Prague Astronomical Clock: Walking of Apostles and Clock Striking

What goes on inside the town hall clock? Count down the arrival of the new year with us. Content 🙂
00:07 Romuald Božek's chronometer
02:18 Starting the apostolic machine
03:20 The striking of midnight
👉Old Town Astronomical Clock
The Old Town Clock or the Prague Clock is a medieval astronomical clock located on the south side of the tower of the Old Town Hall in Prague. The astronomical clock is historically documented for the first time in a document dated October 9, 1410 preserved in the copy. This is a medieval astronomical clock on the south wall of the tower of the Old Town Hall in Prague. Currently, it is probably the best-preserved medieval astronomical clock ever. The entire astronomical clock, pointers, strikes, ringing, movements of the apostles and statues are mostly controlled by the original forged machine, the foundation of which was built in 1410 by Nicholas of Kadana.
👉 Romuald Božek's chronometer
During the repair of the Prague Astronomical Clock in 1866, it was decided by the commission that managed the repair that it was necessary to increase the accuracy and reliability of the operation of the astronomical clock machine. It was decided to supplement the clock with a precise control chronometer, which will start the machine every minute and thus set the exact time. This chronometer was constructed by the Czech inventor, designer and watchmaker ROMUALD BOŽEK (1814 - 1899). It had to withstand variable external conditions (changes in temperature, changes in air humidity, condensation of water vapor on some parts of the machine, ...) and guarantee the precise operation of the machine's mechanical oscillator. The machine was therefore controlled by a pendulum which was temperature compensated. Because of the effect of longitudinal thermal expansion, the length of the pendulum's hinge increases with increasing temperature, and therefore the period of the pendulum's swing also increases. The pendulum was therefore compensated by mercury and the thermal expansion of liquids was therefore used. In the body of the pendulum there is a container with 25 kg of mercury, whose volumetric thermal expansion compensates for the longitudinal thermal expansion of the material of the pendulum hinge. As the liquid increases its volume, the center of gravity of the entire pendulum changes (the position of the center of gravity of the entire pendulum increases in the gravitational field of the Earth), while the longitudinal thermal expansion of the pendulum material decreases the position of the center of gravity in the gravitational field of the Earth. With the correct choice of the volume of the liquid used and the correct combination of the thermal expansion coefficients of the liquid and the material of the pendulum suspension, a constant position of the pendulum's center of gravity can be achieved.
👉Combination of a chronometer with a Gothic tower clock
The connection of the chronometer to the trigger of the original machine is made with a thin copper wire. The wire is led over the glass door of the niche in which the chronometer stands to the stop of the main machine. Once per minute the stopper is released and the clockwork machine makes one step. The own two-stage stop then reconstructs the connection of a modern chronometer with the oldest part of the Old Town Astronomical Clock. The trigger was sensitively built into the original casting machine. Instead of the original crown wheel and spindle, a side gear wheel is used. In this way, it is possible to orient the axes of the discharge gear perpendicular to the existing ones and to bring out the discharge arm with a relatively large braking vane to the side of the frame. The stop release arm rests at rest on the top stop on the bent lever. As soon as Božk's chronometer begins to exert force on the wire connecting it to the casting machine of the astronomical clock, the bent lever rises. The arm is thus released from the upper stop and falls onto the lower stop. When the wire is released, the arm slides off the lower stop, makes almost one complete revolution, and rests again on the upper stop. The bent lever is loaded with a weight, under the influence of which gravity forces it to reliably fold down at the right moment. One revolution of the arm is converted to a pinion, which engages the side gear wheel, by means of two new spur gears. This will move the cutting machine one minute.
👉Thank you
Petr Skálov veznihodiny.cz
Clock Gallery clockgallery.cz...
Academy Mozarteum clockgallery.cz...
To the Czech Horological Association www.muzeumhodi...
Prague City Tourism prague.eu
Jan Reichl
👉Descriptions of individual parts of the Old Town Astronomical Clock were taken from the website orloj.eu and jreichl.com.
#astronomicalclock #orloj #staromestskyorloj #prague #towerclock

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