Another picture taken at the Royal Observatory, Greenwich (UK).
In honour of my current "leisurely reading", Longitude by Dava Sobel, I thought I would share this image I took when I visited Greenwich for the first time, during year 1 of my PhD; Natalie and I went there one afternoon to take in the Prime Meridian of the World. At the time I knew much less about chronometry than I do at the moment (which is saying something, since I still know very little). I'm glad I paused to photograph Harrison's renowned marine chronometer, which is considered to have solved the "Longitude Problem" and which is the only one of his four prototypes that is not currently wound and running. This is partly because it is the only one of the clocks that uses lubrication, and would thus require regular cleaning if it were to keep time (Harrison had ingenious ways of avoiding this in most or all of the other clocks he built).
As Sobel points out, H4 also looks, compared to its three predecessors, like a totally different machine. Harrison's final solution is a unique example of the concession to size and convenience, when his original priorities had been stability and accuracy; a radical shift apparently took place between the creation of the last two models. While H4 was as accurate as the previous three models, the use of lubricant indicates some compromise that might relate to this modification in size.