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EgumsStial Occ i devt, that point of the horizon where the fun fets, when entering aries, or libra.
UJi'tval Occident, that point of the horizon, where the fun fcts at hs entrance into the fign cancer, when the days arelongeft.
Hyhcrnai OCCIDENT, that point of the horizon where the fun lets, when entering the figh of c&pricorn } at which time, the days, with us, are fhortcft.
OCC I PI PAL (CycL) — The os haip'itfs, or occipital bone, is fitu- at'cd in the pofterior and lower part of the cranium ; it repre- ftnts a kind of lozenge, irregularly indented, and is convex without, and concave within. It fometimes, but very rarely, is found to confift of two pieces, being divided, in that cafe, by the continuation of the coronal future. It confifts of an external, and interna] Tide, of the upper, lower, lateral, and middle parts ; the firft four of which may 1 e looked upon as fo many angles ; and has four edges, the two fuperior of which are indented, the two inferior are more or lei's unequal in differ- ent fuhjech. Near the middle of the convex outfide of this bone, the occipital protuberance, or rifing, is obfervable ; un- der this protuberance arc two fuperfirial tranfverfe arches ; thefe are more remarkable in fome fubjecis, than in others, one fuperior, and larger, the other inferior, and lefs, and both reaching to the maftoide procefs on each fide : the inferior arch is cut at right angles by a perpendicular line, called the external, occipital fpine, or criita. Under the fuperior arch are two rough planes, one on each fide of the fpine ; and between the extremities of the two arches are two other i'uch planes, one on the right hand, and the other on the left. We fee likewife two condyles, or condyloide apophyfes, crufted over with cartilages, gently convex, of an oblong oval figure, and
- fituated obliquely ; their pofterior extremities being at a great-
er diftance from one another than their anterior. Alfo a large, cuneiform, production, which, from the condyles, is di- rected upwards, and, in adults, is often joined infeparably to the os fphenoides. This may be termed the apophyfis bafila- ris, or the great apophyfis of the cccipital bone. Laftly, there are fome unequal tubercles on the lower part of this apophy- fis, and two little angular productions in the edge of the bone, over againft the condyles.
There arc likewife in this bone two large notches under the lateral angles, which receive the pofterior apophyfes of the of- fa teniporum, two fmall notches, or portions of the jugular foflas, and of the foramina lacera ; each of thefe is often di- vided by a fmall bony production : alfo the great cccipital hole, on the anterior edge of which there is an impreflion for the infertion of a ligament, two anterior, and two pofterior con- dyloide foifulx, two anterior condyloide holes for the ninth pair of nerves, which are fometimes double, and two pofteior condyloide holes for fmall veins, which are fometimes want- ing. The upper part of this bone is thick, as being much ex- pofed to blows, and other injuries ; the lower part is thinner, but is well guarded by mufcles. It forms the back part of the head ; f<_rves for the articulation of the head with the trunk ; contains a part of the brain, and almoft all the cerebellum j and gives paflage to the medulla oblongata, and a great many of the nerves, and veflels ; and infertion to a great many of the mufcles. IVivJliw's Anatomy, p. 25.
OCCUPIERS of 'walling, a term in the fait works for the per- fons who are the fwom officers, that allot, in particular places, what quantity of fait is to be made, that the markets may not be over-ftocked, and fee that'all is carried fairly and e- ♦jually between the lord and tenant. Thefe perfons always appoint how many houfes fhall work at a time ; and, when, there is fait to be made, thefe appoint a cryer to proclaim it to all the workers, that they may put to their fires at the fame time; and a like proclaiming of the time when they lhall leave off"; and thofe who continue to work after this prohibition, are to have their fait fpoiled, or deftroyed. R a) ' s EnglifhWords.p. 17J '
OCiJXATI lapides, in natural hiftory, a name given by the antients fometimes to exprefs certain Hones, found on the mores, and in the beds of rivers, and naturally marked with the figure of an eye ; and fometimes for fmall round {tones of the fhape of the gtove of the eye, made by art for child- ren to play with, and of the nature of what we call marbles. Suetonius tells us, that Auguftus Cajfar ufed to divert himfelf fometimes with playing nucibus et acel'atis. The word lapidlbus is underftood after the laft word, and the meaning of the author plainly is, that he played, like a boy, with nuts and marbles. The word ocellatus, therefore, here, as in many other pallages of the antients, plainly expreflbs thofe little round Hones, formed by art, of little or no value, and intended only for boys to play with. But we have a- buudant teftimony among the antient naturalifts of the word
O C H
having been uled alio as the name of the gem which we now call cmbn hli, and all thole other (tones of the a^ate, or other femi-pellucid kinds, which had the figure of an eve naturally imprefled upon them, that is, a round fpot of a dif terent colour, in the center of a fmall roundifh (lone. Thefe were fcarce among the antients, becaufe they had none but the true :,!,/. hli, or fuch (tones as were of a particular fpe- cies, and were found naturally of the fhape and fize of an eye; but we have them much more common, becaufe our buppL. Vol.11.
jewellers, whenever they find a natural fpot in ah a<*ate, Ihri rounded with a white circle, cut it out from the reft of the (tone, and fell it as a natural otulus Mi, The name ocellati lapakti is not, by arty means, a (trance; or unnatural one for the genuine (tones thus fhaped, and marked with the refemblance of a pupil ; for the antients uled the name of the eye in a much larger fenfe, cxpref- fing by it any thing that appeared rounded and protube- rant. Pliny, (peaking of the Callais, or Turquoife (tone, fays, that it protuberated from the rocks in the form of an eye, and means no more by it, than that the maffes of it were round, and prominent] as we fee thofe of copper ore- turquoife at this day.
OCHNA, in botany, the name of a genus of plants, the cha- racters of which are thefe: the cup is a perianthium, com- pelled of five fmall leaves, of an oval, but pointed fhape, (landing expanded, and falling with the flower. The flower is compofed of two roundifh petals, with very obtufe ends, and with unguis of the length of the leaves of the cup. The ftamina arc a number of fine (lender filaments, con- verging at the ends. The germen of the piltil is oval, and terminates in a pointed ftyle, which is erect, and longer than the ftamina. The fruit is a very large, and fiefliy receptacle, of a roundifh, truncated form, in either fide of which there is lodged a (ingle berry, of an oval figure. The feeds are Angle, and of an oval figure alfo. Plumicr, il Linnai Gen. PI. p. 819.
OCHRA, 01 gallimla Ochkik, in zoology, the nameofafpe- cies of moorhen. It is all over of a dufky, and obfeure, yellowifh green, and is browner on the bread, and belly, than on the back, yet with the fame yellowifh green pre- dominant. The head, neck, bread, and wings, have feve- ral white fpots; and the face is in part white; the beak is part black, and part red ; and the legs are of a yellowifh cu- lour. A'.drcvancL tie Avib. 1. 20. c. 48.
OcHRA vitr'ali, in natural hiftory, a name given to that yellow j earth, ox ochre, which is one of the principles, or conftituent I parts of all vitriol. This is feparatcd from it by folution in water, and falls to the bottom of the veffel ; and the yel- low fubftance that tinges the fides of fountains, and fprings of chalybeat waters, in many places, is the fame fubftance, and (hews that they are only folutions of vitriol, which, m fuch, muft needs depofit that earth, which, though retained imperceptibly in the vitriol, yet cannot be fuftained in water fo well as while that fait was folid.
Bafil Valentine tells us, that repeated folutions of the fame quantity of vitriol, will, at length free it from all its earth ; and that then it will be found a very different fubftance from what it was before, and fit for feveral wonderful experiments, which he defcribes. This reparation of the earth of vitriol has been tried in vain, by twenty repeated folutions; but there is a much fhorter w'ay of effecting it, which is this : Powder a good quantity of Dantzick, or Hungarian vitriol ; put it into a high and narrow cucurbit, and add to it a con- fiderable quantity of water; keep a fire under it for four days, and the earth will, in a very great quantity, fubfide from it, when cold, in much greater quantity from this one operation, than from feveral repeated ones of the common kind.
Another method, which feparates more than its earth from it, is this : Let the veffel containing the powdered vitriol, without any addition of water, be placed in a balneum Ma- ria:, and kept hot in the fame manner for four days; the vitriol will, in this cafe, melt as if water were put to it. While it continues in this fluid ftate, the ochre, or earth,' and not only that, but with it, the metaliine parts, and the grofs fulpbur, will in a great meafure fubfide, and become a hard cake, the vitriol continuing fluid about it. Let this be poured off, and when cold, it will cryftallize, leaving only a fmall quantity of a liquamen behind. This opera- tion may be repeated two or three times, and the vitriol then becomes a very different fubftance from what it was be- fore, and is fitted for feveraj operations, which it would not otherwife fucceed in. Many have tried to effect this repara- tion by liquation, by means of a dry heat, placing the veffel in (and, in filings of iron, or over the flame of a lamp, burning fpirit of wine, of oil ; but it never will fucceed this way, though the vitriol be ever fo long kept in a iiate of li- quation. Phil. Tranf. N° 103.
The ocbra vitrio/i may be obtained alfo in a great proportion though in another form, if, after a long, and intenfe calci- nation, the vitriol is freed from its fait by an ablution of warm water often repeated The far greater part of the re- maining colcothar, thus dulcified, is earth, with an admixture only of a fmall quantity of fome metalline parts. Another way of obtaining it, is diffolving vitriol in common water, and adding to the folution filings of zink, or falts of tartar, or fome other alkali. See the article Vitriol. A great proof of the earth called ochra vitriali being contained in large quantity in that fait is, that it requires no earth befide to be mixed with it in diftillation : whereas com- mon fait, nitre, and the other falts, require a great quantity of common earth to be added to them, to prevent their fufion. H h Alum,
