One very useful addition which is frequently made to clocks and watches, is the alarum, or contrivance for calling attention at any fixed period of time. An excellent arrangement of this kind is the patent detached alarum watch, invented by Mr. Berollas, of the City Road, which is an improvement upon a former invention of the same gentleman called the warning watch. In the present invention all the useful parts of the watch are retained, while those that were inconvenient or had a tendency to disturb its regular movements are here in a detached state. The advantages that result from this arrangement are, first, the applicability or adaptation of the invention to all kinds of watches, what ever may be the principles of their construction ; second, the alarum being detached from the watch, it can be made to produce a noise sufficiently loud for a house alarum; third, alarum watches as before constructed were inconvenient, from their bulk, to wear—by this contrivance they may be made as fiat and thin as may be desired ; and, lastly, the expense is much less than any watches hitherto made of similar performance. By. 1 represents the mechanism attached to the watch, by which the alarum is locked and unlocked, as it appears when the dial-plate is removed The index by which the alarum is set to the proper time of going off, is attached to a hollow axle fitted upon the arbor of the ordinary hour-wheel. This index may be set by hand ; but a prefer able method is to attach a toothed wheel 4, which works into an inter mediate wheel 7, which works into the wheel 6, and this latter works into a wheel 3, fixed at right an gles to it upon the square end of the steel arbor l,which runs through the pendant, and has at its other extremity a milled nut 2, by turning which nut it is obvious that motion will be conveyed to the alarum wheel and index to set it at any particular hour. To prevent the train being turned the wrong way, and to retain the index in its place, a small ratchet wheel is fixed upon the square part of the steel arbor 1, into which ratchet a spring-pall 5 falls. The hollow axis of the alarum index is made of steel, and on its underside is formed into a fiat circular plate, as at 44, which represents the reverse side of the wheel 4 ; and in this plate a notch is cut straight down on one side, and sloping on the other, as shown at 45, which is a section of the wheel and hollow axle, the straight side of the notch lies in the direction of a radius of the flat plate in 44. The hour-wheel, marked A, By. 2, lies immediately underneath the alarum wheel, and has on its under side an oblong steel plate, 1, 2, 3, in the detached figure A of Fig. 2, which is called the detent. The detent is spring-tempered, has a hole in its centre for the free passage of the cannon arbor, and is fixed flat upon the hour-wheel by a small screw and steady pin at 2; into the opposite end of the detent plate at 1, is rivetted a small pin of sufficient length to pass through a hole in the hour-wheel, and to project beyond the upper surface of the same in such manner, that when the hour wheel and the alarum-wheel are put together in their right places, and this pin presses upon the flat surface of the steel plate 44, the end 1 of the detent is depressed below the under face of the hour-wheel, but when it comes over the notch it falls into the same, and allows the end of the detent to rise and lie fiat in the recess in the hour-wheel. The end 1 of the detent acts upon the circular end 2 of a flat steel spring C, By. 1, and shown detached in the following page ; it is called the elevator, and is fixed in its place by the screw and steady-pin at Z, which end is thicker than the other parts of the spring, so that the end 2 is raised above the plate on which it is fixed ; the degree of elevation may be adjusted by turning the screw-top at y, which works freely through a hole in the elevator. The end 1 of the detent presses upon the elevator in such manner, that whilst the detent is depressed it holds down the end 2 of the elevator ; but so soon as the pin in the detent enters the notch, and the detent rises, the pressure is withdrawn from the elevator, and it likewise rises to discharge the alarm which it does through the medium of another piece called the propeller, drawn in its proper place and form at D, 1, and also shown in the detached figure in the margin. It is a steel lever without spring, and turning upon the screw x as a ful crum ; it has a projecting piece W, which is formed into an inclined plane, and highly polished and har dened ; this inclined plane falls directly under the end 2 of the elevator C, also polished at this part; consequently, whenever the elevator is depressed by the detent, its end 2 will press upon the inclined plane W of the pro peller, and drive its end V outwarth; this end is formed into a portion of a circle not concentric with a, and presses against the locker E, Ffg. 1, which is a cylin drical piece of steel, having .in its outer end a small pin a projecting through the case of the watch ; the locker E moves between two pins, and is pressed against the end of the propeller D by the spring F, and kept at all times in contact with it. The combined effect of the several parts may be briefly recapitulated as follows :—whilst the detent is depressed, it presses down the circular end of the elevator c, which acting upon the inclined plane W of the propeller D, forces its circular end against the locker E, and causes its small pin a to protrude beyond the case, in which state it will remain until, by the revolution of the hour-hand, the pin in the deteut falls into the notch on the alarum arbor ; when the elevator rises, and the pressure being withdrawn from the inclined plane of the propeller, the locker E is pushed in by the spring F, and remains in that position until the sloping side of the notch 44 has been moved round sufficiently to depress the detent spring again. The above is all
that is necessary to form the union between the going parts of any watch, and a detached alarum, because it will be evident that such alarum may be dis engaged or set off by the sudden withdrawal of the locker; we shall therefore proceed to describe the manner in which the alarum movement is operated upon, whether the alarum of the bell, rattle, or any other kind.
An alarum movement in its separate state is repre sented at G H, in the an nexed figure, and consists of a frame, the upper plate of which is nearly half an inch less than the pillar plate, in order that the works may be covered by, and contained within the bell, as shown at fig. 2,which is a section or pro file of the alarum movement.
A going barrel, which contains the mainspring, is placed in the centre of the said frame, and a steel wheel cut with ratchet teeth to work the hammer is fixed on the upper part of the said barrel, its other side carrying the main wheel to drive the tram, which generally consists of three wheels and four pinions. The alarum hammer has a spring and a regulating spring on the opposite side of the plate as shown at K, Fig. 4. The fly pinion has an arm of steel fixed on its arbor, and as this comes in contact with the projecting pin, the works are locked, and the alarum prevented from running down ; but so soon as the pin H is moved, the whole is at liberty, and free to move ; the pin H passes through a hole in the plate, and rises from the locking lever H on the other side of the plate, as shown in Pig. 4, where it may be seen that this locking lever turns on a screw pivot at its inner end, and is constantly pressed to one side by the force of the spring P, which operates in such a direction as to throw the pin out of contact with the steel arm of the fly arbor, and consequently always keeps the alarum work in a free state for motion ; but it may be rocked at any time by pushing the locking lever H, Fig. 4, back wards, or against the action of its spring P; a wire tail, I, rises perpendicularly out of the outer end of the locking lever H, and it is this wire tail that is to be engaged with the small end a of the locker E s, Fig. I, whenever the alarum is to be wound up and set. This locking lever H, with its two pins, is here shown in a detached state.
Pig. 5 shows a watch having all the above described parts appertaining thereto, and placed upon one of the aforesaid detached alarum movements; I being the case of the alarum, formed of open-work, chased or otherwise ornamented, and having the appearance, when empty, of the ordinary receptacle of an external watch case; M being the usual rim that shuts down over the watch with a spring catch, and thereby holds it steadily in its proper position ; the alarm movement is fixed in this external case, with the pillar plate upwards, and the works and bell downward; consequently, the wire tail I, Fig. 4, projects upwards into the case, and in placing the watch within, it is necessary to observe that the projecting end of the locker a, Fig. 1, comes behind, and engages with this wire tail, as seen at H F, IV. 5, in such manner, that it may push back the locking lever, H, Fig. 4, and thereby lock the train of the alarum when the rim M is to be shut down, and the alarm hand set as aforesaid to the time upon the dial when it is to be discharged. The alarm may then be wound up by the key, or milled head K, Fig. 2, which is screwed upon the main spring arbor, so that it can only turn it in one direction without un screwing, and the machine will be ready to operate ; be cause at the assigned hour and minute, the ends of the locker will be withdrawn into the watch, thereby releas ing the wire tail I, and the locking lever H, Fig. 4, by which the alarum will be dis charged, and will instantly run down.
What has been said of the bell alarum movement, equally applies to rattle move ments, because they consist of the same parts, and are constructed and used in the same manner, except only that the bell, the hammer, and the steel ratchet wheel for working the same, and the springs connected therewith, are dis pensed with, and in lieu thereof, the rattle movement, shown in Fig. 6, is sub stituted. This consists of two strong steel wheels N N, so fixed or screwed upon the outside of the upper plate that they may both press in the same direction against the two strong pins or studs q q to receive them, and the upper plate may in this construction be made of the same diameter as the lower plate, because there is no bell to go over it. A coarse steel pinion M is fixed on to a square upon the con tinued arbor of the first wheel in the movement, and which wheel for this purpose is brought nearer to the edge of the plate, in such manner that the lever of the said pinion may engage with the ends of both the springs N N, and by its revo lution may carry them some distance towards r, and on their return they strike against the pins q q, and produce a powerful rattling noise; more or less springs may of course be used for a similar purpose, according to the extent of noise required.