Former Clock & Watchmakers and Their Work: Including an Account of the Development of ... by Frederick James Britten

Author:Frederick James Britten
Language: eng
Format: epub
Publisher: Spon & Chamberlain
Published: 1894-03-25T05:00:00+00:00

now the button in the pendant ia pressed, the shorter end of the Ijent lever which is lying around inside the case is depressed, and the hooked end of the lever draws the ratchet round, so that the tail of the carriage on which the small serrated wheel is mounted is moved far enough to take it from contact with the lai^ef i

wheel, and the chronograph hand consequently stops. At the same time a caatlo tooth, which liaa been keeping a circular brake off the larger serrated wheel, is moved out of the way, so that the brake drops, ihaa keeping the chronogi-aph baud from beiiis shifted by accidental motion of the watch. When the button is again depi-esaed, the castle ratchet ia shifted roand still further, and the returning lever with the pointed end is allowed to drop on to the heart-shaped cam, which is fixed to the larger of the serrated wheels. As the returning lever drops, its tail hfts the brake off the serrated wheel, and the lever impelled by a spring, as shown in the drawing, turns the cam from whatever position it may happen to be in, till the lever rests on that part of the edge of the cam which ia nearest to its centre of motion. The chronograph hand ia then at zero. Each time that the bent lever ia pressed it draws the ratchet round one tooth, and as there are three ratchet-teeth to one castle tooth, it is evident that all the pieces in contact with the castle return to their original position after every three movements of the lever.

Tupetnftl Aa an esaraple of modern perpetual calendar work

Calendar the drawing on p. 238 of a watch arranged by Mr. Witoli, c. H. Audemara may be of interest. The wheel H,

driven by the minute wheel, makes one turn in 2i hoars and carries a movable finger c, which by contact with a pin moves the armed lever D by its extremity p. This levtr, which has its centre of motion at i, acts through its different arms. Firstly, at c it moves the day of the week star wheel (7 teeth). Secondly, at b the atar wheel for the day of the month (31 teeth). The finger a makes engagement and passes one tooth each day of the atar wheel E (5!* teeth), for showing the phases of the moon.

The part of the mechanism which renders the calendar perpetual is composed of a wheel of 31 teeth P, engaging with the star wheel C, This wheel, which makes one turn per month, passes at each turn, by means of the movable finger w, one tooth of the star wheel G (48 teeth), which latter by this means makes a revolution in four years. The circnmferencc of account disc fixed to this star wheel corresponds lo the months of 31 days, the shallowest notches to those of 30 days, and the

FOBMSn CLOCK AND WATCHXAKEJtS.

four quarter notches to the month of Fehraary. At e, which 18 for February in leap jear, the notch is hardly bo deep as the other three-quarter notches.

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