OBSERVATORY RIDGE 



58 1 6 



OCCLUSION 



the telescopes are of great size the 

 floors of the domes are made to 

 rise by means of hydraulic power, 

 to enable the observer to accom- 

 modate himself to the changing 

 height of the instrument. A 

 separate building contains the 

 transit instrument, which, together 

 with a sidereal clock, forms an in- 

 dispensable part of the equipment 

 of an observatory. The transit 

 instrument is fixed to point N. and 

 S., so that it can only move up and 

 down, and it is used for observing 

 the time a star crosses the meridian 

 of the instrument. This observa- 

 tion gives the means of checking 

 the sidereal clock, since the time 

 the star should be on the meridian 

 is known from other considerations. 

 The Lick Observatory is built 

 in the pure, dry atmosphere of Mt. 

 Hamilton, at an alt. of 4,250 ft. 

 The Boyden Observatory, built .by 

 Harvard College out of funds 

 largely provided by a legacy left 

 by Uriah Boyden for the purpose, 

 is established at Arequipa, Peru, 

 at an alt. of 8,060 ft. The Lowell 

 Observatory was established in 

 1894 by Professor Percival Lowell 

 at Flagstaff, Arizona, at a height 

 of 7,000 ft. The Carnegie Solar 

 Observatory was built in 1905 on 

 Mt. Wilson, California. 



The Royal Observatory at Green- 

 wich was founded in 1675, and, 

 during the 18th century it was the 

 only observatory making systema- 

 tic observations of celestial objects. 

 The observatories at Edinburgh 

 and Dublin are also royal observa- 

 tories. In Great Britain there are 

 eight important meteorological ob- 

 servatories, at Kew, Greenwich, 

 Falmouth, Oxford, Stonyhurst, 

 Armagh, Valencia, Glasgow. See 

 Frontispiece to Vol. I; also As- 

 tronomy ; Lick ; Meteorology ; 

 Telescope. 



Observatory Ridge. Ridge of 

 Belgium, in the prov. of W. 

 Flanders. It lies 1 \ m. S. of Hooge 

 and just S. of Sanctuary Wood. It 

 figured prominently in the Great 

 War, and along with Hooge and 

 Sanctuary Wood passed into the 

 hands of the Germans in the autumn 

 of 1914. It was captured by the 

 Allies on July 31, 1917. The Can- 

 adians have erected a war memorial 

 here. See Ypres, Battles of. 



Observer. Official term in use 

 in the Royal Air Force to denote 

 any member of the crew of an air- 

 craft whose 

 duties are dis- 

 tinct from 

 those of the 

 pilot, and who 

 is charged 

 generally with 

 Observer. Badge worn making aerial 

 on left breast observations 



of" any kind. Observers receive a 

 thorough and extensive training of 

 a highly specialised type in military 

 reconnaissance, direction by wire- 

 less of artillery fire, bombing, and 

 aerial gunnery. See Airmanship. 



Observer, THE. Oldest Sunday 

 newspaper of London, devoted 

 primarily to the publication of 

 Saturday's news on the daily paper 

 model. Established Dec. 4, 1791, 

 it achieved great success under the 

 control of William Clement. The 

 paper remained in his family until 

 1870, when it passed into the 

 hands of Julius Beer. Viscount 

 Northcliffe owned it from 1905-11, 

 reducing the price to Id. in 1906 ; 

 previously it had varied between 

 6d. and 2d., at which it stood 

 between 1895 and 1906. The 1st 

 Viscount Astor acquired the pro- 

 perty later, and passed it on to his 

 son, William Waldorf (later Vis- 

 count) Astor, M.P. The editors have 

 included Edward Dicey (1870-89), 

 H. D. Traill (1889-91), and, since 

 1907, J. L. Garvin. The Observer 

 was one of the pioneers of illus- 

 trated journalism. 



Obsidian. In mineralogy, 

 name given to a volcanic vitreous 

 rock consisting of a combination 

 of silica, aluminium, calcium, iron, 

 potassium, and sodium. The 

 mineral, which resembles dark 

 glass, is extremely hard and brittle, 

 and is usually black or dark grey, 

 although occasionally brown or 

 green. It is found in most volcanic 

 regions of the world, and on ac- 

 count of its hardness and capa- 

 bility of taking a high polish, it 

 was used by primitive man for 

 arrow and spear heads, knives, 

 ornaments, and mirrors. 



Obstetrics (Lat. obstetrix, 

 midwife). Art of helping women 

 in pregnancy and childbirth. In 

 the human species the duration of 

 normal labour with a first child is 

 usually from 20 to 24 hours, but 

 after the first delivery the process 

 is easier, and does not usually last 

 more than about 12 hours. Labour 

 is divided into three stages. The 

 first stage is one of preparation for 

 the delivery, and consists in the 

 gradual dilatation of the neck of 

 the, womb ; the second stage is the 

 period from the full dilatation of 

 the neck of the womb to the birth 

 of the child ; and the third stage 

 is the delivery of the afterbirth, 

 or placenta and membrane. 



As soon as the child is born, the 

 eyes should be wiped clean with a 

 little cotton wool soaked in a mild 

 antiseptic solution. The cord 

 which still connects the child with 

 the placenta should be ligatured 

 and divided after pulsation has 

 ceased. The child in most cases 

 breathes or cries freely ; if not, 



steps should be taken to promote 

 respiration. The period following 

 the birth of the child is known as 

 the puerperium, during which the 

 diet should be light and nourish- 

 ing. The mother should remain 

 in bed for at least 10 days. The 

 child should be put to the breast 

 within 12 hours after delivery. 



Obturator (Lat. obturare, stop 

 up). Technical term describing the 

 packing employed in the breech 

 block of B.L. (breech loading) type 

 of guns, to ensure that there shall 

 be no escape of gas between the 

 breech block and barrel. In contra- 

 distinction to Q.F. (quick firing) 

 guns, B.L. guns employ a pro- 

 pellant charge merely contained 

 in a fabric bag. Consequently the 

 actual joint between the breech 

 block and the barrel has to pro- 

 vide complete sealing against the 

 pressure of the gases when the 

 charge is fired. In the British 

 B.L. guns the breech block has 

 a separate head next the charge, 

 and between this and the main 

 portion of the block a ring of im- 

 pregnated canvas or copper gauze, 

 termed an obturator, is placed. 

 When the charge is fired, ths pres- 

 sure on the head of the breech 

 block causes it to compress the 

 obturator, and expand it against 

 the walls of the chamber. See 

 Ammunition ; Breech Block : Guns ; 

 Ordnance. 



O.C. Abbreviation for Officer 

 Commanding. 



Occasional Conformity. Prac- 

 tice by which many Nonconfor- 

 mists avoided the penalties and 

 disabilities of the Test and Corpor- 

 ation Acts. These two Acts forbade 

 anyone to hold any public office 

 unless he took the Sacrament ac- 

 cording to the rites of the Church 

 of England. Many Nonconfor- 

 mist office holders did this now 

 and again. Attempts in Anne's 

 reign to stop this practice failed, 

 owing to the opposition of the 

 House of Lords, but in 1711 the 

 Occasional Conformity Act made 

 it illegal. In 1718 the Act was re- 

 pealed and the practice renewed. 

 However, from 1727 to 1829 it 

 was unnecessary, as Nonconformist 

 office holders were protected by 

 an annual Act of Indemnity. See 

 Toleration. 



Occlusion. Term given to the 

 power of certain solids to absorb 

 gases. Palladium will absorb 935 

 times its own volume of hydrogen 

 at red-heat, and nearly 400 times 

 at normal temperatures, charcoal 

 90 times its volume of ammonia, 

 platinum black 250 times its 

 volume of oxygen, etc. Occlusion 

 is a form of molecular attraction, 

 but a definite chemical compound 

 of the solid and the gas is not 



