If instead of the barrel, in figure 2, on which the catgut from the weight is coiled, the fusee wheel described be supposed to be substituted, and the spiral spring, and its barrel and chain, to be added, a good idea will be ob tained of a spring•clock ; as all the rest of the work may be the same as in the figure.
Spring-clocks are generally used in chambers, in places where weight-moved clocks would take up too much room. They are often so constructed, that their frames do not hide any part of the work, and are then inclosed with glass covers, so that all their movements may be seen ; as they are designed for orna ment as well as use, very elegant and expensive decorations are frequently added to them.
The invention of moving time-pieces by springs first gave rise to portable time-pieces, or watches, for which see the articles CHRONOMETER and Holm LOOT.
Spring clocks are sometimes called portable clocks, but improperly, for no pendulum clocks can be made so as to be portable : for this purpose the balance wheel and its spring must be substituted for the pendulum, and it is this point that makes the grand distinction between clocks and watches, or chronometers : the properties of the balance spring, as a regulating power, will be found in the ar ticles before mentioned.
Clocks for astronomical purposes, in which extraordinary nicety in the exact measurement of time is necessary, have (besides the compensation pendulums, detached escapements with jewelled pal leis, and other improvements before Mentioned) a contrivance added to con tinue their movement, while the weight is winding up, which was first used in spring-moved chronometers. For this purpose, a second larger ratchet wheel is added on the same arbor with that which admits the clock to be wound up, but with teeth pointing the contrary way; a strong spring., usually the great est portion of a circle, connects this large ratchet wheel with the great wheel of the clock, which is on the same axis with it ; one end of this spring being attached to the great wheel, and the other end to the large ratchet ; and a catch proceeds from the inner face of the back plate to the teeth of the ratchet, which prevents its mqving back when the clock is winding up, and serves as a support for the reaction of the maintain ing spring. When the clock is left to the operation of the weight, the small ratchet turns round the large one, and contracts or coils up the spring, till it has strength sufficient to impel the great wheel and train ; amd. when the action of the weight is suspended, as in winding up, the spring, freed from the contracting power of the weight, expands itself, and forces round the great wheel; its action in the contrary direction on the great ratchet being prevented by the catch before mentioned. Le Roy is generally sup posed to have invented this improvement for his chronometers ; but as be has proved that the fusee is unnecessary when a detached escapement is used, the same purpose might be answered, in a much simpler manner, in those time pieces which are moved by springs, by turning round the arbor to which the in ternal end of the main-spring is attached, in order to wind it up, instead of turning round the spring-box in the customary manner.
Though Le Roy was the first who con trived the spring impeller, to prevent loss of time in winding up, Huygens was in reality the person with whom the ides originated ; for he contrived a method, by which the weight of his clock should continue to act on the train while it was drawing up, the weight in his clock hav ing been made to draw up in a similar manner to that used in the common wooden clocks, instead of being wound up as in our metallic clocks. Patou reaux's clock has this contrivance.
The following description of an eight day clock, with reference to the plate, will, it is hoped, sufficiently skew its construction; and the plate will, it is presumed, assist in elucidating the va rious parts of clocks, and improvements, before described.
Plate Clock-work, is a representation of an ordinary eight day clock, with re peating, striking mechanism.
Fig. 1, Clock-work, is an elevation of the clock, sideways, shewing the pendu lum and going part ; the striking move ments are omitted in this figure, to avoid confusion ; fig. 2, is a projection of the
wheel-work of both going and striking part ; and fig. 3, is the dial.work, or me chanism immediately under the dial, (which is removed) and is that part which puts the striking train in motion every hour. A clock of this kind con tains two independent trains of wheel work, each with its separate first mover ; one is constantly going, to indicate the time by the hands on the dial-plate ; the other is put in motion every hour, and strikes a bell, to tell the hour at a dis tance. a. figures 1 and 2, is the barrel of the going part; it has a catgut band b wound round it, suspending the weight which keeps the clock going ; 96 is a wheel, (called the first or great wheel,) of that number of teeth upon the end of the barrel, turning a pinion of eight leaves on an arbor which carries the mi nute hand. 64 is a wheel of 64 teeth on the same arbor, (called the center wheel,) turning the wheel 60 by a pinion of eight leaves on its arbor; this last wheel gives motion to the pinion of eight, on the ar bor of the swing wheel 30, of 30 teeth ; d, h, are the pallets of the escapement fixed on an arbor e, fig. 1, going through the back plate of the clock's frame, and carrying a long lever f; this lever has a small pin projecting from its lower end, going into an oblong hole, made in the rod B of the pendulum. The pendulum consists of an inflexible metallic rod, sus pended by a very slender piece of steel spring, D, from a brass bar E, screwed to the frame of the clock, having a weight or bob at its lower end, in the present case 39.125 inches from the sus pension D ; when this pendulum is mov ed from the perpendicular line in either direction, and suffered to fall back again, it swings nearly as much beyond the per pendicular on the contrary side, and then returns ; this it will continue to do for some time, and each of these vibrations will be performed in one second of time, when the pendulum is of the above length. This is the measurer of the time ; and the office of the clock is only to indi cate the number of vibrations it has made, and give it a small impulse each time, to keep it going, as the resistance of the air and elasticity of the spring D would otherwise in a few hours cause it to stop. By the action of the weight ap plied to the cord b, (which is called the maintaining power,) the wheels are all turned round, and if the pallets d h were removed, the spring wheel 30 would re volve with great velocity in the direction from 30 to d, until the weight reached. the ground : the teeth of these pallets are so made, that one of them always en gages the wheel, and prevents its turning more than half a tooth at a time. In the drawing the pallet d has the nearest tooth of the wheel resting on it, and the pendulum is on the side k of the perpen dicular ; when it returns it moves the pallet d, so as to allow the tooth of the wheel to slip off ; but in the mean time the pallet h has interposed its point in the way of the tooth next it, and stops the wheel till the next vibration or second ; the distance between the two pallets d h is so adjusted, that only half a tooth of the wheel escapes at each vibration ; and as the wheel has 30 teeth, it will revolve, once in 60 vibrations of one second each, or one minute ; consequently a hand on the arbor of this wheel will indicate se conds on the dial-plate F, a circle divid ed into 60 ; the pillion of eight on its ar bor is turned by a wheel of 60, which consequently will turn once in seven turns and a half of the other, or in seven minutes 30 seconds, or one-eighth of an hour ; its pinion of eight is moved by a wheel of 64, or eight times itself, which will turn in one-eighth part of the time ; this will be an hour ; the arbor of this wheel therefore carries the minute hand of the clock. The great wheel of 96, be ing 12 times the number of the pinion eight, will turn once in 12 hours, and the barrel a with it. The gut goes round 16 times, so that the clock will go eight days. The hour hand of the clock is turned by the wheel-work shewn in fig.