You've moved in and bought all the most modern conveniences imaginable. Your wife's overjoyed at her kitchen, and the children almost deliriously happy, playing in the extensive grounds and gardens.



You're sitting at your computer one day, as usual, when your wife ambles in holding a decorative 'something' in her hands.

On further inspection, the design is positively baroque. Whorls and whirligigs cut into two plates of brass. Good grief, it's a clock! What's known as a skeleton clock. All the workings, or the movement, is completely open, not hidden in a wooden case. It's a timepiece; there's no strike or chime train.

"Where did you find this?" you ask her.

"The attic. It's huge. There's some wonderful stuff up there," she tells you enthusiastically.

You take it from her gently and examine it more closely. You know a bit about clocks, because your grandfather was a clockmaker, and you spent many a happy afternoon with him as a youngster.

The poor old clock needs a clean desperately; some places on the brass plates are green. Everything seems to be there, though. The dial, hands, the 'vee' shaped bit at the top, which you've heard your grandfather refer to as the pallets. They go in and out of the saw tooth wheel immediately below them. That's the escapement.

But, oh dear! No pendulum. You clamber up into the attic yourself and have a good look around, but no, no sign of the thing. What to do? There's no maker's name on it. Yes, wait a sec. 'Willis fecit.' On the bottom of the front plate. 'Willis made it.'

You take photographs of it from different angles, jump on the 'Net and find some clock material houses. You pick one, send the photos off to them with a note, asking for a new pendulum. You give your E-mail address and they write back that "sorry, before we can supply you, we must have the count of the train." You know that by 'train,' they mean the gear wheels, but that's as far as your knowledge goes. You're out of your depth, and man enough to admit it! The phone book tells you there's someone in the village who's a clockmaker, so off you go to see him.

He reminds you of your grandfather. He takes the clock and looks at it lovingly.

"A beautiful piece," he murmurs. "I'd love to restore it for you, Sir."

You agree on a price and then ask him about this train count business, and how he can find the correct pendulum for it.

"Piece of cake, Sir. When you come to pick it up, I'll show you."

The great day dawns and off you go to pick up the clock. You don't recognize it. It's quite beautiful. All the brass work shining brilliantly, the steel of the arbors polished, and the new pendulum swinging merrily away with every tick. You compliment the old man and pay him.

"Now then, Sir. You wanted to know how to find the right pendulum. This is how it's done. You see that wheel on the shaft where the hands are set? That's the Center Wheel. You count all the teeth on that wheel and write it down. Then the same thing for the Third Wheel, the wheel immediately above. Write that down. Then the Escape Wheel. Write that down and write 'times 2' after it.

"Now. You see the little steel gears that the wheels mesh with? They're called pinions. You count them, but start from the one where the Third Wheel's set. So you only have two of them to count. You put them below the wheel counts. Now you work it out. In your case, taking each wheel as I've named it, the sum was 96 x 80 x 30 x 2 = 460800. Right, now the number of teeth, or leaves as they're called, in the pinions was 8 for both. Right, that's 64. Divide the 64 into the 460800 and you get 7200.

"Remember, now, that each tooth of the Escape wheel acts twice, once on each pallet. Hence the 'times 2.' Therefore, the pendulum vibrates, or swings, 7,200 times per hour. Divide that by 60, and you get it swinging 120 times per minute.

"Now what they call a Royal pendulum, or one that beats one second per swing, measures 39.14", give or take. To find the length of a half second pendulum, which is the one on your clock, we square the 1/2, thereby coming up with 1/4, multiply that by 39.14. That equals 39.14 and we divide by 4, which equals 9.78". So the count of all the gears, divided by the count of the pinions has a very direct bearing on the pendulum length.

"But there's one more little consideration. You don't work with the overall length of the pendulum, only the theoretical length. That's the distance between half the suspension spring on which the pendulum swings, taken down to the center of the bob, the big weight at the bottom.

"Sounds a lot more complicated than it really is, Sir."

You thank him profusely and leave with your treasure. You've learned a lot, but like most other things. Simple when you know how!

Copyright (c) 2009 Mike Bond