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Post by JordanPost by Alex W.Post by JordanPost by Alex W.Post by JordanIn an historical work on the theory of elasticity by Clifford
Truesdell, when he is talking about the mathematical investigation of
resonance in vibrating systems he writes "By the accidental
observation that a watch when hung up sets itself in vibration as a
pendulum, Krafft reopened the problem of forced oscillations."
Krafft wrote his paper in 1738. What is a good book or website that
shows in full detail and with pictures how watches at this time
worked?
Also, if anyone has a watch that works like a 1738 watch and is
interested in doing an experiment, could you try doing what the quote
describes and saying whether the watch starts making noticeable
vibrations back and forth.
I'm quite interested to hear if anyone tries this!
I couldn't give you websites, but I own a number of such watches,
and yes, they do being to oscillate when suspended. Over time,
the wole watch responds to the oscillations of the balance wheel
and vibrates accordingly.
Can you describe the watches with which you've tried this, so that I
can look up how they work? I don't expect you to send me blueprints,
but any details you can give would be helpful to me.
Many watches will do this, but it is far more noticeable with
18th century pieces because the balance wheels were that much
bigger (and weighted) than modern balance wheels. If you want to
they are solid, reasonably reliable and easy enough to find.
As an interesting sidenote, a number of watchmakers have tried to
turn this principle of resonance to their advantage and use it to
improve precision. They do so by using two pendulums or balance
wheels. As each acts as both emitter and resonator, they should,
over time, synchronise and cancel each other out, thereby
increasing the precision of the beat. Janvier and Breguet
experimented with this technique, and in modern times Dufour and
Journe both made wristwatches with two balance wheels to achieve
this effect.
What I want is to understand how watches in the 18th century worked,
and to understand the phenomenon of a hanging watch starting to
oscillate because of its internal workings. Are there any modern
pocket watches that operate on the same design as the watches in which
I'm interested? I'm
speaking from a position of ignorance because I am still trying fully
to understand how these watches work; I've found that the information
on Wikipedia is not enough to feel like I could explain in detail the
workings of a mechanical watch to someone, so I'm going to consult a
book.
If I were at an antique watch store and asked to see an old English
verge watch, is saying that enough information for them to know what I
meant?
However, I'm not going to spend many hundreds or a few thousand
dollars to buy an 18th century watch for this project (this is part of
a large project on the history of mathematical resonance on which I'm
working), but I'd like to be able to see this with my own eyes.
As Alex W said almost any pocket watch CAN exhibit this behaviour, even
a cheap modern lever watch.
The reason for using a verge escapement for the experiment is more a
matter of physics than any watch making differences.
18thC verge watches work in fundamentally the same way as modern lever
watches, only the details of the way in which the escapement interacts
with the balance wheel differs.
See http://en.wikipedia.org/wiki/Escapement if you want some details, or
google "escapement" - there is lots of excellent research material out
there.
Both kinds of watch use an oscillating "balance wheel" which rotates
back and forth in the plane of the watch movement controlled by a
hairspring.
In old verge watches, because of the design and limitations of the
escapement this wheel is relatively large, relatively heavy and
oscillates relatively slowly compared with the wheel in a modern lever
escapement.
The size and weight of the balance wheel mean that each time the wheel
changes direction a relatively large amount of kinetic energy is
transferred to the hairspring as potential energy. If the movement is
constrained, all (ok most) of this energy is returned to the balance
wheel as it goes the other way. But if the watch is suspended and free
to move, some of the potential energy from the spring transfers to the
watch movement (action & reaction and all that).
A heavy balance wheel means that a higher proportion of the energy
transfers to the movement than would happen with a light wheel.
A balance wheel oscillating slowly means that the frequency of the
transfer ( which sets up the sympathetic oscillation) is more likely to
"match" the natural oscillation frequency (or a close harmonic) of the
suspended watch (which acts as a pendulum).
So a verge watch with more energy transfer at a frequency closer to the
natural frequency of the suspended watch will exhibit sympathetic
vibration much more easily than the light,fast wheels of a modern watch.
If you suspend a modern watch and "tune" the natural frequency of the
suspended watch so that is very close to a sub-harmonic of the beat
frequency of the watch, it will start to oscillate - but the low energy
and high frequency of the modern balance wheels make this fairly tricky.
You want a watch or a small clock with a big balance wheel that ticks
slowly
I hope this helps
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