I

Impulse :
That part of an escapement's cycle during which energy is transferred to the pendulum or balance from the escapement; also called 'lift'.

Impulse Clock :
First invented in the 19th century by Carl August Steinheil of Munich University as a means of indicating time on a number of clocks simultaneously from a central master clock fitted with electrical contacts which allowed pulses of current to flow in a circuit. The impulse clock does not itself keep time it uses the pulses to drive an escapement in reverse, which turns the hands of the clock through a normal train, used as a reduction train only. Steinheil used a pin-wheel escapement rocked by an electromagnet; Daniell cells from England provided the power. About the same time Alexander Bain independently devised several forms of impulse dial; he called his impulse dials 'companion' clocks or 'affiliated' clocks. Victor Reclus of Paris patented the first impulse dial which was locked at all times by two clicks; earlier impulse dials had the disadvantage of being inaccurate in operation by responding to intermittent pulses, or by the minute hand running on two or more spaces for one impulse only. W.E. Palmer, in 1902, and Frank Hope-Jones, later, improved impulse dials so they became completely reliable. George Bennet Bowell invented the first silent type, using a rotary iron armature moved by an electromagnet and locked by a permanent magnet system, first marketed c. 1906. Modern impulse dials differ only in the style of dial and case; the mechanism is virtually unchanged from the earlier ones.

Impulse Face :
The face on an escape-wheel tooth or pallet nib, shaped to give or receive impulse.

Impulse Pallet :
In clocks with escapements such as the chronometer escapement, where locking and impulse are separated, the pallet receiving impulse is called the 'impulse pallet'. The radially mounted stone in a chronometer escapement's impulse roller is termed the impulse pallet.

Impulse Pin :
The ruby pin cemented in the impulse roller mounted on the balance staff in a lever escapement.

Impulse Roller :
The steel disc mounted on the balance staff of a lever or chronometer escapement clock and carrying the impulse pin or impulse pallet.

Incense Clock, Chinese :
The most primitive incense clock is a graded incense (joss) stick; the time elapsed is registered by the speed at which the trail of incense is consumed. Powdered incense was formed into a stick of hardened paste and graded for hour intervals. There are three common types of post-16th century incense seals. All consist of a metal base, tray for the ash bed and powdered incense, perforated grid pattern (the seal), and perforated cover. The utensils include a tamper and a small shovel, stored in the base which insulates the burner. A bed of wood ash is put into the tray and tamped. The grid is placed on the ash and the sharp end of the shovel traces the path of the grid. Powdered incense is placed in the groove and smoothed. The grid is removed and small bamboo pegs, each stamped with an hour character, are placed at regular intervals along the incense track. The seal is then covered with the perforated lid to protect the incense from draughts, and the incense is ignited. The types are: the single seal, round, square or rectangular; the double square seal having two trays and two different seal grids stacked one on top of the other; and the Ju'i sceptre, in the shape of the ancient sacred mushroom. A rarer type is the dragon vessel, of bronze or lacquered wood, lined with pewter and fitted with V-shaped wire racks to hold an incense stick. Strings with metal weights at each end were suspended perpendicular to the body at regular intervals, or at one place only, depending on the specific use; when the heat from the burning incense ignited the string, the balls fell into a metal platter over which the dragon was suspended. The resulting clatter served as an alarm for the light sleeper.

Incense Clock, Japanese :
The Japanese, like the Chinese, used graded joss sticks as the basic method of incense timekeeping; the charge for a geisha's time was in terms of half-hour incense sticks. Incense seals in Japan were solid cubes of hardwood with the seal character carved into the top in a square groove to a depth and width of 1/4in. Powdered incense was placed in the groove and burned along it. The Ji Koban was essentially a large free-standing incense trail in a wooden container with time plates of various materials inserted at regular intervals to mark the hours. The Koban Dokei, in principle, was the same as the Chinese seals or the Ji Koban. A trail of incense was laid out on a bed of ash in a container; in this case the grid was a simple one that rotated a quarter turn, four times, so the seal formed was that for the 'heart of Buddha'. Small hour markers were laid out at intervals and timekeeping proceeded with the burning of the incense.

Inclined Plane Clock :
These clocks were mostly made in the 17th century. The movement was housed in a drum-shaped canister that rolled down a slope; rewinding was effected by placing the clock at the top of the slope again. Sometimes the edges of the slope were marked off in seven-day intervals so the position of the clock could also indicate the day of the week. The clock mechanism contained a heavy weight which, in association with wheel train and escapement, controlled the tendency of the clock to roll down the slope. The time was indicated by a fixed single hand, kept in equilibrium by the weight of the mechanism and the heavy weight working against each other. The idea appears to have been revived by a Dutchman named Isaac Jones Drielsma, working in Liverpool c. 1835, but his plans for producing the clocks in quantity were not fulfilled.

Index :
The lever, also termed 'regulator', which alters the effective length of the balance spring in a clock, allowing alterations in the rate to be made by the clock's owner. The best clocks are free sprung, no index being used, as the effectiveness of costly escapement adjustments is reduced by altering the effective length of the balance spring. Rate adjustments in free-sprung clocks may be made by alterations to the balance, using movable weights or screws.

Index Pins :
The curb pins, carried by the shorter end of the index, which embrace the outer turn of the balance spring, for making adjustments to its effective length.

Inro Clock :
Inro were small, rectangular lacquered wood or metal cases in which Japanese gentlemen carried their necessities, attached to the obi (sash) by a silken rope. Usually they had four compartments, but when a clock movement was put into one, the case was unsegmented. Inro clocks are small and might be classed as watches, but the design of the movement is similar to that of small Japanese clocks. The clock was usually the simple verge variety with a balance wheel and a revolving chapter ring. It was a self-contained unit that slipped in and out of the inro case, which usually had a compartment in the lid for the key.

Interval Timer :
There are two main forms of interval timers. The earlier was devised by Matthaus Hipp, Charles Wheatstone and others for measuring small intervals of time. A clockwork mechanism, controlled by a reed, is started and stopped electrically to measure a particular interval. Bashforth's chronograph of 1865 was used to measure the time of flight of projectiles; modern versions are electronically operated. The other form is a clockwork mechanism which, after a set period of time, sounds a bell or buzzer. It is popular for kitchen operations, telephone calls, car parking and so on. These timers may be incorporated in other equipment, e.g. in an electric oven for starting and stopping a period of cooking, and are also much used in industry for timing processes automatically.

Invar :
At the beginning of this century, Charles Edouard Guillaume, in the course of research into alloys suitable for standards of length, discovered that a steel alloy containing 36 percent of nickel possessed a practically zero coefficient of expansion, some samples even having a negative coefficient. Guillaume suggested the use of this alloy, which he called 'invar', for the pendulum rods in clocks.

Iron Clock :
The mechanism of the earliest clocks was of iron, forged in the case of turret clocks, cut cold with a file in the case of smaller clocks.

Iron-Front Clock :
A shelf clock with a front made of cast-iron.