Celto-Brythonic of the adjective Irish; this was Ersch or Yrisch, were it not inconvenient to use the words Celt and the longer and shorter forms of which appear, used Celtic in two senses.

For while the modern usage without any distinction, by Kennedy in his answer applies them indifferently to the whole family, to the poet Dunbar, when the latter had called Sulpicius indicates a narrower sense; and so, in Kennedy an 'Ersch brybour baird' and an “ Ersch fact, had Cæsar done centuries before, when he katherane,' in reference to his alleged extrac wrote that one of the three peoples of Gaul was tion from the Irish Scots of Galloway and Carrick. called Celta in their own tongue. He states that Kennedy's reply contains the following line (see these Celtæ proper, so to say, were separated by Murray's Dialect of the Southern Counties of Scot the Garonne from the Aquitani, and by the Seine land, 1873, pp. 43-44):

and the Marne from the Belgæ. In other words,

their country extended from the Garonne to the Thou luvis nane Erische, elf, I undirstand,

Seine and Maine, and other Roman writers give it and he goes on to add

the name of Celtica ; and Dionysius of HalicarThy fore fader maid Ersche and Erschmen thin.

nassus had heard of a river Celtus, from which

Celtica was supposed to derive its name. From (2) The Brythonic group embraces the following this narrower Celtica, in the sense which Roman languages : Welsh, Breton, and Cornish, which has writers gave it, one might form the adjective been extinct now for about a century. Two of Celtican, to apply to its people, in order to avoid these belong to Great Britain, and one, the Breton the confusion which must arise from calling them or Armoric, to Little Britain on the other side Celts, whilst using that word also of the whole of the English Channel. These three might be family. collectively termed British or Britannic, but that In order to show the philological reasons for this both these adjectives have connotations which classification, it would be necessary to go into a would be misleading, as they tend to confusion; variety of details ; but let one of these suffice for 80 here, also, a neutral form, Brythonic, is used, the present. The Gallo-Brythonic dialects used p which is derived from Brython, one of the Welsh where the others would have qu. Take, for exwords for the Welsh and the so-called Ancient ample, the early inscriptional Irish for the genitive Britons, whence their language is sometimes called

of the word for son’; it was maqvi, corresponding Brythoneg in Welsh. This last was in Cornish to a nominative which appears as mace or mac in Brethoneć

, and in Breton Brézonek, meaning re the oldest manuscript Irish ; and mac is still the spectively the Celtic of Cornwall and of Brittany. word for · boy' or 'son' in all the Goidelic dialects. Brython or Britto was the national name of all Now the early Brythonic form of this genitive peoples of this branch, just as Goidel or Gael may would have been mapi, while in the oldest manube treated as the national name of the other script Welsh we have map, and in later Welsh branch.

mab, 'boy' or ‘son. From this word was formed All this applies only to the neo-Celtic nations, or another, mabon, a 'boy or “youth;' and this in its those among whom Celtic languages are or have old form appears in Latin inscriptions as maponus been in use in modern times, and a question of in Roman inscriptions found in Britain in honour much greater difficulty presents itself when

one of the Celtic god Apollo Maponus, so called in attempts to classify likewise the continental Celts reference to his youthfulness. Now from Gaul of ancient history. The reason for this is chiefly we have such names as Eporedorix, Parisii, Petrothe fact that the linguistic data become more pre

corii, and many others, with the consonant p; but carious as one goes back. Thus, for example, the every now and then we have also names with language of the ruling people of ancient Gaul has qu, such as Sequana and Aquitani, together with been left us only in a very few inscriptions, so

several instances from Spain, where a people of the that our knowledge of it from that source has to same Celtic branch as those of Celtica had also be complemented by the study of Gaulish proper probably established themselves. names, of which a considerable number is extant So far, then, as one can get philological data to in Latin inscriptions and in the writings of Roman reason upon, it would seem that the west of Europe and Greek authors. Now, when we apply the

had in early times been subjected to two Celtic

58

CELTS

CEMENTS

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invasions; the one is represented by the Celts under BRITTANY, CORNWALL, GAELIC, IRELAND, whose position, geographically speaking, is the WALES. See also ARYAN RACE AND LANGUAGES, farthest from the home of the Aryans. These ETHNOLOGY, PHILOLOGY, DRUIDISM. would be the Celticans of Gaul and Spain, as Besides the works already mentioned, the following compared with the Gallic tribes to the east of should be consulted : Müllenhoff's Deutsche Altertumsthem towards the Rhine and the Alps; the same

kunde (Berlin, 1887); Windisch's article 'Keltische relative position is also taken up by the Goidelic Sprachen' in the Allgemeine Encyklopædie der WissenCelts of the British Islands, occupying, as we find schaften und Künste, together with the reviews on the them doing, the Isle of Man, Ireland, and the

same in the Revue Celtique, vol. vi. pp. 395-400; Scotch Highlands and Islands. The other, here 1876); Brambach's Corpus Inscrip. Rhenanarum ; and the

Hübner's Inscriptiones Britannic Christianc (Berlin, represented by the Brythons, must have come later and driven out the Goidels, or subdued them,

volumes of the Corpus Inscrip. Latinarum, published by

the Berlin Academy, especially those for Britain (vii), in the rest of this island. This may be supposed, Spain (ii.), Gallia Narbonensis (xii.), Gallia Cisalpina also, to have been the case on the Continent, so (v.), and Dlyricum (iii.). that we have to regard the later comers, the Galli, Cements. These may be roughly divided into as invaders and conquerors forming another Celtic three classes : (1) The stone cements, including population. In the eastern portions of Gaul they Roman and Portland cements, and ordinary mortar

, may have formed the bulk of the population, bụt which are used in thickish layers for uniting stone in the rest of that country they probably only and brick work, and for protective coverings to constituted a ruling class of comparatively small buildings; (2) substances which form binding importance in point of numbers. Such a state of joints of much less but still appreciable thickness, things would adequately explain the great dearth such as white lead, red lead, and putty; and (3) of linguistic remains belonging to the older and cements which require to be used in extremely thin subjugated people. Roman authors and other coatings, such as glue, isinglass, and dissolved strangers would naturally speak most of the ruling caoutchouc. classes, and information about the others must Ordinary Mortar is a mixture of slaked lime reach strangers through the medium of the Gallic (calcium hydroxide) and sand, made into a paste rulers and their language, at anyrate, so far as with water. Generally one part of lime to three concerns the time before Latin became the official or four parts of sand are used, but the proportions tongue of all Gaul. A somewhat similar conclusion

vary according to the purity of the lime employed. has been arrived at by studying the burials and very pure or fat lime, such as that made by burnmegalithic monuments of France and the neigh- ing white chalk or white marble does not make bouring lands to the east of it. In Central and so good a mortar as lime obtained from less pure Western France menhirs, dolmens, and cromlechs limestones, which are by far the most abundant. prevail

, while the eastern side of France shows The more thoroughly the ingredients are interthe prevalence of mounds and barrows, which are mixed, the more complete will be the subsequent here and there found penetrating into the other hardening of the mortar. As commonly laid in the domain, giving us a sort of rude sketch, as it were, joints of brick or stone work, mortar sets sufficiof an invasion advancing irregularly towards the ently fast to allow building operations to proceed west. See M. Bertrand's Archéologie Celtique et from day to day with occasional longer intervals, Gauloise; also K. von Becker's Versuch einer but it takes years--perhaps in many cases cenLösung der Celtenfrage (1883), pp. 114-119.

turies—to reach its maximum hardness.

The For reasons already indicated, the question of setting and subsequent slow hardening of mortar Celtic ethnology is a very difficult one, but it is are usually considered to be due, in the first inconsiderably more difficult than would appear from stance, simply to the loss of water, and afterwards what has here been mentioned ; for besides two

to the absorption by the lime of carbonic acid from Celtic sets of invaders, there are also to be taken the atmosphere, the carbonate of lime thus formed into account the non-Aryan races that previously binding together the sand and stone. It is doubtoccupied the countries to which the Celts came. ful, however, if this is an altogether satisfactory These pre-Celtic populations probably survived in explanation. The mortar used in many medieval considerable numbers, and one of the effects of a buildings is largely mixed with small pebbles. In second Celtic invasion may be supposed to have a number of cases this has proved to be of a more been to force the earlier Celtic settlers to amalga- | durable nature than the stone used along with it. mate with the ancient inhabitants, and to make Puzzolana or Pozzuolana, a loosely coherent

ause with them against the later Aryan volcanic sand found at Pozzuoli, near Naples, has hordes. So it may be expected that the language been long celebrated for its property of forming of the Goidelic Celts will prove to have absorbed a hydraulic cement when mixed with ordinary a larger non-Aryan element than that of the lime.

It is composed of silica, with a little Brythons. Similarly, one might take for granted magnesia and potash or soda, alumina, lime, and that the physical type of the people speaking the oxide of iron. Goidelic dialects should prove less purely Aryan ; Roman Cement. Certain natural mixtures of but this feature is obscured by the fact of the lime and clay are called cement-stones. The clays counter-invasions which Wales and other western of some of the newer geological formations in the portions of Britain have undergone in historical south of England, for example, contain courses of times at the hands of Ireland. Lastly, it is right septarian nodules (see SEPTARIA),

which have been to add that in so far as the people, whose language in great request for making the best kinds of is or has been Celtic, are Aryans, one might expect Roman cement. They are concretions of impure the type to be that of tall 'men, with more or less calcareous matter, many of them having this light hair and blue eyes ; on the other hand, the analysis : Carbonate of lime, 66; silica, 18; alumina, smaller men, with dark hair and black eyes, which 7; and protoxide of iron, 6 ; or consist of these subit was the fashion till lately to regard as the

stances in nearly that proportion. Cement-stones genuine and typical Celts, are probably not to be are carefully calcined in kilns, and afterwards regarded as Celts at all, but as Ivernians or ground and sifted. Good Roman cement should representatives of the pre-Celtic and non-Aryan set in about 15 minutes, and this quick-setting race, whose hunting-ground the soil of the British property makes it valuable for work which requires Islands may be said to have been long before the to be executed between tides and for other purposes first Aryan set foot in them.

where the cement used must harden quickly. "It is The Celtic languages and literatures will be found at best of but medium strength. Some natural

common

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cements are slow-setting, and these do not contain stance. But it is also known that objects made of more than 22 per cent. of clay. They set under unmixed Portland cement from the works of some water when half their weight consists of clay. The of the best makers will sometimes keep good for proportion of sand used with Roman cement should nearly twenty years, and then crumble to pieces not much exceed that of the cement.

When em

even when not exposed out of doors at all. Of ployed for external coatings of buildings it is apt course explanations of these failures are forthto effloresce and become unsightly.

coming. They are generally attributed to carelessPortland Cement.—This is considered by far the ness in the manufacture of the cement, or in the most important of the stone cements.

It is an

selection of the materials for it. But if they occur, artificial product, named from its resemblance to as they have done, with cements that have stood Portland Stone, but is much more largely used very well the ordinary mechanical tests, how can than Roman cement. In the manufacture of Port- any cement of this kind be entirely depended upon land cement on the banks of the Thames and the for durability ? Twenty, thirty, or even fifty years Medway by the wet process, three parts of white is far too short a time to test the lasting property chalk are mixed with one part of clay or mud from of a building material of this nature. The use of the lower reaches of these rivers. The two sub. Portland cement in pavements and for architectural stances, along with water, are placed in a 'wash ornaments is not attended with much risk, and mill' in which strong revolving knives or cutters for such purposes it is very suitable. The capital reduce the whole to a creamy slurry or slip. employed in the manufacture in Great Britain is The slurry then passes by gravitation to backs or probably near two millions sterling. For American reservoirs. There it is allowed to settle for some cements, see ROSENDALE. weeks, when the superfluous water is removed by Scott's Selenic Cement consists of burnt limestone decantation. The mixture is next dried on heated mixed with about 5 per cent. of sulphate of lime iron plates or on the floor of a heated chamber, ) in the form of plaster of Paris, and ground to and then burned in kilns. Finally it is ground to powder. The presence of the sulphate arrests the a fine powder. Modifications of the wet process slaking action of the lime, causes the cement to by which the large reservoirs are dispensed with set more quickly, and adnits of more sand being have been introduced in recent years. In other used with it than ordinary lime does. This cement parts of the country Portland cement is manu has been a good deal used for plastering, and to factured by the dry process from the hard lime some extent also for mortar. stones of other formations than the chalk, along Plaster of Paris (see ALABASTER and GYPSUM). with clay or shale. These limestones are crushed - This material is used for cementing marble and small

, mixed in the proper proportion with clay alabaster in much the same way as mortar is in or shale, then roughly burned, and ground to brick-work. It is also employed for uniting the powder. This powder slightly moistened is passed separately moulded pieces of any large object cast through a pug-mill, and then made into bricks, in the same materiál. Sometimes it is selected which are afterwards burned in kilns and reduced to for fixing metal mounts to glass. powder

Keene's Cement is made by saturating plaster of Since Portland cement is hardly ever employed Paris in small lumps with alum and recalcining in the pure or neat state, its strength is perhaps it. It then forms a hard plaster for the projecting best tested when it is mixed with an equal weight portions of halls and rooms, such as pilasters, of sand. The best cement so mixed and moulded columns, and skirtings. It is capable of taking in the state of a stiff mortar, into any convenient a high polish, shape, when tested after the lapse of seven days, Parian or Keating's Cement somewhat resembles during six of which it is customary to keep it Keene's. In its manufacture borax as well as immersed in water, exceeds in tensile strength alum is added to the plaster of Paris. 200 lb, per square inch, and in crushing strength, Martin's Cement is another kind, with plaster of tested by 11-inch cubes, 1000 lb. for the same area. Paris for its basis, but instead of borax, carbonate Its strength in the unmixed state is much greater. of potash is added, and sometimes hydrochloric Much of the Portland cement made is, however, acid as well. With the exception of Scott's, these little more than half as strong as the best kind. plaster of Paris cements are only used in plastering Roman cement of good quality mixed to the same or other internal work—not for mortars. extent with sand as the above, and tested under the Mastic Cement, consisting of a mixture of burnt same conditions, has on an average a tensile strength clay or limestone in a powdered state, with boiled of 30 lb., and a crushing strength of 200 lb. in each oil and litharge, was more in use formerly than case per square inch. Portland cement is slow in now; but though expensive, it is an excellent setting compared with most varieties of Roman material for preventing the admission of rain-water cement. Both Portland and Roman cement format certain joints about buildings, such as where hydraulic mortars--that is, they set under water. wood and stone work come together at windows. No mortar will do this which contains less than It was also used for covering external mouldings. 10 per cent. of silica.

Rust or Iron Cement.Joints in iron-work, such Till close on 1840 Portland cement was hardly as those for hot-water pipes, are filled up with a known, but the use of it has extended rapidly, cement of iron borings or turnings, mixed with especially in recent years. Its most important at least 2 per cent. of sal-ammoniac. Sometimes application is in the construction of docks and sulphur in powder is added. The iron oxidises harbours, many of which are partly or wholly and forms a firm joint. built of it, mixed with sand and broken stones, in Sulphur Cement. - For jointing earthenware the form of a concrete.

In this state, or simply pipes, and occasionally for fixing bars of iron mixed with sand, it is also much employed for into stone, a cement is made of sulphur, resin, and other purposes where strength and durability are brick-dust. It is a cheap but not a strong cement required. *Owing to the nature of some of the where metal is concerned. extensive engineering works in which Portland Water-glass Cements.For furnaces one kind cement is largely used, it is plainly of great con

consists of burnt and unburnt fireclay made sequence that its properties should be thoroughly plastic with silicate of soda water-glass. understood. Numerous failures with it have taken Another cement, capable of standing a high heat, place. The chemical investigation into the case

is formed of asbestos powder made into a paste of the Aberdeen docks in 1887 distinctly showed with silicate of soda. The same silicate mixed the deleterious action of sea-water upon this sub- with ground glass makes an acid-proof cement.

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