Time Telling through the Ages

Dial, Sun – See Sun-dial (#Sun_Dial).

Dial Wheels – The wheels constituting the motion work of a watch.

Diurnal – In an astronomical sense, pertaining to a period covering a mean solar day. See: Solar Time (#Solar_Time).

Dog Screw – A screw with an eccentric head used to attach a watch movement to a dome case.

Dog-Watch – A nautical term for two daily two-hour periods of watching aboard ship. The first begins at 4 P. M., the other at 6 P. M.

Dolmen – A sacred instrument used for astronomical purposes at certain critical periods of the year; formed of four stones at the cardinal points and a leaning stone crossing diagonally and forming with the east stone a sacred "creep-way." The solar hours were indicated by the shadow of the leaning stone touching various prominent points or edges. One at Camp, England, is prehistoric.

Dome – The inner case of a watch which snaps on the band of a case.

Dome-Case – A case in which the inner case or dome snaps to the band of the case.

Dondi, Giacomo – Born at Padua, Italy, in 1298. In 1344 he set up at Padua a famous clock which became a model for later clocks and which earned for him the surname, "Orologio."

Double Bottom Case – A watch case in which the inner cover or bottom is made solid with the middle. The vogue in English cases for a long time; now almost obsolete.

Double-Sunk Dial – A dial in which there are two sinks; one for the hour hand, and a deeper one for the seconds hand.

Draw – 1. The force which holds the lever against its bank, due chiefly to the angle of the locking face of the pallet stone. 2. The angle of the locking faces of pallets in the lever escapement.

Driver – Of two wheels working together, the one which imparts the power. The driven wheel is termed the follower.

Driving Wheel – In a clock the wheel on the main arbor which drives the whole train.

Drop – That part of the motion of the escape wheel when it is not in contact with the pallet.

Drum – The cylinder, or barrel, on the main arbor in a clock on which the driving cord winds, raising the weight, when the clock is being wound.

Dummy Watch – (Fausse Montre.) About 1770 it became the fashion to wear two watches. But because two real watches were too expensive for most people, the custom grew up for having one sham watch – usually worn on the right side. These were called "dummy watches" or "fausse montres."

Earnshaw, Thomas – 1749-1829. An eminent English watchmaker who invented the spring detent escapement and the compensation balance, both essentially the same as are now used in chronometers. He first soldered brass and steel together for the balance instead of riveting them.

East, Edward – Watchmaker to Charles I and an eminent horologist. He was one of the ten original assistants named in the charter of the Clockmakers' Company and at once took a leading part in their proceedings. He was elected master in 1664 and 1682. He was the only treasurer ever appointed by that company. He died probably about 1693. East's watches were often presented as prizes by Charles in tennis tournaments.

Edward VI – King of England from 1546 to 1553. Said to have been the first Englishman to wear a watch.

Electric Clock – A clock in which the pallets moved electrically from a distant mechanism drive the escape wheel and the hands.

Ecliptic – That plane passing through the center of the sun in which lies the orbit of the earth. Also used to designate the apparent path of the sun in the heavens.

Elgin – A city in Illinois, U. S. A., in which is located the Elgin National Watch Company – one of the largest factories in the United States.

End-Shake – Freedom of pivots to move endways. Necessary in a watch or clock because there is no force to spare and a tight pivot would stop the movement.

End-Stone – A small disc of jewel against which the end of a pivot sets. See Capped Jewel (#Capped_Jewel).

End-Stop – In a watch the same as end-stone.

Engaging Friction – Friction which results when the teeth of two wheels gearing together come into action before reaching the line of centers – that is, a line drawn from center to center of the gearing wheels.

Engine-Turning – A pattern of curved lines cut into metal for decoration. Introduced about 1770 by Francis Guerint of Geneva. The earliest specimens were cut very deep but shallower cutting soon became the rule.

Engraving – A form of ornamenting metals in which the design is cut into the metal. In "Champ-leve" engraving the ground is cut away leaving the design in relief.

Epact – The excess in time of the solar year over the period of 12 lunar months, amounting to about 11 days. The new moons will thus fall about 11 days earlier in each succeeding year. In a calendar so arranged 30 days are taken off every fourth year, as an intercalary month, the moon having revolved once in that time, and the three days remaining would be the epact. The epact thus continues to vary until at the end of nineteen years the new moons return as at first.

Epicycloid – A curve generated by any point in the circumference of a circle as it rolls on the outside of the circumference of a fixed circle. This curve is the best for the face of the teeth of a driving wheel.

Equation Clocks – An obsolete form of clock which showed true solar or sun-dial time instead of mean solar, or average time.

Equation of Time – The difference between true time and mean, or averaged time. There are four days in the Gregorian year when the true time and mean time agree, and the equation of time is zero: These are December 24, April 15, June 15, and August 31. Between the first two dates and the last two dates, true time is earlier than mean time; for the other two periods of the year it is later.

Escape Cock – The bracket which supports the upper ends of the escape wheel and pallet staff arbors.

Escapement – The device in a watch or clock which regulates the motion of the train thus distributing the power of the main-spring. It communicates the motive power to the balance or pendulum. Escapements are of three classes: recoil, dead, or dead-beat; and detached.

Escapement, Anchor – The recoil escapement, invented by Hooke, used in most house clocks. A name also applied to one kind of Lever Escapement with an unusually wide impulse pin. The recoil escapement is one in which each tooth of the escape wheel, after it comes to rest, is moved backward by the pallets. Altho one of the easiest escapements to set out correctly the pallets are often improperly formed making an escapement which gives indifferent service. As a timekeeper the anchor escapement is inferior to the dead-beat escapement.

Escapement, Chronometer – A detached escapement in which the escape wheel is locked on a stone carried in a detent, and in which the teeth of the escape wheel impart an impulse to a pallet on the balance staff with every alternate vibration. Used in Marine Chronometers.

Escapement, Crown-Wheel – Of the recoil type, and the earliest known escapement; to be found in Henry de Wyck's clock. Not suitable for watches. Practically the same principle as Verge or Vertical Escapement used in watches for so many years.

Escapement, Cylinder or Horizontal – Invented by Thomas Tompion in 1695 – later improved and brought into general use by Graham. It dispensed with the then common vertical crown-wheel – hence the term "horizontal" and permitted thinner watches. This escapement is frictional, the balance being carried on a hollow cylinder whose bore is large enough to admit the teeth of the escape wheel. The cylinder is cut away where the teeth enter and the impulse is given by the wedge shaped teeth striking against the edge of the cylinder as they enter and leave. Used at this time in the cheaper Swiss watches.

Escapement, Dead-Beat – Any escapement in which the pallet face is so formed that the escape wheel remains dead or motionless during the supplementary arc of the balance or swing of the pendulum. As invented by George Graham, the wheel is much the same as the wheel in the anchor escapement, the difference lying in the shape of the pallets. Each pallet has a driving face and a sliding face. It is so arranged that the impulse is given the pendulum at the midpoint of its swing thus allowing the swing to adapt itself to the impulse and keep the time constant. The pallets are faced with jewels so that there is slight friction. Used in high grade clocks such as regulators and astronomical clocks.

Escapement, Detached – Any escapement in which the balance or pendulum is for some time during each vibration free from the pressure of the train. Detached escapements are used in chronometers, most watches and in turret clocks. They are of value in any movement where the motive power varies greatly – hence in turret clocks. Examples: Chronometer, lever, and gravity escapements.

Escapement, Double Three-Legged Gravity – Invented in 1854 by E. B. Denison, Esq., for the great clock at the Houses of Parliament. It is the best escapement for very large clocks where the hands are exposed to the action of the wind and snow, because it admits of great driving power in the movement without its sensibly affecting the escapement as would be the case in the dead-beat type. The impulse to the pendulum is given by the weight of the lever arms falling through a given distance and is therefore constant. This escapement consists of two gravity impulse pallets pivoted in a line with the bending point of the pendulum. There is a locking wheel made of two thin plates of three teeth each. Between these plates are the three pins that lift the pallets. The locking is effected by blocks screwed to the front of one pallet and the back of the other. Impulse is given by the pallets in turn striking the pendulum rod. The pendulum rod serves to unlock the wheel. The arrangement is such that the lifting pins have a little free run each time. Since the pallets are always lifted the same distance they give a constant impulse to the pendulum.

Escapement, Duplex – Invented by Hook; later improved by Tyrer. Very accurate but as originally made was affected by any sudden motion, and hence of little use in watches. The escape wheel has two sets of teeth. Those farthest from the center lock the wheel by pressing on a hollow ruby cylinder fitted round the balance staff and notched so as to permit the passing of the teeth as the balance moves in a direction opposite to the wheel's motion. The second set stand up from the face of the wheel and one gives impulse to the pallet every time a tooth leaves the notch. This is not a detached escapement, but there is little friction. As improved this escapement was used in the famous Waterbury watches.

Escapement, Foliot – A form of escapement actuated by a foliot balance. See Foliot (#Foliot).

Escapement, Four-Legged Gravity – Invented by E. B. Denison (Sir Edmund Beckett). The same in principle as the Double Three-Legged escapement, only it has but one escape wheel with four teeth or legs instead of two wheels with three legs each. The wheel has two sets of lifting pins – one acting on each pallet. Occasionally used in regulators and other clocks with a seconds pendulum, but of doubtful, if any, advantage over the Graham dead-beat escapement.

Escapement, Frictional – Any escapement in which the balance is never free from the escapement. Examples: The Cylinder, Duplex and Verge types.

Escapement, Gravity – An escapement which gives impulse to the pendulum by means of a weight falling through a constant distance. Of use in turret and other exposed clocks where the hands' movements are affected by wind, rain, and snow. See subtitles under these headings: Double Three-legged Gravity (#Double_Three_Legged_Gravity); Single Three-legged Gravity (#Single_Three_Legged_Gravity); Four-legged Gravity (#Four_Legged_Gravity); Six-legged Gravity (#Six_Legged_Gravity).

Escapement Lever – Invented by Thomas Mudge about 1765. It is the preferred escapement for watches because of the certainty of its performance. Possibly inferior to the chronometer escapement as a timekeeper. Its most noticeable defect is the necessity of applying oil to the pallets, the thickening of which affects the action. There are many other kinds of lever escapements. The Mudge escapement was essentially like the modern Double Roller. The connection between the balance and the escape wheel is made by a lever to which the pallets are fastened, and into the forked end of which plays the ruby pin which is carried on a roller on the same staff as the balance. Each pallet has an impulse face and a locking face. The impulse is given by the escape wheel tooth striking the impulse face of a pallet and is communicated to the balance by the lever, raised by the pallet's movement striking the ruby pin in the roller. This ruby pin also serves to unlock the pallets by causing the lever to lift them in turn. This escapement is of the detached type. The action of the lever is kept within the desired limits by banking pins.

Escapement, Lever – Club Tooth – An escapement like the Table Roller in the action of the lever and roller, but differs in the pallet action. The impulse planes are partly on the teeth and partly on the pallet. This is the standard watch escapement of today.

Escapement, Crank Lever – An escapement with a small roller having a tooth like a pinion leaf projecting from its circumference. This tooth acts in a square notch cut in the end of the lever. The lever is formed like a fork the two points of which act as safety pins against the edge of the roller to prevent the lever from getting out of action with the roller. It necessitated very careful construction and was not so good as the Double Roller or Table Roller.