Hello I'm Oliver Cooke, I'm a curator of horology here at the British Museum and
and welcome to my corner.
Today I'm going to go through how a clock works and to do this I'm going to introduce you to this clock
which is a clock that's nearly entirely made of wood, it was made in 1688 in Davos in Switzerland.
Now to do this we usually like to break it down into five elements
Energy, wheels, escapement, controller, and indicator. 5 elements.
So let us start with energy. Our power source, a clock is a machine
all machines need a source of power, there is no such thing as perpetual energy.
And in this case this clock is driven by a weight and when we hang the weight on the hook
The clock starts ticking. Now weights are a very very good source of energy
they are drawn down by the constant force of gravity
they provide a clock with a very constant supply of power
which is what a clock needs to be as accurate as possible.
When we wind the clock, this is very simple
I tug on the counterweight, this is just there to keep things in place, this is what is powering the clock
and I've just put energy, from my muscles, from my breakfast this morning
into that weight, against gravity and now it's trying to pull pull down and that's how it's driving the clock
So that is our first element- energy.
So our second element- wheels. Now wheels are what we horologists like to call gears
Most people call them gears or cogs, but what we're really referring to are wheels with teeth on
and the teeth are there so that one wheel can drive another with no slippage
they can drive this next wheel very precisely.
And what we have here, we actually have two mechanisms in this clock
this side of this central bar we have the go... what's called the 'going train'
and that, that is responsible for the time keeping of the clock
every clock and mechanical watch has a going train
and on the right-hand side here we have the 'striking train' and that's the mechanism for sounding the bell.
But let's talk about the going train first, the timekeeping side of things.
So we've talked about our source of energy, that weight is pulling down on this cord
and it's trying to drive this pulley around and that wheel there is in fact moving very, very slowly
and we can't see it, but the wheel it's meshing with, our second wheel in the train, you can see moving
and it's meshing just here at the top of the wheel with this very small wheel that we call a 'pinion'
all made in wood. In this wheel of many teeth is driving this small wheel this pinion
with not many teeth so this pinion's got about seven leaves on I think seven teeth on it.
This big wheel only has to move seven teeth to send this wheel around a complete revolution
and that's what's happening here, we're accelerating the speed of this wheel
We can see it's moving quicker here in the last wheel in our training escape wheel which we'll come to next
he's moving around visibly quicker again and the reason we want to do that is because we want the weight
to descend slowly, we want the clock to last for a sensible amount of time between windings.
Up at the business end of the clock if you like
on our third element- the escapement- and controller, our fourth element, things happen more quickly
this is just a virtue of the laws of physics and mother nature.
So we have to increase this speed and this is why we have our wheels, our second element.
And now we move on to element three- the escapement.
Now the escapement is the tick-tock that you hear in a clock or mechanical watch
it's the beating heart of a clock, if you like, and what's happening here
vertically in here we have a metal shaft- there is some metal in this clock
and on that shaft are two flag-like pieces which we call pallets and they're doing this
and so the teeth of the escape wheel, or the pins in this case, are alternately
pushing these pallets one way then the other, one way then the other
and that's the tick-tock you hear are those pins sliding off one face onto another.
In horology the louder that tick-tock the worse because the louder it is the more energy is being wasted
and a good clock should have a quiet tick-tock generally speaking.
What's happening is this rotational motion of this last wheel in our train is being converted to an oscillatory
motion left-right, back and forth and that is driving our fourth element, our controller.
This is the brain of the clock if the escapement is the beating heart of the clock
the controller is the brain of the clock, it's governing the rate at which everything happens
It's governing in the rate of the tick and the tock.
So it's oscillating backwards and forwards. What determines the rate of this happens? several things.
One is the power that the clock's getting, if I give it a bit more power by just tugging on the weight a little bit
you'll hear the clock speed up
What else what else determines the rate? It's the weight of the balance wheel up here, in this case
and the size of it because what's happening is, the power is feeding momentum into this object
so the heavier it is and the bigger it is the more momentum it requires to keep going.
so and in this case the balance wheel has a band of lead around its rim just to give it that bit more weight
This form of controller was with us since the well, the dawn of horology perhaps the 12th or 13th century
we're not sure exactly when or who invented the mechanical clock but around then
and this this form of escapement and controller were in place from the beginning
and it stayed in horology up until 1656 when the Dutch mathematician and physicist Christiaan Huygens
worked out how to apply the pendulum to the clock
and from that point forward that was the main form of controller.
And finally our fifth element is the indicator.
We're most familiar with the dial on a watch or a clock
and we read the time quite happily, we're taught to do it as young children
in this case we have an hour hand here for 12 hours
and down here what should be a minute hand, it's only marked for the quarters but it goes around once an hour
and missing in this little slot here should be a little pointer
and normally we're used to see in the minute hand and our hand concentric
so this is a little bit different and this is typical of these Davos clocks, in fact.
The other form of indicator that this clock has got is a bell, well it hasn't got it because it's missing
as I've mentioned earlier, it should be up here and a hammer would hit it three strikes for three o'clock.
So that's how a clock works in five elements:
Energy, wheels, escapement, controller and indicator or
Every Witch Eats Crunchy Insects is what we tell all the children to help them remember this.
Next week I'll be pulling apart this lovely clock from Davos and putting it back together
and seeing if it still ticks at the end. If you don't to miss that then
please do subscribe to the British Museum YouTube channel. Thank-you