John Harrison - The John Harrison precision wooden regulator ebonised longcase gridiron pendulum.
Join Dr John C Taylor OBE from the Clocktime digital museum as he discusses the movement of the John Harrison Wooden Regulator, dated 1726.
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The wooden wheels, which Harrison made, have a groove into which all these teeth are left, are let into and glued into place. And they're in a group of five or six, so all the grain is coming vertically out along the length of the teeth and the teeth have got parallel sides and they engage with the rollers which rotate on the vertical side of the teeth as it comes around. And so, it's very, very low friction with the lignum vitae roller with a brass pin going through because if it was a steel pin, it would tend to go rusty. The lubrication from the little rollers in the cage comes from the wood itself so that it will last for hundreds of years without any lubrication at all. Harrison put some thought into how to keep the accuracy of a clock and decided that the friction between the escape wheel and the pallets of the escapement itself was an area that needed a lot of thought. And he designed an anchor pendulum using low friction materials. You can see each pallet engaging the wheel and with a slight recoil, it releases the other pallet. Each pallet has an extension with a weight in it, which then lifts the pallet away. And you can see then the impulse, the recoil. And the impulse and the pallet is held against the tooth by the rotation torque of the escape wheel and then it is driven backwards by the recoil. And as the recoil gets to the point of changeover, then the two teeth are engaged. Obviously, one can only continue and because of the recoil they change over. This releases the pallet, which is lifted clear by the counterbalance is then caught on the little retaining pivot and you get this wonderful grasshopper movement. He needed a clock to calibrate any sea clock that he wanted to design in the future. He needed a time base and this is the time base that he created.