Clocks And Watches, instruments for measuring time. In early ages any device for this purpose received the general name of horolo-gium (Gr. hour-teller), whether it was a sun dial, clepsydra, sand glass, or clock. As late as the reign of James I. of England, clocks were often called horologues. Until the 14th century the word clock was applied only to the bell (A. S. clucga, Ger. Glocke) upon which the hour, determined by the horologe, was rung. Even at the present day the clock of Wells cathedral is called the horologe. The most ancient of all instruments for ascertaining the time of the day was probably the sun dial, although for measuring intervals or stated periods of time water vessels, called clepsydras, may have been of contemporary use. It is commonly believed that the first form of sun dial was simply a column which cast a shadow of varying length and position. The earliest mention in history of a sun dial is in 2 Kings xx. 11: "And Isaiah the prophet cried unto the Lord: and he brought the shadow ten degrees backward, by which it had gone down in the dial of Ahaz." As, however, the invention of the sun dial has been attributed to Anaxi-mander, about 200 years later, there is some doubt as to the meaning of the word which has been translated dial, for in the same passage the word degrees has the same derivation.
But the instrument referred to could hardly mean anything else than a sun dial of some form, as otherwise the passage would have no signification. At Rome, the first sun dial is said to have been erected by L. Papirius Cursor, 292 B. C. Another was placed near the rostra about 30 years after by the consul M. Valerius Messala. who brought it from Sicily during the first Punic war. The first form of horologe which measured time by mechanical means was the clepsydra or water clock, but the date of its introduction cannot be traced. It is believed that it was used before the sun dial in China, Chaldea, and Egypt. (See Clepsydra.) Sand glasses took the place of clepsydras in the early part of the Christian era. but the date of their earliest use is uncertain. The candle clock of Alfred the Great, and its conversion into a lantern by means of a translucent horn cover, by which he divided the day into three equal portions, one of which he devoted to religion, one to public affairs, and the third to rest and recreation, is familiar to most readers.
The time of the introduction of wheel clocks moved by weights cannot be fixed with any more certainty than that of clepsydra-. From the time of Archimedes, 220 B. C. to that of Robert Wallingford, abbot of St. Albans, in 132G, many ingenious men have been credited with the invention. ToBoethius (A. D. 510) has been accorded the honor, notwithstanding that it has been disputed whether it was a water or a wheel and weight clock which Pacificus of Verona, who lived nearly four centuries later, constructed, on the ground that the date was too early for such an invention. As. however. Gerbert, who became pope as Sylvester II., did undoubtedlv construct a wheel and weight clock at Magdeburg in 996, when he was archbishop, the belief that Pacificus might also have made one a little more than a century earlier is not unreasonable. But. however much the earlier history of clocks may be involved in doubt, it is certain that clocks driven by weights were in use in the monasteries of Europe in the 11th century. The Catholic clergy are credited with the introduction of clocks into England. They possessed much wealth, and had leisure to cultivate many of the arts, and were probably led to the cultivation of horology from the desirableness of having some means of regulating their religious services.
The first Westminster clock is said to have been erected from the proceeds of a fine which was imposed upon a chief justice of the king's bench about 1290. , The Exeter cathedral clock, the striking part of which is said to be still in use, was constructed before 1317, and one was made by Wallingford in 1326. The cathedral clocks of Wells, Canterbury, and Peterborough were also made about that time. The first clock on record which approached in accuracy of movement the clocks of the present time was constructed for Charles V. of France by Henry Vick, in 1370. In fig. 1, representing this clock, the weight is suspended by a cord wound round the barrel b, which carries a ratchet d. This ratchet, acting upon the great wheel c in one direction, will cause it to be driven by the weight. The great wheel c drives the pinion e, upon whose arbor or shaft is placed the wheel /. This again drives the pinion i, upon whose arbor is placed the crown wheel j, which in this clock forms the scape wheel, the action and office of which in the regulation of time will be described further on.
This scape wheel, constantly moving in one direction, gives an impulse to the pallets or levers I I, whenever they are brought within the range of its teeth; and this they are made to do by the backward and forward vibrations of the weighted balance m m, suspended by the cord n. These vibrations, caused by the action of the teeth in the scape wheel upon the pallets, being isochronous, or nearly so, divide the time of the successive escaping of the teeth of the crown wheel into equal parts. This balance was indeed a rudimentary balance wheel; a rim added, making it the diameter of a circle, and a hair spring in place of the cord, would have made it one. The turning of the single hand once around in 12 hours was accomplished by having the arbor of the barrel pass through the front plate p. A pinion upon this arbor, which turns once in an hour, pitches into the large wheel o, which has 12 times as many teeth as the pinion has leaves, and which will therefore revolve once in 12 hours. The appliance for winding consists of the pinion h at the lower part of the clock, which is made to turn the wheel g by means of an arbor which passes through the face of the clock, and which is squared to fit a key.
The contrivance for regulating the motion of the last wheel is called the escapement, and the wheel is called the scape wheel, whether of the modern form or the old-fashioned crown wheel of Vick, used for nearly three centuries after in clocks, and for a much longer time in watches. It is the most essential part of the timepiece; and upon its adjustment, after the application of the pendulum, nearly all the study relating to the subject of horology has been expended. It is called the escapement, because each tooth of the scape wheel is allowed to escape from certain arms of the pendulum called pallets, after having been arrested during a period of time. But the performance of this clock must have been quite imperfect, although it was a marvel of mechanism in its day. It needed an escapement capable of making a more accurate division of time. It was impossible at that time, although it has since been accomplished, to cause the balance to oscillate in exactly equal spaces of time. The first instrument used for this purpose was the pendulum, which it can scarcely be doubted was employed in the early-ages to measure small periods of time by simply counting its vibrations, without connecting it with mechanism.
It is said that the ancient astronomers measured the duration of eclipses with it, but there is no recorded proof of its use before the discovery of Galileo at Florence in 1582, by observations upon a swinging chandelier, that a pendulum vibrated in arcs of different lengths in the same time, if the arcs were small. It has been said that a pendulum clock was made for St. Paul's church in Covent Garden by Harris, a London clockmaker, in 1(342; but this must be an error, or the controversy could never have taken place between Dr. Hooke and Huygens, who is now universally admitted to have been the first not only to apply the pendulum to clocks, but to demonstrate the mathematical principles involved. A pendulum which oscillates in an arc of less than 10° may have that arc diminished without sensibly affecting the time; but when it moves through larger arcs the time will be sensibly increased, although not in proportion to the increase of the arc. It was demonstrated by Huygens that if the oscillations were made in the curve of a cycloid, they would occupy the same time whether the arcs were small or large.
A simple pendulum may be defined to be a particle of matter suspended by a right line devoid of weight, and oscillating by the force of gravity about a fixed point, called the point of suspension. It follows, therefore, that a truly simple pendulum can only exist in the imagination. The nearest approach to it is a lens-shaped bob, made of the densest matter, as platinum, suspended by a fine steel wire. But it is evident that the particles of matter in the bob which are nearest the point of suspension will tend to oscillate oftener than those at a greater distance, and therefore to accelerate the motion, while those which are furthest will tend to retard it. There will therefore be a certain distance from the point of suspension which will divide those particles which are moving slower than natural from those which are moving faster, which may be designated the centre of oscillation of the system. If all the matter in the pendulum could be collected in this point, the time of vibration would not be changed. The length of a pendulum is understood to be the distance between the point of suspension and the centre of oscillation. The centre of oscillation is generally below the centre of gravity, and within the pendulum; but it may be entirely beyond it, as in the metronome.
The length of a pendulum which oscillates in a given time may be ascertained from the laws of falling bodies. If it moves in a small circular arc, the time of one oscillation is to the time a body occupies in falling freely half the length of a pendulum as the circumference of a circle is to its diameter. It having been demonstrated that the spaces through which a body falls by the force of gravity are in proportion to the square of the time occupied in falling, therefore the time will be equal to the ratio of the circumference of a circle to its diameter (which is 3.14159) multiplied into the square root of the quotient arising from dividing the length of the pendulum by twice the distance through which a body will tall in one second, which in the latitude of Washington is about 16.08 ft. Thus:
Fig. 1. - Vick's Clock.
Time = 3.14159 x from which all calculations as to the number of wheels in the train, the distance through which the weight should descend, etc, may be made. From the above equation, by a very simple algebraic process, the following is derived: Length = square of time x 32.16 ÷ 3.141593; therefore the length of a pendulum is in proportion to the square of its time of oscillation. The length of a pendulum which oscillates in one second in the latitude of Washington will be found by the following equation: L=l2 x 32.16 ft.÷3.141592=39.l in. If the pendulum is required to oscillate once in two seconds, it must be four times the length of a seconds pendulum, because the square of twice the time=4. As it is necessary in a good clock to have the pendulum always of the same length, a difficulty was encountered on account of expansion and contraction from heat and cold. This was obviated by using in its construction two different materials having different degrees of expansion. Such pendulums are called compensation pendulums, and are principally of two kinds, called mercurial and gridiron.
The bob of the mercurial pendulum is made of a hollow cylinder of glass or iron containing mercury, whose expansion tends to shorten the distance of the centre of oscillation, while the expansion of the rod tends to lengthen it. The gridiron pendulum is usually constructed of iron and brass, whose unequal contractions cause the bob to remain during varying degrees of temperature at the same distance from the point of suspension. - The clock constructed by Huygens is represented in fig. 2. The train of wheels resembles that in Vick's clock, with the exception of having two crown wheels, with different-shaped teeth, and a train of wheels behind the dial and in front of the plate for the purpose of turning both hour and minute hands around a common centre. This train of wheels for moving the hands has precisely the same disposition as that now in use for clocks and watches, which is represented in fig". 1G. The fork n, moved by the pendulum p, takes the place of the balance in Vick's clock, and by its more isochronous vibrations produces a more accurate escapement. The pallets I I, carried by the verge, act upon the crown scape wheel k, in a similar manner as in Vick's cluck. The arbor of the wheel g passes through the front plate, and carries a disk upon which there are (SO divisions.
As this wheel turns around once in a minute, each division marks a second, and an index placed upon the dial, at the edge of an opening in it, measures the divisions as they pass. A seconds hand could have been placed upon the arbor in place of the disk, and caused to turn in front of a graduated circle in the manner now employed. The verge and crown wheel escapement which Huygens employed made it necessary to use short pallets, in order to prevent too much recoil, and consequently the use of a short pendulum vibrating in a large arc. Thus there was the unavoidable introduction of more or less error, which he sought to correct by the use of cycloidal cheeks against which a flexible pendulum was made to swing, and thus to carry the bob through a cycloidal curve. But although the theory was an illustration of Huygens's genius, it was found not to be applicable in practice, and the solution of the difficulty was more easily found by making the pendulum longer and the bob heavier, and causing it to swing in a smaller arc.
The application of an escapement by which the pendulum was only required to oscillate in a small arc was accomplished by Dr. Hooke, an English contemporary of Huygens, by means of a pair of anchor-shaped pallets moving in the plane of a spur wheel having ratchet teeth, instead of using a crown wheel. This escapement produces a recoil, and is usually called the recoil escapement. It is shown in fig. 3. When the pendulum swings to the left it lilts the pallet a from the upper face of the tooth t, which has now passed by, while the pallet b has also moved to the left, meeting the tooth t', and by the momentum of the pendulum producing a recoil till it returns and allows the tooth to move on, giving at the same time the pallet an impulse, the pendulum swinging to the left until the pallet a is brought within reach of the tooth c, which strikes it before the pendulum has attained the limit of its vibration, thus producing another recoil of the scape wheel, which lasts till the pendulum begins to return and lift the pallet away. The impulse faces of the pallets are convex; theoretically they should be concave, but on account of friction the convex form has been found to answer the purpose better.
This recoil or anchor-pallet escapement was succeeded by what is called the dead-beat escapement, invented by Graham about 1720, and which is the one now in general use for clocks, and with but little modification for watches. It is represented in fig. 4. When the pendulum swings to the right the tooth a escapes from the pallet &, while the tooth c is brought against the pallet d; but a portion of the exterior surface of this pallet, and also the interior surface of b, are arcs drawn from the centre d; and upon being struck by the teeth of the scape wheel in the direction of d no recoil is produced, neither is there any impulse given to the pallet until the pendulum swings far enough to the left to bring the tooth upon its impulse face. When the pendulum attains the limit of its vibration to the left, the same dead beat is made upon the circular inner face of the pallet b, to be followed by an impulse upon the impulse face when the pendulum has again returned far enough to the right. For the purpose of avoiding friction, and for other reasons of which the limits of this article exclude a statement, it has been found that the teeth should be made to fall upon the dead face of a pallet as near to the angle which divides it from the impulse face as possible.
There is a tendency in the dead-beat escapement to gain time as the arc of vibration of the pendulum decreases, whereas the tendency in the recoil escapement is to lose. The further the pallets are from the centre of motion, the greater will be the distance traversed over them by the teeth, and consequently the greater the friction; therefore the best clock makers place them as near the centre of motion as circumstances will allow, the usual practice being to have them describe an arc whose radius is equal to that of the scape wheel, and to have the dead faces embrace 10 1/2 teeth, or one half tooth over one third the number in the wheel. There is one other form of escapement, often used in turret clocks, called the pin-wheel escapement, shown in fig. 5. The invention is ascribed to Lepaute of Paris in 1755. The form usually described has the pallets placed on opposite sides of the scape wheel; but that is unnecessary, and the construction represented in the figure exhibits the plan better. In the relative position of the pallets and pendulum the action of the pins is downward on both pallets, which have the impulse faces cut to nearly the same angle, the one on the shorter and outside arm being rather the more oblique when they are to receive the pins on a level with the axis of the scape wheel.
It will be observed that the pallets may be made to receive the pins'at any part of the revolution of the wheel by changing their position with the pendulum; and it is also evident that the form of the pins and pallets may be such as to either produce a recoil of the scape wheel or a dead beat. Another kind are called gravity escapements, because the impulse is not given to the pallets directly by the action of the train weight, but by another weight or spring which is caused to act for a sufficient space of time at every beat of the pendulum. There are several forms of gravity escapements, asMudge's, Cumming's, Hardy's, Kater's, Bloxam's, and others. - In order that a timepiece may be kept running, there must be a contrivance for winding up the weight or spring. As it is evident that this must be done without reversing the motion of the train, there has to be provided an arrangement for turning the barrel backward without turning the great wheel. This is effected by means of a ratchet wheel, which is prevented by a click from moving on the great wheel in the direction of the going of the train, but is free to move in the contrary direction.
Without some further contrivance, however, than what is necessary to prevent the great wheel from being turned back, the clock would soon stop, because the propelling power is taken away during the winding. Such a contrivance is called a maintaining power or going barrel, the principal form of which in present use is Harrison's maintaining spring and ratchet, or going barrel. The oldest of all is Huyghens's endless chain shown in fig. 6, which is so contrived as not to take the weight off the barrel during the winding. By pulling down the small weight the large weight is raised without taking the tension of the cord off from the going wheel at all. The pulley may be placed upon the arbor of the great wheel of the striking part, which must then be attached to it by a ratchet and click. Harrison's going barrel is represented in the train of wheels in a clock shown in fig. 7. The weight moves the great wheel c through the spring' d; but during winding the smaller ratchet is turned to the right, taking off the weight, while the spring, acting against the larger ratchet, impels the great wheel a sufficient time to keep it going, and thereby to maintain the motion of the scape wheel and the impulse of its teeth against the pallets.
Common clocks, many of them keeping good time, are now made to be driven by a main spring instead of a weight, in the manner of a watch. Being portable, and occupying less space, they are more convenient and cheaper; but the best clocks, used for regulators, are driven by weights. - It will now be proper to describe the train of wheels and principal parts of a clock. The train comprises those wheels through which the motive power, the weight or spring, exerts its force upon the pallets connected with the pendulum. These wheels are made to act upon each other by means of pinions, which are a kind of small cog wheels. The cogs on the wheels proper are called teeth, while those of the pinions are called leaves. The axis upon which a wheel or pinion turns is called the arbor. The train of wheels in a good modern eight-day clock generally consists of four. In fig. V, a is the first or great wheel, upon whose arbor is the barrel over which the cord passes to which is suspended the weight. The second or centre wheel, b, whose pinion c is driven by the great wheel, always turns round once in an hour, and is therefore made to turn the minute hand. It drives the pinion e of the third wheel d, which again drives the pinion of the scape wheel f.
This last is the fastest-going wheel in the train, and is the one that acts upon the pallets connected with the pendulum. The usual number of teeth in the scape wheel is 30, and if the pendulum is 39.1 inches in length, it will revolve once in a minute, because one tooth will escape at every double vibration (sometimes called a complete vibration), or every two seconds. If the pinion has 7 leaves, and the third wheel, which drives it, has 56 teeth, the latter will revolve once in 8 minutes; and if its pinion has 8 leaves, each leaf will pass a certain point every minute; and therefore, if the centre wheel has 60 teeth, it will revolve once in an hour. If the pinion of the centre wheel has 8 leaves, and there are 96 teeth in the great wheel, the latter will turn round once in 12 hours. This arrangement formerly existed in clocks before the use of the minute hand, but since then wheels separate from the train have been used to move the hands at the proper rate. In the engraving a back view of the wheels is given, not placed in relation to each other just as they are when in actual use, but every wheel, following in order from below upward, placed behind its predecessor, for the purpose of showing the pinions.
The wheels may be arranged in this way, but they are generally placed alternately in front of and behind each other, for economy of space. The second wheel, as has been stated, moves the minute hand. The pinion by which the great wheel drives it is called the centre pinion. This is on the back side of the wheel, but it carries another pinion in front, called the cannon pinion, which is placed on the arbor so that it may be turned by using a certain amount of force, an operation which is required in setting. It is upon a tubular barrel of this cannon pinion that the minute hand is placed. The cannon pinion has a certain number of leaves, which play into a wheel having, we will say, four times as many teeth, which latter has a pinion with a certain number of leaves which again play into another wheel having three times as many teeth. This wheel, called the hour wheel, will then turn round once in 12 hours, and upon its barrel, which is placed over the cannon pinion, the hour hand is fixed. The time during which a clock can be made to run from one winding to another, measured by the number of times the scape wheel can be made to revolve, depends upon the number of teeth in the train of wheels, the distance through which the weight falls, and the length of the pendulum.
The number of teeth may be regulated by the number of wheels in the train, or by the number of teeth in each wheel and pinion. If the weight falls through a small space, the number of teeth must be increased, and this is usually done by increasing the number of wheels, which again requires the gravity of the weight to be increased. The number of teeth in the train remaining the same, the duration of running may be increased by increasing the distance through which the weight falls. - About the year 1840 Prof. Wheatstone exhibited to the royal society of London a clock dial, the hands of which were moved by a wheel acted upon by a small electro-magnet at intervals, the current being formed and broken by means of the oscillations of the pendulum of a common clock. Through this device the same time may be indicated in several distant places simultaneously. In 1848 successful experiments were made upon this principle by the United States coast survey between Cincinnati and Pittsburgh, a distance of 400 miles. A clock placed in the electric circuit recorded its beats at all the offices along the line by means of Morse's apparatus.
The first clock, however, which had any of its own parts moved by electricity, was constructed by Alexander Bain of Edinburgh. In this electricity was used as a motive power in place of the usual weight or spring, and the pendulum was not only employed as a regulator, but as a motor. The bob of the pendulum was formed of a coil of wire which became a magnet at intervals of the oscillations, and, passing over the poles of permanent magnets placed near the ends of the arc of oscillation, was alternately attracted by each. In some of the clocks the two magnets were temporary, and the reversal of their poles by one of the devices used in electrical apparatus caused an alternate attraction and repulsion of the pendulum. Mr. Shepherd exhibited at the international exhibition in London of 1851 a clock in which there was an electrical gravity escapement, the pallets being raised by temporary magnets. A description of it may be found in Wood's "Curiosities of Clocks and Watches," and also in Mr. Denison's treatise. - Watches. The first watches must have been very imperfect timekeepers, as they were not supplied with that necessary piece of apparatus which answers the place of the pendulum in clocks, viz., the balance and balance spring, and the escapement consisted only of a verge and a crown wheel, of a similar form to that used in the verge escapement clocks.
The train of wheels was moved, like that in the modern watch, by a main spring, which is a coil of ribbon-shaped, finely tempered steel, placed around the arbor of the going barrel, having one end attached to the arbor and the other to the inside of the barrel. The train of wheels in a watch is much the same as in a clock, and indeed a watch may be considered as a small clock, in which the weight and pendulum are replaced by the main spring and the balance, which latter part is composed of the balance wheel and balance or hair spring. The devices for regulating the motion of the scape wheel by means of a lever armed with two pallets, against which the teeth of the wheel are caused to exert their force, are much alike in the modern detached lever watch and a good regulator clock; but as the arc in which the pendulum swings varies but very little, while that in which the balance wheel vibrates varies considerably from different causes (the principal one being the motion given to the watch in carrying it in the pocket), it is apparent that there must be considerable variation in the mode of applying the devices.
Fig. 2. - Huygens's Clock.
Fig . 3. - Recoil Escapement of Hooke.
Fig. 4. - Dead-beat Escapement of Graham.
Fig. 5. - Pin-wheel Escapement of Lepaute.
Fig. 6. - Huygens's End-ess Chain.
Fig. 7. - Train of Wheels in a Clock.
The oldest watch escapement was the verge and crown wheel, and had the train of wheels for the going part, as well as for turning the hour and minute hands, arranged in the same way as they were in the clock of Huygens. Fig. 8 represents the old-fashioned English verge escapement watch. At a is shown the barrel containing the main spring; at b the fusee around which the chain is wound, constructed in the form of a conical spiral to increase the leverage, as the spring diminishes in power by uncoiling; c is the centre wheel, turned by the great wheel on the fusee by the centre pinion c'; d is the third, and e the fourth wheel, which drives the crown and scape wheel f. The pallets p, p, moving to and fro upon the verge v, which is the staff of the balance wheel h, regulate the time of escapement of the teeth. The minute hand i is placed upon the cannon pinion, and the hour hand j upon the barrel k of the hour wheel I. The arrangement for turning the hands is the same as that shown in fig. 16. The original lever escapement was invented in France by Hautefeuille about 1722, and differed much in its action from the detached lever now in general use.
It is known as the rack and pinion lever, and is represented in fig. 9. The lever a has a rack, r, having the segment of a cog wheel at one end and pallets, h, h, at the other, and turning upon a pivot called the lever arbor, which is placed in the centre of the circle of which the rack is a segment. The balance wheel d, by its vibrations, causes the pinion to carry the rack backward and forward, and consequently moves the pallets at the other end of the lever in about the same way they are moved by a pendulum. As, however, the arc through which the balance wheel moves is subject to considerable variation on account of the motion given to the watch in carrying, the differences in the extent of the vibrations of the pallets, and the constant lug between the rack and the pinion, caused an imperfection in the movement which was obviated by a modification invented by Mudge, which was called the detached lever, because the end of the lever which formerly carried the rack, but which now was made in the form of a crotch or fork, was detached during certain parts of its oscillation. Fig. 10 represents the invention of Mudge, with several modifications in form which have since been devised.
He placed the pallets one on each side of the lover arbor, instead of placing them at one end, opposite the fork, as in this figure. A pin in the roller which is placed over the arbor of the balance wheel, and a notch in the bottom of the fork, are so arranged that an alternate locking and detachment takes place at every escape of a tooth in the scape wheel. This detachment relieves the parts of the constant lug which existed in the rack and pinion, and allows the pallets to make perfectly equal vibrations, whether the balance wheel does or does not. This kind of lever is the one now in common use, and likely to be for a long time to come, as it is difficult to imagine any device better calculated to produce uniform motion in the train of wheels of a watch which is intended to be worn in the pocket. The top of the scape wheel s is moving to the right, with a constant force derived from the main spring. The pallets a and b have been moved to the left, so that b is out of range, and a within range of the teeth. The tooth c has locked upon the dead surface of the pallet a.
The balance wheel is now moving in the same direction as the scape wheel, its top to the right, and its lower part, which is cut away, to the left; the pin upon the roller of the balance wheel has entered the notch in the fork; as soon as it strikes the side below the angle g it will move the fork to the left, turning the lever upon its arbor k, and consequently lifting the pallet a sufficiently to allow the tooth c to fall upon the impulse face of the pallet. In this way the lever will receive a new impulse in addition to the one it received from the balance wheel, so that before the pin gets beyond reach of the side of the notch in the fork opposite g it will be struck by it, and thus an impulse will be given to the balance wheel by which its vibrations will be maintained. It will be observed that the teeth of the scape wheel in this figure differ in shape from those in any scape wheel which has thus far been described. They are called club teeth, and their use will presently be noticed. Mudge used the old ratchet teeth.
The alternate lifting and depressing of the pallets to liberate and to lock the teeth is the main object of escapements, and may be effected by three different methods: 1, by having the inclined planes on the pallets alone, and moving them by pointed teeth, as in fig. 9; 2, by having the inclined planes on the scape teeth which move against pallet edges; 3, by having the inclined planes both on the pallets and on the scape teeth, as they are in the detached lever, with club teeth on the scape wheel. In this figure it will be seen that if the scape teeth were ratchet-shaped they would still raise the pallets, because their faces are inclined to the radius of the arc in which they move, although they would not be sufficiently raised. It will be noticed, however, that the toes of the scape teeth move in a larger are than the heels, and therefore must increase the elevation of the pallets. In this lever it is necessary to make provision against the untimely unlocking of the pallets by irregularities produced in carrying. This is done by the employment of a guard pin and two banking pins.
The guard pin k is placed at the junction of the fork with the lever, at such a distance from the lever arbor h that when those two points lie in the radius of the balance wheel, or nearly so, the guard pin will be nearer the balance arbor than is the circumference of the roller; therefore a notch must be made in the periphery of the latter, on the side where the impulse pin is placed. This will allow it to pass only at certain periods in the oscillations of the balance wheel. The banking pins, m m, are for the purpose of preventing the lever from being carried too far by any over-impulse of the balance wheel, and their adjustment is a matter of considerable importance, and is secured with great nicety by placing them excentrically upon screws which pass into the pillar plate, as represented in fig. 10. - Before the perfection of the lever, the cylinder, or as it is sometimes termed the horizontal escapement (fig. 11), was introduced by Graham, who invented the dead-beat escapement in clocks. A section of a hollow cylinder is cut out in such a way that its external and internal surfaces are made use of to receive the action of the teeth of the scape wheel, while the edges are cut at such angles as to form impulse pallet faces.
The mode of action in this escapement is like that of the dead-beat escapement in clocks, the outer and inner surfaces of the cylinder forming long dead pallet surfaces, so that the teeth of the scape wheel may slide over them equally well, whether the oscillations of the balance wheel are great or small. Indeed, the general principles upon which all clock and watch escapements are constructed are greatly similar; the chronometer or detached escapement differing more from all the rest than they from each other. The devices and forms are various, but they secure the same desired result by making use of nearly the same mechanical forces and appliances. The production of the chronometer or detached escapement is the work of many ingenious men, but principally of Le Roy, Berthoud, Earnshaw, and Harrison. The construction, as substantially given by Earnshaw, is represented in fig. 12. There has been [ but little change made in it since. The balance wheel B is shown turning in the di-rection of the arrows, the tooth T resting upon the stop S, which has caused it to make a dead beat. The detent, A, is a kind of latch, shown as resting against the pin which is represented opposite the letter A. Attached to its upper end is a light spring, a, projecting beyond its point.
The scape wheel, E, is turning in the direction of the arrow by the constant action of the train of wheels. The detent is held against the pin by the spring a' at its lower end. A tooth, d, on the verge of the balance wheel, is moving with the wheel against the spring d, and will presently push the detent far enough back to allow the tooth T to pass by the stop, and the tooth T', which moves with greater velocity, to overtake and strike upon the impulse face of the pallet p before it gets beyond its reach, and thus impel the balance wheel to its full vibration. The fine spring a is designed to allow the pin d to slip by when the balance wheel returns, but to catch it and force the detent back and allow the tooth T to pass the stop when it again moves in the direction of the arrow. The hair spring of the balance wheel is not seen in the drawing, it being placed upon the hidden side of the roller. - The balance wheel of a chronometer is made to preserve a uniform time of oscillation upon the same principle as the gridiron pendulum; that is, by a combination of two metals having unequal rates of expansion and contraction by variations of temperature. The rim of the wheel is made of brass and steel, the former outside of the latter, with a number of pins screwed into it which serve as weights.
The invention was made by Harrison, but the method of construction which is now generally employed was introduced by Earnshaw about 80 years ago, and consists in soldering a rim of brass around a disk of steel, and then by means of a lathe and other tools cutting away the greater portion of the disk, leaving two arms projecting from the staff, as represented in fig. 13. The rim is then sawed in two places, at its junction with the arms, so that during expansion the other end of the segment of the rim may be free to move toward the centre of the wheel, and thus produce sufficient compensation to prevent a change in the time of oscillation. The proper adjustment can only be accomplished by trial, which requires the employment of considerable time and skill, and constitutes one of the items of expense in a chronometer or a good watch. In regard to chronometers, little more need be said after giving a description of the escapement, and the principle of the compensation balance wheel. The escapement is the most perfect that has ever been devised for a timepiece which is to be kept in one position.
Fig. 8. - Old English Verge Escapement.
Fig. 9. - Rack and Pinion Lever of Hautefeuille.
Fig. 10. - Modern Detached Lever Escapement.
Fig. 11. - Cylinder Escaperifent of Graham.
Fig. 12. - Chronometer Escapement of Earnshaw.
Fig. 13. - Compensation Balance.
It has been attempted to use the chronometer escapement in pocket watches, but without success, great irregularities being produced by change of position, and motion consequent on carrying; but when the timepiece is furnished with a perfectly compensating balance wheel, so that its vibrations are isochronous under any change of temperature to which it may be exposed by the passage of a ship from one zone to another, and it is suspended in gimbals, as represented in fig. 14, so that, whatever angle the deck of the ship may form with the horizon, the chronometer will always maintain the same position, it becomes one of the most perfect pieces of mechanism. Its great use is in making astronomical observations, and it is especially valuable in determining longitude at sea. The first experiment with a chronometer was made in 16G5, in a voyage to the coast of Guinea, by Major Holmes, with a watch made by Huygens. With this the longitude of the island of Fogo was obtained with tolerable precision. In . 1726 Mr. Harrison made a chronometer which was a marvel for correct timekeeping. In 1736 it was sent to Lisbon, and corrected the reckoning on the voyage as much as a degree and a half.
He was paid £500 by the English government to prosecute further experiments, which resulted in his producing an instrument so accurate that it made an error of less than two minutes in a voyage to Jamaica and back, and in obtaining the reward of £20,000 which had been offered. It is not attempted to regulate chronometers to diurnal time, it being only necessary to ascertain their rate, when the correct time can be calculated. - The train of wheels, together with the lever and balance in a modern detached lever escapement, such as is now made in the best watch factories in the United States and in Europe, is represented in fig. 15. It is placed between two plates of brass, the under, called the pillar plate, being an entire circle, while the upper plate, which is removed in the figure, may be either one quarter, one half, three quarters, or a full plate. In many European watches the upper plate is almost entirely replaced by what are called bridges - pieces which are screwed to the pillar plate, and have arms which project far enough to receive the arbors of the wheels.
The barrel b, which contains the main spring, has the great wheel placed around it, instead of being placed upon a fusee and driven by a chain wound upon the barrel as represented in fig. 9, and which is still the construction in most English watches. Of course the tension of the spring becomes less as it uncoils; but if the coil is of considerable length the variation need not be great, and by the nice adjustment of the balance is completely counteracted. One end of the spring is attached to the barrel arbor, the exterior portion of which is shown at a, and squared, to admit of winding by a key. The other end of the spring is attached to the inner surface of the barrel. The arbor carries a ratchet wheel, which is prevented from turning back by a click. The centre wheel d is driven by the action of the great wheel upon its' pinion c, called the centre pinion. The centre wheel drives the third wheel f, by means of its pinion e, and the third wheel again drives the fourth wheel h, which Carries the seconds hand, in a similar manner. The fourth wheel drives the pinion i of the scape wheel j, whose teeth again alternately lock and impel the pallets I I, which are placed on the pallet arms of the lever.
The lever turns upon the pallet arbor k, and by means of the fork gives an impulse to the balance wheel, as has already been described. If the fourth wheel, which revolves once in a minute, has 64 teeth, and the pinion of the scape wheel has 7 leaves, that wheel will turn round once in 6 9/16 seconds; and if it have 15 teeth, each tooth will escape every 7/16 of a second, and consequently there will be one complete oscillation of the balance wheel every 7/16 of a second. If the pinion of the fourth wheel contains 8 leaves, and there are 60 teeth in the third wheel, the latter will make one revolution in 7 1/2 minutes. Again, if the pinion of the third wheel has 8 leaves, and the centre wheel has 64 teeth, the latter will revolve one eighth as often as the third wheel, or once in an hour. It is not necessary that these proportions should be fixed, but the number of teeth in the train must be such that there will be a certain ratio between the number of teeth in the centre wheel, which revolves once in an hour, and the number of leaves in the pinion of the fourth wheel, which revolves once in a minute; and the teeth in the fourth wheel, the leaves in the pinion of the scape wheel, the teeth in the latter, and the vibrations of the balance wheel, must have certain relative proportions to each other.
The hour hand is moved by a train of two wheels and two pinions, placed on the outer side of the pillar plate, and beneath the dial. The arrangement is represented in fig. 16. The cannon pinion is placed on the arbor of the centre pinion, and fits spring-tight, so that it may be moved at pleasure in setting the minute hand. Above the pinion proper there is a barrel upon which the minute hand is placed. If the cannon pinion, which is here hid from view, has 12 leaves, and the wheel into which it pitches has 42 teeth, the latter will revolve once in 4 hours. If, again, the pinion of this wheel has 14 leaves, and the centre wheel has 42 teeth, the latter will revolve one third as often, or once in 12 hours. One of the modern arrangements for winding and setting the watch is also represented in this figure. A crown wheel is placed upon the end of a shaft which passes through the stem. This wheel moves another, which is placed upon a yoke between two other wheels, one of which, the winding wheel, is held in gear by a spring, and the other the setting wheel, thrown into gear at pleasure by the pressure of a button. When one wheel is thrown into gear, of course the other is thrown out, so that the winding of the watch and the setting of the hands are done independently and without interference.
An inspection of the figure will afford all the explanation that could be given in words. - The limits of this article will not allow of a description of the striking and alarm parts of clocks and repeating parts of watches, and other devices, such as for showing the day of the month, without a sacrifice of more important matter which more strictly relates to timekeeping; and as these parts can be best understood by an actual inspection of the timepieces, the reader who may wish to become acquainted with their mode of action is advised to study the subject in that way. - Excellent watches are now made by machinery in the United States: by the American watch company at Waltham, Mass.; E. Howard and company at Boston, Mass.; the United States watch company at Marion, N. J.; the National watch company at Elgin, 111.; the New York watch company at Springfield, Mass.; the Springfield watch company at Springfield, 111.; and the Cornell Watch company at Grand Crossing, 111. Watches made by this method possess the advantage of great accuracy at a comparatively small cost. All the parts' in the train are made perfectly uniform, so that any particular wheel may he replaced without making any sensible variation in the running of the watch; and so of any other part.
The small, fine-threaded screws which are used to hold some of the parts together are made in the most perfect manner and with wonderful rapidity by very ingenious machines, one of which is shown in fig. 17. A steel wire, a, is placed in the spindle and turned by the belt. A die, represented enlarged in the upper part of the cut, made in two sections and held in the end of a tool b, cuts the thread as it is pressed against the wire by a motion communicated by a lever. Previous to this, however, the wire is reduced to the precise length required by the tool c, which is adjusted by a gauge, and the stem of the screw is also turned down by the tool d. After the thread is cut, the tool e is brought against the wire, and the head of. the screw is formed. There is an ingenious device for removing the screw, which is still attached to the wire by a small pedicle. It consists of two disks, represented in fig. 18, which when joined together form a series of tapped holes, made to fit the screws. One of these, being held against the point of the screw while it is revolving in the spindle, receives it, and when the end of the thread is reached the motion breaks; off the pedicle, leaving the screw in the disk.
When all the holes are filled, the disk is placed in an ingenious automatic machine which carries, during proper periods of time, the head of each screw beneath a revolving saw which cuts the slot. A machine for cutting the teeth in wheels is shown in fig. 19. A tool called a quill, an enlarged view of which is presented in fig. 20, a, and which is divided into sections to receive the arms of the wheel, bearing upon its exterior the rim, is fed with from 20 to 40 wheels, the collection being called a stack. This quill is then placed upon a shaft which is turned by a graduated wheel having notches in its rim to correspond with the number of teeth in the wheel. This wheel is stopped at each notch by the click c, whereby the quill holding the stack of wheels is fixed, and in such a position respecting the tool which is carried by the arbor b, that a groove may be cut between two teeth in a radial direction, or any other which may be required. The arbor of the cutting tool is carried backward and forward by means of a slide d, worked by a lever e, by which means the tool is carried along the whole length of the stack of wheels, cutting a notch in each, and thereby forming the teeth. Club-tooth scape wheels require for their cutting several different forms of tools.
These are placed upon arbors which are made to revolve about a common centre, in the manner of a revolving firearm. Many other labor-saving machines are in use whereby great accuracy is attained at a comparatively small cost. The polishing of the leaves of pinions and the teeth of wheels, and the grinding of the faces of the pallet stones to their proper angles, are processes that are performed with much greater facility and accuracy by the use of machinery than by hand. - Most of the internal parts of clocks and watches, except the pinions and arbors, are usually made of brass, because of its ductility at ordinary temperatures. From its resemblance to gold it can be readily and cheaply covered with a frosting of gilt to protect it against corrosion. An alloy of nickel is used instead of brass in many of the Swiss and American watches, which in being finished passes through a process called damaskeening, by which wavy lines resembling those on Damascus swords are produced on the surface. Dials for watches, and also for clocks, are made by fusing enamel upon a thoroughly cleaned disk of copper, and then grinding down the surface evenly upon a stone, after which it is again subjected to enough heat to glaze it.
The required circles are then inscribed upon it, and the proper divisions are made for the figures, which are painted on with a pencil in black porcelain paint and burned in. - Geneva, Neufchatel, Chaux-de-Fonds, and Locle, in Switzerland, are the chief seats of watch manufacture, particularly for exportation, in Europe; but they are made at several places in Germany and France. Liverpool has long been celebrated for timekeepers, and most of the English watches for exportation are made there.
Fig. 14. - Chronometer.
Fig. 15. - Train of Wheels in a Detached Lever.
Fig. 16. - Hand Wheels and Stem Winder.
Fig. 17. - Screw Lathe.
Fig. 18. - Slotting Disk.
Fig. 19. - Lathe for Cutting Teeth.
Fig. 20. - Enlarged View of Cutter.