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Observatory Clock: Clock for astronomical TIME DETERMINTIONS. The very first mechanical clocks with VERGE ESCAPEMENT and FOLIOT, may well have been those that drove GLOBES and other astronomical mechanisms, which only later were simplified for domestic use. The CROSS BEAT followed for astronomical use, but as more accurate time measurements were demanded, astronomers employed a weight on a cord and counted the swings. This was developed into the PENDULUM CLOCK which was made more accurate by the ANCHOR ESCAPEMENT and still more by the DEAD BEAT, in clocks called REGULATORS. The RIEFLER CLOCK bettered timekeeping and was itself much improved on by the SHORTT CLOCK, in turn replaced by the QUARTZ CLOCK, which the ATOMIC CLOCK is now superseding. Some observatory clocks show SIDEREAL TIME and have TWENTY-FOUR HOUR DIALS. See Time Determination, Royal Greenwich Observatory, Greenwich Observatory and Octagon Room.
Octagon Room: The original room from which observations were made in GREENWICH OBSERVATORY. It contained two fine clocks with 13 ft. PENDULUMS above them, specially made by Thos. TOMPION for John FLAMSTEED. These clocks now belong to the BRITISH MUSEUM and the Earl of Leicester, but replicas are in their place at Greenwich.
Oignon: French watches of the early eighteenth century which were larger and thicker than the English and therefore called 'onions'. After 1800, French watches became delicate and original and English ones stolidly reliable.
Oil: Problems of oiling have always been of great concern to watch and clock makers and still are today. A famous clockmaker once said to Napoleon: 'Give me a perfect oil, and I will give you a perfect watch.' This is still true of mechanical watches, yet the public is entirely ignorant of the fact. To give their best service, clocks and watches should be cleaned and re-oiled every two years or so because, unlike other mechanisms, they never stop, day or night, and the extremely tiny amounts of various types of oil in them eventually must dry out, become gummy, or become a kind of grinding paste with dust. Modern horological oils and greases have considerable scientific research behind them. Some are natural and others are synthetic. Church records of 1498 refer to applying 'cowes fatt oil to the pivotts of the clocke'. Freezing of the oil used to stop church clocks, and various inventions of non-freezing oils included calves foot oil mixed with Scotch fir tar, and fish oil with pepper, and other oddities. The problem still arises during arctic and space exploration. Most early makers used animal fat oils-such as neat's foot, sheep's foot, and whale oil (a famous one came from the nose of the porpoise) and vegetable oils-such as olive and palm which they filtered and blended themselves. Mineral oils were not used until the end of the nineteenth century. They usually have to have some animal oil added to improve their wetting properties. Lord GRIMTHORPE advised neat's foot oil for TOWER CLOCKS. Some clockmakers, including HARRISON, tried to eliminate oils altogether. Another problem that still exists is to prevent oil spread. The tiny drops should be held in place by surface tension, like drops of water in the holes of a tea strainer. This is helped by OIL SINKS, but it is not possible to place them on all parts. After ULTRASONIC CLEANING a special coating known as 'EPILAME' is given to the movement to avoid oil spread. The oiling of a precision watch requires considerable skill and knowledge. Too much, or too little, or oil in the wrong places, can affect the RATE of clocks (including tower clocks) and stop smaller watches.
Oil Sink: A small well around a PIVOT in a clock or watch PLATE or JEWEL which retains the oil. See Sully and Le Roy.
Oliver Cromwell's Watch: A plain PURITAN WATCH on a FOB chain which belonged to the Protector and is now in the BRITISH MUSEUM COLLECTION. It was made in 1625 by John Midnall of Fleet Street.
One-Hand Clocks: Before about 1400, clocks had one fixed hand and a dial that turned (see Monastery Clock). Then the dial became fixed and a single hour hand turned. Minute hands were introduced soon after on special clocks, but not generally until after mid-seventeenth century for domestic clocks. Cheaper clocks still continued for some years with one hand. The present Westminster Abbey clock still has only one hand. See Hand, Clock and Hand, Watch.One-Wheel Clock: There was much competition at one time to produce clocks with the fewest gear wheels. A one-wheel clock is recorded in 1598. Pierre LE ROY made an astronomical one, and Lepaute one showing seconds in mid-eighteenth century.
Organ Clock: Clock playing a small pipe organ every three hours. Popular in the second half of the eighteenth century, particularly for export to the East.
Ormskirk Escapement: An ESCAPEMENT for watches employed by English makers in the Ormskirk area in the 1800 period. Invented by Debaufre in 1704. Also called the 'chaffcutter', because the double ESCAPE WHEEL looks like one, or the 'clubfooted verge'.
Orrery: Mechanical model showing the motions of Earth and Moon round the Sun. Named after the Earl of Cork and Orrery. Sometimes worked by clockwork from which it could be disengaged for demonstration. A famous one was made by TOMPION and GRAHAM.
Out of Beat: A PENDULUM releases a tooth of the ESCAPE WHEEL at the end of each swing. If this action is not symmetrical the clock is 'out of beat' and TICKS are alternately loud and soft, or the clock stops because a tooth is not released. The clock itself can be levelled to set it 'in beat', or a more permanent adjustment made by bending the CRUTCH in the direction of the loud PALLET. Other escapements on clocks and watches can become out of beat. TO adjust the LEVER ESCAPEMENT for BEAT it is necessary to alter the POINT OF ATTACHMENT Of the HAIRSPRING. Some watches have special devices to allow the outer point of attachment to be moved without dismantling the balance assembly.
Ovalizing Balance: A BI-METALLIC BALANCE which is not a CUT BALANCE. The arm (spokes) does not expand in the same proportion as the rim as temperature rises, so the balance becomes oval, and, combined with a modern alloy HAIRSPRING, can be arranged to give excellent TEMPERATURE COMPENSATION. First invented by Volet, a Frenchman, in the eighteenth century and reinvented independently by Lord Charnwood in the U.K. in 1927, and the Hamilton Watch Co. in the U.S.A. in 1942 for their MARINE CHRONOMETERS arid DECK WATCHES, theirs having a stainless steel rim and an arm of INVAR.
Overcoil: A HAIRSPRING with the outer quarter turn raised and curved towards the centre. An ordinary spiral spring does not keep good time because the spring becomes lopsided as it opens and closes while the BALANCE swings. The overcoil avoids this. See Breguet Spring.
Over Compensation: A plain BALANCE AND SPRING Will lose time as the temperature rises because of TEMPERATURE ERROR. If it has TEMPERATURE COMPENSATION and gains in heat, it is said to be 'over compensated'.