Page:The New International Encyclopædia 1st ed. v. 14.djvu/844

OBSERVATOBY. 718 OBSTETRICS. tlip lieavonly bodies In- incans of the apparent diurnal movement. W ith the transit and quad- rant Bradley commenced that series of observa- tions of the po.sitions of the sun, moon, planets, and stars, which have continued ever since at Greenwich, and on which, in combination with less extensive series at Paris, Kiinigslierg, and elsewhere, all our tables of the motions of the heavenly bodies are foimded. In modern observa- tories the transit and mural circle have been combined into one instrument, the meridian cir- cle (ii.v. ). which determines both ri>j;lit ascen- sions and declensions at a single observation. In planning observatories a very usual mistake is an over-supply of instruments and too few astronomers. A large telescope really needs si.x persons to keep it busy: two astronomers, two assistants, and two computers. Moreover, the "life" of a telescope is very short. Every few years new instruments are invented, and unless these are supi)licd to the oljservatory its astron- omers will work at a disadvantage, and its astro- nomical output will be diminished in quantity and value. The great observatories of the world may be divided into several classes. In the first place, we have the great Government institutions occu- pied with continuous observations such as are needed to strengthen our knowledge of the funda- mental parts of astronomy. The Royal Observa- tory at Greenwich. England, is perliaps the most important of this class. It was founded by Charles 11. Similar institutions are established at Paris, Berlin. Pulkova (<i.v.). near Saint Pe- tersburg, and Washington. At the last-named place the observatory is called the United States Xaval Observatory (see Xaval Ob-servatory) , and the astronomers are professors of mathe- matics in the United States Xavy. Another class of observatories are maintained by universities and other educational institutions. These are in- tended to combine instructiim with research, and in them an efl'ort is usually maile to extend the .science of special investigations rather than by- long continued routine observation. In the Unit- ed States the principal observatories of this class are the Harvard University Observatory-, the Lick Observatory (q.v. ) of the T'niversity of California, and the Yerkes Observatory (q.v.), belonging to Chicago University. Finally, we have the verj' important class of astrophysical ob.servatories, which are occupied with a study of the physics of the heavenly bodies. Prol>ably the most important of these is at Potsdam, (iermany. Much a>trophysical work is alsn done at the uni- versity observatories of Harvard and Chicago. See Telescope: Meridia.n Circle. For the lately established observatories for the observation of the variations of latitude, see Latiti'de, Vari.v.- TION OF. OBSIDIAIT (from Lat. ohxiilimm, false read- ing for nlisidiia, a sort of mineral, probably ob- sidian, from Obfiidiun, false reading for OhKiiis, name of a man who is said to have discovered it in Ethiopia). A volcanic glass consisting of silica in combination with aluminum, calcium, iron, potassium, and sodium. It is hard and brittle, with a remarkable vitreous lu~lre. and a perfect conchoidal fracture, the edges of the fracture, which are semitran^parcnl or trans- lucent, Ix'ing very sharp and cutting like glass. Obsidian is generally black or very dark gray, but sometimes has a green, red. or brown color, is striped or .spotted, and even chatoyant or aventurine. It occurs in volcanic regions, in round compact pieces, granular or fibrous. It is often found in association with pumice, which is identical with it in chemical composition, but different in structure. Pitchstone is also of similar composition, but contains a larger per- centage of water an<l is without lustre. Obsidian is found principally in the volcanic regions of Iceland, Italy. Hungary, S])ain. Xew Zealand. Siberia, Mexico, Peru, and the western parts of the United States, especially in Georgetown, Col., and at the Obsidian Clill' in the Yellowstone Park, where it occurs in massive form. The famous locality in Mexico is the Cerro de Xavajas, or "Hill of Knives,' in the State of Michoacan. Obsidian takes a high polish, but is very brittle. Xevertheless, it was extensively used among l)rimitive peoples for arrowheads and spearheads, for knives, mirrors, polished figures, and orna- ments, the best sjiccimens of which have been found in ilexico. The early Romans obtained obsidian mirrors from Ethiopia. The mineral is still sometimes employed as material for orna- mental lioxcs. liutti>n<, and other articles. OBSTETRICAL TOAD. See Midwife Frog. OBSTETRICS (from Lat. ohstetricius, re- lating to a midwife, from ohstclrijc. midwife, form ohntare, to stand before, from oil, before, toward + stare, to .stand). Midwifery, or To- kology. That branch of medicine which is concerned with the care of women during pregnancy, and <luring and after labor, whether natural or irregular, with the diseases iM>culiar to the puerperal state, and with the care of the new-born child. It also embraces a knowledge of the anatomy of the female generative organs and the physiology of reproduction in the human species. While among savages little or no as- sistance is given to the parturient woman, and the process is left to luiaided nature, among civilized peoples from the earliest times there has been a class of persons — usually women — who have attended women during this trying period. The .Jews had women (called mrjrt- Icdetb) who acted as midwives, as did the Egyp- tians: and among the Greeks there was a corre- sponding class of women known as mfrculria'. Phanarete. the mother of Socrates, was a mid- wife; and Plato ex])lains the duties undertaken by these women. Ilijipocrates gave considerable attention to midwifery, and describes the opera- tion of turning the child in abnormal laliors. Among the Romans both physicians and mid- wives (obstctrices) attended confinements. Civsa- rian section was i)erformed after the death of the mother, and Pliny mentions that Scipio .fricanus and Manlius were born in this way. There was a royal law ilr.r niiin) providing for the perform- arue of this operation when necessary. Cclsus and Paulus of Ephesus wrote of obstetrics during the first century, and a grailual increase in the knowl- edge of the physiology and mechanism of labor can be traced in the writings of Galen (se<-ond century), .-^etius (fifth eentiiry), and Paulus .Egineta (seventh century). The latter advo- cated the operation of craniotomy in suitable cases. During the Middle .ges there was little progress in obstetric science in Europe, but the xrabian and Persian schools made many im- provemDnts in this branch of medicine as well