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Ilbert Collection: One of the most famous collections of clocks, watches, other timekeepers, and books ever amassed, by C. A. Ilbert (1888-1956). The clocks were bought for the nation by an anonymous donor, and the watches by public appeal and donations, through the efforts of the CLOCKMAKERS COMPANY. They are now in the BRITISH MUSEUM.
Ilbert Library: Famous library of horological books left by C. A. Ilbert in 1957 t0 the BRITISH HOROLOGICAL INSTITUTE.
Impulse: The small force applied at intervals to a PENDULUM or BALANCE to keep it swinging.
Impulse Pin: Small pin by which IMPULSE 1S given to a BALANCE.
Impulse Dial: Another name for a SLAVE DIAL.
Independent Seconds: Clock or watch with seconds hand today usually a CENTRE SECONDS HAND-which jumps from one second to the next, i.e. it is DEAD BEAT, also called 'jump second'. BREGUET invented a jumping hour hand.
Index: A watch REGULATOR which effectively alters the length of the HAIRSPRING for final timekeeping adjustments. The outer end of the spring is fixed and the index, which is a lever, moves two CURB PINS (one each side of the spring) around a short arc of the spring from this point.
Ingold, Pierre-Frederic (1787-1878): Pioneer of mechanized watchmaking from Bienne, who worked for BREGUET in Paris, introduced JEWELS to Switzerland, entered negotiations with the JAPYS, but could not agree and tried to set up a watchmaking factory in France. He transferred to London, where his Soho factory was damaged by hand-made watch workers, so moved to the U.S.A. and became a U.S. citizen. There his ideas were adopted and the first factories set up in Boston, but he personally was expelled without reason. He returned to La Chaux de Fonds and tried again unsuccessfully to set up a factory, dying there at the age of 92. In the meantime watchmaking by machinery had been started by Leschot in Geneva. Ingold drills were used until recently.
Inro Watch: The Japanese used to carry medicines in small decorated wooden boxes called an 'inros'. In the eighteenth century many of these were converted to watches. They were worn attached by cords, and a button (the 'netsuke'), to the kimono belt. There is a small drawer in the inro for the watch key.
Interval Timer: Clock mechanism that can be set to a given time interval and rings a bell or turns a switch at the end of it, such as a kitchen, PROCESS, TELEPHONE, Or PHOTOGRAPHIC TIMER.
Invar: Alloy of 35.6% nickel with the remainder steel, invented by GUILLAUME and named from 'invariable' as its expansion at different temperatures is negligible. Invar PENDULUM rods solve TEMPERATURE COMPENSATION problems. See Compensation Pendulum.
Inverted Escapement: Arrangement with the ANCHOR under the ESCAPE WHEEL instead of on top. The first OBSERVATORY CLOCKS by TOMPION has this; so have some earlier American clocks.
Iron Clock: First domestic clocks (in Italy, Germany, and France), early public clocks and watches too, were made of wrought iron because their makers-blacksmiths and locksmiths-worked in this metal. BRASS was introduced in the sixteenth century on the Continent for cases and dials and spread to England at the beginning of the seventeenth century although used in the fourteenth for DONDI'S CLOCK.
Isochronism: Occupying equal time. Used of a BALANCE or PENDULUM When the time of swing does not vary whatever the arc of swing. Almost impossible to achieve in practice (although some MARINE CHRONOMETERS approach it) thus resulting in POSITIONAL ERRORS in watches. See Circular Error, Galileo and Airy.
Italian Horological Industry: There is paper evidence of the world's first watches being made in Italy before 1488. Mantua was an important centre in the fifteenth century. The earliest ALARM clock in existence is also Italian, an interesting fact being that it is made of brass. The Italians eventually lost the lead to the French, Germans, and English. Clocks of many types including alarms and tower clocks and some watches are made today.
Italian Hours: Early Italian method of dividing EQUAL HOURS into one series numbered from 1 to 24, starting at every sunset. DONDI'S CLOCK employed this system.