مسیح اور مہدیؑ

مسیح اور مہدیؑ — Page 329

مسیح اور مہدی حضرت محمد رسول اللہ کی نظر میں 329 عکس حوالہ نمبر: 112 قیامت سے پہلے دس نشانات PLAGIARISM-PLAGUE 991 tritus of gold-bearing rocks۔Other metals, e۔g۔, tin, are similarly | cleavage flakes (oor and oro), sections cut perpendicular to the deposited۔The gold of the placers consists of grains called "gold- dust and larger pieces, rounded by attrition, called "nuggets۔" The placer of an ancient stream may be deep-lying because cov- ere since its formation with other deposits or even lava۔(See GOLD: Mixing and Metallurgy۔) PLAGIARISM, an appropriation or copying from the work of another, in literature or art, and the passing off of the same as original۔The Lat۔plagiarias meant a kidnapper, stealer or abductor of a slave or child, though it is also used in the modern sense by Martial (I۔53۔g)۔(See COPYRIGHT۔) PLAGIOCLASE, an important group of rock-forming min۔erals constituting an isomorphous series between albite felspar and northite felspur۔The intermediate members are soda-lime felspar which in their crystallographical, optical and other physi- cal properties vary progressively between the two extremes, albite (Ab) NaAISO,, and anorthite (An) CaAISLO۔The name۔plagioclase is derived from the Gr۔hayos, "oblique," and " Aa, "to break" in allusion to the oblique angle between the cleavages۔Names are applied to members of the plagioclase group falling between certain arbitrary composition limits, those now commonly adopted being albite (Al-Ab), oligoclase (Ab Ab), andesine (AA), labradorite (Ab-Ab), bytownite, (Aba-Ab), anorthite: (AA)۔The pure end members are practically unknown in nature۔All the plagioclases crystallize in the triclinic system, and as members of an isomorphous series show closely similar crystallographic constants۔They possess a perfect cleavage parallel to the basal pinacoid (oor) and a less pronounced cleavage parallel to the pinacoid (010), the angle be- tween the two cleavages varying progressively from 86° 24' in albite to 85 50 in anortbite۔The molecular volumes are closely similar (Ab roo) (An 101-5)۔The habit of well-formed crystals is usually tabular on the plane oro, sometimes flattened parallel to oo ar, as in microlitic plagioclases of volcanic rocks, elongated in the direction of the edge oor:oro۔Twinning is a very important character of the plagioclases, being almost invariably present and affording a ready means of distinguishing them from other fel spars۔The chief twin laws are the Carlsbad, albite and pericline; the latter two, being commonly polysynthetic, give rise to numer ous thin langellae, which are the cause of the fine striations seen on cleavage planes, and of the banded character visible in thin sections of the minerals examined in polarized light۔With the exception of the sodic end member (albite), which, owing to the high viscosity of its melts, is with difficulty crystal- lized, the plagioclases are readily prepared from dry melts of the component oxides۔They show a continuous melting curve, the intermediate members exhibiting a melting interval۔The temper- atures of beginning of melting (solidus) have been determined in The laboratory for compositions ranging from pure An to Ab,An,, and of completion of melting (liquidus) for a range An to Ab- An۔These data are shown below۔Composition Albite (AbAng) Temperature of beginning of melting Temperature af completion of melting (liquidas) (solidus) Oligoclase (Aba An۔) 1,100°C Andesine (AL;Am) 1۔175°C Andesine-Labradorite (Ab,An) 1,20°C 1,362°C 1,394°C Ladralorite (Ab,An 1,287°C Bytownite (Abruz 4372°C Anorthite (And 465 C 4۔550°C 1,450°C 1,495°C 1,521°C J۔550°C The density and mean refractive index of the plagioclase felspars vary progressively, the extremes being albite, D=2-605, 1-530; anorthite, 2-765,1۔587 optic axes and bisectrices, and especially those perpendicular to the plane of albite twinning (orc) in multiple-twinned crystals۔Other optical determinations are available for discriminating the various members of the group۔BIBLIOGRAPHY۔-For a detailed summary of the optical characters, and their employment in the recognition of the quantitative composi tion of the ielspars, the following should be consulted: II۔Rosen- (Band i, Zweite Hälfte, s Auflage, revised by O۔Mügge, 127 busch, Mikroskopische Physiographic der Mineralen und Gesteine L۔Dupare and M۔Reinhard, "La Détermination des Plagioclases (Mem۔Soc۔Phys۔Hist۔Nat۔Genète, x1, 1924, fase۔1۔): A۔N۔Winchell, Elements of Optical Mineralogy (pt۔2, 1957, pp۔277-3417 reference may also be made to Schiebold, Fortschritte der For a recent preliminary X-ray study of the plagioclase felspars, Mineralogie, Kristallographie und Petrographic (Bard xil, 1921۔pp۔78-83)۔A more detailed account of the occurrence of the various members is given under ALBITE, OLIGOLASE, ANDESINE, LADEADORITE, BYTOWNITE, ANORTHITE۔See also FELSPAR۔(C۔E۔T۔) PLAGUE, in medicine, a term formerly given to any epidemic disease causing a great nurtality, but now confined to a specific infectious fever caused by b۔pestis۔History to 1880۔-The first historical notice of the plague contained in a fragment of the physician Rufus of Ephesus۔who lived in the time of Trajan, preserved in the Collections of Ori- basius'۔Rufus speaks of the buboes called pestilential as bein specially fatal and as being found chiefly in Libya, Egypt, and Syria۔This passage shows the antiquity of the plague in northern Africa, which for centuries was considered as its home۔It is not till the 6th century of our era, that we find bubonic plague in Europe, as a part of the great cycle of pestilence, which laste fifty years, and spread over the whole Roman world, beginning in maritime towns and radiating inland۔In another direction it c tended from Egypt along the north coast of Africa۔Whether the numerous pestilences recorded in the 7th century were the plate cannot now be said; but it is possible the pestilences in England chronicled by Bede in the years 664, 672, 679 and 683 may have been of this disease, especially as in 690 pestis inguinaria is again recorded in Rome۔In the great cycle of epidemics in the 14th century known as the Black Death, some at least were bubonic plague۔The mortality of the black death was, as is well known, enormous۔It is estimated in various parts of Europe at two-thirds or three-fourths of the population in the first pestilence, in England even higher; bu some countries were much less severely affected۔Hecker calculates that one-fourth of the population of Europe, or 25 millions of persons, died in the whole of the epidemics۔The Great Plague of London۔The great plague of 1664- 1665 must not be regarded as an isolated phenomenon۔Plague had recurred frequently in all parts of Europe in the 15th, 16th and 17th centuries۔Nevertheless in London the preceding years had been unusually free from plague, and it was not mentioned in the bills of mortality till in the autumn of 1664 (Nov۔2) a few isolated cases were observed in Westminster and a few occurred in the fol- lowing winter, which was very severe۔About May 1665 the disease again became noticeable and spread, but somewhat slowly۔Bog- hurst, a contemporary doctor, notices that it crept down IIolborn and took six months to travel from the western suburbs to the castern through the city۔The mortality rapidly rose from 4۔3 in May to 590 in June, 6,137 in July, 17,036 in August, 3۔159 in September, after which it began to decline۔The total number of deaths from plague in that year, according to the bills of mortality was 68,596, in a population estimated at 460,000, out of whom two- number is likely to be underestimated, since of the 6۔43 recorded Thirds are supposed to have fled to escape the contagion۔This deaths from spotted fever many were probably really from plague۔there was a sudden fall in the mortality which continued through though not declared so to avoid painful restrictions۔In December Since the plagioclases are of great importance in petrology much detailed study of their optical properties has been under-the winter; but in 1666 nearly 2۔000 deaths are recorded۔taken, so that it is now possible to determine by simple examina- tion of thin slices of these minerals the exact chemical composi- tion and crystallographic orientation of the selected section۔For this purpose, the chief determinations are the refractive indices, and the optical extinctions of oriented sections, principally on London by bales of merchandise from Holland, which came According to some authorities, the plague was imported inte originally from the Levant; according to others it was introduced 'Lib۔xliv۔cap۔1-Oeuvres de Oribase, ed۔Bussemaker and Darem- berg (Paris, 1851), iii۔607۔ترجمہ: اس وباء سے 25 ملین لوگ ہلاک ہوئے۔