{"id":578,"date":"2014-01-20T23:21:54","date_gmt":"2020-02-18T06:53:26","guid":{"rendered":"https:\/\/redfrontdoor.org\/blg2\/?p=578"},"modified":"2020-07-15T12:57:37","modified_gmt":"2020-07-15T12:57:37","slug":"post-572","status":"publish","type":"post","link":"https:\/\/redfrontdoor.org\/blog\/?p=578","title":{"rendered":"An original escapement design?"},"content":{"rendered":"\n
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\u00a9 Trustees of the British Museum
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On a recent visit to the British Museum in London, I was interested to see a very curious escapement mechanism in one of the clocks, a creation of Thomas Tompion in the 1670s. I am certainly no expert on clocks, but I had never seen an escapement where the pendulum swings across the plane of the gear wheels.<\/p>\n\n\n\n

Frustratingly, the actual mechanism was very small, and in the middle of quite a large glass case, so I could not see it well enough to work out what it was doing. I spent a bit of time thinking about it, and came up with an idea for what might be happening, but now the question was whether I’d got it right.<\/p>\n\n\n\n

Turning to the web, even this lovely photo from the British Museum does not quite make the situation clear:<\/p>\n\n\n\n

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\u00a9 Trustees of the British Museum [source page]<\/a><\/figcaption><\/figure><\/div>\n\n\n\n

Some further research led me to a 1971 pamphlet which contained a drawing detailed enough to understand the mechanism. Conveniently for this post, the drawing is from more or less the same viewpoint as the above photo:<\/p>\n\n\n\n

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The Tompion Clocks at Greenwich and the Dead-Beat Escapement, Derek Howse, (originally Antiquarian Horology, December 1970 and March 1971), p.29, drawing from Donald Cufflin, National Maritime Museum. Annotations ‘P’ and ‘W’ added.<\/p>\n\n\n\n

I had got it nearly<\/em> right.<\/p>\n\n\n\n

The simplified animation below shows the difference. On the left is how I imagined the mechanism, and on the right is the actual mechanism. In each half: The oscillating pair of long black pieces is the forked pallets (‘P’ in the figure above, for the actual mechanism), to be imagined as connected to the swinging pendulum. The central vertical grey band represents an edge-on view of the wheel with radial pins (‘W’ in the figure), as if driven up the screen by the weights.<\/p>\n\n\n\n

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