R

Rack :
A number of gear teeth cut along a bar enabling rotary motion to be converted to linear motion. Also, in striking clocks, the arm cut with ratchet-shaped teeth which count the number of blows to be struck at the hour or quarter.

Rack Clock :
A clock which uses its own weight as motive power and gradually descends a toothed rack which meshes with the first wheel of the train. Winding is effected by pushing the clock to the top of the rack again. The type was popular in south Germany and Austria in the 18th century, especially in a miniature version with a cow tail pendulum which is now being reproduced in quantity. These clocks have the advantage that they rarely run down, because the unbalanced appearance of the movement when it has descended the rack a little way induces one to push it to the top again. A version of this clock was produced in 1919 with a double pendulum beating seconds and a special escapement based on the cylinder escapement used in watches. The advantage of this design was that the clock only fell a short distance and could be used for a mantelpiece or desk.

Rack Hook :
The arm acting as a click for the rack in rack striking clocks.

Rack Tail :
The lower extension of the rack which contacts the snail and determines the number of hours or quarters to be struck next.

Raingo Clock :
A type of orrery clock made by the firm of Raingo freres of Paris. The firm made the usual range of domestic clocks but in the decade 1820-30 became particularly well known for orrery clocks. These take the form of circular, four-pillared clocks of gilt or patinated bronze, the drum movement hanging between the front two pillars, the orrery surmounting the entablature. The case includes four figures representing the seasons. The orrery mechanism, which has its own spring, can be disengaged from that of the clock and rotated by a small handle to show the movements of the planets more quickly.

Ratchet :
A mechanism allowing rotation in one direction only. A ratchet wheel having teeth of saw-tooth shape engaged by a click is used to prevent a mainspring unwinding.

Rating Nut :
The knurled nut supporting the pendulum bob. To bring a losing clock to time, the pendulum bob is raised by rotating the rating nut clockwise. Conversely, to bring a gaining clock to time, the pendulum bob is lowered. Compound pendulums, such as those with the clock movement mounted above the suspension point and forming part of the oscillating structure, require the reverse procedure to bring them to time.

Reflecting Circle :
An elaborated form of the sextant used for measuring the large angles required in the determination of longitude by the method of lunar distances.

Regulator Clock :
Originally a term for any highly accurate clock.

Regulator, American :
About 1870 the term 'regulator' was employed by American clock manufacturers advertising spring-driven (without fusees) recoil escapement, non-temperature-compensating pendulum wall clocks. Frequently these had striking trains and supplementary dials for calendar mechanisms.

Reamer :
Reamers are similar tools to broaches though not made in such small sizes. They have a number of spiral or straight longitudinal flutes to form the cutting edges, and are made for either hand or machine use. The purpose of the reamer is to bring to exact size a hole purposely drilled under-size, or to taper a parallel hole to receive a tapered pin. Some reamers are partly split lengthwise and have an adjusting screw fitted down the center which is used to increase slightly, or decrease, the diameter of the reamer. Expanding reamers are also available, which have a number of cutting blades adjustable for size.

Red Stuff, or Rouge :
A refined red oxide of iron which is used for polishing gold, silver, brass and steel work. It is sold in various grades of fineness; the coarse, hard type, bluish-purple in color, is known as 'crocus'; the finest grade is scarlet and known as 'rouge'. A white preparation known as 'white rouge' can also be obtained.

Remontoire :
A device found in high-quality clocks, which winds an auxially spring or weight at regular short intervals to provide a more constant driving force for the escapement.

Remontoire, Turret-clock :
In most mechanical clocks the source of energy, the weight, drives the escapement through a large step-up gear ratio; thus the impulse the escapement gives to the pendulum at each swing is small. Any changes in friction in the pivots caused by the viscosity of the oil varying with temperature have an appreciable effect on impulse. An even greater effect in turret clocks comes from the action of wind and weather on the exposed hands. Variations in impulse cause changes in the pendulum arc and lead to erratic timekeeping. To overcome this, a device known as a 'remontoire' is sometimes adopted for providing a constant force at the escape wheel arbor. Essentially, it comprises a differential gear. The train proper is connected to the input of the gear through a detent, and the output of the gear drives the escape wheel arbor. The differential cage carries a wieght on the end of an arc, and when the train input is locked the weighted arm provides the torque for driving the escape wheel. When it has dropped through a small arc it unlatches the train detent, the train runs and lifts the arm to its upper position and relocks the train. In this way the torque at the escape wheel and the impulse to the pendulum stay constant. The weighted arm continues to provide the same driving torque during the rewind. Other types of remontoire exist. Christiaan Huygens developed one using his endless-chain principle. In some, two local energy stores are provided so that one is rewinding while the other drives the escapement; they change from rewind to drive at regular intervals. Most turret clocks use weight-driven remontoires, although spring types are known. Taken to its logical conclusion, the remontoire can be fitted to provide a constant store of energy for impulsing the pendulum directly. This arrangement manifests itself in the gravity escapement. Some clocks have a remontoire and a gravity escapement, which is clearly absurd; one or the other is adequate.

Renaissance Clock :
The name now normally given to clocks made from c. 1500 to c. 1650, when regional styles of clockmaking began to evolve in Europe. The style was international in character, most of the clocks of the period being made to similar designs in Italy, south Germany and France, with some English examples later in the period. It has also been called 'the age of decoration', for in general the gilded-brass cases of either spring- or weight-driven clocks were lavishly decorated with engraved, cast and chased ornament, in a style derived from classical prototypes. The introduction of the pendulum c. 1657 suggests a suitable date to mark the end of this period of clockmaking, the date at which accuracy of timekeeping gradually began to assume more importance than splendour of casework.

Repeating Work :
Before the introduction of the match, the difficulty in obtaining a light at night to see the time made it desirable to have clocks capable of striking the time at will by the operation of a lever or by pulling a cord. In the simplest form of trip repeat mechanism, a lever is arranged to lift the rack hook, allowing the clock to strike the previous hour. In clocks with full repeating action, an additional train of wheels is used to control the speed of the hammer blows. It is similar to an ordinary striking train, and is driven by an additional spring wound by operating the repeating action, which allows the clock to be repeated as often as desired. The repeating mainspring, not visible, is mounted on the inner end of the arbor. On pulling the cord, the arbor rotates, winding the mainspring and moving the segment via the pinion until the segment contacts the snail and prevents further winding. The arbor carries a wheel between the plates fitted with twelve lifting pins on one side for the hours; the number of pins which pass the hour hammer tail on pulling the repeating cord is controlled by the snail. When the repeating cord is released, the mainspring drives the repeating train, delivering a blow for each pin which passes the hammer tail. An arm controls the final resting position of the repeating train. The right-hand end of the arm passes between one pair of pins. The position of the arm is controlled by a quarter-snail. The hammer-lifting wheel carries, in addition to the hour-lifting pins, three longer lifting pins which lift both the hour hammer and an additional hammer striking on a higher-toned bell. If the clock is repeated during the first quarter after an hour, the previous hour is struck and the mechanism is stopped by the arm before any of the quarter-lifting pins can act. When the mechanism is operated during the second quarter, the tip of the arm passes between the innermost pair of pins, allowing the arbor to rotate a little more than in the first quarter, which in turn allows one of the quarter-lifting pins to operate both hammers, thereby indicating the time by a ting-tang double blow. The action for the remaining two quarters is similar, with an additional ting-tang for each. Clock repeating mechanisms have never achieved the standardization found in striking and going trains. Many repeating clocks have additional bells and play a short musical phrase or each quarter. Repeating clocks were first made towards the end of the 17th century. By the 19th century, clocks were rarely fitted with full repeating mechanism.

Restoring :
To restore a clock is to make it as nearly as possible as it was when it was first made, bearing in mind that its case, movement and dial will inevitably carry evidence of use which it is not necessarily desirable to remove or disguise. There is considerable difference of opinion on this matter, which involves both ethics and aesthetics; for example, in the restoration of an engraved brass dial. Some people prefer to see the dial looking dull and old, probably scratched and with the silvering gone. Others wish to have the dial filled with new wax in the engraving and the chapter ring resilvered as new, as the maker originally intended. It is a matter of taste when restoring a clock to ensure that it does not look too new yet regains its original dignity and quality.

Rete :
The rotatable circular star map of an astrolabe, in the form of a network of pierced and engraved metal.

Reverse Painting :
A picture or design often used on a clock tablet and painted on the back side of a glass in reverse order of a normal painting.

Revolutionary Clock :
In 1793 the introduction in France of what revolutionaries regarded as rational time measurement, on a decimal base, prompted the production of decimal clocks. Revolutionary fervour was otherwise shown on casework by studied use of revolutionary symbols such as the Phrygian bonnet or the tricolor in place of such royalist motifs as the fleur-de-lys, or by including figures emblematic of liberty, plenty or equality. The rise of Napoleon soon brought a quite different range of motifs and symbols into fashion.

Revolving-band Clock :
A clock on which time is shown by numbered bands revolving past a fixed marker. The idea possibly developed from early Gothic moving-dial clocks which similarly had a fixed pointer, and was first used on globe clocks of the 16th century. In the 18th century, the revolving-band idea became popular, particularly in France where opportunities for elaborate casework were fully exploited. Double bands appeared, giving minute readings as well as hours, and pointers in the form of snakes or lizards, or encrusted with stones, were popular. The revolving bands were ideal in conjunction with vase clocks, but other forms also appeared. The bands might run around the top of a classical ruined pillar, and a clock in the Wallace Collection, London, incorporates hour and minute bands around the edge of a circular table in a sculptural composition of the Toilet of Venus. The band system of showing time continued during the 19th century. In its concentration on numbering and disregard for the traditional visual indication of time on the dial, it was a predecessor of ticket and later digital clocks.

Riefler Clock :
Sigmund Riefler of Munich became the most famous maker of regulator clocks for observatory use, continually striving for perfection of timekeeping. He invented a mercury-in-steel pendulum with mercury almost filling a hollow pendulum rod to avoid temperature differential effects, patented in 1891 but surpassed when Charles Edouard Guillaume invented the alloy invar in 1895. In 1889 Riefler improved his regulators by an escapement which impulsed the pendulum through its suspension spring, making the pendulum virtually 'free' and giving a performance with a daily variation of less than 0.01 second under good conditions. Riefler's final development was to adopt electrical rewinding and place the pendulum and mechanism in an evacuated cylinder to isolate the clock from atmospheric disturbances, making his regulator the standard timekeeper for most of the world's observatories. Riefler's clock represents the final phase of the development of the purely mechanical regulator.

Right Ascension :
The angle between the plane containing any celestial body and passing through the poles, and a similar plane passing through the point of the spring equinox, measured in an easterly direction when looking south from the Earth's surface. It may be expressed in degrees, 0 to 360, or in hours, with minutes and seconds of time, 0 to 24. The Right Ascensions of fixed stars remain constant, apart from any very small proper motion a particular star may have and the small steady drift due to the precession of the equinoxes.

Riveting :
In clockmaking certain parts such as metal plates are sometimes fastened together with rivets, which are pins or pegs generally of the same metal as the parts being joined, with a head of suitable shape. The rivet is passed through corresponding holes in the parts to be joined and hammered or punched to spread the metal out, or to 'rivet' it. By the same method pillars are often riveted to the pillar plate of a clock and finished in such a way that the riveted area hardly shows. Riveting is frequently used for securing arbors, pinions and collets to wheels and for joining levers to arbors, all these operations depending on the burring over of one part to secure the other. To rivet a wheel directly to an arbor the arbor is formed with three diameters. This provides a seat or shoulder to support the wheel and a flange which can be spread at the other side of the wheel.

Riveting Stake :
A block of hardened steel with a polished surface, pierced with a number of different-sized holes to receive arbors, in order that a pinion or staff can be supported while it is being riveted to a wheel. Alternatively, in the form known as riveting tongs, the stake is jointed and can be opened to admit the part required and closed to grip it, supporting the part to be riveted. Riveting stakes are made to be used in a bench vice, or on a block or solid part of a bench.

Rocking Ship :
One of several variations of simple automata used to fill the arch space on the dials of some late 18th-century longcase clocks. The painted cut-out shape of a sailing ship is attached to the arbor of the anchor escapement, and as the pendulum vibrates the ship rocks from side to side.

Rococo :
The decorative style which succeeded baroque during the first half of the 18th century. Compared with the monumental symmetry of baroque ornament, the asymmetrical shapes of rococo are lighter, more feminine and often entertaining. The term 'rococo' is said to be a corruption of the French words rocaille and cocaille which refer to the picturesque formations of rocks and shell patterns frequently forming part of rococo ornament. This style was most popular during the reign of Louis XV. Its arrival in Britain coincided and merged with the Gothic Revival and the often whimsical patterns of Chinoiserie. The rococo style had only a marginal effect on clock decoration. It revealed itself mostly in the flower and shell designs and C scrolls of 18th-century brass spandrel mounts on clock dials, and in the engraving of little landscapes on dial centers and on the backplates of bracket clocks.

Roller :
In the lever escapement, the cylindrical metal piece mounted on the balance staff and carrying the impulse pin; it also performs the safety action. In English work, the single table roller with passing crescent formed in the rim is the most common type, whereas in European and American work a double roller is most often used.

Roller, Anti-friction :
A type of bearing in which two or more rollers are used to carry a pivot. Anti-friction rollers used in clocks take the form of pivoted wheels without teeth, arranged in different planes with the circumferences intersecting to leave an aperture of the pivot's diameter. The pivot friction is reduced by the leverage which the roller radius provides over the roller pivot friction. The provision of anti-friction roller bearings indicates work of the highest quality.

Rolling-ball Clock :
The principle of the rolling-ball clock was defined by Galileo: a ball rolling down a constant slope takes the same time to cover the same distance at any part of the slope. This principle was first put to practical use by Christof Margraf of Vienna in 1597, and in the early 17th century other makers such as Hans Schlotheim and Johann Sayller followed suit. John Evelyn described such a clock, which had been presented to Charles I and was later in the possession of Cromwell. This clock had a crystal ball, but the usual practice was to use a steel one. The idea was superceded by the invention of the pendulum clock, but it was revived in the early 19th century by William Congreve.

Roman Numerals :
Roman letters used as numerals on clock dials, such as I, II, III, IV, etc. On older clocks, four was often represented by IIII, an old Roman numeral for IV. It is said that this form better balances the VIII on the other side of the dial.

Roman Pendulum Clock :
An 18th-century bracket or shelf clock, made almost throughout the century, recognized from the shape of its case and the bronze ornament. The case usually incorporated mirrors, or else was made of ebonized wood, lavishly decorated with fine carving, pilasters, cornices, etc., and adorned with gilded-bronze finials, fillets and borders. The movement generally included striking for the hours (six) and for the quarters, and often an alarm was fitted. The most famous makers of this type of clock were Angelo Passeri, Domenico Crudeli, Agostino Amonier, Gio Batta Villacroce, Pellegrino Amorotti, Gio Batta Vesperiani and Agostino Ajmunier.

Rotten Stone :
A natural friable stone, resulting from the decomposition of a siliceous limestone, which is a powerful abrasive. It is obtained either in crushed form, when it is mixed with oil to form a polishing paste, or in composition blocks, which may be wiped over with oil to obtain a cleaning medium for metal parts. Rotten stone imparts a dull polish to brass and steel and can be mixed with rouge and oil to give a bright polish.

Round Gothic Clock :
The earliest form of American Gothic case design was conceived by Elias Ingraham at Bristol, Connecticut, c. 1840. Subsequently copied and made in large quantities by other firms, it was usually constructed with a mahogany veneer applied to a glued pine frame. J. C. Brown at his Forestville Manufacturing Co. made a limited number, c. 1848-52, in artistically cut fronts, known today as 'rippled fronts'. About 1880 a design patent was issued for an ogee-moulded base, and at this date the E. N. Welch Manufacturing Co. offered this with a single glass door through which a simulated mercury pendulum was visible. This style in both a full rounded top and Gothic form was continued until c. 1890. The earlier form of Gothic rounded arch is referred to among present-day collectors as 'beehive' because of its similarity to the old straw beehives.

Rounding-up Tool :
An ingenious tool or engine for re-cutting or re-shaping wheel teeth. It is also sometimes called a 'topping tool', and with it a wheel can be reduced in diameter or corrected if not perfectly round, or have its teeth re-formed. The wheel which is to be 'topped' is mounted in the tool between centers where it is free to revolve, the cutters being formed in such a way that as each tooth is topped the wheel is automatically turned to bring the next tooth into position. The cutters are discs with cutting serrations on about half the circumference, and the disc is radially split so that its edge forms a shallow screw. The leading edge of the cutter thus picks up a new wheel tooth to be topped at each revolution. A topping tool is used on wheels which have been cut in the wheel-cutting engine, to cut the correct profiles to the teeth.

Rudd's Clock :
A free-pendulum clock made by R. J. Rudd of Croydon, now in the Science Museum, London. A large heavy bob is suspended freely above a fusee clock movement having a small pendulum, used as a slave clock. Every two minutes a constant-force impulse is given to the free pendulum at the center point of its swing by an arm driven by the slave-clock movement, and as the arm leaves the free pendulum it synchronizes the slave clock and simultaneouly adjusts the rate of the slave pendulum, if necessary. Rudd described his invention in the Horological Journal of August 1898 and July 1899, but it was ignored by the rest of the horological world. Rudd's clock did not incorporate the first free pendulum, as is commonly stated; this was achieved by Sir William Thompson in the 1860s with his centrifugal regulator clock.