Big Ben and Its Clock Tower

Interesting video of the clock in the tower of the House of Parliament.

The design was a breakthrough in design of tower clocks which because of the large hands used that were exposed to weather, any ice or snow buildup, or even strong wind could effect the timekeeping by feeding back to the escape wheel which impulsed the pendulum. This clock eliminates that problem by having the escape wheel indirectly impulse the pendulum by lifting a weighted lever which when released provides the impulse.

http://www.parliament.uk/about/living-heritage/bu ... ower/tour/

I saw a documentary on it once, the thing that was really interesting to me was they keep it in time by adding or removing coins from the weight. Adding one or removing one speeds it up or slows it down.

I saw that too. My question is how can something be that sensitive yet not be influenced by other conditions like heat and humidity, expansion and contraction of parts..

Lightning wrote:I saw that too. My question is how can something be that sensitive yet not be influenced by other conditions like heat and humidity, expansion and contraction of parts..

The pendulum is the timekeeper and is the only part where the influences mentioned will make a difference. To that end the shaft of the pendulum is made of well seasoned and sealed wood which is less effected by temperature than metal. The bob is cylindrical rather than lens shaped and is supported at the bottom. With a rise in temperature the pendulum will get longer, but the bob expands upward to compensate, at least partially. The sealed wood is little effected by humidity.

A one second pendulum makes one vibration in one second and is about 40 inches long. This pendulum is two second and is 13 feet long. It is that long because the arc will depart less from the ideal path which is not circular but cycloidal. If I place a ruler on a piece of paper and then a coin against the ruler I can generate a cycloidal path by holding a pencil against the edge of the coin and rolling the coin along the ruler. The gear teech also have a cycloidal shape at their tips. They roll against each other rather than slide.